Research ArticleEffective Carbon Dioxide Photoreduction over Metals(Fe- Co- Ni- and Cu-) Incorporated TiO2Basalt Fiber Films

Jeong Yeon Do1 Byeong Sub Kwak1 Sun-Min Park2 and Misook Kang1

1Department of Chemistry College of Science Yeungnam University Gyeongsan Gyeongbuk 38541 Republic of Korea2Korea Institute of Ceramic Engineering and Technology (KICET) Jinju Gyeongnam 52851 Republic of Korea

Correspondence should be addressed to Sun-Min Park psmkicetrekr and Misook Kang mskangynuackr

Received 11 December 2015 Revised 15 February 2016 Accepted 22 March 2016

Academic Editor Jennifer Strunk

Copyright copy 2016 Jeong Yeon Do et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Mineralogical basalt fibers as a complementary adsorbent were introduced to improve the adsorption of CO2over the surfaces

of photocatalysts TiO2photocatalysts (M-TiO

2) incorporated with 50mol 3d-transition metals (Fe Co Ni and Cu) were

prepared using a solvothermal method and mixed with basalt fibers for applications to CO2photoreduction The resulting

50molM-TiO2powders were characterized by X-ray diffraction scanning electronmicroscopy ultraviolet-visible spectroscopy

photoluminescence Brunauer Emmett and Teller surface area and CO2-temperature-programmed desorption A paste composed

of two materials was coated and fixed on a Pyrex plate by a thermal treatment The 50mol M-TiO2basalt fiber films increased

the adsorption of CO2significantly indicating superior photocatalytic behavior compared to pure TiO

2and basalt fiber films

and produced 158sim360 120583mol gcatminus1 Lminus1 CH

4gases after an 8 h reaction In particular the best performance was observed over

the 50mol Co-TiO2basalt fiber film These results were attributed to the effective CO

2gas adsorption and inhibition of

photogenerated electron-hole pair recombination

1 Introduction

To mitigate the greenhouse effect there has been increasinginterest in converting the greenhouse gas carbon dioxide(CO2) to useful molecules such as carbon monoxide (CO)

[1 2] methane (CH4) [3 4] formic acid (HCOOH) [5]

formaldehyde (HCHO) [6] or methanol (CH3OH) [7 8]

via chemical routes On the other hand because CO2is

a chemically stable compound owing to its carbon-oxygendouble bonds its conversion to some hydrocarbons requiressubstantial energy input for bond cleavage [9] Solar energyprovides a readily available and continuous energy supplythat would be suitable to drive this conversion process InCO2photocatalysis to synthesize some fuels semiconductor

materials with an appropriate band-gap (the energy regionextending from the bottom of the empty conduction bandto the top of the occupied valence band) are required asphotocatalystsWhen a semiconductor photocatalyst absorbslight in a typical photocatalytic process an electron is excitedfrom the fully occupied valence band of the semiconductorto a higher energy empty conduction band forming an

electron-hole pair [10 11] These charge carriers can alsorecombine on the surface or in the bulk before reactingwith adsorbed species dissipating the energy as heat orlight The photoreactions occur continually with electronaccepting or donating species adsorbed on the surface ofthe semiconductor photocatalyst Therefore electron-holerecombination must be minimized for photocatalyticallyinduced redox reactions to take place [12ndash14]

The TiO2semiconductor has been assessed for CO

2

photoreduction because of its chemical stability and naturalabundanceAlthoughTiO

2has several unique features its use

has been limited by its large band-gap (32 eV) meaning itcan only be activated by ultraviolet light which comprises 2ndash5 of sunlight [15 16] and the relatively fast recombinationbetween the electron and holes [17 18] Therefore thephotocatalyst should have a lower band-gap and an increasedlifetime of the photogenerated electrons and holes througheffective charge carrier separation and the suppression ofelectron-hole recombination The photocatalytic activity forvisible light can be increased by coupling semiconductors ofdifferent energy levels or doping with metals or nonmetals

Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2016 Article ID 5195138 12 pageshttpdxdoiorg10115520165195138

2 International Journal of Photoenergy

to suppress the recombination rate and increase the quantumyield [19 20] Considerable efforts have been made to extendthe adsorption of reactive species and the utilization ofthe incident light properties of catalysts to improve theirphotocatalytic efficiency The approaches of combining TiO

2

with a support such as porous materials polycrystallinefibers or tube materials (eg CNTs or polymers magneticmaterials and minerals) to achieve charge separation andthe adsorption of reactive species have decreased the recom-bination rate and maintained excellent catalytic activity [2122]

Therefore this study examined whether a mineral basaltfiber [23] as a complementary material would be sufficientto facilitate both electron-hole charge separation and CO

2

adsorption Basalt is one of the most common rock types inthe world and is found widely in large igneous provincesBasalt contains MgO CaO Fe

2O3 TiO2 Al2O3 and SiO

2

and can be used as a substrate mineral to adsorb carbondioxide Another objective in this study was to examine theeffects of 3d-transition metals as a cocatalyst in the TiO

2

photocatalytic system In general 3d-transition metals withexcellent oxidation-reducing power are often used as thermalcatalysts in some redox reactions In particular Ni Co Feand Cu have been applied widely as the main catalytic speciesfrom CO

2or CO to methanol or hydrocarbons so-called

Fischer-Tropsch synthesis [24ndash26] Consequently this studyexamined the synergistic effects of a basalt mineral absorbent(YJC com Hampyeong Jeonnam Republic of Korea) andadding transition metals (Fe Co Ni and Cu) to the TiO

2

anatase framework on its properties as a photosensitizer forthe photoreduction of CO

2to CH

4

2 Experimental

21 Preparation and Characterization of Nanosized 50molM (Fe- Co- Ni- and Cu-) TiO

2Powders and 50mol M-

TiO2Basalt Fiber Films Before the design of the 50mol

M (Fe- Co- Ni- and Cu-) TiO2basalt fiber films four

types of 50mol M-TiO2powders were prepared using

a solvothermal treatment [27] Titanium tetraisopropoxide(TTIP 9995 Junsei Chem Co Japan) and metal nitrates(M(NO

3)2119909H2O M = Fe Ni Co and Cu 999 Junsei

Chem Co Japan) were used as the precursors for titaniumand other metals respectively and absolute ethanol was usedas the solvent After adding 0095M of TTIP to 250mLof absolute ethanol in a 500mL beaker 04M of distilledwater was dropped carefully and slowly into the solution withstirring for 1 h to avoid aggregation by rapid hydrolysis and0005M (50mol) of the metal precursors was then addedto the solution The final solution was stirred continuouslyfor 2 h at room temperature and moved to an autoclavefor thermal treatment at 200∘C for 8 h under a nitrogenatmosphere at a pressure of approximately 100 atm Theresulting precipitate was washed with distilled water untilthe pH was 70 and dried at 50∘C for 24 h The pure TiO

2

nanoparticles were also obtained using the samemethodTheprepared TiO

2and 50mol M-TiO

2were used as the main

photocatalytic species for CO2reduction

For the design of 50mol M-TiO2basalt fiber films for

application to the CO2photoreduction reaction the basalt

fibers were ground to a small size and 70ndash100 mesh-sizedpowders were filtered and selected for use as the support sub-strate The paste was composed of 20 g of 50mol M-TiO

2

powders and basalt fiber pieces with a mixture containing50 g of 120572-terpineol 05 g of cellulose and 20mL of ethanolThe paste was then sonicated for 24 h at 1200Wcmminus3 Subse-quently a Pyrex plate was coated with the mixed paste withthe M-TiO

2powders and basalt fiber pieces using a squeeze

printing technique The size of the formulated 50mol M-TiO2basalt fiber films was 80mm times 50mm The 50mol

M-TiO2basalt fiber films were then heat treated at 450∘C for

30 minutes to remove the additivesThe synthesized 50mol M-TiO

2powders were

examined by X-ray diffraction (XRD MPD PANalytical)using nickel-filtered CuK120572 radiation (30 kV 30mA) Thereflectance UV-vis spectra of the 50mol M-TiO

2powders

were obtained using a Cary 500 spectrometer with areflectance sphere in the range 200sim800 nm The BrunauerEmmett and Teller (BET) surface areas of the 50mol M-TiO2powders were measured using a Belsorp II instrument

The recombination tendency of the photogenerated electron-hole pairs (eminush+) in 50mol M-TiO

2powder was

estimated by photoluminescence (PL PhotoluminescenceSpectrometer PerkinElmer) spectroscopy using a He-Cdlaser source at awavelength of 325 nmThe adsorption ofCO

2

on the 50mol M-TiO2powders was measured from CO

2-

TPD (temperature-programmed desorption) experimentsin the same manner used for thermogravimetric analysis(TGA Sinco Co Republic of Korea)

The morphology of the 50mol M-TiO2basalt fiber

films was observed by scanning electron microscopy (SEMJEOL 2000EX) and the atomic compositions of the films weredetermined by energy-dispersive X-ray spectroscopy (EDAXEX-250 Horiba)

22 Photocatalytic Activities over 50mol M (Fe- Co- Ni-and Cu-) TiO

2Basalt Fiber Films A batch type photoreactor

was designed in the laboratory as shown in Figure 1 Thereactor consisted of a rectangular quartz cell with a totalvolume of 600mLThe photocatalytic activity was examinedusing the formulated 50mol M (Fe- Co- Ni- and Cu-)TiO2basalt fiber films (80 times 50mm2 size) fixed uniformly

to the bottom of the reaction chamber A 10mm thickquartz glass window cover was placed on the top of thereactor to enable the effective transfer of irradiation fromtwo 60-Wcm2 mercury lamps with a 365 nm wavelengthThe reactor chamber and lamp were covered with aluminumfoil to ensure that all the radiation that participated in thereaction had passed through the quartz windowThe reactorwhich had been checked for leakage at atmospheric pressurefor several hours was purged with helium carrier gas Thereaction temperature and pressure were maintained at 313 Kand 10 atm respectively Before starting the experiment thereactor was purged for one hour with a mixture of CO

2and

helium The CO2 H2O ratio was fixed to 1 2 During the

photocatalysis process the product mixture was sampled

International Journal of Photoenergy 3

Quartz

Water

UV-lamp

and FIDGC-TCD

Reaction conditionsUV-lamp 2ea (6W 365nm)

Volume 60mLTemperature 40∘C

CO2

20m

m8

mm

15mm

5mm

Heizung(rpm)

Ruhrger at(∘C)

EinausEinaus

= 2 (10 mmol) 1 (05 mmol)Water CO2

Figure 1 Batch type photoreactor used for CO2photoreduction to CH

4

off-line using a gas tight syringe (Agilent 250 120583m) with thesame volume and analyzed by gas chromatography (GCiGC7200 Donam Co Republic of Korea) equipped with athermal conductivity detector (TCD) and a flame-ionizeddetector (FID) First the gaseous products produced by thein situ system were flowed into the TCD detector that wasconnected to a Carboxen 1000 (Young Lin InstrumentalsCo Republic of Korea) column to analyze the light gases(H2 O2 CO CO

2 CH3OH and CH

3COOH) The extracted

gases were then inserted into the FID detector to separatethe C

1(methane)ndashC

3light hydrocarbons The selectivity of

the product was calculated using the following equation C119894

() = C119894moles in producttotal moles of C produced times 100

3 Results and Discussion

31 Physical Properties of the 50mol M (Fe- Co- Ni-and Cu-) TiO

2Powders Figure 2 presents XRD patterns of

the basalt fiber pure TiO2 and 50mol M (Fe- Co- Ni-

and Cu-) TiO2powders All the peaks for the 50mol M-

TiO2powders were assigned to the anatase TiO

2tetragonal

structure [28] The XRD patterns showed the main peaksat 2535∘ 3779∘ 4808∘ 5392∘ 5512∘ 6273∘ 6860∘ 7036∘7509∘ 8314∘ and 9518∘ 2120579 whichwere assigned to the (d101)(d004) (d200) (d105) (d211) (d204) (d116) (d220) (d215)(d312) and (d321) planes respectively Depending on theaddition of other transition metals to the TiO

2framework

the peak intensities decreased slightly with some broadeningOn the other hand no peaks were observed for the addedmetals oxide forms which mean that the metal ions hadbeen well-inserted into the TiO

2framework Generally peak

broadening indicates a decrease in crystallite size [29] Peakbroadening of the d101 peak is related to the crystallite size ofthe tetragonal crystalline phase of anatase Debye-Scherrerrsquosequation [30] was used to determine the crystallite size and

lattice strain Based on the full width at half maximum heightof the d101 peak the crystallite sizes (lattice strains) for TiO

2

and 50mol Fe- Co- Ni- and Cu-TiO2were 13 (0013)

and 14 (0012) 14 (0012) 16 (0010) and 17 (0009) nmrespectively

Figures 3(a) and 3(b) show the UV-visible absorptionspectra and their Taucrsquos plots of the prepared 50mol M(Fe- Co- Ni- and Cu-) TiO

2powders An absorption band

for the anatase structured TiO2(Figure 3(a)) was observed

in the UV-region around 378 nm when extrapolated whichis similar to the absorption wavelength reported elsewhere[31] According to the addition of transition metal speciesthere are different absorption band shifts which were shiftedto higher wavelengths compared to the absorption band ofTiO2 The 50mol M-TiO

2samples showed broad curves

for the metal oxides in the visible region the maximumabsorption was observed at 490 580 700 (too broad) and650 (too broad) nm for 50mol Fe- Co- Ni- and Cu-TiO2 respectively These bands can convert to the following

absorption terms using Tanabe-Suganorsquos energy absorption[32] 5T

2g rarr5Eg for d6-FeO 4T

1g rarr4T2g for d7-CoO

3A2g rarr

3T2g for d8-NiO and 2Eg rarr

2T2g for the d9

electron configuration CuO Generally the band-gap in asemiconductor material is closely related to the wave rangeabsorbed the larger the absorption wavelength the narrowerthe band-gap [33] Using Taucrsquos equation [34] the band-gapsfor the absorption of TiO

2and 50mol Fe- Co- Ni- and

Cu-TiO2in the UV-region were estimated to be 318 and 280

248 298 and 310 eV respectively as shown in Figure 3(b)The inserted transition metals could alter the band-gap ofTiO2significantly leading to easy absorption and eventually

efficient photocatalysisFigure 4 presents the PL spectra of the prepared 50mol

M (Fe- Co- Ni- and Cu-) TiO2particles The PL curve

4 International Journal of Photoenergy

20 30 40 50 60 70 80

Inte

nsity

(au

)(f) Basalt fiber

20 30 40 50 60 70 80100

100

200

300

400

500

600

Inte

nsity

(cps

)

(a) TiO2

1205722120579CuK

1205722120579CuK

(e) 50mol Cu-TiO2

(d) 50mol Ni-TiO2

(b) 50mol Fe-TiO2

(c) 50mol Co-TiO2

Figure 2 XRD patterns of the basalt fiber pure TiO2 and 50mol M-TiO

2powders

Basalt fiberTiO2

400 500 600 700 800300Wavelength (nm)

00

02

04

06

08

10

12

14

16

Abso

rban

ce (a

u)

50mol Fe-TiO2

50mol Co-TiO2

50mol Ni-TiO2

50mol Cu-TiO2

(a)

Sample Band-gap (eV)TiO2

310 (387nm)298 (403nm)248 (485nm)280 (428nm)318 (378nm)

(120572h

)2

2 3 4 51Photon energy (eV)

00

01

02

03

50mol Cu-TiO2

50mol Ni-TiO2

50mol Fe-TiO2

50mol Co-TiO2

(b)

Figure 3 Diffuse reflectance-UV-visible absorption spectra (a) and their Taucrsquos plots (b) of the prepared 50mol M-TiO2powders

International Journal of Photoenergy 5

Table 1 Physical properties of 50mol M-TiO2particles

Physical properties of catalysts Atomic compositionsTi M O

Specific surface areas[m2 gminus1]

Total pore volume[cm3 gminus1]

Average pore diameter[nm]

TiO2 320 00 680 131 020 617

50mol Fe-TiO2 302 37 660 165 064 1556

50mol Co-TiO2 306 34 670 124 017 563

50mol Ni-TiO2 289 31 680 130 018 563

50mol Cu-TiO2 316 29 655 67 042 2495

Basalt fiberTiO2

400 500 600 700 800300Wavelength (nm)

00

05

10

15

20

25

Inte

nsity

(V)

50mol Cu-TiO2

50mol Ni-TiO2

50mol Co-TiO2

50mol Fe-TiO2

Figure 4 PL spectra of the prepared 50mol M-TiO2particles

suggests that the electrons in the valence band are transferredto the conduction band and are stabilized by photoemissionIn general the PL intensity increases with increasing numberof electrons emitted resulting from recombination betweenthe excited electrons and holes and a consequent decreasein photoactivity [35] Therefore there is a strong relationshipbetween the PL intensity and photoactivity In particularthe PL intensity decreases significantly when a metal cancapture excited electrons or exhibit conductivity which isknown as the relaxation process The 50mol M-TiO

2

samples exhibited a PL signal with a similar curve shapedemonstrating the presence of TiO

2 Pure TiO

2exhibited a

strong PL signal in the range 400ndash550 nm with a maximumexcitation wavelength of 445 nm whereas the 50molM-TiO

2curve intensities were weakened dramatically The

decreasing tendency was observed in the following orderTiO2gt 50mol Fe-TiO

2gt Cu-TiO

2gt Ni-TiO

2gt Co-

TiO2 which was possibly due to the new oxygen vacancies

produced by metal-doping The photogenerated electronsin the conduction band initially reached the vacant spaceand then recombined with the photogenerated holes in thevalance band to produce fluorescence emission The reducedPL intensities of 50mol M-TiO

2might be due to defects

generated by the transition metal ions inserted into the TiO2

structures which accelerate electron transfer and hinder

electron-hole pair recombination on the 50mol M-TiO2

surfaceFigure 5 shows the adsorption-desorption isotherm

curves of N2at 77 K for the as-synthesized 50mol M (Fe-

Co- Ni- and Cu-) TiO2particles With the exception of the

50mol Fe-TiO2and Cu-TiO

2samples all isotherms were

close to type II according to the IUPAC classification [36]indicating the lack of pores in the particles Otherwise theisotherms of the 50mol Fe-TiO

2and Cu-TiO

2samples

were attributed to type IV indicating bulk pores by aggre-gation between each nanoparticle The hysteresis slopes wereobserved at intermediate and relative pressures greater than119901119901

0= 07 in all samples

Table 1 lists the specific surface areas of the 50molM-TiO

2samples The specific surface areas were located in

the range 68sim165m2 gminus1 In particular the surface area wasthe largest at 165m2 gminus1 in 50mol Fe-TiO

2 In general

the surface area increases with decreasing particle size [37]These results showed some degree of reliability and were wellmatched to their calculated crystallite sizes (Figure 2) Fromthe results of the average bulk pore diameter for the samplesit is believed that the 50mol Fe-TiO

2and Cu-TiO

2may

contain bulk mesopores approximately 15sim24 nm due toaggregation between their nanoparticles Otherwise the porevolumes of the samples were varied from 017 to 064 cm3 gminus1The atomic compositions calculated the energy-dispersive X-ray spectra that are also included in this table The TiO

2

surface showed only two elements Ti and O whereas threeelements were observed in theM-TiO

2samples In contrast to

expectations the amount of doped metals was much higherthan the Ti amount in all samples and the M Ti ratios wereapproximately 1 10This was calculated from EDAX analysisand the values were different from the actual amount Theamount of metal doped in TiO

2was reduced to the order of

Fe gt Co gt Ni gt CuDuring the CO

2photoreduction reaction CO

2is

adsorbed onto the surface of the photocatalysts in the firststep and the photoreduction reaction progresses Thereforethe photocatalytic performance depends on the adsorptioncapacities of CO

2 Accordingly the CO

2adsorption abilities

of the 50mol M (Fe- Co- Ni- and Cu-) TiO2samples

need to be determined The CO2desorption profiles were

obtained over the range 50sim900∘C as shown in Figure 6Thecurve intensity for CO

2desorption was higher in 50mol

M-TiO2than in pure TiO

2 which means considerably more

CO2molecules had been adsorbed on the surfaces of the

50mol M-TiO2samples In addition TiO

2generally has

6 International Journal of Photoenergy

ADSDES

0

50

100

150V

ac

m3(S

TP) g

minus1

05 10

pp0

(a) TiO2

ADSDES

0

200

400

600

Vac

m3(S

TP) g

minus1

05 10

pp0

(b) 50mol- Fe-TiO2

ADSDES

0

50

100

150

Vac

m3(S

TP) g

minus1

05 10

pp0

(c) 50mol- Co-TiO2

ADSDES

05 10

pp0

0

50

100

150

Vac

m3(S

TP) g

minus1

(d) 50mol- Ni-TiO2

ADSDES

05 10

pp0

0

120

240

360

Vac

m3(S

TP) g

minus1

(e) 50mol- Cu-TiO2

Figure 5 Adsorption-desorption isotherm curves of N2at 77 K for the as-synthesized 50mol M-TiO

2particles

Area integ(Gaussian) 27983665 33278233 66855506 68781188 60435286 10310403

Basalt fiber

2075000208000020850002090000209500021000002105000

TCD

(mV

)

400 600 800200

62750006300000632500063500006375000640000064250006450000

TCD

(mV

)

TiO2

6800000

6900000

7000000

7100000

7200000

7300000

7400000

7500000

7600000

7700000

TCD

(120583V

)

400 600 800200Temperature (∘C)

400 600 800200Temperature (∘C)

Basalt fiber TiO2

50mol Fe-TiO2

50mol Co-TiO2

50mol Ni-TiO2

50mol Fe-TiO2 50mol Co-TiO2 50mol Ni-TiO2 50mol Cu-TiO2

50mol Cu-TiO2

Figure 6 CO2desorption profiles over the 50mol M-TiO

2particles in the range 50sim900∘C

International Journal of Photoenergy 7

30120583m

ldquoTop viewrdquoldquoSide viewrdquo

20120583m

Basalt fiber (b) TiO2basalt fiber(a) Basalt fiber

basalt fiber

basalt fiber

basalt fiber basalt fiber basalt fiber

(c) 50mol Fe-TiO2

50mol Co-TiO2 (d) 50mol Co-TiO2 (e) 50mol Ni-TiO2 (f) 50mol Cu-TiO2

Figure 7 SEM images of the pure basalt fiber film and 50mol M-TiO2basalt fiber films

hydrophilic properties [38] which suggests that duringthe CO

2photoreduction reaction CO

2and H

2O will

be adsorbed preferentially on the metal ions and TiO2

respectively The adsorption abilities were observed inthe following order 50mol Co-TiO

2gt Ni-TiO

2gt

Fe-TiO2gt TiO

2gt Cu-TiO

2samples In general a rapid

catalytic reaction occurs when many reactants are well-adsorbed over the catalyst The presence of transition metalsin the 50mol M-TiO

2samples most likely caused the

relative increase in the number of CO2and H

2O molecules

adsorbed compared to pure TiO2 This synergy contributed

significantly to improving the catalytic performance of the50mol M-TiO

2samples

32 Characteristics and CO2

Photoreduction over the50mol M (Fe- Co- Ni- and Cu-) TiO

2Basalt Fiber Films

Figure 7 presents SEM images (top and side views) of the sixsamples of pure basalt fiber and TiO

2films and 50mol

M (Fe- Co- Ni- and Cu-) TiO2basalt fiber films The

basalt fiber in the films was approximately 15 120583m in diameterwith different lengths and the surfaces were smooth The50mol M-TiO

2materials were mixed with basalt fibers

and were fabricated as thick films by coating on a Pyrex plateThe regular array of composites could be observed clearlythrough both the side and top directions The TiO

2basalt

fiber and 50mol Fe-TiO2basalt fiber composites did not

cover the Pyrex plate surface completely and bulk poreswere observed On the other hand the coating parts werequite uniform and fine particles were well-dispersed Incontrast the surfaces of the films fabricated from 50mol

Co-TiO2basalt fiber 50mol Ni-TiO

2basalt fiber and

50mol Cu-TiO2basalt fiber composites were quite dense

despite containing some cracks In particular the surfacewas the most compact over the 50mol Co-TiO

2basalt

fiber film The thickness of the films in all samples wasapproximately 30sim35 120583m with the exception of the purebasalt fiber film (20 120583m)

Energy-dispersive X-ray spectroscopy (EDAX) con-firmed the presence of metals on the surfaces of the basaltfiber and 50mol M (Fe- Co- Ni- and Cu-) TiO

2basalt

fiber films as shown in Figure 8 and the table below liststhe atomic compositions determined by EDAX For the basaltfiber various metal oxides were observed such as Na KCa Mg Al Si Fe and Ti Pure basalt fiber exhibited acomposition of 1928wt Si 314 wt total alkali metals166wt Ti 1177 wt Fe and 561 wt Al As a CO

2

adsorbent the Ca and Mg contents were 531 and 209wtrespectively Ti contained on the 50mol M (Fe- Co-Ni- and Cu-) TiO

2basalt fiber films decreased in the

following order 50mol Ni-TiO2(4774wt) gt Co-TiO

2

(4268wt) gt TiO2(4094wt) gt Fe-TiO

2(3344wt)

The amounts of transitionmetal specieswere in the range 269to 302wt with the exception of copper (098wt) Thesevalues did not appear to be perfectly quantitative EDAXis a very good surface analytical method but it is prone toerror because the composition can vary according to thelocation In particular the variation is large when the sampleis nonuniform [39]

The efficiencies of the photogenerated electron-hole pro-duction in the basalt fiber and 50mol M (Fe- Co- Ni-

8 International Journal of Photoenergy

MaterialselementAtomic compositions (wt-)

(a)

(b)

(c)

(d)

(e)

Na

204

mdash

mdash

192

160

Mg

209

mdash

mdash

mdash

mdash

Al

561

mdash

mdash

059

mdash

Si

1928

mdash

mdash

228

032

K

110

mdash

mdash

mdash

mdash

Ca

531

mdash

mdash

066

mdash

Fe

1177

mdash

286

114

mdash

Co

mdash

mdash

mdash

269

mdash

Ni

mdash

mdash

mdash

mdash

302

(f)

O

5114

5906

4122

4803

4732

4543

Ti

166

4094

3344

4268

4774

3615

Cu

mdash

mdash

mdash

mdash

mdash

098

Spectrum 1Ca Si

FeTi

OAl

Mg

NaK

CaK

Ti FeFe

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 1

Ti

O

Ti

2 4 6 1810 16 200 128 14(keV)

Spectrum 3

TiO

Ti

FeFe

Fe

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 2Ti

O

CuCuCu

Ti

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 4

NiNiNi Si

Ti

O

NaTi

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 2Ca

Si

Fe

Ti

O

AlNa

Ca

Co

Co

Co

Ti

FeFe

2 4 6 8 10 12 14 16 18 200(keV)

Full scale 767 cts cursor 0000Full scale 4345 cts cursor 0000Full scale 1548 cts cursor 0000

Full scale 1428 cts cursor 0000 Full scale 2264 cts cursor 0000 Full scale 830 cts cursor 0000

(b) TiO2basalt fiber(a) Basalt fiber

(d) 50mol Co-TiO2basalt fiber (f) 50mol Cu-TiO2basalt fiber(e) 50mol Ni-TiO2basalt fiber

(c) 50mol Fe-TiO2basalt fiber

Figure 8 Energy-dispersive X-ray spectra of the surfaces of the pure basalt fiber and 50mol M-TiO2basalt fiber films and the atomic

compositions

and Cu-) TiO2basalt fiber films were measured from the

photocurrent response under solar light irradiation at anapplied potential of 07 V versus SCE Figure 9 shows thetypical real time photocurrent response of the films whenthe light source is switched on and off exhibiting a rapidphotocurrent rise and decay In semiconductor systemswhen irradiation provides an energy higher than the band-gap of a semiconductor the energy excites an electron fromthe valence band to the conduction band leaving a hole inthe valence band The electron-hole pair is responsible forthe photocurrent When the light was turned on a rapidincrease in the photoreduction current was observed andthe photocurrent then turned to a steady state after a fewseconds When the light was turned off the photocurrentdecreased instantaneously to almost zero [40]When the lightwas turned on the maximum photocurrents obtained forthe 50mol Co-TiO

2and Ni-TiO

2basalt fiber films were

31049 and 30075mA cmminus2 respectively which were morethan four times higher than that achieved on pure basalt fiber

(7123mA cmminus2) andTiO2basalt fiber films (7401mA cmminus2)

Themaximumphotocurrent of the 50molCu-TiO2basalt

fiber film was too small due to trapping of excited elec-trons by copper with strong oxidation agency In additionthe TiO

2basalt fiber 50mol Cu-TiO

2basalt fiber and

50mol Ni-TiO2basalt fiber films showed no current

transients in both the light-on and the light-off regions inthe samples falling off with time in 50 s to a steady statewhich indicates that few surface recombination processeshad occurred Clearly some electron-hole recombinationwas observed in the 50mol Fe-TiO

2basalt fiber and Co-

TiO2basalt fiber films but it was negligible compared to

the total current value Therefore the 3d-transition metalingredients have a beneficial effect on the photocurrent itplays a role as an intermediate for the efficient separation ofphotogenerated hole-electron pairs

Figure 10 presents the photoreduction abilities of CO2

with H2O vapor to CH

4over the pure basalt fiber film and

50mol M (Fe- Co- Ni- and Cu-) TiO2basalt fiber films

International Journal of Photoenergy 9

3104930075

20974

7123 74016450

TiO2basalt fiberBasalt fiber

50 100 150 200 250 300 3500Time (s)

minus50

0

50

100

150

200

250

300

350

Curr

ent (

mA

cm

2)

50mol Cu-TiO2basalt fiber50mol Ni-TiO2basalt fiber

50mol Fe-TiO2basalt fiber50mol Co-TiO2basalt fiber

Figure 9 Photocurrent responses of the pure basalt fiber and50mol M-TiO

2basalt fiber films when the light source was

switched on and off

after 8 h Generally CH4production from CO

2reduction

with H2O can be divided into the following three subpro-

cesses [41] proton production from H2O photodecompo-

sition CO radical production from CO2photo cleavage

and methane production from photosynthesis between theCO radical and proton The photogenerated electrons onthe photocatalysts by UV-radiation induce CO

2reduction

to produce CO2radicals whereas the holes react with the

adsorbed H2Omolecules to perform oxidationThe interme-

diate photogenerated species undergo different reactions toproduce CO CH

3OH andCH

4The production of CH

4from

methyl radicals (∙CH3) was confirmed which are dependent

directly on the formation of the intermediate product CO[42] As shown in this figure almost no methane wasobserved when only the lamp was turned on On the otherhand the amounts of CO and O

2generation increased and

a small amount of hydrogen was observed This means thatthe light does not induce photoreduction processes aloneOn the other hand there are different product distributionsaccording to the loaded metal species excessive methane isgenerated over the catalysts loaded with Ni and Co and thequantities of CO and CH

3OH gases are increased over the

catalysts loaded with Cu and Fe The M-TiO2basalt fiber

films showed higher CH4production from CO

2photoreduc-

tion than the pure basalt fiber and TiO2basalt fiber films

700 120583mol gcatminus1 Lminus1 CH

4was emitted over the pure basalt

fiber film suggesting that it contains a small amount of TiO2

On the other hand CH4production was 1121 120583mol gcat

minus1 Lminus1over the TiO

2basalt fiber film In contrast the maximum

Lamp turned on only

TiO2basalt fiberBasalt fiber

1 2 3 4 5 6 7 80Time (h)

0

50

100

150

200

250

300

350

400

Met

hane

yie

ld (120583

mol

g-c

atlowast

L)

50mol Cu-TiO2basalt fiber50mol Ni-TiO2basalt fiber

50mol Fe-TiO2basalt fiber50mol Co-TiO2basalt fiber

Figure 10 Photoreduction abilities of CO2with H

2O vapor to CH

4

over the pure basalt fiber film and 50mol M-TiO2basalt fiber

films after 8 h

CH4yields over the 50mol Co-TiO

2basalt fiber and Ni-

TiO2basalt fiber films were 3605 and 3073 120583mol gcat

minus1 Lminus1respectively The differences in yields were attributed to theirband-gaps electron-hole recombination tendencies and thegas adsorption abilities of the 50mol M-TiO

2basalt fiber

films In particular this study confirmed that the 50molCo-TiO

2particles show synergistic performance when the

basalt fiber is mixedThe reduction ofCO

2requires amultiple electron transfer

and leads to production of a variety of products dependingon the number of transferred electrons which determinethe final oxidation state of the carbon atom The standardredox potentials of the CO

2reduction half-reactions vary

from CO2HCOOH [43] to CO

2CH4[44] CO

2adsorbed

on a photocatalyst surface can be reduced to ∙CO2

minus anionradical which can react withH+ and eminus for formingHCOOHor HCOOminus or which can go to the postulated disproportion-ation reaction of two ∙CO

2

minus anion radicals into CO (afterall to be C radical) and CO

3

2minus to react with H radical Thisstudy seems to follow the latter Scheme 1 presents a modelfor CO

2photoreduction over the M-TiO

2basalt fiber films

based on the relationships between the optical propertiesof the photocatalysts and the catalytic activities Photonexcitation in M-TiO

2over the M-TiO

2basalt fiber films

will begin rapidly because M-TiO2has a shorter band-gap

than pure TiO2 and the excited electrons can be transferred

efficiently to CO2molecules In addition CO

2molecules

are adsorbed preferentially and easily on the basalt fibersurface The positive holes on the valance band of M-TiO

2

can be trapped byH2Ospecies and transferred toOH radicals

and protons The protons obtained are transformed to H

10 International Journal of Photoenergy

O

Basalt fiberFTO glass

FTO glass

H2

CO2

Basalt fiber (i) More CO2 adsorption good

H2O

∙H

∙CO2minus

+ ∙H rarr ∙CHrarr ∙CH2 rarr ∙CH3 rarr CH4

Reduction CO2 + eminus rarr ∙CO2minus

h+

eminus

h+

eminus

pasteM-TiO2basalt fiber

M-TiO2

ldquoMetal incorporatedrdquoUV light

decreaseTiO2 M-TiO2 M-TiO2

(i) Easy electron transfer(ii) Water (H2O) adsorption goodM-TiO2

Oxidation H2O + h+ rarr ∙OH + H+ H+ + O2997888rarr

Scheme 1 Model for CH4production from the photoreduction of CO

2with H

2O vapor over the M-TiO

2basalt fiber films

radicals by electrons and the H radicals then react with Cand CO radicals formed from the reduction of CO

2

minus overM-TiO

2 particularly over Co- or Ni-TiO

2semiconductors

resulting methane production [45] The mixed films ofbasalt fibers and M-TiO

2can also promote the separation

of photogenerated electron-hole pairs (eminush+) on M-TiO2

Therefore the synergetic effects of the basalt fibers and M-TiO2in the M-TiO

2basalt fiber films achieved higher CO

2

reduction efficiency

4 Conclusions

The 50mol M (Fe- Co- Ni- and Cu-) incorporated TiO2

photocatalysts obtained by the solvothermal method werecoated densely with basalt fibers on a Pyrex plate usinga squeeze technique and applied to the photoreduction ofCO2to CH

4 The CO

2adsorption abilities were improved

over the basalt fiber and CH4generation was enhanced

dramatically over 50mol M-TiO2basalt fiber films with

a threefold higher yield compared to the pure basalt fiberand TiO

2basalt fiber films In particular the photoreduction

of CO2with H

2O revealed a remarkable increase in CH

4

generation over the 50mol Co-TiO2basalt fiber film to

3605 120583mol gcatminus1sdotLminus1 after an 8 h reaction

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

This research was supported by ceramic fiber commercialcenter project of Korea Institute of Ceramic Engineeringamp Technology (KICET) funded by the Ministry of TradeIndustry amp Energy (MOTIE)

References

[1] M Tahir and N S Amin ldquoIndium-doped TiO2nanoparticles

for photocatalytic CO2reduction with H

2O vapors to CH

4rdquo

Applied Catalysis B Environmental vol 162 pp 98ndash109 2015[2] B S Kwak andM Kang ldquoPhotocatalytic reduction of CO

2with

H2O using perovskite Ca

119909Ti119910O3rdquo Applied Surface Science vol

337 pp 138ndash144 2015[3] C Fletcher Y Jiang and R Amal ldquoProduction of formic acid

from CO2reduction by means of potassium borohydride at

ambient conditionsrdquo Chemical Engineering Science vol 137 pp301ndash307 2015

[4] G Mahmodi S Sharifnia M Madani and V VatanpourldquoPhotoreduction of carbon dioxide in the presence of H

2 H2O

and CH4over TiO

2and ZnO photocatalystsrdquo Solar Energy vol

97 pp 186ndash194 2013[5] J Albo A Saez J Solla-Gullon V Montiel and A Irabien

ldquoProduction of methanol from CO2electroreduction at Cu

2O

and Cu2OZnO-based electrodes in aqueous solutionrdquo Applied

Catalysis B Environmental vol 176-177 pp 709ndash717 2015[6] P Akhter M Hussain G Saracco and N Russo ldquoNew nanos-

tructured silica incorporated with isolated Ti material for the

International Journal of Photoenergy 11

photocatalytic conversion of CO2to fuelsrdquo Nanoscale Research

Letters vol 9 article 158 2014[7] M Anpo ldquoPhotocatalytic reduction of CO

2with H

2O on

highly dispersed Ti-oxide catalysts as a model of artificialphotosynthesisrdquo Journal of CO

2Utilization vol 1 pp 8ndash17 2013

[8] H Abdullah M R Khan M Pudukudy Z Yaakob and NA Ismail ldquoCeO

2-TiO2as a visible light active catalyst for the

photoreduction ofCO2tomethanolrdquo Journal of Rare Earths vol

33 no 11 pp 1155ndash1161 2015[9] O Ola and M Mercedes Maroto-Valer ldquoReview of material

design and reactor engineering on TiO2photocatalysis for

CO2reductionrdquo Journal of Photochemistry and Photobiology C

Photochemistry Reviews vol 24 pp 16ndash42 2015[10] X Zhang L Wang Q Du Z Wang S Ma and M Yu

ldquoPhotocatalytic CO2reduction over B

4CC3N4with internal

electric field under visible light irradiationrdquo Journal of Colloidand Interface Science vol 464 pp 89ndash95 2016

[11] R Gusain P Kumar O P Sharma S L Jain and O PKhatri ldquoReduced graphene oxide-CuO nanocomposites forphotocatalytic conversion of CO

2into methanol under visible

light irradiationrdquo Applied Catalysis B Environmental vol 181pp 352ndash362 2016

[12] N M Nursam X Wang and R A Caruso ldquoHigh-throughputsynthesis and screening of titania-based photocatalystsrdquo ACSCombinatorial Science vol 17 no 10 pp 548ndash569 2015

[13] M V Dozzi S Marzorati M Longhi M Coduri L Artigliaand E Selli ldquoPhotocatalytic activity of TiO

2-WO3mixed oxides

in relation to electron transfer efficiencyrdquo Applied Catalysis BEnvironmental vol 186 pp 157ndash165 2016

[14] Y Qu and X Duan ldquoProgress challenge and perspective ofheterogeneous photocatalystsrdquo Chemical Society Reviews vol42 no 7 pp 2568ndash2580 2013

[15] J C Colmenares R Luque J M Campelo F Colmenares ZKarpinski and A A Romero ldquoNanostructured photocatalystsand their applications in the photocatalytic transformation oflignocellulosic biomass an overviewrdquo Materials vol 2 no 4pp 2228ndash2258 2009

[16] M Kitano M Matsuoka M Ueshima and M Anpo ldquoRecentdevelopments in titanium oxide-based photocatalystsrdquo AppliedCatalysis A General vol 325 no 1 pp 1ndash14 2007

[17] P Silija Z Yaakob V Suraja N N Binitha and Z S Akmal ldquoAnenthusiastic glance in to the visible responsive photocatalystsfor energy production and pollutant removal with specialemphasis on titaniardquo International Journal of Photoenergy vol2012 Article ID 503839 19 pages 2012

[18] H Xu S Ouyang L Liu P Reunchan N Umezawa and JYe ldquoRecent advances in TiO

2-based photocatalysisrdquo Journal of

Materials Chemistry A vol 2 no 32 pp 12642ndash12661 2014[19] Z He J Tang J Shen J Chen and S Song ldquoEnhancement of

photocatalytic reduction of CO2to CH

4over TiO

2nanosheets

by modifying with sulfuric acidrdquo Applied Surface Science vol364 pp 416ndash427 2016

[20] O Ola and M M Maroto-Valer ldquoTransition metal oxide basedTiO2nanoparticles for visible light induced CO

2photoreduc-

tionrdquo Applied Catalysis A General vol 502 pp 114ndash121 2015[21] D Eder ldquoCarbon nanotube-inorganic hybridsrdquo Chemical

Reviews vol 110 no 3 pp 1348ndash1385 2010[22] L Zhang R JamalQ ZhaoMWang andTAbdiryim ldquoPrepa-

ration of PEDOTGO PEDOTMnO2 and PEDOTGOMnO

2

nanocomposites and their application in catalytic degradationof methylene bluerdquo Nanoscale Research Letters vol 10 p 1482015

[23] M Urbanski A Lapko and A Garbacz ldquoInvestigation onconcrete beams reinforced with basalt rebars as an effectivealternative of conventional RC structuresrdquo Procedia Engineer-ing vol 57 pp 1183ndash1191 2013

[24] S A Chernyak E V Suslova A V Egorov L Lu S V Savilovand V V Lunin ldquoNew hybrid CNT-alumina supports for Co-based Fischer-Tropsch catalystsrdquo Fuel Processing Technologyvol 140 pp 267ndash275 2015

[25] K Shimura T Miyazawa T Hanaoka and S Hirata ldquoFischerndashTropsch synthesis over alumina supported bimetallic CondashNicatalyst effect of impregnation sequence and solutionrdquo Journalof Molecular Catalysis A Chemical vol 407 pp 15ndash24 2015

[26] F Fazlollahi M Sarkari A Zare A A Mirzaei and HAtashi ldquoDevelopment of a kinetic model for Fischer-Tropschsynthesis over CoNiAl

2O3catalystrdquo Journal of Industrial and

Engineering Chemistry vol 18 no 4 pp 1223ndash1232 2012[27] J Zhao W Xing Y Li and K Lu ldquoSolvothermal synthesis and

visible light absorption of anatase TiO2rdquo Materials Letters vol

145 pp 332ndash335 2015[28] S Liu J Yu and M Jaroniec ldquoAnatase TiO

2with dominant

high-energy 001 facets Synthesis properties and applicationsrdquoChemistry of Materials vol 23 no 18 pp 4085ndash4093 2011

[29] T Ungar ldquoMicrostructural parameters from X-ray diffractionpeak broadeningrdquo Scripta Materialia vol 51 no 8 pp 777ndash7812004

[30] A W Burton K Ong T Rea and I Y Chan ldquoOn the esti-mation of average crystallite size of zeolites from the Scherrerequation a critical evaluation of its application to zeolites withone-dimensional pore systemsrdquo Microporous and MesoporousMaterials vol 117 no 1-2 pp 75ndash90 2009

[31] A Jaroenworaluck N Pijarn N Kosachan and R StevensldquoNanocomposite TiO

2ndashSiO2gel for UV absorptionrdquo Chemical

Engineering Journal vol 181-182 pp 45ndash55 2012[32] J I Pena-Flores A F Palomec-Garfias C Marquez-Beltran

E Sanchez-Mora E Gomez-Barojas and F Perez-RodrıguezldquoFe effect on the optical properties of TiO

2Fe2O3nanostruc-

tured composites supported on SiO2microsphere assembliesrdquo

Nanoscale Research Letters vol 9 article 499 2014[33] D Kim Y Im K M Jeong S-M Park M-H Um and M

Kang ldquoEnhanced 2-chorophenol photodecomposition usingnano-sized Mn-incorporated TiO

2powders prepared by a

solvothermal methodrdquo Bulletin of the Korean Chemical Societyvol 35 no 8 pp 2295ndash2298 2014

[34] C C Huang C C Wu K Knight and D W Hewak ldquoOpticalproperties of CVD grown amorphous Ge-Sb-S thin filmsrdquoJournal of Non-Crystalline Solids vol 356 no 4-5 pp 281ndash2852010

[35] J Kim J S Lee and M Kang ldquoSynthesis of nanoporousstructured SnO

2and its photocatalytic ability for bisphenol a

destructionrdquo Bulletin of the Korean Chemical Society vol 32 no5 pp 1715ndash1720 2011

[36] M Thommes ldquoPhysical adsorption characterization ofnanoporous materialsrdquo Chemie Ingenieur Technik vol 82 no 7pp 1059ndash1073 2010

[37] A A Gribb and J F Banfield ldquoParticle size effects on trans-formation kinetics and phase stability in nanocrystalline TiO

2rdquo

American Mineralogist vol 82 no 7-8 pp 717ndash728 1997[38] S-H Nam S-J Cho C-K Jung et al ldquoComparison of

hydrophilic properties of TiO2thin films prepared by solndashgel

method and reactive magnetron sputtering systemrdquo Thin SolidFilms vol 519 no 20 pp 6944ndash6950 2011

12 International Journal of Photoenergy

[39] H G Feichtinger K Grochenig and T Strohmer ldquoEffi-cient numerical methods in non-uniform sampling theoryrdquoNumerische Mathematik vol 69 no 4 pp 423ndash440 1995

[40] S W Jo B S Kwak K M Kim et al ldquoEffectively CO2

photoreduction toCH4by the synergistic effects of Ca andTi on

Ca-loaded TiSiMCM-41 mesoporous photocatalytic systemsrdquoApplied Surface Science vol 355 pp 891ndash901 2015

[41] J Y Do Y Im B S Kwak J-Y Kim and M Kang ldquoDramaticCO2photoreduction with H

2O vapors for CH

4production

using the TiO2(bottom)FendashTiO

2(top) double-layered filmsrdquo

Chemical Engineering Journal vol 275 pp 288ndash297 2015[42] M Tahir andN SaidinaAmin ldquoPhotocatalytic reduction of car-

bon dioxide with water vapors over montmorillonite modifiedTiO2nanocompositesrdquo Applied Catalysis B Environmental vol

142-143 pp 512ndash522 2013[43] Y Kohno H Hayashi S Takenaka T Tanaka T Funabiki

and S Yoshida ldquoPhoto-enhanced reduction of carbon dioxidewith hydrogen over RhTiO

2rdquo Journal of Photochemistry and

Photobiology A Chemistry vol 126 no 1ndash3 pp 117ndash123 1999[44] M Subrahmanyam S Kaneco and N Alonso-Vante ldquoA screen-

ing for the photo reduction of carbon dioxide supported onmetal oxide catalysts for C

1-C3selectivityrdquo Applied Catalysis B

Environmental vol 23 no 2-3 pp 169ndash174 1999[45] S S Tan L Zou and E Hu ldquoKinetic modelling for photosyn-

thesis of hydrogen and methane through catalytic reduction ofcarbon dioxide with water vapourrdquo Catalysis Today vol 131 no1ndash4 pp 125ndash129 2008

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

2 International Journal of Photoenergy

to suppress the recombination rate and increase the quantumyield [19 20] Considerable efforts have been made to extendthe adsorption of reactive species and the utilization ofthe incident light properties of catalysts to improve theirphotocatalytic efficiency The approaches of combining TiO

2

with a support such as porous materials polycrystallinefibers or tube materials (eg CNTs or polymers magneticmaterials and minerals) to achieve charge separation andthe adsorption of reactive species have decreased the recom-bination rate and maintained excellent catalytic activity [2122]

Therefore this study examined whether a mineral basaltfiber [23] as a complementary material would be sufficientto facilitate both electron-hole charge separation and CO

2

adsorption Basalt is one of the most common rock types inthe world and is found widely in large igneous provincesBasalt contains MgO CaO Fe

2O3 TiO2 Al2O3 and SiO

2

and can be used as a substrate mineral to adsorb carbondioxide Another objective in this study was to examine theeffects of 3d-transition metals as a cocatalyst in the TiO

2

photocatalytic system In general 3d-transition metals withexcellent oxidation-reducing power are often used as thermalcatalysts in some redox reactions In particular Ni Co Feand Cu have been applied widely as the main catalytic speciesfrom CO

2or CO to methanol or hydrocarbons so-called

Fischer-Tropsch synthesis [24ndash26] Consequently this studyexamined the synergistic effects of a basalt mineral absorbent(YJC com Hampyeong Jeonnam Republic of Korea) andadding transition metals (Fe Co Ni and Cu) to the TiO

2

anatase framework on its properties as a photosensitizer forthe photoreduction of CO

2to CH

4

2 Experimental

21 Preparation and Characterization of Nanosized 50molM (Fe- Co- Ni- and Cu-) TiO

2Powders and 50mol M-

TiO2Basalt Fiber Films Before the design of the 50mol

M (Fe- Co- Ni- and Cu-) TiO2basalt fiber films four

types of 50mol M-TiO2powders were prepared using

a solvothermal treatment [27] Titanium tetraisopropoxide(TTIP 9995 Junsei Chem Co Japan) and metal nitrates(M(NO

3)2119909H2O M = Fe Ni Co and Cu 999 Junsei

Chem Co Japan) were used as the precursors for titaniumand other metals respectively and absolute ethanol was usedas the solvent After adding 0095M of TTIP to 250mLof absolute ethanol in a 500mL beaker 04M of distilledwater was dropped carefully and slowly into the solution withstirring for 1 h to avoid aggregation by rapid hydrolysis and0005M (50mol) of the metal precursors was then addedto the solution The final solution was stirred continuouslyfor 2 h at room temperature and moved to an autoclavefor thermal treatment at 200∘C for 8 h under a nitrogenatmosphere at a pressure of approximately 100 atm Theresulting precipitate was washed with distilled water untilthe pH was 70 and dried at 50∘C for 24 h The pure TiO

2

nanoparticles were also obtained using the samemethodTheprepared TiO

2and 50mol M-TiO

2were used as the main

photocatalytic species for CO2reduction

For the design of 50mol M-TiO2basalt fiber films for

application to the CO2photoreduction reaction the basalt

fibers were ground to a small size and 70ndash100 mesh-sizedpowders were filtered and selected for use as the support sub-strate The paste was composed of 20 g of 50mol M-TiO

2

powders and basalt fiber pieces with a mixture containing50 g of 120572-terpineol 05 g of cellulose and 20mL of ethanolThe paste was then sonicated for 24 h at 1200Wcmminus3 Subse-quently a Pyrex plate was coated with the mixed paste withthe M-TiO

2powders and basalt fiber pieces using a squeeze

printing technique The size of the formulated 50mol M-TiO2basalt fiber films was 80mm times 50mm The 50mol

M-TiO2basalt fiber films were then heat treated at 450∘C for

30 minutes to remove the additivesThe synthesized 50mol M-TiO

2powders were

examined by X-ray diffraction (XRD MPD PANalytical)using nickel-filtered CuK120572 radiation (30 kV 30mA) Thereflectance UV-vis spectra of the 50mol M-TiO

2powders

were obtained using a Cary 500 spectrometer with areflectance sphere in the range 200sim800 nm The BrunauerEmmett and Teller (BET) surface areas of the 50mol M-TiO2powders were measured using a Belsorp II instrument

The recombination tendency of the photogenerated electron-hole pairs (eminush+) in 50mol M-TiO

2powder was

estimated by photoluminescence (PL PhotoluminescenceSpectrometer PerkinElmer) spectroscopy using a He-Cdlaser source at awavelength of 325 nmThe adsorption ofCO

2

on the 50mol M-TiO2powders was measured from CO

2-

TPD (temperature-programmed desorption) experimentsin the same manner used for thermogravimetric analysis(TGA Sinco Co Republic of Korea)

The morphology of the 50mol M-TiO2basalt fiber

films was observed by scanning electron microscopy (SEMJEOL 2000EX) and the atomic compositions of the films weredetermined by energy-dispersive X-ray spectroscopy (EDAXEX-250 Horiba)

22 Photocatalytic Activities over 50mol M (Fe- Co- Ni-and Cu-) TiO

2Basalt Fiber Films A batch type photoreactor

was designed in the laboratory as shown in Figure 1 Thereactor consisted of a rectangular quartz cell with a totalvolume of 600mLThe photocatalytic activity was examinedusing the formulated 50mol M (Fe- Co- Ni- and Cu-)TiO2basalt fiber films (80 times 50mm2 size) fixed uniformly

to the bottom of the reaction chamber A 10mm thickquartz glass window cover was placed on the top of thereactor to enable the effective transfer of irradiation fromtwo 60-Wcm2 mercury lamps with a 365 nm wavelengthThe reactor chamber and lamp were covered with aluminumfoil to ensure that all the radiation that participated in thereaction had passed through the quartz windowThe reactorwhich had been checked for leakage at atmospheric pressurefor several hours was purged with helium carrier gas Thereaction temperature and pressure were maintained at 313 Kand 10 atm respectively Before starting the experiment thereactor was purged for one hour with a mixture of CO

2and

helium The CO2 H2O ratio was fixed to 1 2 During the

photocatalysis process the product mixture was sampled

International Journal of Photoenergy 3

Quartz

Water

UV-lamp

and FIDGC-TCD

Reaction conditionsUV-lamp 2ea (6W 365nm)

Volume 60mLTemperature 40∘C

CO2

20m

m8

mm

15mm

5mm

Heizung(rpm)

Ruhrger at(∘C)

EinausEinaus

= 2 (10 mmol) 1 (05 mmol)Water CO2

Figure 1 Batch type photoreactor used for CO2photoreduction to CH

4

off-line using a gas tight syringe (Agilent 250 120583m) with thesame volume and analyzed by gas chromatography (GCiGC7200 Donam Co Republic of Korea) equipped with athermal conductivity detector (TCD) and a flame-ionizeddetector (FID) First the gaseous products produced by thein situ system were flowed into the TCD detector that wasconnected to a Carboxen 1000 (Young Lin InstrumentalsCo Republic of Korea) column to analyze the light gases(H2 O2 CO CO

2 CH3OH and CH

3COOH) The extracted

gases were then inserted into the FID detector to separatethe C

1(methane)ndashC

3light hydrocarbons The selectivity of

the product was calculated using the following equation C119894

() = C119894moles in producttotal moles of C produced times 100

3 Results and Discussion

31 Physical Properties of the 50mol M (Fe- Co- Ni-and Cu-) TiO

2Powders Figure 2 presents XRD patterns of

the basalt fiber pure TiO2 and 50mol M (Fe- Co- Ni-

and Cu-) TiO2powders All the peaks for the 50mol M-

TiO2powders were assigned to the anatase TiO

2tetragonal

structure [28] The XRD patterns showed the main peaksat 2535∘ 3779∘ 4808∘ 5392∘ 5512∘ 6273∘ 6860∘ 7036∘7509∘ 8314∘ and 9518∘ 2120579 whichwere assigned to the (d101)(d004) (d200) (d105) (d211) (d204) (d116) (d220) (d215)(d312) and (d321) planes respectively Depending on theaddition of other transition metals to the TiO

2framework

the peak intensities decreased slightly with some broadeningOn the other hand no peaks were observed for the addedmetals oxide forms which mean that the metal ions hadbeen well-inserted into the TiO

2framework Generally peak

broadening indicates a decrease in crystallite size [29] Peakbroadening of the d101 peak is related to the crystallite size ofthe tetragonal crystalline phase of anatase Debye-Scherrerrsquosequation [30] was used to determine the crystallite size and

lattice strain Based on the full width at half maximum heightof the d101 peak the crystallite sizes (lattice strains) for TiO

2

and 50mol Fe- Co- Ni- and Cu-TiO2were 13 (0013)

and 14 (0012) 14 (0012) 16 (0010) and 17 (0009) nmrespectively

Figures 3(a) and 3(b) show the UV-visible absorptionspectra and their Taucrsquos plots of the prepared 50mol M(Fe- Co- Ni- and Cu-) TiO

2powders An absorption band

for the anatase structured TiO2(Figure 3(a)) was observed

in the UV-region around 378 nm when extrapolated whichis similar to the absorption wavelength reported elsewhere[31] According to the addition of transition metal speciesthere are different absorption band shifts which were shiftedto higher wavelengths compared to the absorption band ofTiO2 The 50mol M-TiO

2samples showed broad curves

for the metal oxides in the visible region the maximumabsorption was observed at 490 580 700 (too broad) and650 (too broad) nm for 50mol Fe- Co- Ni- and Cu-TiO2 respectively These bands can convert to the following

absorption terms using Tanabe-Suganorsquos energy absorption[32] 5T

2g rarr5Eg for d6-FeO 4T

1g rarr4T2g for d7-CoO

3A2g rarr

3T2g for d8-NiO and 2Eg rarr

2T2g for the d9

electron configuration CuO Generally the band-gap in asemiconductor material is closely related to the wave rangeabsorbed the larger the absorption wavelength the narrowerthe band-gap [33] Using Taucrsquos equation [34] the band-gapsfor the absorption of TiO

2and 50mol Fe- Co- Ni- and

Cu-TiO2in the UV-region were estimated to be 318 and 280

248 298 and 310 eV respectively as shown in Figure 3(b)The inserted transition metals could alter the band-gap ofTiO2significantly leading to easy absorption and eventually

efficient photocatalysisFigure 4 presents the PL spectra of the prepared 50mol

M (Fe- Co- Ni- and Cu-) TiO2particles The PL curve

4 International Journal of Photoenergy

20 30 40 50 60 70 80

Inte

nsity

(au

)(f) Basalt fiber

20 30 40 50 60 70 80100

100

200

300

400

500

600

Inte

nsity

(cps

)

(a) TiO2

1205722120579CuK

1205722120579CuK

(e) 50mol Cu-TiO2

(d) 50mol Ni-TiO2

(b) 50mol Fe-TiO2

(c) 50mol Co-TiO2

Figure 2 XRD patterns of the basalt fiber pure TiO2 and 50mol M-TiO

2powders

Basalt fiberTiO2

400 500 600 700 800300Wavelength (nm)

00

02

04

06

08

10

12

14

16

Abso

rban

ce (a

u)

50mol Fe-TiO2

50mol Co-TiO2

50mol Ni-TiO2

50mol Cu-TiO2

(a)

Sample Band-gap (eV)TiO2

310 (387nm)298 (403nm)248 (485nm)280 (428nm)318 (378nm)

(120572h

)2

2 3 4 51Photon energy (eV)

00

01

02

03

50mol Cu-TiO2

50mol Ni-TiO2

50mol Fe-TiO2

50mol Co-TiO2

(b)

Figure 3 Diffuse reflectance-UV-visible absorption spectra (a) and their Taucrsquos plots (b) of the prepared 50mol M-TiO2powders

International Journal of Photoenergy 5

Table 1 Physical properties of 50mol M-TiO2particles

Physical properties of catalysts Atomic compositionsTi M O

Specific surface areas[m2 gminus1]

Total pore volume[cm3 gminus1]

Average pore diameter[nm]

TiO2 320 00 680 131 020 617

50mol Fe-TiO2 302 37 660 165 064 1556

50mol Co-TiO2 306 34 670 124 017 563

50mol Ni-TiO2 289 31 680 130 018 563

50mol Cu-TiO2 316 29 655 67 042 2495

Basalt fiberTiO2

400 500 600 700 800300Wavelength (nm)

00

05

10

15

20

25

Inte

nsity

(V)

50mol Cu-TiO2

50mol Ni-TiO2

50mol Co-TiO2

50mol Fe-TiO2

Figure 4 PL spectra of the prepared 50mol M-TiO2particles

suggests that the electrons in the valence band are transferredto the conduction band and are stabilized by photoemissionIn general the PL intensity increases with increasing numberof electrons emitted resulting from recombination betweenthe excited electrons and holes and a consequent decreasein photoactivity [35] Therefore there is a strong relationshipbetween the PL intensity and photoactivity In particularthe PL intensity decreases significantly when a metal cancapture excited electrons or exhibit conductivity which isknown as the relaxation process The 50mol M-TiO

2

samples exhibited a PL signal with a similar curve shapedemonstrating the presence of TiO

2 Pure TiO

2exhibited a

strong PL signal in the range 400ndash550 nm with a maximumexcitation wavelength of 445 nm whereas the 50molM-TiO

2curve intensities were weakened dramatically The

decreasing tendency was observed in the following orderTiO2gt 50mol Fe-TiO

2gt Cu-TiO

2gt Ni-TiO

2gt Co-

TiO2 which was possibly due to the new oxygen vacancies

produced by metal-doping The photogenerated electronsin the conduction band initially reached the vacant spaceand then recombined with the photogenerated holes in thevalance band to produce fluorescence emission The reducedPL intensities of 50mol M-TiO

2might be due to defects

generated by the transition metal ions inserted into the TiO2

structures which accelerate electron transfer and hinder

electron-hole pair recombination on the 50mol M-TiO2

surfaceFigure 5 shows the adsorption-desorption isotherm

curves of N2at 77 K for the as-synthesized 50mol M (Fe-

Co- Ni- and Cu-) TiO2particles With the exception of the

50mol Fe-TiO2and Cu-TiO

2samples all isotherms were

close to type II according to the IUPAC classification [36]indicating the lack of pores in the particles Otherwise theisotherms of the 50mol Fe-TiO

2and Cu-TiO

2samples

were attributed to type IV indicating bulk pores by aggre-gation between each nanoparticle The hysteresis slopes wereobserved at intermediate and relative pressures greater than119901119901

0= 07 in all samples

Table 1 lists the specific surface areas of the 50molM-TiO

2samples The specific surface areas were located in

the range 68sim165m2 gminus1 In particular the surface area wasthe largest at 165m2 gminus1 in 50mol Fe-TiO

2 In general

the surface area increases with decreasing particle size [37]These results showed some degree of reliability and were wellmatched to their calculated crystallite sizes (Figure 2) Fromthe results of the average bulk pore diameter for the samplesit is believed that the 50mol Fe-TiO

2and Cu-TiO

2may

contain bulk mesopores approximately 15sim24 nm due toaggregation between their nanoparticles Otherwise the porevolumes of the samples were varied from 017 to 064 cm3 gminus1The atomic compositions calculated the energy-dispersive X-ray spectra that are also included in this table The TiO

2

surface showed only two elements Ti and O whereas threeelements were observed in theM-TiO

2samples In contrast to

expectations the amount of doped metals was much higherthan the Ti amount in all samples and the M Ti ratios wereapproximately 1 10This was calculated from EDAX analysisand the values were different from the actual amount Theamount of metal doped in TiO

2was reduced to the order of

Fe gt Co gt Ni gt CuDuring the CO

2photoreduction reaction CO

2is

adsorbed onto the surface of the photocatalysts in the firststep and the photoreduction reaction progresses Thereforethe photocatalytic performance depends on the adsorptioncapacities of CO

2 Accordingly the CO

2adsorption abilities

of the 50mol M (Fe- Co- Ni- and Cu-) TiO2samples

need to be determined The CO2desorption profiles were

obtained over the range 50sim900∘C as shown in Figure 6Thecurve intensity for CO

2desorption was higher in 50mol

M-TiO2than in pure TiO

2 which means considerably more

CO2molecules had been adsorbed on the surfaces of the

50mol M-TiO2samples In addition TiO

2generally has

6 International Journal of Photoenergy

ADSDES

0

50

100

150V

ac

m3(S

TP) g

minus1

05 10

pp0

(a) TiO2

ADSDES

0

200

400

600

Vac

m3(S

TP) g

minus1

05 10

pp0

(b) 50mol- Fe-TiO2

ADSDES

0

50

100

150

Vac

m3(S

TP) g

minus1

05 10

pp0

(c) 50mol- Co-TiO2

ADSDES

05 10

pp0

0

50

100

150

Vac

m3(S

TP) g

minus1

(d) 50mol- Ni-TiO2

ADSDES

05 10

pp0

0

120

240

360

Vac

m3(S

TP) g

minus1

(e) 50mol- Cu-TiO2

Figure 5 Adsorption-desorption isotherm curves of N2at 77 K for the as-synthesized 50mol M-TiO

2particles

Area integ(Gaussian) 27983665 33278233 66855506 68781188 60435286 10310403

Basalt fiber

2075000208000020850002090000209500021000002105000

TCD

(mV

)

400 600 800200

62750006300000632500063500006375000640000064250006450000

TCD

(mV

)

TiO2

6800000

6900000

7000000

7100000

7200000

7300000

7400000

7500000

7600000

7700000

TCD

(120583V

)

400 600 800200Temperature (∘C)

400 600 800200Temperature (∘C)

Basalt fiber TiO2

50mol Fe-TiO2

50mol Co-TiO2

50mol Ni-TiO2

50mol Fe-TiO2 50mol Co-TiO2 50mol Ni-TiO2 50mol Cu-TiO2

50mol Cu-TiO2

Figure 6 CO2desorption profiles over the 50mol M-TiO

2particles in the range 50sim900∘C

International Journal of Photoenergy 7

30120583m

ldquoTop viewrdquoldquoSide viewrdquo

20120583m

Basalt fiber (b) TiO2basalt fiber(a) Basalt fiber

basalt fiber

basalt fiber

basalt fiber basalt fiber basalt fiber

(c) 50mol Fe-TiO2

50mol Co-TiO2 (d) 50mol Co-TiO2 (e) 50mol Ni-TiO2 (f) 50mol Cu-TiO2

Figure 7 SEM images of the pure basalt fiber film and 50mol M-TiO2basalt fiber films

hydrophilic properties [38] which suggests that duringthe CO

2photoreduction reaction CO

2and H

2O will

be adsorbed preferentially on the metal ions and TiO2

respectively The adsorption abilities were observed inthe following order 50mol Co-TiO

2gt Ni-TiO

2gt

Fe-TiO2gt TiO

2gt Cu-TiO

2samples In general a rapid

catalytic reaction occurs when many reactants are well-adsorbed over the catalyst The presence of transition metalsin the 50mol M-TiO

2samples most likely caused the

relative increase in the number of CO2and H

2O molecules

adsorbed compared to pure TiO2 This synergy contributed

significantly to improving the catalytic performance of the50mol M-TiO

2samples

32 Characteristics and CO2

Photoreduction over the50mol M (Fe- Co- Ni- and Cu-) TiO

2Basalt Fiber Films

Figure 7 presents SEM images (top and side views) of the sixsamples of pure basalt fiber and TiO

2films and 50mol

M (Fe- Co- Ni- and Cu-) TiO2basalt fiber films The

basalt fiber in the films was approximately 15 120583m in diameterwith different lengths and the surfaces were smooth The50mol M-TiO

2materials were mixed with basalt fibers

and were fabricated as thick films by coating on a Pyrex plateThe regular array of composites could be observed clearlythrough both the side and top directions The TiO

2basalt

fiber and 50mol Fe-TiO2basalt fiber composites did not

cover the Pyrex plate surface completely and bulk poreswere observed On the other hand the coating parts werequite uniform and fine particles were well-dispersed Incontrast the surfaces of the films fabricated from 50mol

Co-TiO2basalt fiber 50mol Ni-TiO

2basalt fiber and

50mol Cu-TiO2basalt fiber composites were quite dense

despite containing some cracks In particular the surfacewas the most compact over the 50mol Co-TiO

2basalt

fiber film The thickness of the films in all samples wasapproximately 30sim35 120583m with the exception of the purebasalt fiber film (20 120583m)

Energy-dispersive X-ray spectroscopy (EDAX) con-firmed the presence of metals on the surfaces of the basaltfiber and 50mol M (Fe- Co- Ni- and Cu-) TiO

2basalt

fiber films as shown in Figure 8 and the table below liststhe atomic compositions determined by EDAX For the basaltfiber various metal oxides were observed such as Na KCa Mg Al Si Fe and Ti Pure basalt fiber exhibited acomposition of 1928wt Si 314 wt total alkali metals166wt Ti 1177 wt Fe and 561 wt Al As a CO

2

adsorbent the Ca and Mg contents were 531 and 209wtrespectively Ti contained on the 50mol M (Fe- Co-Ni- and Cu-) TiO

2basalt fiber films decreased in the

following order 50mol Ni-TiO2(4774wt) gt Co-TiO

2

(4268wt) gt TiO2(4094wt) gt Fe-TiO

2(3344wt)

The amounts of transitionmetal specieswere in the range 269to 302wt with the exception of copper (098wt) Thesevalues did not appear to be perfectly quantitative EDAXis a very good surface analytical method but it is prone toerror because the composition can vary according to thelocation In particular the variation is large when the sampleis nonuniform [39]

The efficiencies of the photogenerated electron-hole pro-duction in the basalt fiber and 50mol M (Fe- Co- Ni-

8 International Journal of Photoenergy

MaterialselementAtomic compositions (wt-)

(a)

(b)

(c)

(d)

(e)

Na

204

mdash

mdash

192

160

Mg

209

mdash

mdash

mdash

mdash

Al

561

mdash

mdash

059

mdash

Si

1928

mdash

mdash

228

032

K

110

mdash

mdash

mdash

mdash

Ca

531

mdash

mdash

066

mdash

Fe

1177

mdash

286

114

mdash

Co

mdash

mdash

mdash

269

mdash

Ni

mdash

mdash

mdash

mdash

302

(f)

O

5114

5906

4122

4803

4732

4543

Ti

166

4094

3344

4268

4774

3615

Cu

mdash

mdash

mdash

mdash

mdash

098

Spectrum 1Ca Si

FeTi

OAl

Mg

NaK

CaK

Ti FeFe

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 1

Ti

O

Ti

2 4 6 1810 16 200 128 14(keV)

Spectrum 3

TiO

Ti

FeFe

Fe

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 2Ti

O

CuCuCu

Ti

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 4

NiNiNi Si

Ti

O

NaTi

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 2Ca

Si

Fe

Ti

O

AlNa

Ca

Co

Co

Co

Ti

FeFe

2 4 6 8 10 12 14 16 18 200(keV)

Full scale 767 cts cursor 0000Full scale 4345 cts cursor 0000Full scale 1548 cts cursor 0000

Full scale 1428 cts cursor 0000 Full scale 2264 cts cursor 0000 Full scale 830 cts cursor 0000

(b) TiO2basalt fiber(a) Basalt fiber

(d) 50mol Co-TiO2basalt fiber (f) 50mol Cu-TiO2basalt fiber(e) 50mol Ni-TiO2basalt fiber

(c) 50mol Fe-TiO2basalt fiber

Figure 8 Energy-dispersive X-ray spectra of the surfaces of the pure basalt fiber and 50mol M-TiO2basalt fiber films and the atomic

compositions

and Cu-) TiO2basalt fiber films were measured from the

photocurrent response under solar light irradiation at anapplied potential of 07 V versus SCE Figure 9 shows thetypical real time photocurrent response of the films whenthe light source is switched on and off exhibiting a rapidphotocurrent rise and decay In semiconductor systemswhen irradiation provides an energy higher than the band-gap of a semiconductor the energy excites an electron fromthe valence band to the conduction band leaving a hole inthe valence band The electron-hole pair is responsible forthe photocurrent When the light was turned on a rapidincrease in the photoreduction current was observed andthe photocurrent then turned to a steady state after a fewseconds When the light was turned off the photocurrentdecreased instantaneously to almost zero [40]When the lightwas turned on the maximum photocurrents obtained forthe 50mol Co-TiO

2and Ni-TiO

2basalt fiber films were

31049 and 30075mA cmminus2 respectively which were morethan four times higher than that achieved on pure basalt fiber

(7123mA cmminus2) andTiO2basalt fiber films (7401mA cmminus2)

Themaximumphotocurrent of the 50molCu-TiO2basalt

fiber film was too small due to trapping of excited elec-trons by copper with strong oxidation agency In additionthe TiO

2basalt fiber 50mol Cu-TiO

2basalt fiber and

50mol Ni-TiO2basalt fiber films showed no current

transients in both the light-on and the light-off regions inthe samples falling off with time in 50 s to a steady statewhich indicates that few surface recombination processeshad occurred Clearly some electron-hole recombinationwas observed in the 50mol Fe-TiO

2basalt fiber and Co-

TiO2basalt fiber films but it was negligible compared to

the total current value Therefore the 3d-transition metalingredients have a beneficial effect on the photocurrent itplays a role as an intermediate for the efficient separation ofphotogenerated hole-electron pairs

Figure 10 presents the photoreduction abilities of CO2

with H2O vapor to CH

4over the pure basalt fiber film and

50mol M (Fe- Co- Ni- and Cu-) TiO2basalt fiber films

International Journal of Photoenergy 9

3104930075

20974

7123 74016450

TiO2basalt fiberBasalt fiber

50 100 150 200 250 300 3500Time (s)

minus50

0

50

100

150

200

250

300

350

Curr

ent (

mA

cm

2)

50mol Cu-TiO2basalt fiber50mol Ni-TiO2basalt fiber

50mol Fe-TiO2basalt fiber50mol Co-TiO2basalt fiber

Figure 9 Photocurrent responses of the pure basalt fiber and50mol M-TiO

2basalt fiber films when the light source was

switched on and off

after 8 h Generally CH4production from CO

2reduction

with H2O can be divided into the following three subpro-

cesses [41] proton production from H2O photodecompo-

sition CO radical production from CO2photo cleavage

and methane production from photosynthesis between theCO radical and proton The photogenerated electrons onthe photocatalysts by UV-radiation induce CO

2reduction

to produce CO2radicals whereas the holes react with the

adsorbed H2Omolecules to perform oxidationThe interme-

diate photogenerated species undergo different reactions toproduce CO CH

3OH andCH

4The production of CH

4from

methyl radicals (∙CH3) was confirmed which are dependent

directly on the formation of the intermediate product CO[42] As shown in this figure almost no methane wasobserved when only the lamp was turned on On the otherhand the amounts of CO and O

2generation increased and

a small amount of hydrogen was observed This means thatthe light does not induce photoreduction processes aloneOn the other hand there are different product distributionsaccording to the loaded metal species excessive methane isgenerated over the catalysts loaded with Ni and Co and thequantities of CO and CH

3OH gases are increased over the

catalysts loaded with Cu and Fe The M-TiO2basalt fiber

films showed higher CH4production from CO

2photoreduc-

tion than the pure basalt fiber and TiO2basalt fiber films

700 120583mol gcatminus1 Lminus1 CH

4was emitted over the pure basalt

fiber film suggesting that it contains a small amount of TiO2

On the other hand CH4production was 1121 120583mol gcat

minus1 Lminus1over the TiO

2basalt fiber film In contrast the maximum

Lamp turned on only

TiO2basalt fiberBasalt fiber

1 2 3 4 5 6 7 80Time (h)

0

50

100

150

200

250

300

350

400

Met

hane

yie

ld (120583

mol

g-c

atlowast

L)

50mol Cu-TiO2basalt fiber50mol Ni-TiO2basalt fiber

50mol Fe-TiO2basalt fiber50mol Co-TiO2basalt fiber

Figure 10 Photoreduction abilities of CO2with H

2O vapor to CH

4

over the pure basalt fiber film and 50mol M-TiO2basalt fiber

films after 8 h

CH4yields over the 50mol Co-TiO

2basalt fiber and Ni-

TiO2basalt fiber films were 3605 and 3073 120583mol gcat

minus1 Lminus1respectively The differences in yields were attributed to theirband-gaps electron-hole recombination tendencies and thegas adsorption abilities of the 50mol M-TiO

2basalt fiber

films In particular this study confirmed that the 50molCo-TiO

2particles show synergistic performance when the

basalt fiber is mixedThe reduction ofCO

2requires amultiple electron transfer

and leads to production of a variety of products dependingon the number of transferred electrons which determinethe final oxidation state of the carbon atom The standardredox potentials of the CO

2reduction half-reactions vary

from CO2HCOOH [43] to CO

2CH4[44] CO

2adsorbed

on a photocatalyst surface can be reduced to ∙CO2

minus anionradical which can react withH+ and eminus for formingHCOOHor HCOOminus or which can go to the postulated disproportion-ation reaction of two ∙CO

2

minus anion radicals into CO (afterall to be C radical) and CO

3

2minus to react with H radical Thisstudy seems to follow the latter Scheme 1 presents a modelfor CO

2photoreduction over the M-TiO

2basalt fiber films

based on the relationships between the optical propertiesof the photocatalysts and the catalytic activities Photonexcitation in M-TiO

2over the M-TiO

2basalt fiber films

will begin rapidly because M-TiO2has a shorter band-gap

than pure TiO2 and the excited electrons can be transferred

efficiently to CO2molecules In addition CO

2molecules

are adsorbed preferentially and easily on the basalt fibersurface The positive holes on the valance band of M-TiO

2

can be trapped byH2Ospecies and transferred toOH radicals

and protons The protons obtained are transformed to H

10 International Journal of Photoenergy

O

Basalt fiberFTO glass

FTO glass

H2

CO2

Basalt fiber (i) More CO2 adsorption good

H2O

∙H

∙CO2minus

+ ∙H rarr ∙CHrarr ∙CH2 rarr ∙CH3 rarr CH4

Reduction CO2 + eminus rarr ∙CO2minus

h+

eminus

h+

eminus

pasteM-TiO2basalt fiber

M-TiO2

ldquoMetal incorporatedrdquoUV light

decreaseTiO2 M-TiO2 M-TiO2

(i) Easy electron transfer(ii) Water (H2O) adsorption goodM-TiO2

Oxidation H2O + h+ rarr ∙OH + H+ H+ + O2997888rarr

Scheme 1 Model for CH4production from the photoreduction of CO

2with H

2O vapor over the M-TiO

2basalt fiber films

radicals by electrons and the H radicals then react with Cand CO radicals formed from the reduction of CO

2

minus overM-TiO

2 particularly over Co- or Ni-TiO

2semiconductors

resulting methane production [45] The mixed films ofbasalt fibers and M-TiO

2can also promote the separation

of photogenerated electron-hole pairs (eminush+) on M-TiO2

Therefore the synergetic effects of the basalt fibers and M-TiO2in the M-TiO

2basalt fiber films achieved higher CO

2

reduction efficiency

4 Conclusions

The 50mol M (Fe- Co- Ni- and Cu-) incorporated TiO2

photocatalysts obtained by the solvothermal method werecoated densely with basalt fibers on a Pyrex plate usinga squeeze technique and applied to the photoreduction ofCO2to CH

4 The CO

2adsorption abilities were improved

over the basalt fiber and CH4generation was enhanced

dramatically over 50mol M-TiO2basalt fiber films with

a threefold higher yield compared to the pure basalt fiberand TiO

2basalt fiber films In particular the photoreduction

of CO2with H

2O revealed a remarkable increase in CH

4

generation over the 50mol Co-TiO2basalt fiber film to

3605 120583mol gcatminus1sdotLminus1 after an 8 h reaction

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

This research was supported by ceramic fiber commercialcenter project of Korea Institute of Ceramic Engineeringamp Technology (KICET) funded by the Ministry of TradeIndustry amp Energy (MOTIE)

References

[1] M Tahir and N S Amin ldquoIndium-doped TiO2nanoparticles

for photocatalytic CO2reduction with H

2O vapors to CH

4rdquo

Applied Catalysis B Environmental vol 162 pp 98ndash109 2015[2] B S Kwak andM Kang ldquoPhotocatalytic reduction of CO

2with

H2O using perovskite Ca

119909Ti119910O3rdquo Applied Surface Science vol

337 pp 138ndash144 2015[3] C Fletcher Y Jiang and R Amal ldquoProduction of formic acid

from CO2reduction by means of potassium borohydride at

ambient conditionsrdquo Chemical Engineering Science vol 137 pp301ndash307 2015

[4] G Mahmodi S Sharifnia M Madani and V VatanpourldquoPhotoreduction of carbon dioxide in the presence of H

2 H2O

and CH4over TiO

2and ZnO photocatalystsrdquo Solar Energy vol

97 pp 186ndash194 2013[5] J Albo A Saez J Solla-Gullon V Montiel and A Irabien

ldquoProduction of methanol from CO2electroreduction at Cu

2O

and Cu2OZnO-based electrodes in aqueous solutionrdquo Applied

Catalysis B Environmental vol 176-177 pp 709ndash717 2015[6] P Akhter M Hussain G Saracco and N Russo ldquoNew nanos-

tructured silica incorporated with isolated Ti material for the

International Journal of Photoenergy 11

photocatalytic conversion of CO2to fuelsrdquo Nanoscale Research

Letters vol 9 article 158 2014[7] M Anpo ldquoPhotocatalytic reduction of CO

2with H

2O on

highly dispersed Ti-oxide catalysts as a model of artificialphotosynthesisrdquo Journal of CO

2Utilization vol 1 pp 8ndash17 2013

[8] H Abdullah M R Khan M Pudukudy Z Yaakob and NA Ismail ldquoCeO

2-TiO2as a visible light active catalyst for the

photoreduction ofCO2tomethanolrdquo Journal of Rare Earths vol

33 no 11 pp 1155ndash1161 2015[9] O Ola and M Mercedes Maroto-Valer ldquoReview of material

design and reactor engineering on TiO2photocatalysis for

CO2reductionrdquo Journal of Photochemistry and Photobiology C

Photochemistry Reviews vol 24 pp 16ndash42 2015[10] X Zhang L Wang Q Du Z Wang S Ma and M Yu

ldquoPhotocatalytic CO2reduction over B

4CC3N4with internal

electric field under visible light irradiationrdquo Journal of Colloidand Interface Science vol 464 pp 89ndash95 2016

[11] R Gusain P Kumar O P Sharma S L Jain and O PKhatri ldquoReduced graphene oxide-CuO nanocomposites forphotocatalytic conversion of CO

2into methanol under visible

light irradiationrdquo Applied Catalysis B Environmental vol 181pp 352ndash362 2016

[12] N M Nursam X Wang and R A Caruso ldquoHigh-throughputsynthesis and screening of titania-based photocatalystsrdquo ACSCombinatorial Science vol 17 no 10 pp 548ndash569 2015

[13] M V Dozzi S Marzorati M Longhi M Coduri L Artigliaand E Selli ldquoPhotocatalytic activity of TiO

2-WO3mixed oxides

in relation to electron transfer efficiencyrdquo Applied Catalysis BEnvironmental vol 186 pp 157ndash165 2016

[14] Y Qu and X Duan ldquoProgress challenge and perspective ofheterogeneous photocatalystsrdquo Chemical Society Reviews vol42 no 7 pp 2568ndash2580 2013

[15] J C Colmenares R Luque J M Campelo F Colmenares ZKarpinski and A A Romero ldquoNanostructured photocatalystsand their applications in the photocatalytic transformation oflignocellulosic biomass an overviewrdquo Materials vol 2 no 4pp 2228ndash2258 2009

[16] M Kitano M Matsuoka M Ueshima and M Anpo ldquoRecentdevelopments in titanium oxide-based photocatalystsrdquo AppliedCatalysis A General vol 325 no 1 pp 1ndash14 2007

[17] P Silija Z Yaakob V Suraja N N Binitha and Z S Akmal ldquoAnenthusiastic glance in to the visible responsive photocatalystsfor energy production and pollutant removal with specialemphasis on titaniardquo International Journal of Photoenergy vol2012 Article ID 503839 19 pages 2012

[18] H Xu S Ouyang L Liu P Reunchan N Umezawa and JYe ldquoRecent advances in TiO

2-based photocatalysisrdquo Journal of

Materials Chemistry A vol 2 no 32 pp 12642ndash12661 2014[19] Z He J Tang J Shen J Chen and S Song ldquoEnhancement of

photocatalytic reduction of CO2to CH

4over TiO

2nanosheets

by modifying with sulfuric acidrdquo Applied Surface Science vol364 pp 416ndash427 2016

[20] O Ola and M M Maroto-Valer ldquoTransition metal oxide basedTiO2nanoparticles for visible light induced CO

2photoreduc-

tionrdquo Applied Catalysis A General vol 502 pp 114ndash121 2015[21] D Eder ldquoCarbon nanotube-inorganic hybridsrdquo Chemical

Reviews vol 110 no 3 pp 1348ndash1385 2010[22] L Zhang R JamalQ ZhaoMWang andTAbdiryim ldquoPrepa-

ration of PEDOTGO PEDOTMnO2 and PEDOTGOMnO

2

nanocomposites and their application in catalytic degradationof methylene bluerdquo Nanoscale Research Letters vol 10 p 1482015

[23] M Urbanski A Lapko and A Garbacz ldquoInvestigation onconcrete beams reinforced with basalt rebars as an effectivealternative of conventional RC structuresrdquo Procedia Engineer-ing vol 57 pp 1183ndash1191 2013

[24] S A Chernyak E V Suslova A V Egorov L Lu S V Savilovand V V Lunin ldquoNew hybrid CNT-alumina supports for Co-based Fischer-Tropsch catalystsrdquo Fuel Processing Technologyvol 140 pp 267ndash275 2015

[25] K Shimura T Miyazawa T Hanaoka and S Hirata ldquoFischerndashTropsch synthesis over alumina supported bimetallic CondashNicatalyst effect of impregnation sequence and solutionrdquo Journalof Molecular Catalysis A Chemical vol 407 pp 15ndash24 2015

[26] F Fazlollahi M Sarkari A Zare A A Mirzaei and HAtashi ldquoDevelopment of a kinetic model for Fischer-Tropschsynthesis over CoNiAl

2O3catalystrdquo Journal of Industrial and

Engineering Chemistry vol 18 no 4 pp 1223ndash1232 2012[27] J Zhao W Xing Y Li and K Lu ldquoSolvothermal synthesis and

visible light absorption of anatase TiO2rdquo Materials Letters vol

145 pp 332ndash335 2015[28] S Liu J Yu and M Jaroniec ldquoAnatase TiO

2with dominant

high-energy 001 facets Synthesis properties and applicationsrdquoChemistry of Materials vol 23 no 18 pp 4085ndash4093 2011

[29] T Ungar ldquoMicrostructural parameters from X-ray diffractionpeak broadeningrdquo Scripta Materialia vol 51 no 8 pp 777ndash7812004

[30] A W Burton K Ong T Rea and I Y Chan ldquoOn the esti-mation of average crystallite size of zeolites from the Scherrerequation a critical evaluation of its application to zeolites withone-dimensional pore systemsrdquo Microporous and MesoporousMaterials vol 117 no 1-2 pp 75ndash90 2009

[31] A Jaroenworaluck N Pijarn N Kosachan and R StevensldquoNanocomposite TiO

2ndashSiO2gel for UV absorptionrdquo Chemical

Engineering Journal vol 181-182 pp 45ndash55 2012[32] J I Pena-Flores A F Palomec-Garfias C Marquez-Beltran

E Sanchez-Mora E Gomez-Barojas and F Perez-RodrıguezldquoFe effect on the optical properties of TiO

2Fe2O3nanostruc-

tured composites supported on SiO2microsphere assembliesrdquo

Nanoscale Research Letters vol 9 article 499 2014[33] D Kim Y Im K M Jeong S-M Park M-H Um and M

Kang ldquoEnhanced 2-chorophenol photodecomposition usingnano-sized Mn-incorporated TiO

2powders prepared by a

solvothermal methodrdquo Bulletin of the Korean Chemical Societyvol 35 no 8 pp 2295ndash2298 2014

[34] C C Huang C C Wu K Knight and D W Hewak ldquoOpticalproperties of CVD grown amorphous Ge-Sb-S thin filmsrdquoJournal of Non-Crystalline Solids vol 356 no 4-5 pp 281ndash2852010

[35] J Kim J S Lee and M Kang ldquoSynthesis of nanoporousstructured SnO

2and its photocatalytic ability for bisphenol a

destructionrdquo Bulletin of the Korean Chemical Society vol 32 no5 pp 1715ndash1720 2011

[36] M Thommes ldquoPhysical adsorption characterization ofnanoporous materialsrdquo Chemie Ingenieur Technik vol 82 no 7pp 1059ndash1073 2010

[37] A A Gribb and J F Banfield ldquoParticle size effects on trans-formation kinetics and phase stability in nanocrystalline TiO

2rdquo

American Mineralogist vol 82 no 7-8 pp 717ndash728 1997[38] S-H Nam S-J Cho C-K Jung et al ldquoComparison of

hydrophilic properties of TiO2thin films prepared by solndashgel

method and reactive magnetron sputtering systemrdquo Thin SolidFilms vol 519 no 20 pp 6944ndash6950 2011

12 International Journal of Photoenergy

[39] H G Feichtinger K Grochenig and T Strohmer ldquoEffi-cient numerical methods in non-uniform sampling theoryrdquoNumerische Mathematik vol 69 no 4 pp 423ndash440 1995

[40] S W Jo B S Kwak K M Kim et al ldquoEffectively CO2

photoreduction toCH4by the synergistic effects of Ca andTi on

Ca-loaded TiSiMCM-41 mesoporous photocatalytic systemsrdquoApplied Surface Science vol 355 pp 891ndash901 2015

[41] J Y Do Y Im B S Kwak J-Y Kim and M Kang ldquoDramaticCO2photoreduction with H

2O vapors for CH

4production

using the TiO2(bottom)FendashTiO

2(top) double-layered filmsrdquo

Chemical Engineering Journal vol 275 pp 288ndash297 2015[42] M Tahir andN SaidinaAmin ldquoPhotocatalytic reduction of car-

bon dioxide with water vapors over montmorillonite modifiedTiO2nanocompositesrdquo Applied Catalysis B Environmental vol

142-143 pp 512ndash522 2013[43] Y Kohno H Hayashi S Takenaka T Tanaka T Funabiki

and S Yoshida ldquoPhoto-enhanced reduction of carbon dioxidewith hydrogen over RhTiO

2rdquo Journal of Photochemistry and

Photobiology A Chemistry vol 126 no 1ndash3 pp 117ndash123 1999[44] M Subrahmanyam S Kaneco and N Alonso-Vante ldquoA screen-

ing for the photo reduction of carbon dioxide supported onmetal oxide catalysts for C

1-C3selectivityrdquo Applied Catalysis B

Environmental vol 23 no 2-3 pp 169ndash174 1999[45] S S Tan L Zou and E Hu ldquoKinetic modelling for photosyn-

thesis of hydrogen and methane through catalytic reduction ofcarbon dioxide with water vapourrdquo Catalysis Today vol 131 no1ndash4 pp 125ndash129 2008

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

International Journal of Photoenergy 3

Quartz

Water

UV-lamp

and FIDGC-TCD

Reaction conditionsUV-lamp 2ea (6W 365nm)

Volume 60mLTemperature 40∘C

CO2

20m

m8

mm

15mm

5mm

Heizung(rpm)

Ruhrger at(∘C)

EinausEinaus

= 2 (10 mmol) 1 (05 mmol)Water CO2

Figure 1 Batch type photoreactor used for CO2photoreduction to CH

4

off-line using a gas tight syringe (Agilent 250 120583m) with thesame volume and analyzed by gas chromatography (GCiGC7200 Donam Co Republic of Korea) equipped with athermal conductivity detector (TCD) and a flame-ionizeddetector (FID) First the gaseous products produced by thein situ system were flowed into the TCD detector that wasconnected to a Carboxen 1000 (Young Lin InstrumentalsCo Republic of Korea) column to analyze the light gases(H2 O2 CO CO

2 CH3OH and CH

3COOH) The extracted

gases were then inserted into the FID detector to separatethe C

1(methane)ndashC

3light hydrocarbons The selectivity of

the product was calculated using the following equation C119894

() = C119894moles in producttotal moles of C produced times 100

3 Results and Discussion

31 Physical Properties of the 50mol M (Fe- Co- Ni-and Cu-) TiO

2Powders Figure 2 presents XRD patterns of

the basalt fiber pure TiO2 and 50mol M (Fe- Co- Ni-

and Cu-) TiO2powders All the peaks for the 50mol M-

TiO2powders were assigned to the anatase TiO

2tetragonal

structure [28] The XRD patterns showed the main peaksat 2535∘ 3779∘ 4808∘ 5392∘ 5512∘ 6273∘ 6860∘ 7036∘7509∘ 8314∘ and 9518∘ 2120579 whichwere assigned to the (d101)(d004) (d200) (d105) (d211) (d204) (d116) (d220) (d215)(d312) and (d321) planes respectively Depending on theaddition of other transition metals to the TiO

2framework

the peak intensities decreased slightly with some broadeningOn the other hand no peaks were observed for the addedmetals oxide forms which mean that the metal ions hadbeen well-inserted into the TiO

2framework Generally peak

broadening indicates a decrease in crystallite size [29] Peakbroadening of the d101 peak is related to the crystallite size ofthe tetragonal crystalline phase of anatase Debye-Scherrerrsquosequation [30] was used to determine the crystallite size and

lattice strain Based on the full width at half maximum heightof the d101 peak the crystallite sizes (lattice strains) for TiO

2

and 50mol Fe- Co- Ni- and Cu-TiO2were 13 (0013)

and 14 (0012) 14 (0012) 16 (0010) and 17 (0009) nmrespectively

Figures 3(a) and 3(b) show the UV-visible absorptionspectra and their Taucrsquos plots of the prepared 50mol M(Fe- Co- Ni- and Cu-) TiO

2powders An absorption band

for the anatase structured TiO2(Figure 3(a)) was observed

in the UV-region around 378 nm when extrapolated whichis similar to the absorption wavelength reported elsewhere[31] According to the addition of transition metal speciesthere are different absorption band shifts which were shiftedto higher wavelengths compared to the absorption band ofTiO2 The 50mol M-TiO

2samples showed broad curves

for the metal oxides in the visible region the maximumabsorption was observed at 490 580 700 (too broad) and650 (too broad) nm for 50mol Fe- Co- Ni- and Cu-TiO2 respectively These bands can convert to the following

absorption terms using Tanabe-Suganorsquos energy absorption[32] 5T

2g rarr5Eg for d6-FeO 4T

1g rarr4T2g for d7-CoO

3A2g rarr

3T2g for d8-NiO and 2Eg rarr

2T2g for the d9

electron configuration CuO Generally the band-gap in asemiconductor material is closely related to the wave rangeabsorbed the larger the absorption wavelength the narrowerthe band-gap [33] Using Taucrsquos equation [34] the band-gapsfor the absorption of TiO

2and 50mol Fe- Co- Ni- and

Cu-TiO2in the UV-region were estimated to be 318 and 280

248 298 and 310 eV respectively as shown in Figure 3(b)The inserted transition metals could alter the band-gap ofTiO2significantly leading to easy absorption and eventually

efficient photocatalysisFigure 4 presents the PL spectra of the prepared 50mol

M (Fe- Co- Ni- and Cu-) TiO2particles The PL curve

4 International Journal of Photoenergy

20 30 40 50 60 70 80

Inte

nsity

(au

)(f) Basalt fiber

20 30 40 50 60 70 80100

100

200

300

400

500

600

Inte

nsity

(cps

)

(a) TiO2

1205722120579CuK

1205722120579CuK

(e) 50mol Cu-TiO2

(d) 50mol Ni-TiO2

(b) 50mol Fe-TiO2

(c) 50mol Co-TiO2

Figure 2 XRD patterns of the basalt fiber pure TiO2 and 50mol M-TiO

2powders

Basalt fiberTiO2

400 500 600 700 800300Wavelength (nm)

00

02

04

06

08

10

12

14

16

Abso

rban

ce (a

u)

50mol Fe-TiO2

50mol Co-TiO2

50mol Ni-TiO2

50mol Cu-TiO2

(a)

Sample Band-gap (eV)TiO2

310 (387nm)298 (403nm)248 (485nm)280 (428nm)318 (378nm)

(120572h

)2

2 3 4 51Photon energy (eV)

00

01

02

03

50mol Cu-TiO2

50mol Ni-TiO2

50mol Fe-TiO2

50mol Co-TiO2

(b)

Figure 3 Diffuse reflectance-UV-visible absorption spectra (a) and their Taucrsquos plots (b) of the prepared 50mol M-TiO2powders

International Journal of Photoenergy 5

Table 1 Physical properties of 50mol M-TiO2particles

Physical properties of catalysts Atomic compositionsTi M O

Specific surface areas[m2 gminus1]

Total pore volume[cm3 gminus1]

Average pore diameter[nm]

TiO2 320 00 680 131 020 617

50mol Fe-TiO2 302 37 660 165 064 1556

50mol Co-TiO2 306 34 670 124 017 563

50mol Ni-TiO2 289 31 680 130 018 563

50mol Cu-TiO2 316 29 655 67 042 2495

Basalt fiberTiO2

400 500 600 700 800300Wavelength (nm)

00

05

10

15

20

25

Inte

nsity

(V)

50mol Cu-TiO2

50mol Ni-TiO2

50mol Co-TiO2

50mol Fe-TiO2

Figure 4 PL spectra of the prepared 50mol M-TiO2particles

suggests that the electrons in the valence band are transferredto the conduction band and are stabilized by photoemissionIn general the PL intensity increases with increasing numberof electrons emitted resulting from recombination betweenthe excited electrons and holes and a consequent decreasein photoactivity [35] Therefore there is a strong relationshipbetween the PL intensity and photoactivity In particularthe PL intensity decreases significantly when a metal cancapture excited electrons or exhibit conductivity which isknown as the relaxation process The 50mol M-TiO

2

samples exhibited a PL signal with a similar curve shapedemonstrating the presence of TiO

2 Pure TiO

2exhibited a

strong PL signal in the range 400ndash550 nm with a maximumexcitation wavelength of 445 nm whereas the 50molM-TiO

2curve intensities were weakened dramatically The

decreasing tendency was observed in the following orderTiO2gt 50mol Fe-TiO

2gt Cu-TiO

2gt Ni-TiO

2gt Co-

TiO2 which was possibly due to the new oxygen vacancies

produced by metal-doping The photogenerated electronsin the conduction band initially reached the vacant spaceand then recombined with the photogenerated holes in thevalance band to produce fluorescence emission The reducedPL intensities of 50mol M-TiO

2might be due to defects

generated by the transition metal ions inserted into the TiO2

structures which accelerate electron transfer and hinder

electron-hole pair recombination on the 50mol M-TiO2

surfaceFigure 5 shows the adsorption-desorption isotherm

curves of N2at 77 K for the as-synthesized 50mol M (Fe-

Co- Ni- and Cu-) TiO2particles With the exception of the

50mol Fe-TiO2and Cu-TiO

2samples all isotherms were

close to type II according to the IUPAC classification [36]indicating the lack of pores in the particles Otherwise theisotherms of the 50mol Fe-TiO

2and Cu-TiO

2samples

were attributed to type IV indicating bulk pores by aggre-gation between each nanoparticle The hysteresis slopes wereobserved at intermediate and relative pressures greater than119901119901

0= 07 in all samples

Table 1 lists the specific surface areas of the 50molM-TiO

2samples The specific surface areas were located in

the range 68sim165m2 gminus1 In particular the surface area wasthe largest at 165m2 gminus1 in 50mol Fe-TiO

2 In general

the surface area increases with decreasing particle size [37]These results showed some degree of reliability and were wellmatched to their calculated crystallite sizes (Figure 2) Fromthe results of the average bulk pore diameter for the samplesit is believed that the 50mol Fe-TiO

2and Cu-TiO

2may

contain bulk mesopores approximately 15sim24 nm due toaggregation between their nanoparticles Otherwise the porevolumes of the samples were varied from 017 to 064 cm3 gminus1The atomic compositions calculated the energy-dispersive X-ray spectra that are also included in this table The TiO

2

surface showed only two elements Ti and O whereas threeelements were observed in theM-TiO

2samples In contrast to

expectations the amount of doped metals was much higherthan the Ti amount in all samples and the M Ti ratios wereapproximately 1 10This was calculated from EDAX analysisand the values were different from the actual amount Theamount of metal doped in TiO

2was reduced to the order of

Fe gt Co gt Ni gt CuDuring the CO

2photoreduction reaction CO

2is

adsorbed onto the surface of the photocatalysts in the firststep and the photoreduction reaction progresses Thereforethe photocatalytic performance depends on the adsorptioncapacities of CO

2 Accordingly the CO

2adsorption abilities

of the 50mol M (Fe- Co- Ni- and Cu-) TiO2samples

need to be determined The CO2desorption profiles were

obtained over the range 50sim900∘C as shown in Figure 6Thecurve intensity for CO

2desorption was higher in 50mol

M-TiO2than in pure TiO

2 which means considerably more

CO2molecules had been adsorbed on the surfaces of the

50mol M-TiO2samples In addition TiO

2generally has

6 International Journal of Photoenergy

ADSDES

0

50

100

150V

ac

m3(S

TP) g

minus1

05 10

pp0

(a) TiO2

ADSDES

0

200

400

600

Vac

m3(S

TP) g

minus1

05 10

pp0

(b) 50mol- Fe-TiO2

ADSDES

0

50

100

150

Vac

m3(S

TP) g

minus1

05 10

pp0

(c) 50mol- Co-TiO2

ADSDES

05 10

pp0

0

50

100

150

Vac

m3(S

TP) g

minus1

(d) 50mol- Ni-TiO2

ADSDES

05 10

pp0

0

120

240

360

Vac

m3(S

TP) g

minus1

(e) 50mol- Cu-TiO2

Figure 5 Adsorption-desorption isotherm curves of N2at 77 K for the as-synthesized 50mol M-TiO

2particles

Area integ(Gaussian) 27983665 33278233 66855506 68781188 60435286 10310403

Basalt fiber

2075000208000020850002090000209500021000002105000

TCD

(mV

)

400 600 800200

62750006300000632500063500006375000640000064250006450000

TCD

(mV

)

TiO2

6800000

6900000

7000000

7100000

7200000

7300000

7400000

7500000

7600000

7700000

TCD

(120583V

)

400 600 800200Temperature (∘C)

400 600 800200Temperature (∘C)

Basalt fiber TiO2

50mol Fe-TiO2

50mol Co-TiO2

50mol Ni-TiO2

50mol Fe-TiO2 50mol Co-TiO2 50mol Ni-TiO2 50mol Cu-TiO2

50mol Cu-TiO2

Figure 6 CO2desorption profiles over the 50mol M-TiO

2particles in the range 50sim900∘C

International Journal of Photoenergy 7

30120583m

ldquoTop viewrdquoldquoSide viewrdquo

20120583m

Basalt fiber (b) TiO2basalt fiber(a) Basalt fiber

basalt fiber

basalt fiber

basalt fiber basalt fiber basalt fiber

(c) 50mol Fe-TiO2

50mol Co-TiO2 (d) 50mol Co-TiO2 (e) 50mol Ni-TiO2 (f) 50mol Cu-TiO2

Figure 7 SEM images of the pure basalt fiber film and 50mol M-TiO2basalt fiber films

hydrophilic properties [38] which suggests that duringthe CO

2photoreduction reaction CO

2and H

2O will

be adsorbed preferentially on the metal ions and TiO2

respectively The adsorption abilities were observed inthe following order 50mol Co-TiO

2gt Ni-TiO

2gt

Fe-TiO2gt TiO

2gt Cu-TiO

2samples In general a rapid

catalytic reaction occurs when many reactants are well-adsorbed over the catalyst The presence of transition metalsin the 50mol M-TiO

2samples most likely caused the

relative increase in the number of CO2and H

2O molecules

adsorbed compared to pure TiO2 This synergy contributed

significantly to improving the catalytic performance of the50mol M-TiO

2samples

32 Characteristics and CO2

Photoreduction over the50mol M (Fe- Co- Ni- and Cu-) TiO

2Basalt Fiber Films

Figure 7 presents SEM images (top and side views) of the sixsamples of pure basalt fiber and TiO

2films and 50mol

M (Fe- Co- Ni- and Cu-) TiO2basalt fiber films The

basalt fiber in the films was approximately 15 120583m in diameterwith different lengths and the surfaces were smooth The50mol M-TiO

2materials were mixed with basalt fibers

and were fabricated as thick films by coating on a Pyrex plateThe regular array of composites could be observed clearlythrough both the side and top directions The TiO

2basalt

fiber and 50mol Fe-TiO2basalt fiber composites did not

cover the Pyrex plate surface completely and bulk poreswere observed On the other hand the coating parts werequite uniform and fine particles were well-dispersed Incontrast the surfaces of the films fabricated from 50mol

Co-TiO2basalt fiber 50mol Ni-TiO

2basalt fiber and

50mol Cu-TiO2basalt fiber composites were quite dense

despite containing some cracks In particular the surfacewas the most compact over the 50mol Co-TiO

2basalt

fiber film The thickness of the films in all samples wasapproximately 30sim35 120583m with the exception of the purebasalt fiber film (20 120583m)

Energy-dispersive X-ray spectroscopy (EDAX) con-firmed the presence of metals on the surfaces of the basaltfiber and 50mol M (Fe- Co- Ni- and Cu-) TiO

2basalt

fiber films as shown in Figure 8 and the table below liststhe atomic compositions determined by EDAX For the basaltfiber various metal oxides were observed such as Na KCa Mg Al Si Fe and Ti Pure basalt fiber exhibited acomposition of 1928wt Si 314 wt total alkali metals166wt Ti 1177 wt Fe and 561 wt Al As a CO

2

adsorbent the Ca and Mg contents were 531 and 209wtrespectively Ti contained on the 50mol M (Fe- Co-Ni- and Cu-) TiO

2basalt fiber films decreased in the

following order 50mol Ni-TiO2(4774wt) gt Co-TiO

2

(4268wt) gt TiO2(4094wt) gt Fe-TiO

2(3344wt)

The amounts of transitionmetal specieswere in the range 269to 302wt with the exception of copper (098wt) Thesevalues did not appear to be perfectly quantitative EDAXis a very good surface analytical method but it is prone toerror because the composition can vary according to thelocation In particular the variation is large when the sampleis nonuniform [39]

The efficiencies of the photogenerated electron-hole pro-duction in the basalt fiber and 50mol M (Fe- Co- Ni-

8 International Journal of Photoenergy

MaterialselementAtomic compositions (wt-)

(a)

(b)

(c)

(d)

(e)

Na

204

mdash

mdash

192

160

Mg

209

mdash

mdash

mdash

mdash

Al

561

mdash

mdash

059

mdash

Si

1928

mdash

mdash

228

032

K

110

mdash

mdash

mdash

mdash

Ca

531

mdash

mdash

066

mdash

Fe

1177

mdash

286

114

mdash

Co

mdash

mdash

mdash

269

mdash

Ni

mdash

mdash

mdash

mdash

302

(f)

O

5114

5906

4122

4803

4732

4543

Ti

166

4094

3344

4268

4774

3615

Cu

mdash

mdash

mdash

mdash

mdash

098

Spectrum 1Ca Si

FeTi

OAl

Mg

NaK

CaK

Ti FeFe

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 1

Ti

O

Ti

2 4 6 1810 16 200 128 14(keV)

Spectrum 3

TiO

Ti

FeFe

Fe

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 2Ti

O

CuCuCu

Ti

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 4

NiNiNi Si

Ti

O

NaTi

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 2Ca

Si

Fe

Ti

O

AlNa

Ca

Co

Co

Co

Ti

FeFe

2 4 6 8 10 12 14 16 18 200(keV)

Full scale 767 cts cursor 0000Full scale 4345 cts cursor 0000Full scale 1548 cts cursor 0000

Full scale 1428 cts cursor 0000 Full scale 2264 cts cursor 0000 Full scale 830 cts cursor 0000

(b) TiO2basalt fiber(a) Basalt fiber

(d) 50mol Co-TiO2basalt fiber (f) 50mol Cu-TiO2basalt fiber(e) 50mol Ni-TiO2basalt fiber

(c) 50mol Fe-TiO2basalt fiber

Figure 8 Energy-dispersive X-ray spectra of the surfaces of the pure basalt fiber and 50mol M-TiO2basalt fiber films and the atomic

compositions

and Cu-) TiO2basalt fiber films were measured from the

photocurrent response under solar light irradiation at anapplied potential of 07 V versus SCE Figure 9 shows thetypical real time photocurrent response of the films whenthe light source is switched on and off exhibiting a rapidphotocurrent rise and decay In semiconductor systemswhen irradiation provides an energy higher than the band-gap of a semiconductor the energy excites an electron fromthe valence band to the conduction band leaving a hole inthe valence band The electron-hole pair is responsible forthe photocurrent When the light was turned on a rapidincrease in the photoreduction current was observed andthe photocurrent then turned to a steady state after a fewseconds When the light was turned off the photocurrentdecreased instantaneously to almost zero [40]When the lightwas turned on the maximum photocurrents obtained forthe 50mol Co-TiO

2and Ni-TiO

2basalt fiber films were

31049 and 30075mA cmminus2 respectively which were morethan four times higher than that achieved on pure basalt fiber

(7123mA cmminus2) andTiO2basalt fiber films (7401mA cmminus2)

Themaximumphotocurrent of the 50molCu-TiO2basalt

fiber film was too small due to trapping of excited elec-trons by copper with strong oxidation agency In additionthe TiO

2basalt fiber 50mol Cu-TiO

2basalt fiber and

50mol Ni-TiO2basalt fiber films showed no current

transients in both the light-on and the light-off regions inthe samples falling off with time in 50 s to a steady statewhich indicates that few surface recombination processeshad occurred Clearly some electron-hole recombinationwas observed in the 50mol Fe-TiO

2basalt fiber and Co-

TiO2basalt fiber films but it was negligible compared to

the total current value Therefore the 3d-transition metalingredients have a beneficial effect on the photocurrent itplays a role as an intermediate for the efficient separation ofphotogenerated hole-electron pairs

Figure 10 presents the photoreduction abilities of CO2

with H2O vapor to CH

4over the pure basalt fiber film and

50mol M (Fe- Co- Ni- and Cu-) TiO2basalt fiber films

International Journal of Photoenergy 9

3104930075

20974

7123 74016450

TiO2basalt fiberBasalt fiber

50 100 150 200 250 300 3500Time (s)

minus50

0

50

100

150

200

250

300

350

Curr

ent (

mA

cm

2)

50mol Cu-TiO2basalt fiber50mol Ni-TiO2basalt fiber

50mol Fe-TiO2basalt fiber50mol Co-TiO2basalt fiber

Figure 9 Photocurrent responses of the pure basalt fiber and50mol M-TiO

2basalt fiber films when the light source was

switched on and off

after 8 h Generally CH4production from CO

2reduction

with H2O can be divided into the following three subpro-

cesses [41] proton production from H2O photodecompo-

sition CO radical production from CO2photo cleavage

and methane production from photosynthesis between theCO radical and proton The photogenerated electrons onthe photocatalysts by UV-radiation induce CO

2reduction

to produce CO2radicals whereas the holes react with the

adsorbed H2Omolecules to perform oxidationThe interme-

diate photogenerated species undergo different reactions toproduce CO CH

3OH andCH

4The production of CH

4from

methyl radicals (∙CH3) was confirmed which are dependent

directly on the formation of the intermediate product CO[42] As shown in this figure almost no methane wasobserved when only the lamp was turned on On the otherhand the amounts of CO and O

2generation increased and

a small amount of hydrogen was observed This means thatthe light does not induce photoreduction processes aloneOn the other hand there are different product distributionsaccording to the loaded metal species excessive methane isgenerated over the catalysts loaded with Ni and Co and thequantities of CO and CH

3OH gases are increased over the

catalysts loaded with Cu and Fe The M-TiO2basalt fiber

films showed higher CH4production from CO

2photoreduc-

tion than the pure basalt fiber and TiO2basalt fiber films

700 120583mol gcatminus1 Lminus1 CH

4was emitted over the pure basalt

fiber film suggesting that it contains a small amount of TiO2

On the other hand CH4production was 1121 120583mol gcat

minus1 Lminus1over the TiO

2basalt fiber film In contrast the maximum

Lamp turned on only

TiO2basalt fiberBasalt fiber

1 2 3 4 5 6 7 80Time (h)

0

50

100

150

200

250

300

350

400

Met

hane

yie

ld (120583

mol

g-c

atlowast

L)

50mol Cu-TiO2basalt fiber50mol Ni-TiO2basalt fiber

50mol Fe-TiO2basalt fiber50mol Co-TiO2basalt fiber

Figure 10 Photoreduction abilities of CO2with H

2O vapor to CH

4

over the pure basalt fiber film and 50mol M-TiO2basalt fiber

films after 8 h

CH4yields over the 50mol Co-TiO

2basalt fiber and Ni-

TiO2basalt fiber films were 3605 and 3073 120583mol gcat

minus1 Lminus1respectively The differences in yields were attributed to theirband-gaps electron-hole recombination tendencies and thegas adsorption abilities of the 50mol M-TiO

2basalt fiber

films In particular this study confirmed that the 50molCo-TiO

2particles show synergistic performance when the

basalt fiber is mixedThe reduction ofCO

2requires amultiple electron transfer

and leads to production of a variety of products dependingon the number of transferred electrons which determinethe final oxidation state of the carbon atom The standardredox potentials of the CO

2reduction half-reactions vary

from CO2HCOOH [43] to CO

2CH4[44] CO

2adsorbed

on a photocatalyst surface can be reduced to ∙CO2

minus anionradical which can react withH+ and eminus for formingHCOOHor HCOOminus or which can go to the postulated disproportion-ation reaction of two ∙CO

2

minus anion radicals into CO (afterall to be C radical) and CO

3

2minus to react with H radical Thisstudy seems to follow the latter Scheme 1 presents a modelfor CO

2photoreduction over the M-TiO

2basalt fiber films

based on the relationships between the optical propertiesof the photocatalysts and the catalytic activities Photonexcitation in M-TiO

2over the M-TiO

2basalt fiber films

will begin rapidly because M-TiO2has a shorter band-gap

than pure TiO2 and the excited electrons can be transferred

efficiently to CO2molecules In addition CO

2molecules

are adsorbed preferentially and easily on the basalt fibersurface The positive holes on the valance band of M-TiO

2

can be trapped byH2Ospecies and transferred toOH radicals

and protons The protons obtained are transformed to H

10 International Journal of Photoenergy

O

Basalt fiberFTO glass

FTO glass

H2

CO2

Basalt fiber (i) More CO2 adsorption good

H2O

∙H

∙CO2minus

+ ∙H rarr ∙CHrarr ∙CH2 rarr ∙CH3 rarr CH4

Reduction CO2 + eminus rarr ∙CO2minus

h+

eminus

h+

eminus

pasteM-TiO2basalt fiber

M-TiO2

ldquoMetal incorporatedrdquoUV light

decreaseTiO2 M-TiO2 M-TiO2

(i) Easy electron transfer(ii) Water (H2O) adsorption goodM-TiO2

Oxidation H2O + h+ rarr ∙OH + H+ H+ + O2997888rarr

Scheme 1 Model for CH4production from the photoreduction of CO

2with H

2O vapor over the M-TiO

2basalt fiber films

radicals by electrons and the H radicals then react with Cand CO radicals formed from the reduction of CO

2

minus overM-TiO

2 particularly over Co- or Ni-TiO

2semiconductors

resulting methane production [45] The mixed films ofbasalt fibers and M-TiO

2can also promote the separation

of photogenerated electron-hole pairs (eminush+) on M-TiO2

Therefore the synergetic effects of the basalt fibers and M-TiO2in the M-TiO

2basalt fiber films achieved higher CO

2

reduction efficiency

4 Conclusions

The 50mol M (Fe- Co- Ni- and Cu-) incorporated TiO2

photocatalysts obtained by the solvothermal method werecoated densely with basalt fibers on a Pyrex plate usinga squeeze technique and applied to the photoreduction ofCO2to CH

4 The CO

2adsorption abilities were improved

over the basalt fiber and CH4generation was enhanced

dramatically over 50mol M-TiO2basalt fiber films with

a threefold higher yield compared to the pure basalt fiberand TiO

2basalt fiber films In particular the photoreduction

of CO2with H

2O revealed a remarkable increase in CH

4

generation over the 50mol Co-TiO2basalt fiber film to

3605 120583mol gcatminus1sdotLminus1 after an 8 h reaction

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

This research was supported by ceramic fiber commercialcenter project of Korea Institute of Ceramic Engineeringamp Technology (KICET) funded by the Ministry of TradeIndustry amp Energy (MOTIE)

References

[1] M Tahir and N S Amin ldquoIndium-doped TiO2nanoparticles

for photocatalytic CO2reduction with H

2O vapors to CH

4rdquo

Applied Catalysis B Environmental vol 162 pp 98ndash109 2015[2] B S Kwak andM Kang ldquoPhotocatalytic reduction of CO

2with

H2O using perovskite Ca

119909Ti119910O3rdquo Applied Surface Science vol

337 pp 138ndash144 2015[3] C Fletcher Y Jiang and R Amal ldquoProduction of formic acid

from CO2reduction by means of potassium borohydride at

ambient conditionsrdquo Chemical Engineering Science vol 137 pp301ndash307 2015

[4] G Mahmodi S Sharifnia M Madani and V VatanpourldquoPhotoreduction of carbon dioxide in the presence of H

2 H2O

and CH4over TiO

2and ZnO photocatalystsrdquo Solar Energy vol

97 pp 186ndash194 2013[5] J Albo A Saez J Solla-Gullon V Montiel and A Irabien

ldquoProduction of methanol from CO2electroreduction at Cu

2O

and Cu2OZnO-based electrodes in aqueous solutionrdquo Applied

Catalysis B Environmental vol 176-177 pp 709ndash717 2015[6] P Akhter M Hussain G Saracco and N Russo ldquoNew nanos-

tructured silica incorporated with isolated Ti material for the

International Journal of Photoenergy 11

photocatalytic conversion of CO2to fuelsrdquo Nanoscale Research

Letters vol 9 article 158 2014[7] M Anpo ldquoPhotocatalytic reduction of CO

2with H

2O on

highly dispersed Ti-oxide catalysts as a model of artificialphotosynthesisrdquo Journal of CO

2Utilization vol 1 pp 8ndash17 2013

[8] H Abdullah M R Khan M Pudukudy Z Yaakob and NA Ismail ldquoCeO

2-TiO2as a visible light active catalyst for the

photoreduction ofCO2tomethanolrdquo Journal of Rare Earths vol

33 no 11 pp 1155ndash1161 2015[9] O Ola and M Mercedes Maroto-Valer ldquoReview of material

design and reactor engineering on TiO2photocatalysis for

CO2reductionrdquo Journal of Photochemistry and Photobiology C

Photochemistry Reviews vol 24 pp 16ndash42 2015[10] X Zhang L Wang Q Du Z Wang S Ma and M Yu

ldquoPhotocatalytic CO2reduction over B

4CC3N4with internal

electric field under visible light irradiationrdquo Journal of Colloidand Interface Science vol 464 pp 89ndash95 2016

[11] R Gusain P Kumar O P Sharma S L Jain and O PKhatri ldquoReduced graphene oxide-CuO nanocomposites forphotocatalytic conversion of CO

2into methanol under visible

light irradiationrdquo Applied Catalysis B Environmental vol 181pp 352ndash362 2016

[12] N M Nursam X Wang and R A Caruso ldquoHigh-throughputsynthesis and screening of titania-based photocatalystsrdquo ACSCombinatorial Science vol 17 no 10 pp 548ndash569 2015

[13] M V Dozzi S Marzorati M Longhi M Coduri L Artigliaand E Selli ldquoPhotocatalytic activity of TiO

2-WO3mixed oxides

in relation to electron transfer efficiencyrdquo Applied Catalysis BEnvironmental vol 186 pp 157ndash165 2016

[14] Y Qu and X Duan ldquoProgress challenge and perspective ofheterogeneous photocatalystsrdquo Chemical Society Reviews vol42 no 7 pp 2568ndash2580 2013

[15] J C Colmenares R Luque J M Campelo F Colmenares ZKarpinski and A A Romero ldquoNanostructured photocatalystsand their applications in the photocatalytic transformation oflignocellulosic biomass an overviewrdquo Materials vol 2 no 4pp 2228ndash2258 2009

[16] M Kitano M Matsuoka M Ueshima and M Anpo ldquoRecentdevelopments in titanium oxide-based photocatalystsrdquo AppliedCatalysis A General vol 325 no 1 pp 1ndash14 2007

[17] P Silija Z Yaakob V Suraja N N Binitha and Z S Akmal ldquoAnenthusiastic glance in to the visible responsive photocatalystsfor energy production and pollutant removal with specialemphasis on titaniardquo International Journal of Photoenergy vol2012 Article ID 503839 19 pages 2012

[18] H Xu S Ouyang L Liu P Reunchan N Umezawa and JYe ldquoRecent advances in TiO

2-based photocatalysisrdquo Journal of

Materials Chemistry A vol 2 no 32 pp 12642ndash12661 2014[19] Z He J Tang J Shen J Chen and S Song ldquoEnhancement of

photocatalytic reduction of CO2to CH

4over TiO

2nanosheets

by modifying with sulfuric acidrdquo Applied Surface Science vol364 pp 416ndash427 2016

[20] O Ola and M M Maroto-Valer ldquoTransition metal oxide basedTiO2nanoparticles for visible light induced CO

2photoreduc-

tionrdquo Applied Catalysis A General vol 502 pp 114ndash121 2015[21] D Eder ldquoCarbon nanotube-inorganic hybridsrdquo Chemical

Reviews vol 110 no 3 pp 1348ndash1385 2010[22] L Zhang R JamalQ ZhaoMWang andTAbdiryim ldquoPrepa-

ration of PEDOTGO PEDOTMnO2 and PEDOTGOMnO

2

nanocomposites and their application in catalytic degradationof methylene bluerdquo Nanoscale Research Letters vol 10 p 1482015

[23] M Urbanski A Lapko and A Garbacz ldquoInvestigation onconcrete beams reinforced with basalt rebars as an effectivealternative of conventional RC structuresrdquo Procedia Engineer-ing vol 57 pp 1183ndash1191 2013

[24] S A Chernyak E V Suslova A V Egorov L Lu S V Savilovand V V Lunin ldquoNew hybrid CNT-alumina supports for Co-based Fischer-Tropsch catalystsrdquo Fuel Processing Technologyvol 140 pp 267ndash275 2015

[25] K Shimura T Miyazawa T Hanaoka and S Hirata ldquoFischerndashTropsch synthesis over alumina supported bimetallic CondashNicatalyst effect of impregnation sequence and solutionrdquo Journalof Molecular Catalysis A Chemical vol 407 pp 15ndash24 2015

[26] F Fazlollahi M Sarkari A Zare A A Mirzaei and HAtashi ldquoDevelopment of a kinetic model for Fischer-Tropschsynthesis over CoNiAl

2O3catalystrdquo Journal of Industrial and

Engineering Chemistry vol 18 no 4 pp 1223ndash1232 2012[27] J Zhao W Xing Y Li and K Lu ldquoSolvothermal synthesis and

visible light absorption of anatase TiO2rdquo Materials Letters vol

145 pp 332ndash335 2015[28] S Liu J Yu and M Jaroniec ldquoAnatase TiO

2with dominant

high-energy 001 facets Synthesis properties and applicationsrdquoChemistry of Materials vol 23 no 18 pp 4085ndash4093 2011

[29] T Ungar ldquoMicrostructural parameters from X-ray diffractionpeak broadeningrdquo Scripta Materialia vol 51 no 8 pp 777ndash7812004

[30] A W Burton K Ong T Rea and I Y Chan ldquoOn the esti-mation of average crystallite size of zeolites from the Scherrerequation a critical evaluation of its application to zeolites withone-dimensional pore systemsrdquo Microporous and MesoporousMaterials vol 117 no 1-2 pp 75ndash90 2009

[31] A Jaroenworaluck N Pijarn N Kosachan and R StevensldquoNanocomposite TiO

2ndashSiO2gel for UV absorptionrdquo Chemical

Engineering Journal vol 181-182 pp 45ndash55 2012[32] J I Pena-Flores A F Palomec-Garfias C Marquez-Beltran

E Sanchez-Mora E Gomez-Barojas and F Perez-RodrıguezldquoFe effect on the optical properties of TiO

2Fe2O3nanostruc-

tured composites supported on SiO2microsphere assembliesrdquo

Nanoscale Research Letters vol 9 article 499 2014[33] D Kim Y Im K M Jeong S-M Park M-H Um and M

Kang ldquoEnhanced 2-chorophenol photodecomposition usingnano-sized Mn-incorporated TiO

2powders prepared by a

solvothermal methodrdquo Bulletin of the Korean Chemical Societyvol 35 no 8 pp 2295ndash2298 2014

[34] C C Huang C C Wu K Knight and D W Hewak ldquoOpticalproperties of CVD grown amorphous Ge-Sb-S thin filmsrdquoJournal of Non-Crystalline Solids vol 356 no 4-5 pp 281ndash2852010

[35] J Kim J S Lee and M Kang ldquoSynthesis of nanoporousstructured SnO

2and its photocatalytic ability for bisphenol a

destructionrdquo Bulletin of the Korean Chemical Society vol 32 no5 pp 1715ndash1720 2011

[36] M Thommes ldquoPhysical adsorption characterization ofnanoporous materialsrdquo Chemie Ingenieur Technik vol 82 no 7pp 1059ndash1073 2010

[37] A A Gribb and J F Banfield ldquoParticle size effects on trans-formation kinetics and phase stability in nanocrystalline TiO

2rdquo

American Mineralogist vol 82 no 7-8 pp 717ndash728 1997[38] S-H Nam S-J Cho C-K Jung et al ldquoComparison of

hydrophilic properties of TiO2thin films prepared by solndashgel

method and reactive magnetron sputtering systemrdquo Thin SolidFilms vol 519 no 20 pp 6944ndash6950 2011

12 International Journal of Photoenergy

[39] H G Feichtinger K Grochenig and T Strohmer ldquoEffi-cient numerical methods in non-uniform sampling theoryrdquoNumerische Mathematik vol 69 no 4 pp 423ndash440 1995

[40] S W Jo B S Kwak K M Kim et al ldquoEffectively CO2

photoreduction toCH4by the synergistic effects of Ca andTi on

Ca-loaded TiSiMCM-41 mesoporous photocatalytic systemsrdquoApplied Surface Science vol 355 pp 891ndash901 2015

[41] J Y Do Y Im B S Kwak J-Y Kim and M Kang ldquoDramaticCO2photoreduction with H

2O vapors for CH

4production

using the TiO2(bottom)FendashTiO

2(top) double-layered filmsrdquo

Chemical Engineering Journal vol 275 pp 288ndash297 2015[42] M Tahir andN SaidinaAmin ldquoPhotocatalytic reduction of car-

bon dioxide with water vapors over montmorillonite modifiedTiO2nanocompositesrdquo Applied Catalysis B Environmental vol

142-143 pp 512ndash522 2013[43] Y Kohno H Hayashi S Takenaka T Tanaka T Funabiki

and S Yoshida ldquoPhoto-enhanced reduction of carbon dioxidewith hydrogen over RhTiO

2rdquo Journal of Photochemistry and

Photobiology A Chemistry vol 126 no 1ndash3 pp 117ndash123 1999[44] M Subrahmanyam S Kaneco and N Alonso-Vante ldquoA screen-

ing for the photo reduction of carbon dioxide supported onmetal oxide catalysts for C

1-C3selectivityrdquo Applied Catalysis B

Environmental vol 23 no 2-3 pp 169ndash174 1999[45] S S Tan L Zou and E Hu ldquoKinetic modelling for photosyn-

thesis of hydrogen and methane through catalytic reduction ofcarbon dioxide with water vapourrdquo Catalysis Today vol 131 no1ndash4 pp 125ndash129 2008

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

4 International Journal of Photoenergy

20 30 40 50 60 70 80

Inte

nsity

(au

)(f) Basalt fiber

20 30 40 50 60 70 80100

100

200

300

400

500

600

Inte

nsity

(cps

)

(a) TiO2

1205722120579CuK

1205722120579CuK

(e) 50mol Cu-TiO2

(d) 50mol Ni-TiO2

(b) 50mol Fe-TiO2

(c) 50mol Co-TiO2

Figure 2 XRD patterns of the basalt fiber pure TiO2 and 50mol M-TiO

2powders

Basalt fiberTiO2

400 500 600 700 800300Wavelength (nm)

00

02

04

06

08

10

12

14

16

Abso

rban

ce (a

u)

50mol Fe-TiO2

50mol Co-TiO2

50mol Ni-TiO2

50mol Cu-TiO2

(a)

Sample Band-gap (eV)TiO2

310 (387nm)298 (403nm)248 (485nm)280 (428nm)318 (378nm)

(120572h

)2

2 3 4 51Photon energy (eV)

00

01

02

03

50mol Cu-TiO2

50mol Ni-TiO2

50mol Fe-TiO2

50mol Co-TiO2

(b)

Figure 3 Diffuse reflectance-UV-visible absorption spectra (a) and their Taucrsquos plots (b) of the prepared 50mol M-TiO2powders

International Journal of Photoenergy 5

Table 1 Physical properties of 50mol M-TiO2particles

Physical properties of catalysts Atomic compositionsTi M O

Specific surface areas[m2 gminus1]

Total pore volume[cm3 gminus1]

Average pore diameter[nm]

TiO2 320 00 680 131 020 617

50mol Fe-TiO2 302 37 660 165 064 1556

50mol Co-TiO2 306 34 670 124 017 563

50mol Ni-TiO2 289 31 680 130 018 563

50mol Cu-TiO2 316 29 655 67 042 2495

Basalt fiberTiO2

400 500 600 700 800300Wavelength (nm)

00

05

10

15

20

25

Inte

nsity

(V)

50mol Cu-TiO2

50mol Ni-TiO2

50mol Co-TiO2

50mol Fe-TiO2

Figure 4 PL spectra of the prepared 50mol M-TiO2particles

suggests that the electrons in the valence band are transferredto the conduction band and are stabilized by photoemissionIn general the PL intensity increases with increasing numberof electrons emitted resulting from recombination betweenthe excited electrons and holes and a consequent decreasein photoactivity [35] Therefore there is a strong relationshipbetween the PL intensity and photoactivity In particularthe PL intensity decreases significantly when a metal cancapture excited electrons or exhibit conductivity which isknown as the relaxation process The 50mol M-TiO

2

samples exhibited a PL signal with a similar curve shapedemonstrating the presence of TiO

2 Pure TiO

2exhibited a

strong PL signal in the range 400ndash550 nm with a maximumexcitation wavelength of 445 nm whereas the 50molM-TiO

2curve intensities were weakened dramatically The

decreasing tendency was observed in the following orderTiO2gt 50mol Fe-TiO

2gt Cu-TiO

2gt Ni-TiO

2gt Co-

TiO2 which was possibly due to the new oxygen vacancies

produced by metal-doping The photogenerated electronsin the conduction band initially reached the vacant spaceand then recombined with the photogenerated holes in thevalance band to produce fluorescence emission The reducedPL intensities of 50mol M-TiO

2might be due to defects

generated by the transition metal ions inserted into the TiO2

structures which accelerate electron transfer and hinder

electron-hole pair recombination on the 50mol M-TiO2

surfaceFigure 5 shows the adsorption-desorption isotherm

curves of N2at 77 K for the as-synthesized 50mol M (Fe-

Co- Ni- and Cu-) TiO2particles With the exception of the

50mol Fe-TiO2and Cu-TiO

2samples all isotherms were

close to type II according to the IUPAC classification [36]indicating the lack of pores in the particles Otherwise theisotherms of the 50mol Fe-TiO

2and Cu-TiO

2samples

were attributed to type IV indicating bulk pores by aggre-gation between each nanoparticle The hysteresis slopes wereobserved at intermediate and relative pressures greater than119901119901

0= 07 in all samples

Table 1 lists the specific surface areas of the 50molM-TiO

2samples The specific surface areas were located in

the range 68sim165m2 gminus1 In particular the surface area wasthe largest at 165m2 gminus1 in 50mol Fe-TiO

2 In general

the surface area increases with decreasing particle size [37]These results showed some degree of reliability and were wellmatched to their calculated crystallite sizes (Figure 2) Fromthe results of the average bulk pore diameter for the samplesit is believed that the 50mol Fe-TiO

2and Cu-TiO

2may

contain bulk mesopores approximately 15sim24 nm due toaggregation between their nanoparticles Otherwise the porevolumes of the samples were varied from 017 to 064 cm3 gminus1The atomic compositions calculated the energy-dispersive X-ray spectra that are also included in this table The TiO

2

surface showed only two elements Ti and O whereas threeelements were observed in theM-TiO

2samples In contrast to

expectations the amount of doped metals was much higherthan the Ti amount in all samples and the M Ti ratios wereapproximately 1 10This was calculated from EDAX analysisand the values were different from the actual amount Theamount of metal doped in TiO

2was reduced to the order of

Fe gt Co gt Ni gt CuDuring the CO

2photoreduction reaction CO

2is

adsorbed onto the surface of the photocatalysts in the firststep and the photoreduction reaction progresses Thereforethe photocatalytic performance depends on the adsorptioncapacities of CO

2 Accordingly the CO

2adsorption abilities

of the 50mol M (Fe- Co- Ni- and Cu-) TiO2samples

need to be determined The CO2desorption profiles were

obtained over the range 50sim900∘C as shown in Figure 6Thecurve intensity for CO

2desorption was higher in 50mol

M-TiO2than in pure TiO

2 which means considerably more

CO2molecules had been adsorbed on the surfaces of the

50mol M-TiO2samples In addition TiO

2generally has

6 International Journal of Photoenergy

ADSDES

0

50

100

150V

ac

m3(S

TP) g

minus1

05 10

pp0

(a) TiO2

ADSDES

0

200

400

600

Vac

m3(S

TP) g

minus1

05 10

pp0

(b) 50mol- Fe-TiO2

ADSDES

0

50

100

150

Vac

m3(S

TP) g

minus1

05 10

pp0

(c) 50mol- Co-TiO2

ADSDES

05 10

pp0

0

50

100

150

Vac

m3(S

TP) g

minus1

(d) 50mol- Ni-TiO2

ADSDES

05 10

pp0

0

120

240

360

Vac

m3(S

TP) g

minus1

(e) 50mol- Cu-TiO2

Figure 5 Adsorption-desorption isotherm curves of N2at 77 K for the as-synthesized 50mol M-TiO

2particles

Area integ(Gaussian) 27983665 33278233 66855506 68781188 60435286 10310403

Basalt fiber

2075000208000020850002090000209500021000002105000

TCD

(mV

)

400 600 800200

62750006300000632500063500006375000640000064250006450000

TCD

(mV

)

TiO2

6800000

6900000

7000000

7100000

7200000

7300000

7400000

7500000

7600000

7700000

TCD

(120583V

)

400 600 800200Temperature (∘C)

400 600 800200Temperature (∘C)

Basalt fiber TiO2

50mol Fe-TiO2

50mol Co-TiO2

50mol Ni-TiO2

50mol Fe-TiO2 50mol Co-TiO2 50mol Ni-TiO2 50mol Cu-TiO2

50mol Cu-TiO2

Figure 6 CO2desorption profiles over the 50mol M-TiO

2particles in the range 50sim900∘C

International Journal of Photoenergy 7

30120583m

ldquoTop viewrdquoldquoSide viewrdquo

20120583m

Basalt fiber (b) TiO2basalt fiber(a) Basalt fiber

basalt fiber

basalt fiber

basalt fiber basalt fiber basalt fiber

(c) 50mol Fe-TiO2

50mol Co-TiO2 (d) 50mol Co-TiO2 (e) 50mol Ni-TiO2 (f) 50mol Cu-TiO2

Figure 7 SEM images of the pure basalt fiber film and 50mol M-TiO2basalt fiber films

hydrophilic properties [38] which suggests that duringthe CO

2photoreduction reaction CO

2and H

2O will

be adsorbed preferentially on the metal ions and TiO2

respectively The adsorption abilities were observed inthe following order 50mol Co-TiO

2gt Ni-TiO

2gt

Fe-TiO2gt TiO

2gt Cu-TiO

2samples In general a rapid

catalytic reaction occurs when many reactants are well-adsorbed over the catalyst The presence of transition metalsin the 50mol M-TiO

2samples most likely caused the

relative increase in the number of CO2and H

2O molecules

adsorbed compared to pure TiO2 This synergy contributed

significantly to improving the catalytic performance of the50mol M-TiO

2samples

32 Characteristics and CO2

Photoreduction over the50mol M (Fe- Co- Ni- and Cu-) TiO

2Basalt Fiber Films

Figure 7 presents SEM images (top and side views) of the sixsamples of pure basalt fiber and TiO

2films and 50mol

M (Fe- Co- Ni- and Cu-) TiO2basalt fiber films The

basalt fiber in the films was approximately 15 120583m in diameterwith different lengths and the surfaces were smooth The50mol M-TiO

2materials were mixed with basalt fibers

and were fabricated as thick films by coating on a Pyrex plateThe regular array of composites could be observed clearlythrough both the side and top directions The TiO

2basalt

fiber and 50mol Fe-TiO2basalt fiber composites did not

cover the Pyrex plate surface completely and bulk poreswere observed On the other hand the coating parts werequite uniform and fine particles were well-dispersed Incontrast the surfaces of the films fabricated from 50mol

Co-TiO2basalt fiber 50mol Ni-TiO

2basalt fiber and

50mol Cu-TiO2basalt fiber composites were quite dense

despite containing some cracks In particular the surfacewas the most compact over the 50mol Co-TiO

2basalt

fiber film The thickness of the films in all samples wasapproximately 30sim35 120583m with the exception of the purebasalt fiber film (20 120583m)

Energy-dispersive X-ray spectroscopy (EDAX) con-firmed the presence of metals on the surfaces of the basaltfiber and 50mol M (Fe- Co- Ni- and Cu-) TiO

2basalt

fiber films as shown in Figure 8 and the table below liststhe atomic compositions determined by EDAX For the basaltfiber various metal oxides were observed such as Na KCa Mg Al Si Fe and Ti Pure basalt fiber exhibited acomposition of 1928wt Si 314 wt total alkali metals166wt Ti 1177 wt Fe and 561 wt Al As a CO

2

adsorbent the Ca and Mg contents were 531 and 209wtrespectively Ti contained on the 50mol M (Fe- Co-Ni- and Cu-) TiO

2basalt fiber films decreased in the

following order 50mol Ni-TiO2(4774wt) gt Co-TiO

2

(4268wt) gt TiO2(4094wt) gt Fe-TiO

2(3344wt)

The amounts of transitionmetal specieswere in the range 269to 302wt with the exception of copper (098wt) Thesevalues did not appear to be perfectly quantitative EDAXis a very good surface analytical method but it is prone toerror because the composition can vary according to thelocation In particular the variation is large when the sampleis nonuniform [39]

The efficiencies of the photogenerated electron-hole pro-duction in the basalt fiber and 50mol M (Fe- Co- Ni-

8 International Journal of Photoenergy

MaterialselementAtomic compositions (wt-)

(a)

(b)

(c)

(d)

(e)

Na

204

mdash

mdash

192

160

Mg

209

mdash

mdash

mdash

mdash

Al

561

mdash

mdash

059

mdash

Si

1928

mdash

mdash

228

032

K

110

mdash

mdash

mdash

mdash

Ca

531

mdash

mdash

066

mdash

Fe

1177

mdash

286

114

mdash

Co

mdash

mdash

mdash

269

mdash

Ni

mdash

mdash

mdash

mdash

302

(f)

O

5114

5906

4122

4803

4732

4543

Ti

166

4094

3344

4268

4774

3615

Cu

mdash

mdash

mdash

mdash

mdash

098

Spectrum 1Ca Si

FeTi

OAl

Mg

NaK

CaK

Ti FeFe

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 1

Ti

O

Ti

2 4 6 1810 16 200 128 14(keV)

Spectrum 3

TiO

Ti

FeFe

Fe

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 2Ti

O

CuCuCu

Ti

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 4

NiNiNi Si

Ti

O

NaTi

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 2Ca

Si

Fe

Ti

O

AlNa

Ca

Co

Co

Co

Ti

FeFe

2 4 6 8 10 12 14 16 18 200(keV)

Full scale 767 cts cursor 0000Full scale 4345 cts cursor 0000Full scale 1548 cts cursor 0000

Full scale 1428 cts cursor 0000 Full scale 2264 cts cursor 0000 Full scale 830 cts cursor 0000

(b) TiO2basalt fiber(a) Basalt fiber

(d) 50mol Co-TiO2basalt fiber (f) 50mol Cu-TiO2basalt fiber(e) 50mol Ni-TiO2basalt fiber

(c) 50mol Fe-TiO2basalt fiber

Figure 8 Energy-dispersive X-ray spectra of the surfaces of the pure basalt fiber and 50mol M-TiO2basalt fiber films and the atomic

compositions

and Cu-) TiO2basalt fiber films were measured from the

photocurrent response under solar light irradiation at anapplied potential of 07 V versus SCE Figure 9 shows thetypical real time photocurrent response of the films whenthe light source is switched on and off exhibiting a rapidphotocurrent rise and decay In semiconductor systemswhen irradiation provides an energy higher than the band-gap of a semiconductor the energy excites an electron fromthe valence band to the conduction band leaving a hole inthe valence band The electron-hole pair is responsible forthe photocurrent When the light was turned on a rapidincrease in the photoreduction current was observed andthe photocurrent then turned to a steady state after a fewseconds When the light was turned off the photocurrentdecreased instantaneously to almost zero [40]When the lightwas turned on the maximum photocurrents obtained forthe 50mol Co-TiO

2and Ni-TiO

2basalt fiber films were

31049 and 30075mA cmminus2 respectively which were morethan four times higher than that achieved on pure basalt fiber

(7123mA cmminus2) andTiO2basalt fiber films (7401mA cmminus2)

Themaximumphotocurrent of the 50molCu-TiO2basalt

fiber film was too small due to trapping of excited elec-trons by copper with strong oxidation agency In additionthe TiO

2basalt fiber 50mol Cu-TiO

2basalt fiber and

50mol Ni-TiO2basalt fiber films showed no current

transients in both the light-on and the light-off regions inthe samples falling off with time in 50 s to a steady statewhich indicates that few surface recombination processeshad occurred Clearly some electron-hole recombinationwas observed in the 50mol Fe-TiO

2basalt fiber and Co-

TiO2basalt fiber films but it was negligible compared to

the total current value Therefore the 3d-transition metalingredients have a beneficial effect on the photocurrent itplays a role as an intermediate for the efficient separation ofphotogenerated hole-electron pairs

Figure 10 presents the photoreduction abilities of CO2

with H2O vapor to CH

4over the pure basalt fiber film and

50mol M (Fe- Co- Ni- and Cu-) TiO2basalt fiber films

International Journal of Photoenergy 9

3104930075

20974

7123 74016450

TiO2basalt fiberBasalt fiber

50 100 150 200 250 300 3500Time (s)

minus50

0

50

100

150

200

250

300

350

Curr

ent (

mA

cm

2)

50mol Cu-TiO2basalt fiber50mol Ni-TiO2basalt fiber

50mol Fe-TiO2basalt fiber50mol Co-TiO2basalt fiber

Figure 9 Photocurrent responses of the pure basalt fiber and50mol M-TiO

2basalt fiber films when the light source was

switched on and off

after 8 h Generally CH4production from CO

2reduction

with H2O can be divided into the following three subpro-

cesses [41] proton production from H2O photodecompo-

sition CO radical production from CO2photo cleavage

and methane production from photosynthesis between theCO radical and proton The photogenerated electrons onthe photocatalysts by UV-radiation induce CO

2reduction

to produce CO2radicals whereas the holes react with the

adsorbed H2Omolecules to perform oxidationThe interme-

diate photogenerated species undergo different reactions toproduce CO CH

3OH andCH

4The production of CH

4from

methyl radicals (∙CH3) was confirmed which are dependent

directly on the formation of the intermediate product CO[42] As shown in this figure almost no methane wasobserved when only the lamp was turned on On the otherhand the amounts of CO and O

2generation increased and

a small amount of hydrogen was observed This means thatthe light does not induce photoreduction processes aloneOn the other hand there are different product distributionsaccording to the loaded metal species excessive methane isgenerated over the catalysts loaded with Ni and Co and thequantities of CO and CH

3OH gases are increased over the

catalysts loaded with Cu and Fe The M-TiO2basalt fiber

films showed higher CH4production from CO

2photoreduc-

tion than the pure basalt fiber and TiO2basalt fiber films

700 120583mol gcatminus1 Lminus1 CH

4was emitted over the pure basalt

fiber film suggesting that it contains a small amount of TiO2

On the other hand CH4production was 1121 120583mol gcat

minus1 Lminus1over the TiO

2basalt fiber film In contrast the maximum

Lamp turned on only

TiO2basalt fiberBasalt fiber

1 2 3 4 5 6 7 80Time (h)

0

50

100

150

200

250

300

350

400

Met

hane

yie

ld (120583

mol

g-c

atlowast

L)

50mol Cu-TiO2basalt fiber50mol Ni-TiO2basalt fiber

50mol Fe-TiO2basalt fiber50mol Co-TiO2basalt fiber

Figure 10 Photoreduction abilities of CO2with H

2O vapor to CH

4

over the pure basalt fiber film and 50mol M-TiO2basalt fiber

films after 8 h

CH4yields over the 50mol Co-TiO

2basalt fiber and Ni-

TiO2basalt fiber films were 3605 and 3073 120583mol gcat

minus1 Lminus1respectively The differences in yields were attributed to theirband-gaps electron-hole recombination tendencies and thegas adsorption abilities of the 50mol M-TiO

2basalt fiber

films In particular this study confirmed that the 50molCo-TiO

2particles show synergistic performance when the

basalt fiber is mixedThe reduction ofCO

2requires amultiple electron transfer

and leads to production of a variety of products dependingon the number of transferred electrons which determinethe final oxidation state of the carbon atom The standardredox potentials of the CO

2reduction half-reactions vary

from CO2HCOOH [43] to CO

2CH4[44] CO

2adsorbed

on a photocatalyst surface can be reduced to ∙CO2

minus anionradical which can react withH+ and eminus for formingHCOOHor HCOOminus or which can go to the postulated disproportion-ation reaction of two ∙CO

2

minus anion radicals into CO (afterall to be C radical) and CO

3

2minus to react with H radical Thisstudy seems to follow the latter Scheme 1 presents a modelfor CO

2photoreduction over the M-TiO

2basalt fiber films

based on the relationships between the optical propertiesof the photocatalysts and the catalytic activities Photonexcitation in M-TiO

2over the M-TiO

2basalt fiber films

will begin rapidly because M-TiO2has a shorter band-gap

than pure TiO2 and the excited electrons can be transferred

efficiently to CO2molecules In addition CO

2molecules

are adsorbed preferentially and easily on the basalt fibersurface The positive holes on the valance band of M-TiO

2

can be trapped byH2Ospecies and transferred toOH radicals

and protons The protons obtained are transformed to H

10 International Journal of Photoenergy

O

Basalt fiberFTO glass

FTO glass

H2

CO2

Basalt fiber (i) More CO2 adsorption good

H2O

∙H

∙CO2minus

+ ∙H rarr ∙CHrarr ∙CH2 rarr ∙CH3 rarr CH4

Reduction CO2 + eminus rarr ∙CO2minus

h+

eminus

h+

eminus

pasteM-TiO2basalt fiber

M-TiO2

ldquoMetal incorporatedrdquoUV light

decreaseTiO2 M-TiO2 M-TiO2

(i) Easy electron transfer(ii) Water (H2O) adsorption goodM-TiO2

Oxidation H2O + h+ rarr ∙OH + H+ H+ + O2997888rarr

Scheme 1 Model for CH4production from the photoreduction of CO

2with H

2O vapor over the M-TiO

2basalt fiber films

radicals by electrons and the H radicals then react with Cand CO radicals formed from the reduction of CO

2

minus overM-TiO

2 particularly over Co- or Ni-TiO

2semiconductors

resulting methane production [45] The mixed films ofbasalt fibers and M-TiO

2can also promote the separation

of photogenerated electron-hole pairs (eminush+) on M-TiO2

Therefore the synergetic effects of the basalt fibers and M-TiO2in the M-TiO

2basalt fiber films achieved higher CO

2

reduction efficiency

4 Conclusions

The 50mol M (Fe- Co- Ni- and Cu-) incorporated TiO2

photocatalysts obtained by the solvothermal method werecoated densely with basalt fibers on a Pyrex plate usinga squeeze technique and applied to the photoreduction ofCO2to CH

4 The CO

2adsorption abilities were improved

over the basalt fiber and CH4generation was enhanced

dramatically over 50mol M-TiO2basalt fiber films with

a threefold higher yield compared to the pure basalt fiberand TiO

2basalt fiber films In particular the photoreduction

of CO2with H

2O revealed a remarkable increase in CH

4

generation over the 50mol Co-TiO2basalt fiber film to

3605 120583mol gcatminus1sdotLminus1 after an 8 h reaction

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

This research was supported by ceramic fiber commercialcenter project of Korea Institute of Ceramic Engineeringamp Technology (KICET) funded by the Ministry of TradeIndustry amp Energy (MOTIE)

References

[1] M Tahir and N S Amin ldquoIndium-doped TiO2nanoparticles

for photocatalytic CO2reduction with H

2O vapors to CH

4rdquo

Applied Catalysis B Environmental vol 162 pp 98ndash109 2015[2] B S Kwak andM Kang ldquoPhotocatalytic reduction of CO

2with

H2O using perovskite Ca

119909Ti119910O3rdquo Applied Surface Science vol

337 pp 138ndash144 2015[3] C Fletcher Y Jiang and R Amal ldquoProduction of formic acid

from CO2reduction by means of potassium borohydride at

ambient conditionsrdquo Chemical Engineering Science vol 137 pp301ndash307 2015

[4] G Mahmodi S Sharifnia M Madani and V VatanpourldquoPhotoreduction of carbon dioxide in the presence of H

2 H2O

and CH4over TiO

2and ZnO photocatalystsrdquo Solar Energy vol

97 pp 186ndash194 2013[5] J Albo A Saez J Solla-Gullon V Montiel and A Irabien

ldquoProduction of methanol from CO2electroreduction at Cu

2O

and Cu2OZnO-based electrodes in aqueous solutionrdquo Applied

Catalysis B Environmental vol 176-177 pp 709ndash717 2015[6] P Akhter M Hussain G Saracco and N Russo ldquoNew nanos-

tructured silica incorporated with isolated Ti material for the

International Journal of Photoenergy 11

photocatalytic conversion of CO2to fuelsrdquo Nanoscale Research

Letters vol 9 article 158 2014[7] M Anpo ldquoPhotocatalytic reduction of CO

2with H

2O on

highly dispersed Ti-oxide catalysts as a model of artificialphotosynthesisrdquo Journal of CO

2Utilization vol 1 pp 8ndash17 2013

[8] H Abdullah M R Khan M Pudukudy Z Yaakob and NA Ismail ldquoCeO

2-TiO2as a visible light active catalyst for the

photoreduction ofCO2tomethanolrdquo Journal of Rare Earths vol

33 no 11 pp 1155ndash1161 2015[9] O Ola and M Mercedes Maroto-Valer ldquoReview of material

design and reactor engineering on TiO2photocatalysis for

CO2reductionrdquo Journal of Photochemistry and Photobiology C

Photochemistry Reviews vol 24 pp 16ndash42 2015[10] X Zhang L Wang Q Du Z Wang S Ma and M Yu

ldquoPhotocatalytic CO2reduction over B

4CC3N4with internal

electric field under visible light irradiationrdquo Journal of Colloidand Interface Science vol 464 pp 89ndash95 2016

[11] R Gusain P Kumar O P Sharma S L Jain and O PKhatri ldquoReduced graphene oxide-CuO nanocomposites forphotocatalytic conversion of CO

2into methanol under visible

light irradiationrdquo Applied Catalysis B Environmental vol 181pp 352ndash362 2016

[12] N M Nursam X Wang and R A Caruso ldquoHigh-throughputsynthesis and screening of titania-based photocatalystsrdquo ACSCombinatorial Science vol 17 no 10 pp 548ndash569 2015

[13] M V Dozzi S Marzorati M Longhi M Coduri L Artigliaand E Selli ldquoPhotocatalytic activity of TiO

2-WO3mixed oxides

in relation to electron transfer efficiencyrdquo Applied Catalysis BEnvironmental vol 186 pp 157ndash165 2016

[14] Y Qu and X Duan ldquoProgress challenge and perspective ofheterogeneous photocatalystsrdquo Chemical Society Reviews vol42 no 7 pp 2568ndash2580 2013

[15] J C Colmenares R Luque J M Campelo F Colmenares ZKarpinski and A A Romero ldquoNanostructured photocatalystsand their applications in the photocatalytic transformation oflignocellulosic biomass an overviewrdquo Materials vol 2 no 4pp 2228ndash2258 2009

[16] M Kitano M Matsuoka M Ueshima and M Anpo ldquoRecentdevelopments in titanium oxide-based photocatalystsrdquo AppliedCatalysis A General vol 325 no 1 pp 1ndash14 2007

[17] P Silija Z Yaakob V Suraja N N Binitha and Z S Akmal ldquoAnenthusiastic glance in to the visible responsive photocatalystsfor energy production and pollutant removal with specialemphasis on titaniardquo International Journal of Photoenergy vol2012 Article ID 503839 19 pages 2012

[18] H Xu S Ouyang L Liu P Reunchan N Umezawa and JYe ldquoRecent advances in TiO

2-based photocatalysisrdquo Journal of

Materials Chemistry A vol 2 no 32 pp 12642ndash12661 2014[19] Z He J Tang J Shen J Chen and S Song ldquoEnhancement of

photocatalytic reduction of CO2to CH

4over TiO

2nanosheets

by modifying with sulfuric acidrdquo Applied Surface Science vol364 pp 416ndash427 2016

[20] O Ola and M M Maroto-Valer ldquoTransition metal oxide basedTiO2nanoparticles for visible light induced CO

2photoreduc-

tionrdquo Applied Catalysis A General vol 502 pp 114ndash121 2015[21] D Eder ldquoCarbon nanotube-inorganic hybridsrdquo Chemical

Reviews vol 110 no 3 pp 1348ndash1385 2010[22] L Zhang R JamalQ ZhaoMWang andTAbdiryim ldquoPrepa-

ration of PEDOTGO PEDOTMnO2 and PEDOTGOMnO

2

nanocomposites and their application in catalytic degradationof methylene bluerdquo Nanoscale Research Letters vol 10 p 1482015

[23] M Urbanski A Lapko and A Garbacz ldquoInvestigation onconcrete beams reinforced with basalt rebars as an effectivealternative of conventional RC structuresrdquo Procedia Engineer-ing vol 57 pp 1183ndash1191 2013

[24] S A Chernyak E V Suslova A V Egorov L Lu S V Savilovand V V Lunin ldquoNew hybrid CNT-alumina supports for Co-based Fischer-Tropsch catalystsrdquo Fuel Processing Technologyvol 140 pp 267ndash275 2015

[25] K Shimura T Miyazawa T Hanaoka and S Hirata ldquoFischerndashTropsch synthesis over alumina supported bimetallic CondashNicatalyst effect of impregnation sequence and solutionrdquo Journalof Molecular Catalysis A Chemical vol 407 pp 15ndash24 2015

[26] F Fazlollahi M Sarkari A Zare A A Mirzaei and HAtashi ldquoDevelopment of a kinetic model for Fischer-Tropschsynthesis over CoNiAl

2O3catalystrdquo Journal of Industrial and

Engineering Chemistry vol 18 no 4 pp 1223ndash1232 2012[27] J Zhao W Xing Y Li and K Lu ldquoSolvothermal synthesis and

visible light absorption of anatase TiO2rdquo Materials Letters vol

145 pp 332ndash335 2015[28] S Liu J Yu and M Jaroniec ldquoAnatase TiO

2with dominant

high-energy 001 facets Synthesis properties and applicationsrdquoChemistry of Materials vol 23 no 18 pp 4085ndash4093 2011

[29] T Ungar ldquoMicrostructural parameters from X-ray diffractionpeak broadeningrdquo Scripta Materialia vol 51 no 8 pp 777ndash7812004

[30] A W Burton K Ong T Rea and I Y Chan ldquoOn the esti-mation of average crystallite size of zeolites from the Scherrerequation a critical evaluation of its application to zeolites withone-dimensional pore systemsrdquo Microporous and MesoporousMaterials vol 117 no 1-2 pp 75ndash90 2009

[31] A Jaroenworaluck N Pijarn N Kosachan and R StevensldquoNanocomposite TiO

2ndashSiO2gel for UV absorptionrdquo Chemical

Engineering Journal vol 181-182 pp 45ndash55 2012[32] J I Pena-Flores A F Palomec-Garfias C Marquez-Beltran

E Sanchez-Mora E Gomez-Barojas and F Perez-RodrıguezldquoFe effect on the optical properties of TiO

2Fe2O3nanostruc-

tured composites supported on SiO2microsphere assembliesrdquo

Nanoscale Research Letters vol 9 article 499 2014[33] D Kim Y Im K M Jeong S-M Park M-H Um and M

Kang ldquoEnhanced 2-chorophenol photodecomposition usingnano-sized Mn-incorporated TiO

2powders prepared by a

solvothermal methodrdquo Bulletin of the Korean Chemical Societyvol 35 no 8 pp 2295ndash2298 2014

[34] C C Huang C C Wu K Knight and D W Hewak ldquoOpticalproperties of CVD grown amorphous Ge-Sb-S thin filmsrdquoJournal of Non-Crystalline Solids vol 356 no 4-5 pp 281ndash2852010

[35] J Kim J S Lee and M Kang ldquoSynthesis of nanoporousstructured SnO

2and its photocatalytic ability for bisphenol a

destructionrdquo Bulletin of the Korean Chemical Society vol 32 no5 pp 1715ndash1720 2011

[36] M Thommes ldquoPhysical adsorption characterization ofnanoporous materialsrdquo Chemie Ingenieur Technik vol 82 no 7pp 1059ndash1073 2010

[37] A A Gribb and J F Banfield ldquoParticle size effects on trans-formation kinetics and phase stability in nanocrystalline TiO

2rdquo

American Mineralogist vol 82 no 7-8 pp 717ndash728 1997[38] S-H Nam S-J Cho C-K Jung et al ldquoComparison of

hydrophilic properties of TiO2thin films prepared by solndashgel

method and reactive magnetron sputtering systemrdquo Thin SolidFilms vol 519 no 20 pp 6944ndash6950 2011

12 International Journal of Photoenergy

[39] H G Feichtinger K Grochenig and T Strohmer ldquoEffi-cient numerical methods in non-uniform sampling theoryrdquoNumerische Mathematik vol 69 no 4 pp 423ndash440 1995

[40] S W Jo B S Kwak K M Kim et al ldquoEffectively CO2

photoreduction toCH4by the synergistic effects of Ca andTi on

Ca-loaded TiSiMCM-41 mesoporous photocatalytic systemsrdquoApplied Surface Science vol 355 pp 891ndash901 2015

[41] J Y Do Y Im B S Kwak J-Y Kim and M Kang ldquoDramaticCO2photoreduction with H

2O vapors for CH

4production

using the TiO2(bottom)FendashTiO

2(top) double-layered filmsrdquo

Chemical Engineering Journal vol 275 pp 288ndash297 2015[42] M Tahir andN SaidinaAmin ldquoPhotocatalytic reduction of car-

bon dioxide with water vapors over montmorillonite modifiedTiO2nanocompositesrdquo Applied Catalysis B Environmental vol

142-143 pp 512ndash522 2013[43] Y Kohno H Hayashi S Takenaka T Tanaka T Funabiki

and S Yoshida ldquoPhoto-enhanced reduction of carbon dioxidewith hydrogen over RhTiO

2rdquo Journal of Photochemistry and

Photobiology A Chemistry vol 126 no 1ndash3 pp 117ndash123 1999[44] M Subrahmanyam S Kaneco and N Alonso-Vante ldquoA screen-

ing for the photo reduction of carbon dioxide supported onmetal oxide catalysts for C

1-C3selectivityrdquo Applied Catalysis B

Environmental vol 23 no 2-3 pp 169ndash174 1999[45] S S Tan L Zou and E Hu ldquoKinetic modelling for photosyn-

thesis of hydrogen and methane through catalytic reduction ofcarbon dioxide with water vapourrdquo Catalysis Today vol 131 no1ndash4 pp 125ndash129 2008

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

International Journal of Photoenergy 5

Table 1 Physical properties of 50mol M-TiO2particles

Physical properties of catalysts Atomic compositionsTi M O

Specific surface areas[m2 gminus1]

Total pore volume[cm3 gminus1]

Average pore diameter[nm]

TiO2 320 00 680 131 020 617

50mol Fe-TiO2 302 37 660 165 064 1556

50mol Co-TiO2 306 34 670 124 017 563

50mol Ni-TiO2 289 31 680 130 018 563

50mol Cu-TiO2 316 29 655 67 042 2495

Basalt fiberTiO2

400 500 600 700 800300Wavelength (nm)

00

05

10

15

20

25

Inte

nsity

(V)

50mol Cu-TiO2

50mol Ni-TiO2

50mol Co-TiO2

50mol Fe-TiO2

Figure 4 PL spectra of the prepared 50mol M-TiO2particles

suggests that the electrons in the valence band are transferredto the conduction band and are stabilized by photoemissionIn general the PL intensity increases with increasing numberof electrons emitted resulting from recombination betweenthe excited electrons and holes and a consequent decreasein photoactivity [35] Therefore there is a strong relationshipbetween the PL intensity and photoactivity In particularthe PL intensity decreases significantly when a metal cancapture excited electrons or exhibit conductivity which isknown as the relaxation process The 50mol M-TiO

2

samples exhibited a PL signal with a similar curve shapedemonstrating the presence of TiO

2 Pure TiO

2exhibited a

strong PL signal in the range 400ndash550 nm with a maximumexcitation wavelength of 445 nm whereas the 50molM-TiO

2curve intensities were weakened dramatically The

decreasing tendency was observed in the following orderTiO2gt 50mol Fe-TiO

2gt Cu-TiO

2gt Ni-TiO

2gt Co-

TiO2 which was possibly due to the new oxygen vacancies

produced by metal-doping The photogenerated electronsin the conduction band initially reached the vacant spaceand then recombined with the photogenerated holes in thevalance band to produce fluorescence emission The reducedPL intensities of 50mol M-TiO

2might be due to defects

generated by the transition metal ions inserted into the TiO2

structures which accelerate electron transfer and hinder

electron-hole pair recombination on the 50mol M-TiO2

surfaceFigure 5 shows the adsorption-desorption isotherm

curves of N2at 77 K for the as-synthesized 50mol M (Fe-

Co- Ni- and Cu-) TiO2particles With the exception of the

50mol Fe-TiO2and Cu-TiO

2samples all isotherms were

close to type II according to the IUPAC classification [36]indicating the lack of pores in the particles Otherwise theisotherms of the 50mol Fe-TiO

2and Cu-TiO

2samples

were attributed to type IV indicating bulk pores by aggre-gation between each nanoparticle The hysteresis slopes wereobserved at intermediate and relative pressures greater than119901119901

0= 07 in all samples

Table 1 lists the specific surface areas of the 50molM-TiO

2samples The specific surface areas were located in

the range 68sim165m2 gminus1 In particular the surface area wasthe largest at 165m2 gminus1 in 50mol Fe-TiO

2 In general

the surface area increases with decreasing particle size [37]These results showed some degree of reliability and were wellmatched to their calculated crystallite sizes (Figure 2) Fromthe results of the average bulk pore diameter for the samplesit is believed that the 50mol Fe-TiO

2and Cu-TiO

2may

contain bulk mesopores approximately 15sim24 nm due toaggregation between their nanoparticles Otherwise the porevolumes of the samples were varied from 017 to 064 cm3 gminus1The atomic compositions calculated the energy-dispersive X-ray spectra that are also included in this table The TiO

2

surface showed only two elements Ti and O whereas threeelements were observed in theM-TiO

2samples In contrast to

expectations the amount of doped metals was much higherthan the Ti amount in all samples and the M Ti ratios wereapproximately 1 10This was calculated from EDAX analysisand the values were different from the actual amount Theamount of metal doped in TiO

2was reduced to the order of

Fe gt Co gt Ni gt CuDuring the CO

2photoreduction reaction CO

2is

adsorbed onto the surface of the photocatalysts in the firststep and the photoreduction reaction progresses Thereforethe photocatalytic performance depends on the adsorptioncapacities of CO

2 Accordingly the CO

2adsorption abilities

of the 50mol M (Fe- Co- Ni- and Cu-) TiO2samples

need to be determined The CO2desorption profiles were

obtained over the range 50sim900∘C as shown in Figure 6Thecurve intensity for CO

2desorption was higher in 50mol

M-TiO2than in pure TiO

2 which means considerably more

CO2molecules had been adsorbed on the surfaces of the

50mol M-TiO2samples In addition TiO

2generally has

6 International Journal of Photoenergy

ADSDES

0

50

100

150V

ac

m3(S

TP) g

minus1

05 10

pp0

(a) TiO2

ADSDES

0

200

400

600

Vac

m3(S

TP) g

minus1

05 10

pp0

(b) 50mol- Fe-TiO2

ADSDES

0

50

100

150

Vac

m3(S

TP) g

minus1

05 10

pp0

(c) 50mol- Co-TiO2

ADSDES

05 10

pp0

0

50

100

150

Vac

m3(S

TP) g

minus1

(d) 50mol- Ni-TiO2

ADSDES

05 10

pp0

0

120

240

360

Vac

m3(S

TP) g

minus1

(e) 50mol- Cu-TiO2

Figure 5 Adsorption-desorption isotherm curves of N2at 77 K for the as-synthesized 50mol M-TiO

2particles

Area integ(Gaussian) 27983665 33278233 66855506 68781188 60435286 10310403

Basalt fiber

2075000208000020850002090000209500021000002105000

TCD

(mV

)

400 600 800200

62750006300000632500063500006375000640000064250006450000

TCD

(mV

)

TiO2

6800000

6900000

7000000

7100000

7200000

7300000

7400000

7500000

7600000

7700000

TCD

(120583V

)

400 600 800200Temperature (∘C)

400 600 800200Temperature (∘C)

Basalt fiber TiO2

50mol Fe-TiO2

50mol Co-TiO2

50mol Ni-TiO2

50mol Fe-TiO2 50mol Co-TiO2 50mol Ni-TiO2 50mol Cu-TiO2

50mol Cu-TiO2

Figure 6 CO2desorption profiles over the 50mol M-TiO

2particles in the range 50sim900∘C

International Journal of Photoenergy 7

30120583m

ldquoTop viewrdquoldquoSide viewrdquo

20120583m

Basalt fiber (b) TiO2basalt fiber(a) Basalt fiber

basalt fiber

basalt fiber

basalt fiber basalt fiber basalt fiber

(c) 50mol Fe-TiO2

50mol Co-TiO2 (d) 50mol Co-TiO2 (e) 50mol Ni-TiO2 (f) 50mol Cu-TiO2

Figure 7 SEM images of the pure basalt fiber film and 50mol M-TiO2basalt fiber films

hydrophilic properties [38] which suggests that duringthe CO

2photoreduction reaction CO

2and H

2O will

be adsorbed preferentially on the metal ions and TiO2

respectively The adsorption abilities were observed inthe following order 50mol Co-TiO

2gt Ni-TiO

2gt

Fe-TiO2gt TiO

2gt Cu-TiO

2samples In general a rapid

catalytic reaction occurs when many reactants are well-adsorbed over the catalyst The presence of transition metalsin the 50mol M-TiO

2samples most likely caused the

relative increase in the number of CO2and H

2O molecules

adsorbed compared to pure TiO2 This synergy contributed

significantly to improving the catalytic performance of the50mol M-TiO

2samples

32 Characteristics and CO2

Photoreduction over the50mol M (Fe- Co- Ni- and Cu-) TiO

2Basalt Fiber Films

Figure 7 presents SEM images (top and side views) of the sixsamples of pure basalt fiber and TiO

2films and 50mol

M (Fe- Co- Ni- and Cu-) TiO2basalt fiber films The

basalt fiber in the films was approximately 15 120583m in diameterwith different lengths and the surfaces were smooth The50mol M-TiO

2materials were mixed with basalt fibers

and were fabricated as thick films by coating on a Pyrex plateThe regular array of composites could be observed clearlythrough both the side and top directions The TiO

2basalt

fiber and 50mol Fe-TiO2basalt fiber composites did not

cover the Pyrex plate surface completely and bulk poreswere observed On the other hand the coating parts werequite uniform and fine particles were well-dispersed Incontrast the surfaces of the films fabricated from 50mol

Co-TiO2basalt fiber 50mol Ni-TiO

2basalt fiber and

50mol Cu-TiO2basalt fiber composites were quite dense

despite containing some cracks In particular the surfacewas the most compact over the 50mol Co-TiO

2basalt

fiber film The thickness of the films in all samples wasapproximately 30sim35 120583m with the exception of the purebasalt fiber film (20 120583m)

Energy-dispersive X-ray spectroscopy (EDAX) con-firmed the presence of metals on the surfaces of the basaltfiber and 50mol M (Fe- Co- Ni- and Cu-) TiO

2basalt

fiber films as shown in Figure 8 and the table below liststhe atomic compositions determined by EDAX For the basaltfiber various metal oxides were observed such as Na KCa Mg Al Si Fe and Ti Pure basalt fiber exhibited acomposition of 1928wt Si 314 wt total alkali metals166wt Ti 1177 wt Fe and 561 wt Al As a CO

2

adsorbent the Ca and Mg contents were 531 and 209wtrespectively Ti contained on the 50mol M (Fe- Co-Ni- and Cu-) TiO

2basalt fiber films decreased in the

following order 50mol Ni-TiO2(4774wt) gt Co-TiO

2

(4268wt) gt TiO2(4094wt) gt Fe-TiO

2(3344wt)

The amounts of transitionmetal specieswere in the range 269to 302wt with the exception of copper (098wt) Thesevalues did not appear to be perfectly quantitative EDAXis a very good surface analytical method but it is prone toerror because the composition can vary according to thelocation In particular the variation is large when the sampleis nonuniform [39]

The efficiencies of the photogenerated electron-hole pro-duction in the basalt fiber and 50mol M (Fe- Co- Ni-

8 International Journal of Photoenergy

MaterialselementAtomic compositions (wt-)

(a)

(b)

(c)

(d)

(e)

Na

204

mdash

mdash

192

160

Mg

209

mdash

mdash

mdash

mdash

Al

561

mdash

mdash

059

mdash

Si

1928

mdash

mdash

228

032

K

110

mdash

mdash

mdash

mdash

Ca

531

mdash

mdash

066

mdash

Fe

1177

mdash

286

114

mdash

Co

mdash

mdash

mdash

269

mdash

Ni

mdash

mdash

mdash

mdash

302

(f)

O

5114

5906

4122

4803

4732

4543

Ti

166

4094

3344

4268

4774

3615

Cu

mdash

mdash

mdash

mdash

mdash

098

Spectrum 1Ca Si

FeTi

OAl

Mg

NaK

CaK

Ti FeFe

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 1

Ti

O

Ti

2 4 6 1810 16 200 128 14(keV)

Spectrum 3

TiO

Ti

FeFe

Fe

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 2Ti

O

CuCuCu

Ti

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 4

NiNiNi Si

Ti

O

NaTi

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 2Ca

Si

Fe

Ti

O

AlNa

Ca

Co

Co

Co

Ti

FeFe

2 4 6 8 10 12 14 16 18 200(keV)

Full scale 767 cts cursor 0000Full scale 4345 cts cursor 0000Full scale 1548 cts cursor 0000

Full scale 1428 cts cursor 0000 Full scale 2264 cts cursor 0000 Full scale 830 cts cursor 0000

(b) TiO2basalt fiber(a) Basalt fiber

(d) 50mol Co-TiO2basalt fiber (f) 50mol Cu-TiO2basalt fiber(e) 50mol Ni-TiO2basalt fiber

(c) 50mol Fe-TiO2basalt fiber

Figure 8 Energy-dispersive X-ray spectra of the surfaces of the pure basalt fiber and 50mol M-TiO2basalt fiber films and the atomic

compositions

and Cu-) TiO2basalt fiber films were measured from the

photocurrent response under solar light irradiation at anapplied potential of 07 V versus SCE Figure 9 shows thetypical real time photocurrent response of the films whenthe light source is switched on and off exhibiting a rapidphotocurrent rise and decay In semiconductor systemswhen irradiation provides an energy higher than the band-gap of a semiconductor the energy excites an electron fromthe valence band to the conduction band leaving a hole inthe valence band The electron-hole pair is responsible forthe photocurrent When the light was turned on a rapidincrease in the photoreduction current was observed andthe photocurrent then turned to a steady state after a fewseconds When the light was turned off the photocurrentdecreased instantaneously to almost zero [40]When the lightwas turned on the maximum photocurrents obtained forthe 50mol Co-TiO

2and Ni-TiO

2basalt fiber films were

31049 and 30075mA cmminus2 respectively which were morethan four times higher than that achieved on pure basalt fiber

(7123mA cmminus2) andTiO2basalt fiber films (7401mA cmminus2)

Themaximumphotocurrent of the 50molCu-TiO2basalt

fiber film was too small due to trapping of excited elec-trons by copper with strong oxidation agency In additionthe TiO

2basalt fiber 50mol Cu-TiO

2basalt fiber and

50mol Ni-TiO2basalt fiber films showed no current

transients in both the light-on and the light-off regions inthe samples falling off with time in 50 s to a steady statewhich indicates that few surface recombination processeshad occurred Clearly some electron-hole recombinationwas observed in the 50mol Fe-TiO

2basalt fiber and Co-

TiO2basalt fiber films but it was negligible compared to

the total current value Therefore the 3d-transition metalingredients have a beneficial effect on the photocurrent itplays a role as an intermediate for the efficient separation ofphotogenerated hole-electron pairs

Figure 10 presents the photoreduction abilities of CO2

with H2O vapor to CH

4over the pure basalt fiber film and

50mol M (Fe- Co- Ni- and Cu-) TiO2basalt fiber films

International Journal of Photoenergy 9

3104930075

20974

7123 74016450

TiO2basalt fiberBasalt fiber

50 100 150 200 250 300 3500Time (s)

minus50

0

50

100

150

200

250

300

350

Curr

ent (

mA

cm

2)

50mol Cu-TiO2basalt fiber50mol Ni-TiO2basalt fiber

50mol Fe-TiO2basalt fiber50mol Co-TiO2basalt fiber

Figure 9 Photocurrent responses of the pure basalt fiber and50mol M-TiO

2basalt fiber films when the light source was

switched on and off

after 8 h Generally CH4production from CO

2reduction

with H2O can be divided into the following three subpro-

cesses [41] proton production from H2O photodecompo-

sition CO radical production from CO2photo cleavage

and methane production from photosynthesis between theCO radical and proton The photogenerated electrons onthe photocatalysts by UV-radiation induce CO

2reduction

to produce CO2radicals whereas the holes react with the

adsorbed H2Omolecules to perform oxidationThe interme-

diate photogenerated species undergo different reactions toproduce CO CH

3OH andCH

4The production of CH

4from

methyl radicals (∙CH3) was confirmed which are dependent

directly on the formation of the intermediate product CO[42] As shown in this figure almost no methane wasobserved when only the lamp was turned on On the otherhand the amounts of CO and O

2generation increased and

a small amount of hydrogen was observed This means thatthe light does not induce photoreduction processes aloneOn the other hand there are different product distributionsaccording to the loaded metal species excessive methane isgenerated over the catalysts loaded with Ni and Co and thequantities of CO and CH

3OH gases are increased over the

catalysts loaded with Cu and Fe The M-TiO2basalt fiber

films showed higher CH4production from CO

2photoreduc-

tion than the pure basalt fiber and TiO2basalt fiber films

700 120583mol gcatminus1 Lminus1 CH

4was emitted over the pure basalt

fiber film suggesting that it contains a small amount of TiO2

On the other hand CH4production was 1121 120583mol gcat

minus1 Lminus1over the TiO

2basalt fiber film In contrast the maximum

Lamp turned on only

TiO2basalt fiberBasalt fiber

1 2 3 4 5 6 7 80Time (h)

0

50

100

150

200

250

300

350

400

Met

hane

yie

ld (120583

mol

g-c

atlowast

L)

50mol Cu-TiO2basalt fiber50mol Ni-TiO2basalt fiber

50mol Fe-TiO2basalt fiber50mol Co-TiO2basalt fiber

Figure 10 Photoreduction abilities of CO2with H

2O vapor to CH

4

over the pure basalt fiber film and 50mol M-TiO2basalt fiber

films after 8 h

CH4yields over the 50mol Co-TiO

2basalt fiber and Ni-

TiO2basalt fiber films were 3605 and 3073 120583mol gcat

minus1 Lminus1respectively The differences in yields were attributed to theirband-gaps electron-hole recombination tendencies and thegas adsorption abilities of the 50mol M-TiO

2basalt fiber

films In particular this study confirmed that the 50molCo-TiO

2particles show synergistic performance when the

basalt fiber is mixedThe reduction ofCO

2requires amultiple electron transfer

and leads to production of a variety of products dependingon the number of transferred electrons which determinethe final oxidation state of the carbon atom The standardredox potentials of the CO

2reduction half-reactions vary

from CO2HCOOH [43] to CO

2CH4[44] CO

2adsorbed

on a photocatalyst surface can be reduced to ∙CO2

minus anionradical which can react withH+ and eminus for formingHCOOHor HCOOminus or which can go to the postulated disproportion-ation reaction of two ∙CO

2

minus anion radicals into CO (afterall to be C radical) and CO

3

2minus to react with H radical Thisstudy seems to follow the latter Scheme 1 presents a modelfor CO

2photoreduction over the M-TiO

2basalt fiber films

based on the relationships between the optical propertiesof the photocatalysts and the catalytic activities Photonexcitation in M-TiO

2over the M-TiO

2basalt fiber films

will begin rapidly because M-TiO2has a shorter band-gap

than pure TiO2 and the excited electrons can be transferred

efficiently to CO2molecules In addition CO

2molecules

are adsorbed preferentially and easily on the basalt fibersurface The positive holes on the valance band of M-TiO

2

can be trapped byH2Ospecies and transferred toOH radicals

and protons The protons obtained are transformed to H

10 International Journal of Photoenergy

O

Basalt fiberFTO glass

FTO glass

H2

CO2

Basalt fiber (i) More CO2 adsorption good

H2O

∙H

∙CO2minus

+ ∙H rarr ∙CHrarr ∙CH2 rarr ∙CH3 rarr CH4

Reduction CO2 + eminus rarr ∙CO2minus

h+

eminus

h+

eminus

pasteM-TiO2basalt fiber

M-TiO2

ldquoMetal incorporatedrdquoUV light

decreaseTiO2 M-TiO2 M-TiO2

(i) Easy electron transfer(ii) Water (H2O) adsorption goodM-TiO2

Oxidation H2O + h+ rarr ∙OH + H+ H+ + O2997888rarr

Scheme 1 Model for CH4production from the photoreduction of CO

2with H

2O vapor over the M-TiO

2basalt fiber films

radicals by electrons and the H radicals then react with Cand CO radicals formed from the reduction of CO

2

minus overM-TiO

2 particularly over Co- or Ni-TiO

2semiconductors

resulting methane production [45] The mixed films ofbasalt fibers and M-TiO

2can also promote the separation

of photogenerated electron-hole pairs (eminush+) on M-TiO2

Therefore the synergetic effects of the basalt fibers and M-TiO2in the M-TiO

2basalt fiber films achieved higher CO

2

reduction efficiency

4 Conclusions

The 50mol M (Fe- Co- Ni- and Cu-) incorporated TiO2

photocatalysts obtained by the solvothermal method werecoated densely with basalt fibers on a Pyrex plate usinga squeeze technique and applied to the photoreduction ofCO2to CH

4 The CO

2adsorption abilities were improved

over the basalt fiber and CH4generation was enhanced

dramatically over 50mol M-TiO2basalt fiber films with

a threefold higher yield compared to the pure basalt fiberand TiO

2basalt fiber films In particular the photoreduction

of CO2with H

2O revealed a remarkable increase in CH

4

generation over the 50mol Co-TiO2basalt fiber film to

3605 120583mol gcatminus1sdotLminus1 after an 8 h reaction

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

This research was supported by ceramic fiber commercialcenter project of Korea Institute of Ceramic Engineeringamp Technology (KICET) funded by the Ministry of TradeIndustry amp Energy (MOTIE)

References

[1] M Tahir and N S Amin ldquoIndium-doped TiO2nanoparticles

for photocatalytic CO2reduction with H

2O vapors to CH

4rdquo

Applied Catalysis B Environmental vol 162 pp 98ndash109 2015[2] B S Kwak andM Kang ldquoPhotocatalytic reduction of CO

2with

H2O using perovskite Ca

119909Ti119910O3rdquo Applied Surface Science vol

337 pp 138ndash144 2015[3] C Fletcher Y Jiang and R Amal ldquoProduction of formic acid

from CO2reduction by means of potassium borohydride at

ambient conditionsrdquo Chemical Engineering Science vol 137 pp301ndash307 2015

[4] G Mahmodi S Sharifnia M Madani and V VatanpourldquoPhotoreduction of carbon dioxide in the presence of H

2 H2O

and CH4over TiO

2and ZnO photocatalystsrdquo Solar Energy vol

97 pp 186ndash194 2013[5] J Albo A Saez J Solla-Gullon V Montiel and A Irabien

ldquoProduction of methanol from CO2electroreduction at Cu

2O

and Cu2OZnO-based electrodes in aqueous solutionrdquo Applied

Catalysis B Environmental vol 176-177 pp 709ndash717 2015[6] P Akhter M Hussain G Saracco and N Russo ldquoNew nanos-

tructured silica incorporated with isolated Ti material for the

International Journal of Photoenergy 11

photocatalytic conversion of CO2to fuelsrdquo Nanoscale Research

Letters vol 9 article 158 2014[7] M Anpo ldquoPhotocatalytic reduction of CO

2with H

2O on

highly dispersed Ti-oxide catalysts as a model of artificialphotosynthesisrdquo Journal of CO

2Utilization vol 1 pp 8ndash17 2013

[8] H Abdullah M R Khan M Pudukudy Z Yaakob and NA Ismail ldquoCeO

2-TiO2as a visible light active catalyst for the

photoreduction ofCO2tomethanolrdquo Journal of Rare Earths vol

33 no 11 pp 1155ndash1161 2015[9] O Ola and M Mercedes Maroto-Valer ldquoReview of material

design and reactor engineering on TiO2photocatalysis for

CO2reductionrdquo Journal of Photochemistry and Photobiology C

Photochemistry Reviews vol 24 pp 16ndash42 2015[10] X Zhang L Wang Q Du Z Wang S Ma and M Yu

ldquoPhotocatalytic CO2reduction over B

4CC3N4with internal

electric field under visible light irradiationrdquo Journal of Colloidand Interface Science vol 464 pp 89ndash95 2016

[11] R Gusain P Kumar O P Sharma S L Jain and O PKhatri ldquoReduced graphene oxide-CuO nanocomposites forphotocatalytic conversion of CO

2into methanol under visible

light irradiationrdquo Applied Catalysis B Environmental vol 181pp 352ndash362 2016

[12] N M Nursam X Wang and R A Caruso ldquoHigh-throughputsynthesis and screening of titania-based photocatalystsrdquo ACSCombinatorial Science vol 17 no 10 pp 548ndash569 2015

[13] M V Dozzi S Marzorati M Longhi M Coduri L Artigliaand E Selli ldquoPhotocatalytic activity of TiO

2-WO3mixed oxides

in relation to electron transfer efficiencyrdquo Applied Catalysis BEnvironmental vol 186 pp 157ndash165 2016

[14] Y Qu and X Duan ldquoProgress challenge and perspective ofheterogeneous photocatalystsrdquo Chemical Society Reviews vol42 no 7 pp 2568ndash2580 2013

[15] J C Colmenares R Luque J M Campelo F Colmenares ZKarpinski and A A Romero ldquoNanostructured photocatalystsand their applications in the photocatalytic transformation oflignocellulosic biomass an overviewrdquo Materials vol 2 no 4pp 2228ndash2258 2009

[16] M Kitano M Matsuoka M Ueshima and M Anpo ldquoRecentdevelopments in titanium oxide-based photocatalystsrdquo AppliedCatalysis A General vol 325 no 1 pp 1ndash14 2007

[17] P Silija Z Yaakob V Suraja N N Binitha and Z S Akmal ldquoAnenthusiastic glance in to the visible responsive photocatalystsfor energy production and pollutant removal with specialemphasis on titaniardquo International Journal of Photoenergy vol2012 Article ID 503839 19 pages 2012

[18] H Xu S Ouyang L Liu P Reunchan N Umezawa and JYe ldquoRecent advances in TiO

2-based photocatalysisrdquo Journal of

Materials Chemistry A vol 2 no 32 pp 12642ndash12661 2014[19] Z He J Tang J Shen J Chen and S Song ldquoEnhancement of

photocatalytic reduction of CO2to CH

4over TiO

2nanosheets

by modifying with sulfuric acidrdquo Applied Surface Science vol364 pp 416ndash427 2016

[20] O Ola and M M Maroto-Valer ldquoTransition metal oxide basedTiO2nanoparticles for visible light induced CO

2photoreduc-

tionrdquo Applied Catalysis A General vol 502 pp 114ndash121 2015[21] D Eder ldquoCarbon nanotube-inorganic hybridsrdquo Chemical

Reviews vol 110 no 3 pp 1348ndash1385 2010[22] L Zhang R JamalQ ZhaoMWang andTAbdiryim ldquoPrepa-

ration of PEDOTGO PEDOTMnO2 and PEDOTGOMnO

2

nanocomposites and their application in catalytic degradationof methylene bluerdquo Nanoscale Research Letters vol 10 p 1482015

[23] M Urbanski A Lapko and A Garbacz ldquoInvestigation onconcrete beams reinforced with basalt rebars as an effectivealternative of conventional RC structuresrdquo Procedia Engineer-ing vol 57 pp 1183ndash1191 2013

[24] S A Chernyak E V Suslova A V Egorov L Lu S V Savilovand V V Lunin ldquoNew hybrid CNT-alumina supports for Co-based Fischer-Tropsch catalystsrdquo Fuel Processing Technologyvol 140 pp 267ndash275 2015

[25] K Shimura T Miyazawa T Hanaoka and S Hirata ldquoFischerndashTropsch synthesis over alumina supported bimetallic CondashNicatalyst effect of impregnation sequence and solutionrdquo Journalof Molecular Catalysis A Chemical vol 407 pp 15ndash24 2015

[26] F Fazlollahi M Sarkari A Zare A A Mirzaei and HAtashi ldquoDevelopment of a kinetic model for Fischer-Tropschsynthesis over CoNiAl

2O3catalystrdquo Journal of Industrial and

Engineering Chemistry vol 18 no 4 pp 1223ndash1232 2012[27] J Zhao W Xing Y Li and K Lu ldquoSolvothermal synthesis and

visible light absorption of anatase TiO2rdquo Materials Letters vol

145 pp 332ndash335 2015[28] S Liu J Yu and M Jaroniec ldquoAnatase TiO

2with dominant

high-energy 001 facets Synthesis properties and applicationsrdquoChemistry of Materials vol 23 no 18 pp 4085ndash4093 2011

[29] T Ungar ldquoMicrostructural parameters from X-ray diffractionpeak broadeningrdquo Scripta Materialia vol 51 no 8 pp 777ndash7812004

[30] A W Burton K Ong T Rea and I Y Chan ldquoOn the esti-mation of average crystallite size of zeolites from the Scherrerequation a critical evaluation of its application to zeolites withone-dimensional pore systemsrdquo Microporous and MesoporousMaterials vol 117 no 1-2 pp 75ndash90 2009

[31] A Jaroenworaluck N Pijarn N Kosachan and R StevensldquoNanocomposite TiO

2ndashSiO2gel for UV absorptionrdquo Chemical

Engineering Journal vol 181-182 pp 45ndash55 2012[32] J I Pena-Flores A F Palomec-Garfias C Marquez-Beltran

E Sanchez-Mora E Gomez-Barojas and F Perez-RodrıguezldquoFe effect on the optical properties of TiO

2Fe2O3nanostruc-

tured composites supported on SiO2microsphere assembliesrdquo

Nanoscale Research Letters vol 9 article 499 2014[33] D Kim Y Im K M Jeong S-M Park M-H Um and M

Kang ldquoEnhanced 2-chorophenol photodecomposition usingnano-sized Mn-incorporated TiO

2powders prepared by a

solvothermal methodrdquo Bulletin of the Korean Chemical Societyvol 35 no 8 pp 2295ndash2298 2014

[34] C C Huang C C Wu K Knight and D W Hewak ldquoOpticalproperties of CVD grown amorphous Ge-Sb-S thin filmsrdquoJournal of Non-Crystalline Solids vol 356 no 4-5 pp 281ndash2852010

[35] J Kim J S Lee and M Kang ldquoSynthesis of nanoporousstructured SnO

2and its photocatalytic ability for bisphenol a

destructionrdquo Bulletin of the Korean Chemical Society vol 32 no5 pp 1715ndash1720 2011

[36] M Thommes ldquoPhysical adsorption characterization ofnanoporous materialsrdquo Chemie Ingenieur Technik vol 82 no 7pp 1059ndash1073 2010

[37] A A Gribb and J F Banfield ldquoParticle size effects on trans-formation kinetics and phase stability in nanocrystalline TiO

2rdquo

American Mineralogist vol 82 no 7-8 pp 717ndash728 1997[38] S-H Nam S-J Cho C-K Jung et al ldquoComparison of

hydrophilic properties of TiO2thin films prepared by solndashgel

method and reactive magnetron sputtering systemrdquo Thin SolidFilms vol 519 no 20 pp 6944ndash6950 2011

12 International Journal of Photoenergy

[39] H G Feichtinger K Grochenig and T Strohmer ldquoEffi-cient numerical methods in non-uniform sampling theoryrdquoNumerische Mathematik vol 69 no 4 pp 423ndash440 1995

[40] S W Jo B S Kwak K M Kim et al ldquoEffectively CO2

photoreduction toCH4by the synergistic effects of Ca andTi on

Ca-loaded TiSiMCM-41 mesoporous photocatalytic systemsrdquoApplied Surface Science vol 355 pp 891ndash901 2015

[41] J Y Do Y Im B S Kwak J-Y Kim and M Kang ldquoDramaticCO2photoreduction with H

2O vapors for CH

4production

using the TiO2(bottom)FendashTiO

2(top) double-layered filmsrdquo

Chemical Engineering Journal vol 275 pp 288ndash297 2015[42] M Tahir andN SaidinaAmin ldquoPhotocatalytic reduction of car-

bon dioxide with water vapors over montmorillonite modifiedTiO2nanocompositesrdquo Applied Catalysis B Environmental vol

142-143 pp 512ndash522 2013[43] Y Kohno H Hayashi S Takenaka T Tanaka T Funabiki

and S Yoshida ldquoPhoto-enhanced reduction of carbon dioxidewith hydrogen over RhTiO

2rdquo Journal of Photochemistry and

Photobiology A Chemistry vol 126 no 1ndash3 pp 117ndash123 1999[44] M Subrahmanyam S Kaneco and N Alonso-Vante ldquoA screen-

ing for the photo reduction of carbon dioxide supported onmetal oxide catalysts for C

1-C3selectivityrdquo Applied Catalysis B

Environmental vol 23 no 2-3 pp 169ndash174 1999[45] S S Tan L Zou and E Hu ldquoKinetic modelling for photosyn-

thesis of hydrogen and methane through catalytic reduction ofcarbon dioxide with water vapourrdquo Catalysis Today vol 131 no1ndash4 pp 125ndash129 2008

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

6 International Journal of Photoenergy

ADSDES

0

50

100

150V

ac

m3(S

TP) g

minus1

05 10

pp0

(a) TiO2

ADSDES

0

200

400

600

Vac

m3(S

TP) g

minus1

05 10

pp0

(b) 50mol- Fe-TiO2

ADSDES

0

50

100

150

Vac

m3(S

TP) g

minus1

05 10

pp0

(c) 50mol- Co-TiO2

ADSDES

05 10

pp0

0

50

100

150

Vac

m3(S

TP) g

minus1

(d) 50mol- Ni-TiO2

ADSDES

05 10

pp0

0

120

240

360

Vac

m3(S

TP) g

minus1

(e) 50mol- Cu-TiO2

Figure 5 Adsorption-desorption isotherm curves of N2at 77 K for the as-synthesized 50mol M-TiO

2particles

Area integ(Gaussian) 27983665 33278233 66855506 68781188 60435286 10310403

Basalt fiber

2075000208000020850002090000209500021000002105000

TCD

(mV

)

400 600 800200

62750006300000632500063500006375000640000064250006450000

TCD

(mV

)

TiO2

6800000

6900000

7000000

7100000

7200000

7300000

7400000

7500000

7600000

7700000

TCD

(120583V

)

400 600 800200Temperature (∘C)

400 600 800200Temperature (∘C)

Basalt fiber TiO2

50mol Fe-TiO2

50mol Co-TiO2

50mol Ni-TiO2

50mol Fe-TiO2 50mol Co-TiO2 50mol Ni-TiO2 50mol Cu-TiO2

50mol Cu-TiO2

Figure 6 CO2desorption profiles over the 50mol M-TiO

2particles in the range 50sim900∘C

International Journal of Photoenergy 7

30120583m

ldquoTop viewrdquoldquoSide viewrdquo

20120583m

Basalt fiber (b) TiO2basalt fiber(a) Basalt fiber

basalt fiber

basalt fiber

basalt fiber basalt fiber basalt fiber

(c) 50mol Fe-TiO2

50mol Co-TiO2 (d) 50mol Co-TiO2 (e) 50mol Ni-TiO2 (f) 50mol Cu-TiO2

Figure 7 SEM images of the pure basalt fiber film and 50mol M-TiO2basalt fiber films

hydrophilic properties [38] which suggests that duringthe CO

2photoreduction reaction CO

2and H

2O will

be adsorbed preferentially on the metal ions and TiO2

respectively The adsorption abilities were observed inthe following order 50mol Co-TiO

2gt Ni-TiO

2gt

Fe-TiO2gt TiO

2gt Cu-TiO

2samples In general a rapid

catalytic reaction occurs when many reactants are well-adsorbed over the catalyst The presence of transition metalsin the 50mol M-TiO

2samples most likely caused the

relative increase in the number of CO2and H

2O molecules

adsorbed compared to pure TiO2 This synergy contributed

significantly to improving the catalytic performance of the50mol M-TiO

2samples

32 Characteristics and CO2

Photoreduction over the50mol M (Fe- Co- Ni- and Cu-) TiO

2Basalt Fiber Films

Figure 7 presents SEM images (top and side views) of the sixsamples of pure basalt fiber and TiO

2films and 50mol

M (Fe- Co- Ni- and Cu-) TiO2basalt fiber films The

basalt fiber in the films was approximately 15 120583m in diameterwith different lengths and the surfaces were smooth The50mol M-TiO

2materials were mixed with basalt fibers

and were fabricated as thick films by coating on a Pyrex plateThe regular array of composites could be observed clearlythrough both the side and top directions The TiO

2basalt

fiber and 50mol Fe-TiO2basalt fiber composites did not

cover the Pyrex plate surface completely and bulk poreswere observed On the other hand the coating parts werequite uniform and fine particles were well-dispersed Incontrast the surfaces of the films fabricated from 50mol

Co-TiO2basalt fiber 50mol Ni-TiO

2basalt fiber and

50mol Cu-TiO2basalt fiber composites were quite dense

despite containing some cracks In particular the surfacewas the most compact over the 50mol Co-TiO

2basalt

fiber film The thickness of the films in all samples wasapproximately 30sim35 120583m with the exception of the purebasalt fiber film (20 120583m)

Energy-dispersive X-ray spectroscopy (EDAX) con-firmed the presence of metals on the surfaces of the basaltfiber and 50mol M (Fe- Co- Ni- and Cu-) TiO

2basalt

fiber films as shown in Figure 8 and the table below liststhe atomic compositions determined by EDAX For the basaltfiber various metal oxides were observed such as Na KCa Mg Al Si Fe and Ti Pure basalt fiber exhibited acomposition of 1928wt Si 314 wt total alkali metals166wt Ti 1177 wt Fe and 561 wt Al As a CO

2

adsorbent the Ca and Mg contents were 531 and 209wtrespectively Ti contained on the 50mol M (Fe- Co-Ni- and Cu-) TiO

2basalt fiber films decreased in the

following order 50mol Ni-TiO2(4774wt) gt Co-TiO

2

(4268wt) gt TiO2(4094wt) gt Fe-TiO

2(3344wt)

The amounts of transitionmetal specieswere in the range 269to 302wt with the exception of copper (098wt) Thesevalues did not appear to be perfectly quantitative EDAXis a very good surface analytical method but it is prone toerror because the composition can vary according to thelocation In particular the variation is large when the sampleis nonuniform [39]

The efficiencies of the photogenerated electron-hole pro-duction in the basalt fiber and 50mol M (Fe- Co- Ni-

8 International Journal of Photoenergy

MaterialselementAtomic compositions (wt-)

(a)

(b)

(c)

(d)

(e)

Na

204

mdash

mdash

192

160

Mg

209

mdash

mdash

mdash

mdash

Al

561

mdash

mdash

059

mdash

Si

1928

mdash

mdash

228

032

K

110

mdash

mdash

mdash

mdash

Ca

531

mdash

mdash

066

mdash

Fe

1177

mdash

286

114

mdash

Co

mdash

mdash

mdash

269

mdash

Ni

mdash

mdash

mdash

mdash

302

(f)

O

5114

5906

4122

4803

4732

4543

Ti

166

4094

3344

4268

4774

3615

Cu

mdash

mdash

mdash

mdash

mdash

098

Spectrum 1Ca Si

FeTi

OAl

Mg

NaK

CaK

Ti FeFe

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 1

Ti

O

Ti

2 4 6 1810 16 200 128 14(keV)

Spectrum 3

TiO

Ti

FeFe

Fe

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 2Ti

O

CuCuCu

Ti

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 4

NiNiNi Si

Ti

O

NaTi

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 2Ca

Si

Fe

Ti

O

AlNa

Ca

Co

Co

Co

Ti

FeFe

2 4 6 8 10 12 14 16 18 200(keV)

Full scale 767 cts cursor 0000Full scale 4345 cts cursor 0000Full scale 1548 cts cursor 0000

Full scale 1428 cts cursor 0000 Full scale 2264 cts cursor 0000 Full scale 830 cts cursor 0000

(b) TiO2basalt fiber(a) Basalt fiber

(d) 50mol Co-TiO2basalt fiber (f) 50mol Cu-TiO2basalt fiber(e) 50mol Ni-TiO2basalt fiber

(c) 50mol Fe-TiO2basalt fiber

Figure 8 Energy-dispersive X-ray spectra of the surfaces of the pure basalt fiber and 50mol M-TiO2basalt fiber films and the atomic

compositions

and Cu-) TiO2basalt fiber films were measured from the

photocurrent response under solar light irradiation at anapplied potential of 07 V versus SCE Figure 9 shows thetypical real time photocurrent response of the films whenthe light source is switched on and off exhibiting a rapidphotocurrent rise and decay In semiconductor systemswhen irradiation provides an energy higher than the band-gap of a semiconductor the energy excites an electron fromthe valence band to the conduction band leaving a hole inthe valence band The electron-hole pair is responsible forthe photocurrent When the light was turned on a rapidincrease in the photoreduction current was observed andthe photocurrent then turned to a steady state after a fewseconds When the light was turned off the photocurrentdecreased instantaneously to almost zero [40]When the lightwas turned on the maximum photocurrents obtained forthe 50mol Co-TiO

2and Ni-TiO

2basalt fiber films were

31049 and 30075mA cmminus2 respectively which were morethan four times higher than that achieved on pure basalt fiber

(7123mA cmminus2) andTiO2basalt fiber films (7401mA cmminus2)

Themaximumphotocurrent of the 50molCu-TiO2basalt

fiber film was too small due to trapping of excited elec-trons by copper with strong oxidation agency In additionthe TiO

2basalt fiber 50mol Cu-TiO

2basalt fiber and

50mol Ni-TiO2basalt fiber films showed no current

transients in both the light-on and the light-off regions inthe samples falling off with time in 50 s to a steady statewhich indicates that few surface recombination processeshad occurred Clearly some electron-hole recombinationwas observed in the 50mol Fe-TiO

2basalt fiber and Co-

TiO2basalt fiber films but it was negligible compared to

the total current value Therefore the 3d-transition metalingredients have a beneficial effect on the photocurrent itplays a role as an intermediate for the efficient separation ofphotogenerated hole-electron pairs

Figure 10 presents the photoreduction abilities of CO2

with H2O vapor to CH

4over the pure basalt fiber film and

50mol M (Fe- Co- Ni- and Cu-) TiO2basalt fiber films

International Journal of Photoenergy 9

3104930075

20974

7123 74016450

TiO2basalt fiberBasalt fiber

50 100 150 200 250 300 3500Time (s)

minus50

0

50

100

150

200

250

300

350

Curr

ent (

mA

cm

2)

50mol Cu-TiO2basalt fiber50mol Ni-TiO2basalt fiber

50mol Fe-TiO2basalt fiber50mol Co-TiO2basalt fiber

Figure 9 Photocurrent responses of the pure basalt fiber and50mol M-TiO

2basalt fiber films when the light source was

switched on and off

after 8 h Generally CH4production from CO

2reduction

with H2O can be divided into the following three subpro-

cesses [41] proton production from H2O photodecompo-

sition CO radical production from CO2photo cleavage

and methane production from photosynthesis between theCO radical and proton The photogenerated electrons onthe photocatalysts by UV-radiation induce CO

2reduction

to produce CO2radicals whereas the holes react with the

adsorbed H2Omolecules to perform oxidationThe interme-

diate photogenerated species undergo different reactions toproduce CO CH

3OH andCH

4The production of CH

4from

methyl radicals (∙CH3) was confirmed which are dependent

directly on the formation of the intermediate product CO[42] As shown in this figure almost no methane wasobserved when only the lamp was turned on On the otherhand the amounts of CO and O

2generation increased and

a small amount of hydrogen was observed This means thatthe light does not induce photoreduction processes aloneOn the other hand there are different product distributionsaccording to the loaded metal species excessive methane isgenerated over the catalysts loaded with Ni and Co and thequantities of CO and CH

3OH gases are increased over the

catalysts loaded with Cu and Fe The M-TiO2basalt fiber

films showed higher CH4production from CO

2photoreduc-

tion than the pure basalt fiber and TiO2basalt fiber films

700 120583mol gcatminus1 Lminus1 CH

4was emitted over the pure basalt

fiber film suggesting that it contains a small amount of TiO2

On the other hand CH4production was 1121 120583mol gcat

minus1 Lminus1over the TiO

2basalt fiber film In contrast the maximum

Lamp turned on only

TiO2basalt fiberBasalt fiber

1 2 3 4 5 6 7 80Time (h)

0

50

100

150

200

250

300

350

400

Met

hane

yie

ld (120583

mol

g-c

atlowast

L)

50mol Cu-TiO2basalt fiber50mol Ni-TiO2basalt fiber

50mol Fe-TiO2basalt fiber50mol Co-TiO2basalt fiber

Figure 10 Photoreduction abilities of CO2with H

2O vapor to CH

4

over the pure basalt fiber film and 50mol M-TiO2basalt fiber

films after 8 h

CH4yields over the 50mol Co-TiO

2basalt fiber and Ni-

TiO2basalt fiber films were 3605 and 3073 120583mol gcat

minus1 Lminus1respectively The differences in yields were attributed to theirband-gaps electron-hole recombination tendencies and thegas adsorption abilities of the 50mol M-TiO

2basalt fiber

films In particular this study confirmed that the 50molCo-TiO

2particles show synergistic performance when the

basalt fiber is mixedThe reduction ofCO

2requires amultiple electron transfer

and leads to production of a variety of products dependingon the number of transferred electrons which determinethe final oxidation state of the carbon atom The standardredox potentials of the CO

2reduction half-reactions vary

from CO2HCOOH [43] to CO

2CH4[44] CO

2adsorbed

on a photocatalyst surface can be reduced to ∙CO2

minus anionradical which can react withH+ and eminus for formingHCOOHor HCOOminus or which can go to the postulated disproportion-ation reaction of two ∙CO

2

minus anion radicals into CO (afterall to be C radical) and CO

3

2minus to react with H radical Thisstudy seems to follow the latter Scheme 1 presents a modelfor CO

2photoreduction over the M-TiO

2basalt fiber films

based on the relationships between the optical propertiesof the photocatalysts and the catalytic activities Photonexcitation in M-TiO

2over the M-TiO

2basalt fiber films

will begin rapidly because M-TiO2has a shorter band-gap

than pure TiO2 and the excited electrons can be transferred

efficiently to CO2molecules In addition CO

2molecules

are adsorbed preferentially and easily on the basalt fibersurface The positive holes on the valance band of M-TiO

2

can be trapped byH2Ospecies and transferred toOH radicals

and protons The protons obtained are transformed to H

10 International Journal of Photoenergy

O

Basalt fiberFTO glass

FTO glass

H2

CO2

Basalt fiber (i) More CO2 adsorption good

H2O

∙H

∙CO2minus

+ ∙H rarr ∙CHrarr ∙CH2 rarr ∙CH3 rarr CH4

Reduction CO2 + eminus rarr ∙CO2minus

h+

eminus

h+

eminus

pasteM-TiO2basalt fiber

M-TiO2

ldquoMetal incorporatedrdquoUV light

decreaseTiO2 M-TiO2 M-TiO2

(i) Easy electron transfer(ii) Water (H2O) adsorption goodM-TiO2

Oxidation H2O + h+ rarr ∙OH + H+ H+ + O2997888rarr

Scheme 1 Model for CH4production from the photoreduction of CO

2with H

2O vapor over the M-TiO

2basalt fiber films

radicals by electrons and the H radicals then react with Cand CO radicals formed from the reduction of CO

2

minus overM-TiO

2 particularly over Co- or Ni-TiO

2semiconductors

resulting methane production [45] The mixed films ofbasalt fibers and M-TiO

2can also promote the separation

of photogenerated electron-hole pairs (eminush+) on M-TiO2

Therefore the synergetic effects of the basalt fibers and M-TiO2in the M-TiO

2basalt fiber films achieved higher CO

2

reduction efficiency

4 Conclusions

The 50mol M (Fe- Co- Ni- and Cu-) incorporated TiO2

photocatalysts obtained by the solvothermal method werecoated densely with basalt fibers on a Pyrex plate usinga squeeze technique and applied to the photoreduction ofCO2to CH

4 The CO

2adsorption abilities were improved

over the basalt fiber and CH4generation was enhanced

dramatically over 50mol M-TiO2basalt fiber films with

a threefold higher yield compared to the pure basalt fiberand TiO

2basalt fiber films In particular the photoreduction

of CO2with H

2O revealed a remarkable increase in CH

4

generation over the 50mol Co-TiO2basalt fiber film to

3605 120583mol gcatminus1sdotLminus1 after an 8 h reaction

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

This research was supported by ceramic fiber commercialcenter project of Korea Institute of Ceramic Engineeringamp Technology (KICET) funded by the Ministry of TradeIndustry amp Energy (MOTIE)

References

[1] M Tahir and N S Amin ldquoIndium-doped TiO2nanoparticles

for photocatalytic CO2reduction with H

2O vapors to CH

4rdquo

Applied Catalysis B Environmental vol 162 pp 98ndash109 2015[2] B S Kwak andM Kang ldquoPhotocatalytic reduction of CO

2with

H2O using perovskite Ca

119909Ti119910O3rdquo Applied Surface Science vol

337 pp 138ndash144 2015[3] C Fletcher Y Jiang and R Amal ldquoProduction of formic acid

from CO2reduction by means of potassium borohydride at

ambient conditionsrdquo Chemical Engineering Science vol 137 pp301ndash307 2015

[4] G Mahmodi S Sharifnia M Madani and V VatanpourldquoPhotoreduction of carbon dioxide in the presence of H

2 H2O

and CH4over TiO

2and ZnO photocatalystsrdquo Solar Energy vol

97 pp 186ndash194 2013[5] J Albo A Saez J Solla-Gullon V Montiel and A Irabien

ldquoProduction of methanol from CO2electroreduction at Cu

2O

and Cu2OZnO-based electrodes in aqueous solutionrdquo Applied

Catalysis B Environmental vol 176-177 pp 709ndash717 2015[6] P Akhter M Hussain G Saracco and N Russo ldquoNew nanos-

tructured silica incorporated with isolated Ti material for the

International Journal of Photoenergy 11

photocatalytic conversion of CO2to fuelsrdquo Nanoscale Research

Letters vol 9 article 158 2014[7] M Anpo ldquoPhotocatalytic reduction of CO

2with H

2O on

highly dispersed Ti-oxide catalysts as a model of artificialphotosynthesisrdquo Journal of CO

2Utilization vol 1 pp 8ndash17 2013

[8] H Abdullah M R Khan M Pudukudy Z Yaakob and NA Ismail ldquoCeO

2-TiO2as a visible light active catalyst for the

photoreduction ofCO2tomethanolrdquo Journal of Rare Earths vol

33 no 11 pp 1155ndash1161 2015[9] O Ola and M Mercedes Maroto-Valer ldquoReview of material

design and reactor engineering on TiO2photocatalysis for

CO2reductionrdquo Journal of Photochemistry and Photobiology C

Photochemistry Reviews vol 24 pp 16ndash42 2015[10] X Zhang L Wang Q Du Z Wang S Ma and M Yu

ldquoPhotocatalytic CO2reduction over B

4CC3N4with internal

electric field under visible light irradiationrdquo Journal of Colloidand Interface Science vol 464 pp 89ndash95 2016

[11] R Gusain P Kumar O P Sharma S L Jain and O PKhatri ldquoReduced graphene oxide-CuO nanocomposites forphotocatalytic conversion of CO

2into methanol under visible

light irradiationrdquo Applied Catalysis B Environmental vol 181pp 352ndash362 2016

[12] N M Nursam X Wang and R A Caruso ldquoHigh-throughputsynthesis and screening of titania-based photocatalystsrdquo ACSCombinatorial Science vol 17 no 10 pp 548ndash569 2015

[13] M V Dozzi S Marzorati M Longhi M Coduri L Artigliaand E Selli ldquoPhotocatalytic activity of TiO

2-WO3mixed oxides

in relation to electron transfer efficiencyrdquo Applied Catalysis BEnvironmental vol 186 pp 157ndash165 2016

[14] Y Qu and X Duan ldquoProgress challenge and perspective ofheterogeneous photocatalystsrdquo Chemical Society Reviews vol42 no 7 pp 2568ndash2580 2013

[15] J C Colmenares R Luque J M Campelo F Colmenares ZKarpinski and A A Romero ldquoNanostructured photocatalystsand their applications in the photocatalytic transformation oflignocellulosic biomass an overviewrdquo Materials vol 2 no 4pp 2228ndash2258 2009

[16] M Kitano M Matsuoka M Ueshima and M Anpo ldquoRecentdevelopments in titanium oxide-based photocatalystsrdquo AppliedCatalysis A General vol 325 no 1 pp 1ndash14 2007

[17] P Silija Z Yaakob V Suraja N N Binitha and Z S Akmal ldquoAnenthusiastic glance in to the visible responsive photocatalystsfor energy production and pollutant removal with specialemphasis on titaniardquo International Journal of Photoenergy vol2012 Article ID 503839 19 pages 2012

[18] H Xu S Ouyang L Liu P Reunchan N Umezawa and JYe ldquoRecent advances in TiO

2-based photocatalysisrdquo Journal of

Materials Chemistry A vol 2 no 32 pp 12642ndash12661 2014[19] Z He J Tang J Shen J Chen and S Song ldquoEnhancement of

photocatalytic reduction of CO2to CH

4over TiO

2nanosheets

by modifying with sulfuric acidrdquo Applied Surface Science vol364 pp 416ndash427 2016

[20] O Ola and M M Maroto-Valer ldquoTransition metal oxide basedTiO2nanoparticles for visible light induced CO

2photoreduc-

tionrdquo Applied Catalysis A General vol 502 pp 114ndash121 2015[21] D Eder ldquoCarbon nanotube-inorganic hybridsrdquo Chemical

Reviews vol 110 no 3 pp 1348ndash1385 2010[22] L Zhang R JamalQ ZhaoMWang andTAbdiryim ldquoPrepa-

ration of PEDOTGO PEDOTMnO2 and PEDOTGOMnO

2

nanocomposites and their application in catalytic degradationof methylene bluerdquo Nanoscale Research Letters vol 10 p 1482015

[23] M Urbanski A Lapko and A Garbacz ldquoInvestigation onconcrete beams reinforced with basalt rebars as an effectivealternative of conventional RC structuresrdquo Procedia Engineer-ing vol 57 pp 1183ndash1191 2013

[24] S A Chernyak E V Suslova A V Egorov L Lu S V Savilovand V V Lunin ldquoNew hybrid CNT-alumina supports for Co-based Fischer-Tropsch catalystsrdquo Fuel Processing Technologyvol 140 pp 267ndash275 2015

[25] K Shimura T Miyazawa T Hanaoka and S Hirata ldquoFischerndashTropsch synthesis over alumina supported bimetallic CondashNicatalyst effect of impregnation sequence and solutionrdquo Journalof Molecular Catalysis A Chemical vol 407 pp 15ndash24 2015

[26] F Fazlollahi M Sarkari A Zare A A Mirzaei and HAtashi ldquoDevelopment of a kinetic model for Fischer-Tropschsynthesis over CoNiAl

2O3catalystrdquo Journal of Industrial and

Engineering Chemistry vol 18 no 4 pp 1223ndash1232 2012[27] J Zhao W Xing Y Li and K Lu ldquoSolvothermal synthesis and

visible light absorption of anatase TiO2rdquo Materials Letters vol

145 pp 332ndash335 2015[28] S Liu J Yu and M Jaroniec ldquoAnatase TiO

2with dominant

high-energy 001 facets Synthesis properties and applicationsrdquoChemistry of Materials vol 23 no 18 pp 4085ndash4093 2011

[29] T Ungar ldquoMicrostructural parameters from X-ray diffractionpeak broadeningrdquo Scripta Materialia vol 51 no 8 pp 777ndash7812004

[30] A W Burton K Ong T Rea and I Y Chan ldquoOn the esti-mation of average crystallite size of zeolites from the Scherrerequation a critical evaluation of its application to zeolites withone-dimensional pore systemsrdquo Microporous and MesoporousMaterials vol 117 no 1-2 pp 75ndash90 2009

[31] A Jaroenworaluck N Pijarn N Kosachan and R StevensldquoNanocomposite TiO

2ndashSiO2gel for UV absorptionrdquo Chemical

Engineering Journal vol 181-182 pp 45ndash55 2012[32] J I Pena-Flores A F Palomec-Garfias C Marquez-Beltran

E Sanchez-Mora E Gomez-Barojas and F Perez-RodrıguezldquoFe effect on the optical properties of TiO

2Fe2O3nanostruc-

tured composites supported on SiO2microsphere assembliesrdquo

Nanoscale Research Letters vol 9 article 499 2014[33] D Kim Y Im K M Jeong S-M Park M-H Um and M

Kang ldquoEnhanced 2-chorophenol photodecomposition usingnano-sized Mn-incorporated TiO

2powders prepared by a

solvothermal methodrdquo Bulletin of the Korean Chemical Societyvol 35 no 8 pp 2295ndash2298 2014

[34] C C Huang C C Wu K Knight and D W Hewak ldquoOpticalproperties of CVD grown amorphous Ge-Sb-S thin filmsrdquoJournal of Non-Crystalline Solids vol 356 no 4-5 pp 281ndash2852010

[35] J Kim J S Lee and M Kang ldquoSynthesis of nanoporousstructured SnO

2and its photocatalytic ability for bisphenol a

destructionrdquo Bulletin of the Korean Chemical Society vol 32 no5 pp 1715ndash1720 2011

[36] M Thommes ldquoPhysical adsorption characterization ofnanoporous materialsrdquo Chemie Ingenieur Technik vol 82 no 7pp 1059ndash1073 2010

[37] A A Gribb and J F Banfield ldquoParticle size effects on trans-formation kinetics and phase stability in nanocrystalline TiO

2rdquo

American Mineralogist vol 82 no 7-8 pp 717ndash728 1997[38] S-H Nam S-J Cho C-K Jung et al ldquoComparison of

hydrophilic properties of TiO2thin films prepared by solndashgel

method and reactive magnetron sputtering systemrdquo Thin SolidFilms vol 519 no 20 pp 6944ndash6950 2011

12 International Journal of Photoenergy

[39] H G Feichtinger K Grochenig and T Strohmer ldquoEffi-cient numerical methods in non-uniform sampling theoryrdquoNumerische Mathematik vol 69 no 4 pp 423ndash440 1995

[40] S W Jo B S Kwak K M Kim et al ldquoEffectively CO2

photoreduction toCH4by the synergistic effects of Ca andTi on

Ca-loaded TiSiMCM-41 mesoporous photocatalytic systemsrdquoApplied Surface Science vol 355 pp 891ndash901 2015

[41] J Y Do Y Im B S Kwak J-Y Kim and M Kang ldquoDramaticCO2photoreduction with H

2O vapors for CH

4production

using the TiO2(bottom)FendashTiO

2(top) double-layered filmsrdquo

Chemical Engineering Journal vol 275 pp 288ndash297 2015[42] M Tahir andN SaidinaAmin ldquoPhotocatalytic reduction of car-

bon dioxide with water vapors over montmorillonite modifiedTiO2nanocompositesrdquo Applied Catalysis B Environmental vol

142-143 pp 512ndash522 2013[43] Y Kohno H Hayashi S Takenaka T Tanaka T Funabiki

and S Yoshida ldquoPhoto-enhanced reduction of carbon dioxidewith hydrogen over RhTiO

2rdquo Journal of Photochemistry and

Photobiology A Chemistry vol 126 no 1ndash3 pp 117ndash123 1999[44] M Subrahmanyam S Kaneco and N Alonso-Vante ldquoA screen-

ing for the photo reduction of carbon dioxide supported onmetal oxide catalysts for C

1-C3selectivityrdquo Applied Catalysis B

Environmental vol 23 no 2-3 pp 169ndash174 1999[45] S S Tan L Zou and E Hu ldquoKinetic modelling for photosyn-

thesis of hydrogen and methane through catalytic reduction ofcarbon dioxide with water vapourrdquo Catalysis Today vol 131 no1ndash4 pp 125ndash129 2008

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

International Journal of Photoenergy 7

30120583m

ldquoTop viewrdquoldquoSide viewrdquo

20120583m

Basalt fiber (b) TiO2basalt fiber(a) Basalt fiber

basalt fiber

basalt fiber

basalt fiber basalt fiber basalt fiber

(c) 50mol Fe-TiO2

50mol Co-TiO2 (d) 50mol Co-TiO2 (e) 50mol Ni-TiO2 (f) 50mol Cu-TiO2

Figure 7 SEM images of the pure basalt fiber film and 50mol M-TiO2basalt fiber films

hydrophilic properties [38] which suggests that duringthe CO

2photoreduction reaction CO

2and H

2O will

be adsorbed preferentially on the metal ions and TiO2

respectively The adsorption abilities were observed inthe following order 50mol Co-TiO

2gt Ni-TiO

2gt

Fe-TiO2gt TiO

2gt Cu-TiO

2samples In general a rapid

catalytic reaction occurs when many reactants are well-adsorbed over the catalyst The presence of transition metalsin the 50mol M-TiO

2samples most likely caused the

relative increase in the number of CO2and H

2O molecules

adsorbed compared to pure TiO2 This synergy contributed

significantly to improving the catalytic performance of the50mol M-TiO

2samples

32 Characteristics and CO2

Photoreduction over the50mol M (Fe- Co- Ni- and Cu-) TiO

2Basalt Fiber Films

Figure 7 presents SEM images (top and side views) of the sixsamples of pure basalt fiber and TiO

2films and 50mol

M (Fe- Co- Ni- and Cu-) TiO2basalt fiber films The

basalt fiber in the films was approximately 15 120583m in diameterwith different lengths and the surfaces were smooth The50mol M-TiO

2materials were mixed with basalt fibers

and were fabricated as thick films by coating on a Pyrex plateThe regular array of composites could be observed clearlythrough both the side and top directions The TiO

2basalt

fiber and 50mol Fe-TiO2basalt fiber composites did not

cover the Pyrex plate surface completely and bulk poreswere observed On the other hand the coating parts werequite uniform and fine particles were well-dispersed Incontrast the surfaces of the films fabricated from 50mol

Co-TiO2basalt fiber 50mol Ni-TiO

2basalt fiber and

50mol Cu-TiO2basalt fiber composites were quite dense

despite containing some cracks In particular the surfacewas the most compact over the 50mol Co-TiO

2basalt

fiber film The thickness of the films in all samples wasapproximately 30sim35 120583m with the exception of the purebasalt fiber film (20 120583m)

Energy-dispersive X-ray spectroscopy (EDAX) con-firmed the presence of metals on the surfaces of the basaltfiber and 50mol M (Fe- Co- Ni- and Cu-) TiO

2basalt

fiber films as shown in Figure 8 and the table below liststhe atomic compositions determined by EDAX For the basaltfiber various metal oxides were observed such as Na KCa Mg Al Si Fe and Ti Pure basalt fiber exhibited acomposition of 1928wt Si 314 wt total alkali metals166wt Ti 1177 wt Fe and 561 wt Al As a CO

2

adsorbent the Ca and Mg contents were 531 and 209wtrespectively Ti contained on the 50mol M (Fe- Co-Ni- and Cu-) TiO

2basalt fiber films decreased in the

following order 50mol Ni-TiO2(4774wt) gt Co-TiO

2

(4268wt) gt TiO2(4094wt) gt Fe-TiO

2(3344wt)

The amounts of transitionmetal specieswere in the range 269to 302wt with the exception of copper (098wt) Thesevalues did not appear to be perfectly quantitative EDAXis a very good surface analytical method but it is prone toerror because the composition can vary according to thelocation In particular the variation is large when the sampleis nonuniform [39]

The efficiencies of the photogenerated electron-hole pro-duction in the basalt fiber and 50mol M (Fe- Co- Ni-

8 International Journal of Photoenergy

MaterialselementAtomic compositions (wt-)

(a)

(b)

(c)

(d)

(e)

Na

204

mdash

mdash

192

160

Mg

209

mdash

mdash

mdash

mdash

Al

561

mdash

mdash

059

mdash

Si

1928

mdash

mdash

228

032

K

110

mdash

mdash

mdash

mdash

Ca

531

mdash

mdash

066

mdash

Fe

1177

mdash

286

114

mdash

Co

mdash

mdash

mdash

269

mdash

Ni

mdash

mdash

mdash

mdash

302

(f)

O

5114

5906

4122

4803

4732

4543

Ti

166

4094

3344

4268

4774

3615

Cu

mdash

mdash

mdash

mdash

mdash

098

Spectrum 1Ca Si

FeTi

OAl

Mg

NaK

CaK

Ti FeFe

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 1

Ti

O

Ti

2 4 6 1810 16 200 128 14(keV)

Spectrum 3

TiO

Ti

FeFe

Fe

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 2Ti

O

CuCuCu

Ti

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 4

NiNiNi Si

Ti

O

NaTi

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 2Ca

Si

Fe

Ti

O

AlNa

Ca

Co

Co

Co

Ti

FeFe

2 4 6 8 10 12 14 16 18 200(keV)

Full scale 767 cts cursor 0000Full scale 4345 cts cursor 0000Full scale 1548 cts cursor 0000

Full scale 1428 cts cursor 0000 Full scale 2264 cts cursor 0000 Full scale 830 cts cursor 0000

(b) TiO2basalt fiber(a) Basalt fiber

(d) 50mol Co-TiO2basalt fiber (f) 50mol Cu-TiO2basalt fiber(e) 50mol Ni-TiO2basalt fiber

(c) 50mol Fe-TiO2basalt fiber

Figure 8 Energy-dispersive X-ray spectra of the surfaces of the pure basalt fiber and 50mol M-TiO2basalt fiber films and the atomic

compositions

and Cu-) TiO2basalt fiber films were measured from the

photocurrent response under solar light irradiation at anapplied potential of 07 V versus SCE Figure 9 shows thetypical real time photocurrent response of the films whenthe light source is switched on and off exhibiting a rapidphotocurrent rise and decay In semiconductor systemswhen irradiation provides an energy higher than the band-gap of a semiconductor the energy excites an electron fromthe valence band to the conduction band leaving a hole inthe valence band The electron-hole pair is responsible forthe photocurrent When the light was turned on a rapidincrease in the photoreduction current was observed andthe photocurrent then turned to a steady state after a fewseconds When the light was turned off the photocurrentdecreased instantaneously to almost zero [40]When the lightwas turned on the maximum photocurrents obtained forthe 50mol Co-TiO

2and Ni-TiO

2basalt fiber films were

31049 and 30075mA cmminus2 respectively which were morethan four times higher than that achieved on pure basalt fiber

(7123mA cmminus2) andTiO2basalt fiber films (7401mA cmminus2)

Themaximumphotocurrent of the 50molCu-TiO2basalt

fiber film was too small due to trapping of excited elec-trons by copper with strong oxidation agency In additionthe TiO

2basalt fiber 50mol Cu-TiO

2basalt fiber and

50mol Ni-TiO2basalt fiber films showed no current

transients in both the light-on and the light-off regions inthe samples falling off with time in 50 s to a steady statewhich indicates that few surface recombination processeshad occurred Clearly some electron-hole recombinationwas observed in the 50mol Fe-TiO

2basalt fiber and Co-

TiO2basalt fiber films but it was negligible compared to

the total current value Therefore the 3d-transition metalingredients have a beneficial effect on the photocurrent itplays a role as an intermediate for the efficient separation ofphotogenerated hole-electron pairs

Figure 10 presents the photoreduction abilities of CO2

with H2O vapor to CH

4over the pure basalt fiber film and

50mol M (Fe- Co- Ni- and Cu-) TiO2basalt fiber films

International Journal of Photoenergy 9

3104930075

20974

7123 74016450

TiO2basalt fiberBasalt fiber

50 100 150 200 250 300 3500Time (s)

minus50

0

50

100

150

200

250

300

350

Curr

ent (

mA

cm

2)

50mol Cu-TiO2basalt fiber50mol Ni-TiO2basalt fiber

50mol Fe-TiO2basalt fiber50mol Co-TiO2basalt fiber

Figure 9 Photocurrent responses of the pure basalt fiber and50mol M-TiO

2basalt fiber films when the light source was

switched on and off

after 8 h Generally CH4production from CO

2reduction

with H2O can be divided into the following three subpro-

cesses [41] proton production from H2O photodecompo-

sition CO radical production from CO2photo cleavage

and methane production from photosynthesis between theCO radical and proton The photogenerated electrons onthe photocatalysts by UV-radiation induce CO

2reduction

to produce CO2radicals whereas the holes react with the

adsorbed H2Omolecules to perform oxidationThe interme-

diate photogenerated species undergo different reactions toproduce CO CH

3OH andCH

4The production of CH

4from

methyl radicals (∙CH3) was confirmed which are dependent

directly on the formation of the intermediate product CO[42] As shown in this figure almost no methane wasobserved when only the lamp was turned on On the otherhand the amounts of CO and O

2generation increased and

a small amount of hydrogen was observed This means thatthe light does not induce photoreduction processes aloneOn the other hand there are different product distributionsaccording to the loaded metal species excessive methane isgenerated over the catalysts loaded with Ni and Co and thequantities of CO and CH

3OH gases are increased over the

catalysts loaded with Cu and Fe The M-TiO2basalt fiber

films showed higher CH4production from CO

2photoreduc-

tion than the pure basalt fiber and TiO2basalt fiber films

700 120583mol gcatminus1 Lminus1 CH

4was emitted over the pure basalt

fiber film suggesting that it contains a small amount of TiO2

On the other hand CH4production was 1121 120583mol gcat

minus1 Lminus1over the TiO

2basalt fiber film In contrast the maximum

Lamp turned on only

TiO2basalt fiberBasalt fiber

1 2 3 4 5 6 7 80Time (h)

0

50

100

150

200

250

300

350

400

Met

hane

yie

ld (120583

mol

g-c

atlowast

L)

50mol Cu-TiO2basalt fiber50mol Ni-TiO2basalt fiber

50mol Fe-TiO2basalt fiber50mol Co-TiO2basalt fiber

Figure 10 Photoreduction abilities of CO2with H

2O vapor to CH

4

over the pure basalt fiber film and 50mol M-TiO2basalt fiber

films after 8 h

CH4yields over the 50mol Co-TiO

2basalt fiber and Ni-

TiO2basalt fiber films were 3605 and 3073 120583mol gcat

minus1 Lminus1respectively The differences in yields were attributed to theirband-gaps electron-hole recombination tendencies and thegas adsorption abilities of the 50mol M-TiO

2basalt fiber

films In particular this study confirmed that the 50molCo-TiO

2particles show synergistic performance when the

basalt fiber is mixedThe reduction ofCO

2requires amultiple electron transfer

and leads to production of a variety of products dependingon the number of transferred electrons which determinethe final oxidation state of the carbon atom The standardredox potentials of the CO

2reduction half-reactions vary

from CO2HCOOH [43] to CO

2CH4[44] CO

2adsorbed

on a photocatalyst surface can be reduced to ∙CO2

minus anionradical which can react withH+ and eminus for formingHCOOHor HCOOminus or which can go to the postulated disproportion-ation reaction of two ∙CO

2

minus anion radicals into CO (afterall to be C radical) and CO

3

2minus to react with H radical Thisstudy seems to follow the latter Scheme 1 presents a modelfor CO

2photoreduction over the M-TiO

2basalt fiber films

based on the relationships between the optical propertiesof the photocatalysts and the catalytic activities Photonexcitation in M-TiO

2over the M-TiO

2basalt fiber films

will begin rapidly because M-TiO2has a shorter band-gap

than pure TiO2 and the excited electrons can be transferred

efficiently to CO2molecules In addition CO

2molecules

are adsorbed preferentially and easily on the basalt fibersurface The positive holes on the valance band of M-TiO

2

can be trapped byH2Ospecies and transferred toOH radicals

and protons The protons obtained are transformed to H

10 International Journal of Photoenergy

O

Basalt fiberFTO glass

FTO glass

H2

CO2

Basalt fiber (i) More CO2 adsorption good

H2O

∙H

∙CO2minus

+ ∙H rarr ∙CHrarr ∙CH2 rarr ∙CH3 rarr CH4

Reduction CO2 + eminus rarr ∙CO2minus

h+

eminus

h+

eminus

pasteM-TiO2basalt fiber

M-TiO2

ldquoMetal incorporatedrdquoUV light

decreaseTiO2 M-TiO2 M-TiO2

(i) Easy electron transfer(ii) Water (H2O) adsorption goodM-TiO2

Oxidation H2O + h+ rarr ∙OH + H+ H+ + O2997888rarr

Scheme 1 Model for CH4production from the photoreduction of CO

2with H

2O vapor over the M-TiO

2basalt fiber films

radicals by electrons and the H radicals then react with Cand CO radicals formed from the reduction of CO

2

minus overM-TiO

2 particularly over Co- or Ni-TiO

2semiconductors

resulting methane production [45] The mixed films ofbasalt fibers and M-TiO

2can also promote the separation

of photogenerated electron-hole pairs (eminush+) on M-TiO2

Therefore the synergetic effects of the basalt fibers and M-TiO2in the M-TiO

2basalt fiber films achieved higher CO

2

reduction efficiency

4 Conclusions

The 50mol M (Fe- Co- Ni- and Cu-) incorporated TiO2

photocatalysts obtained by the solvothermal method werecoated densely with basalt fibers on a Pyrex plate usinga squeeze technique and applied to the photoreduction ofCO2to CH

4 The CO

2adsorption abilities were improved

over the basalt fiber and CH4generation was enhanced

dramatically over 50mol M-TiO2basalt fiber films with

a threefold higher yield compared to the pure basalt fiberand TiO

2basalt fiber films In particular the photoreduction

of CO2with H

2O revealed a remarkable increase in CH

4

generation over the 50mol Co-TiO2basalt fiber film to

3605 120583mol gcatminus1sdotLminus1 after an 8 h reaction

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

This research was supported by ceramic fiber commercialcenter project of Korea Institute of Ceramic Engineeringamp Technology (KICET) funded by the Ministry of TradeIndustry amp Energy (MOTIE)

References

[1] M Tahir and N S Amin ldquoIndium-doped TiO2nanoparticles

for photocatalytic CO2reduction with H

2O vapors to CH

4rdquo

Applied Catalysis B Environmental vol 162 pp 98ndash109 2015[2] B S Kwak andM Kang ldquoPhotocatalytic reduction of CO

2with

H2O using perovskite Ca

119909Ti119910O3rdquo Applied Surface Science vol

337 pp 138ndash144 2015[3] C Fletcher Y Jiang and R Amal ldquoProduction of formic acid

from CO2reduction by means of potassium borohydride at

ambient conditionsrdquo Chemical Engineering Science vol 137 pp301ndash307 2015

[4] G Mahmodi S Sharifnia M Madani and V VatanpourldquoPhotoreduction of carbon dioxide in the presence of H

2 H2O

and CH4over TiO

2and ZnO photocatalystsrdquo Solar Energy vol

97 pp 186ndash194 2013[5] J Albo A Saez J Solla-Gullon V Montiel and A Irabien

ldquoProduction of methanol from CO2electroreduction at Cu

2O

and Cu2OZnO-based electrodes in aqueous solutionrdquo Applied

Catalysis B Environmental vol 176-177 pp 709ndash717 2015[6] P Akhter M Hussain G Saracco and N Russo ldquoNew nanos-

tructured silica incorporated with isolated Ti material for the

International Journal of Photoenergy 11

photocatalytic conversion of CO2to fuelsrdquo Nanoscale Research

Letters vol 9 article 158 2014[7] M Anpo ldquoPhotocatalytic reduction of CO

2with H

2O on

highly dispersed Ti-oxide catalysts as a model of artificialphotosynthesisrdquo Journal of CO

2Utilization vol 1 pp 8ndash17 2013

[8] H Abdullah M R Khan M Pudukudy Z Yaakob and NA Ismail ldquoCeO

2-TiO2as a visible light active catalyst for the

photoreduction ofCO2tomethanolrdquo Journal of Rare Earths vol

33 no 11 pp 1155ndash1161 2015[9] O Ola and M Mercedes Maroto-Valer ldquoReview of material

design and reactor engineering on TiO2photocatalysis for

CO2reductionrdquo Journal of Photochemistry and Photobiology C

Photochemistry Reviews vol 24 pp 16ndash42 2015[10] X Zhang L Wang Q Du Z Wang S Ma and M Yu

ldquoPhotocatalytic CO2reduction over B

4CC3N4with internal

electric field under visible light irradiationrdquo Journal of Colloidand Interface Science vol 464 pp 89ndash95 2016

[11] R Gusain P Kumar O P Sharma S L Jain and O PKhatri ldquoReduced graphene oxide-CuO nanocomposites forphotocatalytic conversion of CO

2into methanol under visible

light irradiationrdquo Applied Catalysis B Environmental vol 181pp 352ndash362 2016

[12] N M Nursam X Wang and R A Caruso ldquoHigh-throughputsynthesis and screening of titania-based photocatalystsrdquo ACSCombinatorial Science vol 17 no 10 pp 548ndash569 2015

[13] M V Dozzi S Marzorati M Longhi M Coduri L Artigliaand E Selli ldquoPhotocatalytic activity of TiO

2-WO3mixed oxides

in relation to electron transfer efficiencyrdquo Applied Catalysis BEnvironmental vol 186 pp 157ndash165 2016

[14] Y Qu and X Duan ldquoProgress challenge and perspective ofheterogeneous photocatalystsrdquo Chemical Society Reviews vol42 no 7 pp 2568ndash2580 2013

[15] J C Colmenares R Luque J M Campelo F Colmenares ZKarpinski and A A Romero ldquoNanostructured photocatalystsand their applications in the photocatalytic transformation oflignocellulosic biomass an overviewrdquo Materials vol 2 no 4pp 2228ndash2258 2009

[16] M Kitano M Matsuoka M Ueshima and M Anpo ldquoRecentdevelopments in titanium oxide-based photocatalystsrdquo AppliedCatalysis A General vol 325 no 1 pp 1ndash14 2007

[17] P Silija Z Yaakob V Suraja N N Binitha and Z S Akmal ldquoAnenthusiastic glance in to the visible responsive photocatalystsfor energy production and pollutant removal with specialemphasis on titaniardquo International Journal of Photoenergy vol2012 Article ID 503839 19 pages 2012

[18] H Xu S Ouyang L Liu P Reunchan N Umezawa and JYe ldquoRecent advances in TiO

2-based photocatalysisrdquo Journal of

Materials Chemistry A vol 2 no 32 pp 12642ndash12661 2014[19] Z He J Tang J Shen J Chen and S Song ldquoEnhancement of

photocatalytic reduction of CO2to CH

4over TiO

2nanosheets

by modifying with sulfuric acidrdquo Applied Surface Science vol364 pp 416ndash427 2016

[20] O Ola and M M Maroto-Valer ldquoTransition metal oxide basedTiO2nanoparticles for visible light induced CO

2photoreduc-

tionrdquo Applied Catalysis A General vol 502 pp 114ndash121 2015[21] D Eder ldquoCarbon nanotube-inorganic hybridsrdquo Chemical

Reviews vol 110 no 3 pp 1348ndash1385 2010[22] L Zhang R JamalQ ZhaoMWang andTAbdiryim ldquoPrepa-

ration of PEDOTGO PEDOTMnO2 and PEDOTGOMnO

2

nanocomposites and their application in catalytic degradationof methylene bluerdquo Nanoscale Research Letters vol 10 p 1482015

[23] M Urbanski A Lapko and A Garbacz ldquoInvestigation onconcrete beams reinforced with basalt rebars as an effectivealternative of conventional RC structuresrdquo Procedia Engineer-ing vol 57 pp 1183ndash1191 2013

[24] S A Chernyak E V Suslova A V Egorov L Lu S V Savilovand V V Lunin ldquoNew hybrid CNT-alumina supports for Co-based Fischer-Tropsch catalystsrdquo Fuel Processing Technologyvol 140 pp 267ndash275 2015

[25] K Shimura T Miyazawa T Hanaoka and S Hirata ldquoFischerndashTropsch synthesis over alumina supported bimetallic CondashNicatalyst effect of impregnation sequence and solutionrdquo Journalof Molecular Catalysis A Chemical vol 407 pp 15ndash24 2015

[26] F Fazlollahi M Sarkari A Zare A A Mirzaei and HAtashi ldquoDevelopment of a kinetic model for Fischer-Tropschsynthesis over CoNiAl

2O3catalystrdquo Journal of Industrial and

Engineering Chemistry vol 18 no 4 pp 1223ndash1232 2012[27] J Zhao W Xing Y Li and K Lu ldquoSolvothermal synthesis and

visible light absorption of anatase TiO2rdquo Materials Letters vol

145 pp 332ndash335 2015[28] S Liu J Yu and M Jaroniec ldquoAnatase TiO

2with dominant

high-energy 001 facets Synthesis properties and applicationsrdquoChemistry of Materials vol 23 no 18 pp 4085ndash4093 2011

[29] T Ungar ldquoMicrostructural parameters from X-ray diffractionpeak broadeningrdquo Scripta Materialia vol 51 no 8 pp 777ndash7812004

[30] A W Burton K Ong T Rea and I Y Chan ldquoOn the esti-mation of average crystallite size of zeolites from the Scherrerequation a critical evaluation of its application to zeolites withone-dimensional pore systemsrdquo Microporous and MesoporousMaterials vol 117 no 1-2 pp 75ndash90 2009

[31] A Jaroenworaluck N Pijarn N Kosachan and R StevensldquoNanocomposite TiO

2ndashSiO2gel for UV absorptionrdquo Chemical

Engineering Journal vol 181-182 pp 45ndash55 2012[32] J I Pena-Flores A F Palomec-Garfias C Marquez-Beltran

E Sanchez-Mora E Gomez-Barojas and F Perez-RodrıguezldquoFe effect on the optical properties of TiO

2Fe2O3nanostruc-

tured composites supported on SiO2microsphere assembliesrdquo

Nanoscale Research Letters vol 9 article 499 2014[33] D Kim Y Im K M Jeong S-M Park M-H Um and M

Kang ldquoEnhanced 2-chorophenol photodecomposition usingnano-sized Mn-incorporated TiO

2powders prepared by a

solvothermal methodrdquo Bulletin of the Korean Chemical Societyvol 35 no 8 pp 2295ndash2298 2014

[34] C C Huang C C Wu K Knight and D W Hewak ldquoOpticalproperties of CVD grown amorphous Ge-Sb-S thin filmsrdquoJournal of Non-Crystalline Solids vol 356 no 4-5 pp 281ndash2852010

[35] J Kim J S Lee and M Kang ldquoSynthesis of nanoporousstructured SnO

2and its photocatalytic ability for bisphenol a

destructionrdquo Bulletin of the Korean Chemical Society vol 32 no5 pp 1715ndash1720 2011

[36] M Thommes ldquoPhysical adsorption characterization ofnanoporous materialsrdquo Chemie Ingenieur Technik vol 82 no 7pp 1059ndash1073 2010

[37] A A Gribb and J F Banfield ldquoParticle size effects on trans-formation kinetics and phase stability in nanocrystalline TiO

2rdquo

American Mineralogist vol 82 no 7-8 pp 717ndash728 1997[38] S-H Nam S-J Cho C-K Jung et al ldquoComparison of

hydrophilic properties of TiO2thin films prepared by solndashgel

method and reactive magnetron sputtering systemrdquo Thin SolidFilms vol 519 no 20 pp 6944ndash6950 2011

12 International Journal of Photoenergy

[39] H G Feichtinger K Grochenig and T Strohmer ldquoEffi-cient numerical methods in non-uniform sampling theoryrdquoNumerische Mathematik vol 69 no 4 pp 423ndash440 1995

[40] S W Jo B S Kwak K M Kim et al ldquoEffectively CO2

photoreduction toCH4by the synergistic effects of Ca andTi on

Ca-loaded TiSiMCM-41 mesoporous photocatalytic systemsrdquoApplied Surface Science vol 355 pp 891ndash901 2015

[41] J Y Do Y Im B S Kwak J-Y Kim and M Kang ldquoDramaticCO2photoreduction with H

2O vapors for CH

4production

using the TiO2(bottom)FendashTiO

2(top) double-layered filmsrdquo

Chemical Engineering Journal vol 275 pp 288ndash297 2015[42] M Tahir andN SaidinaAmin ldquoPhotocatalytic reduction of car-

bon dioxide with water vapors over montmorillonite modifiedTiO2nanocompositesrdquo Applied Catalysis B Environmental vol

142-143 pp 512ndash522 2013[43] Y Kohno H Hayashi S Takenaka T Tanaka T Funabiki

and S Yoshida ldquoPhoto-enhanced reduction of carbon dioxidewith hydrogen over RhTiO

2rdquo Journal of Photochemistry and

Photobiology A Chemistry vol 126 no 1ndash3 pp 117ndash123 1999[44] M Subrahmanyam S Kaneco and N Alonso-Vante ldquoA screen-

ing for the photo reduction of carbon dioxide supported onmetal oxide catalysts for C

1-C3selectivityrdquo Applied Catalysis B

Environmental vol 23 no 2-3 pp 169ndash174 1999[45] S S Tan L Zou and E Hu ldquoKinetic modelling for photosyn-

thesis of hydrogen and methane through catalytic reduction ofcarbon dioxide with water vapourrdquo Catalysis Today vol 131 no1ndash4 pp 125ndash129 2008

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

8 International Journal of Photoenergy

MaterialselementAtomic compositions (wt-)

(a)

(b)

(c)

(d)

(e)

Na

204

mdash

mdash

192

160

Mg

209

mdash

mdash

mdash

mdash

Al

561

mdash

mdash

059

mdash

Si

1928

mdash

mdash

228

032

K

110

mdash

mdash

mdash

mdash

Ca

531

mdash

mdash

066

mdash

Fe

1177

mdash

286

114

mdash

Co

mdash

mdash

mdash

269

mdash

Ni

mdash

mdash

mdash

mdash

302

(f)

O

5114

5906

4122

4803

4732

4543

Ti

166

4094

3344

4268

4774

3615

Cu

mdash

mdash

mdash

mdash

mdash

098

Spectrum 1Ca Si

FeTi

OAl

Mg

NaK

CaK

Ti FeFe

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 1

Ti

O

Ti

2 4 6 1810 16 200 128 14(keV)

Spectrum 3

TiO

Ti

FeFe

Fe

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 2Ti

O

CuCuCu

Ti

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 4

NiNiNi Si

Ti

O

NaTi

2 4 6 8 10 12 14 16 18 200(keV)

Spectrum 2Ca

Si

Fe

Ti

O

AlNa

Ca

Co

Co

Co

Ti

FeFe

2 4 6 8 10 12 14 16 18 200(keV)

Full scale 767 cts cursor 0000Full scale 4345 cts cursor 0000Full scale 1548 cts cursor 0000

Full scale 1428 cts cursor 0000 Full scale 2264 cts cursor 0000 Full scale 830 cts cursor 0000

(b) TiO2basalt fiber(a) Basalt fiber

(d) 50mol Co-TiO2basalt fiber (f) 50mol Cu-TiO2basalt fiber(e) 50mol Ni-TiO2basalt fiber

(c) 50mol Fe-TiO2basalt fiber

Figure 8 Energy-dispersive X-ray spectra of the surfaces of the pure basalt fiber and 50mol M-TiO2basalt fiber films and the atomic

compositions

and Cu-) TiO2basalt fiber films were measured from the

photocurrent response under solar light irradiation at anapplied potential of 07 V versus SCE Figure 9 shows thetypical real time photocurrent response of the films whenthe light source is switched on and off exhibiting a rapidphotocurrent rise and decay In semiconductor systemswhen irradiation provides an energy higher than the band-gap of a semiconductor the energy excites an electron fromthe valence band to the conduction band leaving a hole inthe valence band The electron-hole pair is responsible forthe photocurrent When the light was turned on a rapidincrease in the photoreduction current was observed andthe photocurrent then turned to a steady state after a fewseconds When the light was turned off the photocurrentdecreased instantaneously to almost zero [40]When the lightwas turned on the maximum photocurrents obtained forthe 50mol Co-TiO

2and Ni-TiO

2basalt fiber films were

31049 and 30075mA cmminus2 respectively which were morethan four times higher than that achieved on pure basalt fiber

(7123mA cmminus2) andTiO2basalt fiber films (7401mA cmminus2)

Themaximumphotocurrent of the 50molCu-TiO2basalt

fiber film was too small due to trapping of excited elec-trons by copper with strong oxidation agency In additionthe TiO

2basalt fiber 50mol Cu-TiO

2basalt fiber and

50mol Ni-TiO2basalt fiber films showed no current

transients in both the light-on and the light-off regions inthe samples falling off with time in 50 s to a steady statewhich indicates that few surface recombination processeshad occurred Clearly some electron-hole recombinationwas observed in the 50mol Fe-TiO

2basalt fiber and Co-

TiO2basalt fiber films but it was negligible compared to

the total current value Therefore the 3d-transition metalingredients have a beneficial effect on the photocurrent itplays a role as an intermediate for the efficient separation ofphotogenerated hole-electron pairs

Figure 10 presents the photoreduction abilities of CO2

with H2O vapor to CH

4over the pure basalt fiber film and

50mol M (Fe- Co- Ni- and Cu-) TiO2basalt fiber films

International Journal of Photoenergy 9

3104930075

20974

7123 74016450

TiO2basalt fiberBasalt fiber

50 100 150 200 250 300 3500Time (s)

minus50

0

50

100

150

200

250

300

350

Curr

ent (

mA

cm

2)

50mol Cu-TiO2basalt fiber50mol Ni-TiO2basalt fiber

50mol Fe-TiO2basalt fiber50mol Co-TiO2basalt fiber

Figure 9 Photocurrent responses of the pure basalt fiber and50mol M-TiO

2basalt fiber films when the light source was

switched on and off

after 8 h Generally CH4production from CO

2reduction

with H2O can be divided into the following three subpro-

cesses [41] proton production from H2O photodecompo-

sition CO radical production from CO2photo cleavage

and methane production from photosynthesis between theCO radical and proton The photogenerated electrons onthe photocatalysts by UV-radiation induce CO

2reduction

to produce CO2radicals whereas the holes react with the

adsorbed H2Omolecules to perform oxidationThe interme-

diate photogenerated species undergo different reactions toproduce CO CH

3OH andCH

4The production of CH

4from

methyl radicals (∙CH3) was confirmed which are dependent

directly on the formation of the intermediate product CO[42] As shown in this figure almost no methane wasobserved when only the lamp was turned on On the otherhand the amounts of CO and O

2generation increased and

a small amount of hydrogen was observed This means thatthe light does not induce photoreduction processes aloneOn the other hand there are different product distributionsaccording to the loaded metal species excessive methane isgenerated over the catalysts loaded with Ni and Co and thequantities of CO and CH

3OH gases are increased over the

catalysts loaded with Cu and Fe The M-TiO2basalt fiber

films showed higher CH4production from CO

2photoreduc-

tion than the pure basalt fiber and TiO2basalt fiber films

700 120583mol gcatminus1 Lminus1 CH

4was emitted over the pure basalt

fiber film suggesting that it contains a small amount of TiO2

On the other hand CH4production was 1121 120583mol gcat

minus1 Lminus1over the TiO

2basalt fiber film In contrast the maximum

Lamp turned on only

TiO2basalt fiberBasalt fiber

1 2 3 4 5 6 7 80Time (h)

0

50

100

150

200

250

300

350

400

Met

hane

yie

ld (120583

mol

g-c

atlowast

L)

50mol Cu-TiO2basalt fiber50mol Ni-TiO2basalt fiber

50mol Fe-TiO2basalt fiber50mol Co-TiO2basalt fiber

Figure 10 Photoreduction abilities of CO2with H

2O vapor to CH

4

over the pure basalt fiber film and 50mol M-TiO2basalt fiber

films after 8 h

CH4yields over the 50mol Co-TiO

2basalt fiber and Ni-

TiO2basalt fiber films were 3605 and 3073 120583mol gcat

minus1 Lminus1respectively The differences in yields were attributed to theirband-gaps electron-hole recombination tendencies and thegas adsorption abilities of the 50mol M-TiO

2basalt fiber

films In particular this study confirmed that the 50molCo-TiO

2particles show synergistic performance when the

basalt fiber is mixedThe reduction ofCO

2requires amultiple electron transfer

and leads to production of a variety of products dependingon the number of transferred electrons which determinethe final oxidation state of the carbon atom The standardredox potentials of the CO

2reduction half-reactions vary

from CO2HCOOH [43] to CO

2CH4[44] CO

2adsorbed

on a photocatalyst surface can be reduced to ∙CO2

minus anionradical which can react withH+ and eminus for formingHCOOHor HCOOminus or which can go to the postulated disproportion-ation reaction of two ∙CO

2

minus anion radicals into CO (afterall to be C radical) and CO

3

2minus to react with H radical Thisstudy seems to follow the latter Scheme 1 presents a modelfor CO

2photoreduction over the M-TiO

2basalt fiber films

based on the relationships between the optical propertiesof the photocatalysts and the catalytic activities Photonexcitation in M-TiO

2over the M-TiO

2basalt fiber films

will begin rapidly because M-TiO2has a shorter band-gap

than pure TiO2 and the excited electrons can be transferred

efficiently to CO2molecules In addition CO

2molecules

are adsorbed preferentially and easily on the basalt fibersurface The positive holes on the valance band of M-TiO

2

can be trapped byH2Ospecies and transferred toOH radicals

and protons The protons obtained are transformed to H

10 International Journal of Photoenergy

O

Basalt fiberFTO glass

FTO glass

H2

CO2

Basalt fiber (i) More CO2 adsorption good

H2O

∙H

∙CO2minus

+ ∙H rarr ∙CHrarr ∙CH2 rarr ∙CH3 rarr CH4

Reduction CO2 + eminus rarr ∙CO2minus

h+

eminus

h+

eminus

pasteM-TiO2basalt fiber

M-TiO2

ldquoMetal incorporatedrdquoUV light

decreaseTiO2 M-TiO2 M-TiO2

(i) Easy electron transfer(ii) Water (H2O) adsorption goodM-TiO2

Oxidation H2O + h+ rarr ∙OH + H+ H+ + O2997888rarr

Scheme 1 Model for CH4production from the photoreduction of CO

2with H

2O vapor over the M-TiO

2basalt fiber films

radicals by electrons and the H radicals then react with Cand CO radicals formed from the reduction of CO

2

minus overM-TiO

2 particularly over Co- or Ni-TiO

2semiconductors

resulting methane production [45] The mixed films ofbasalt fibers and M-TiO

2can also promote the separation

of photogenerated electron-hole pairs (eminush+) on M-TiO2

Therefore the synergetic effects of the basalt fibers and M-TiO2in the M-TiO

2basalt fiber films achieved higher CO

2

reduction efficiency

4 Conclusions

The 50mol M (Fe- Co- Ni- and Cu-) incorporated TiO2

photocatalysts obtained by the solvothermal method werecoated densely with basalt fibers on a Pyrex plate usinga squeeze technique and applied to the photoreduction ofCO2to CH

4 The CO

2adsorption abilities were improved

over the basalt fiber and CH4generation was enhanced

dramatically over 50mol M-TiO2basalt fiber films with

a threefold higher yield compared to the pure basalt fiberand TiO

2basalt fiber films In particular the photoreduction

of CO2with H

2O revealed a remarkable increase in CH

4

generation over the 50mol Co-TiO2basalt fiber film to

3605 120583mol gcatminus1sdotLminus1 after an 8 h reaction

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

This research was supported by ceramic fiber commercialcenter project of Korea Institute of Ceramic Engineeringamp Technology (KICET) funded by the Ministry of TradeIndustry amp Energy (MOTIE)

References

[1] M Tahir and N S Amin ldquoIndium-doped TiO2nanoparticles

for photocatalytic CO2reduction with H

2O vapors to CH

4rdquo

Applied Catalysis B Environmental vol 162 pp 98ndash109 2015[2] B S Kwak andM Kang ldquoPhotocatalytic reduction of CO

2with

H2O using perovskite Ca

119909Ti119910O3rdquo Applied Surface Science vol

337 pp 138ndash144 2015[3] C Fletcher Y Jiang and R Amal ldquoProduction of formic acid

from CO2reduction by means of potassium borohydride at

ambient conditionsrdquo Chemical Engineering Science vol 137 pp301ndash307 2015

[4] G Mahmodi S Sharifnia M Madani and V VatanpourldquoPhotoreduction of carbon dioxide in the presence of H

2 H2O

and CH4over TiO

2and ZnO photocatalystsrdquo Solar Energy vol

97 pp 186ndash194 2013[5] J Albo A Saez J Solla-Gullon V Montiel and A Irabien

ldquoProduction of methanol from CO2electroreduction at Cu

2O

and Cu2OZnO-based electrodes in aqueous solutionrdquo Applied

Catalysis B Environmental vol 176-177 pp 709ndash717 2015[6] P Akhter M Hussain G Saracco and N Russo ldquoNew nanos-

tructured silica incorporated with isolated Ti material for the

International Journal of Photoenergy 11

photocatalytic conversion of CO2to fuelsrdquo Nanoscale Research

Letters vol 9 article 158 2014[7] M Anpo ldquoPhotocatalytic reduction of CO

2with H

2O on

highly dispersed Ti-oxide catalysts as a model of artificialphotosynthesisrdquo Journal of CO

2Utilization vol 1 pp 8ndash17 2013

[8] H Abdullah M R Khan M Pudukudy Z Yaakob and NA Ismail ldquoCeO

2-TiO2as a visible light active catalyst for the

photoreduction ofCO2tomethanolrdquo Journal of Rare Earths vol

33 no 11 pp 1155ndash1161 2015[9] O Ola and M Mercedes Maroto-Valer ldquoReview of material

design and reactor engineering on TiO2photocatalysis for

CO2reductionrdquo Journal of Photochemistry and Photobiology C

Photochemistry Reviews vol 24 pp 16ndash42 2015[10] X Zhang L Wang Q Du Z Wang S Ma and M Yu

ldquoPhotocatalytic CO2reduction over B

4CC3N4with internal

electric field under visible light irradiationrdquo Journal of Colloidand Interface Science vol 464 pp 89ndash95 2016

[11] R Gusain P Kumar O P Sharma S L Jain and O PKhatri ldquoReduced graphene oxide-CuO nanocomposites forphotocatalytic conversion of CO

2into methanol under visible

light irradiationrdquo Applied Catalysis B Environmental vol 181pp 352ndash362 2016

[12] N M Nursam X Wang and R A Caruso ldquoHigh-throughputsynthesis and screening of titania-based photocatalystsrdquo ACSCombinatorial Science vol 17 no 10 pp 548ndash569 2015

[13] M V Dozzi S Marzorati M Longhi M Coduri L Artigliaand E Selli ldquoPhotocatalytic activity of TiO

2-WO3mixed oxides

in relation to electron transfer efficiencyrdquo Applied Catalysis BEnvironmental vol 186 pp 157ndash165 2016

[14] Y Qu and X Duan ldquoProgress challenge and perspective ofheterogeneous photocatalystsrdquo Chemical Society Reviews vol42 no 7 pp 2568ndash2580 2013

[15] J C Colmenares R Luque J M Campelo F Colmenares ZKarpinski and A A Romero ldquoNanostructured photocatalystsand their applications in the photocatalytic transformation oflignocellulosic biomass an overviewrdquo Materials vol 2 no 4pp 2228ndash2258 2009

[16] M Kitano M Matsuoka M Ueshima and M Anpo ldquoRecentdevelopments in titanium oxide-based photocatalystsrdquo AppliedCatalysis A General vol 325 no 1 pp 1ndash14 2007

[17] P Silija Z Yaakob V Suraja N N Binitha and Z S Akmal ldquoAnenthusiastic glance in to the visible responsive photocatalystsfor energy production and pollutant removal with specialemphasis on titaniardquo International Journal of Photoenergy vol2012 Article ID 503839 19 pages 2012

[18] H Xu S Ouyang L Liu P Reunchan N Umezawa and JYe ldquoRecent advances in TiO

2-based photocatalysisrdquo Journal of

Materials Chemistry A vol 2 no 32 pp 12642ndash12661 2014[19] Z He J Tang J Shen J Chen and S Song ldquoEnhancement of

photocatalytic reduction of CO2to CH

4over TiO

2nanosheets

by modifying with sulfuric acidrdquo Applied Surface Science vol364 pp 416ndash427 2016

[20] O Ola and M M Maroto-Valer ldquoTransition metal oxide basedTiO2nanoparticles for visible light induced CO

2photoreduc-

tionrdquo Applied Catalysis A General vol 502 pp 114ndash121 2015[21] D Eder ldquoCarbon nanotube-inorganic hybridsrdquo Chemical

Reviews vol 110 no 3 pp 1348ndash1385 2010[22] L Zhang R JamalQ ZhaoMWang andTAbdiryim ldquoPrepa-

ration of PEDOTGO PEDOTMnO2 and PEDOTGOMnO

2

nanocomposites and their application in catalytic degradationof methylene bluerdquo Nanoscale Research Letters vol 10 p 1482015

[23] M Urbanski A Lapko and A Garbacz ldquoInvestigation onconcrete beams reinforced with basalt rebars as an effectivealternative of conventional RC structuresrdquo Procedia Engineer-ing vol 57 pp 1183ndash1191 2013

[24] S A Chernyak E V Suslova A V Egorov L Lu S V Savilovand V V Lunin ldquoNew hybrid CNT-alumina supports for Co-based Fischer-Tropsch catalystsrdquo Fuel Processing Technologyvol 140 pp 267ndash275 2015

[25] K Shimura T Miyazawa T Hanaoka and S Hirata ldquoFischerndashTropsch synthesis over alumina supported bimetallic CondashNicatalyst effect of impregnation sequence and solutionrdquo Journalof Molecular Catalysis A Chemical vol 407 pp 15ndash24 2015

[26] F Fazlollahi M Sarkari A Zare A A Mirzaei and HAtashi ldquoDevelopment of a kinetic model for Fischer-Tropschsynthesis over CoNiAl

2O3catalystrdquo Journal of Industrial and

Engineering Chemistry vol 18 no 4 pp 1223ndash1232 2012[27] J Zhao W Xing Y Li and K Lu ldquoSolvothermal synthesis and

visible light absorption of anatase TiO2rdquo Materials Letters vol

145 pp 332ndash335 2015[28] S Liu J Yu and M Jaroniec ldquoAnatase TiO

2with dominant

high-energy 001 facets Synthesis properties and applicationsrdquoChemistry of Materials vol 23 no 18 pp 4085ndash4093 2011

[29] T Ungar ldquoMicrostructural parameters from X-ray diffractionpeak broadeningrdquo Scripta Materialia vol 51 no 8 pp 777ndash7812004

[30] A W Burton K Ong T Rea and I Y Chan ldquoOn the esti-mation of average crystallite size of zeolites from the Scherrerequation a critical evaluation of its application to zeolites withone-dimensional pore systemsrdquo Microporous and MesoporousMaterials vol 117 no 1-2 pp 75ndash90 2009

[31] A Jaroenworaluck N Pijarn N Kosachan and R StevensldquoNanocomposite TiO

2ndashSiO2gel for UV absorptionrdquo Chemical

Engineering Journal vol 181-182 pp 45ndash55 2012[32] J I Pena-Flores A F Palomec-Garfias C Marquez-Beltran

E Sanchez-Mora E Gomez-Barojas and F Perez-RodrıguezldquoFe effect on the optical properties of TiO

2Fe2O3nanostruc-

tured composites supported on SiO2microsphere assembliesrdquo

Nanoscale Research Letters vol 9 article 499 2014[33] D Kim Y Im K M Jeong S-M Park M-H Um and M

Kang ldquoEnhanced 2-chorophenol photodecomposition usingnano-sized Mn-incorporated TiO

2powders prepared by a

solvothermal methodrdquo Bulletin of the Korean Chemical Societyvol 35 no 8 pp 2295ndash2298 2014

[34] C C Huang C C Wu K Knight and D W Hewak ldquoOpticalproperties of CVD grown amorphous Ge-Sb-S thin filmsrdquoJournal of Non-Crystalline Solids vol 356 no 4-5 pp 281ndash2852010

[35] J Kim J S Lee and M Kang ldquoSynthesis of nanoporousstructured SnO

2and its photocatalytic ability for bisphenol a

destructionrdquo Bulletin of the Korean Chemical Society vol 32 no5 pp 1715ndash1720 2011

[36] M Thommes ldquoPhysical adsorption characterization ofnanoporous materialsrdquo Chemie Ingenieur Technik vol 82 no 7pp 1059ndash1073 2010

[37] A A Gribb and J F Banfield ldquoParticle size effects on trans-formation kinetics and phase stability in nanocrystalline TiO

2rdquo

American Mineralogist vol 82 no 7-8 pp 717ndash728 1997[38] S-H Nam S-J Cho C-K Jung et al ldquoComparison of

hydrophilic properties of TiO2thin films prepared by solndashgel

method and reactive magnetron sputtering systemrdquo Thin SolidFilms vol 519 no 20 pp 6944ndash6950 2011

12 International Journal of Photoenergy

[39] H G Feichtinger K Grochenig and T Strohmer ldquoEffi-cient numerical methods in non-uniform sampling theoryrdquoNumerische Mathematik vol 69 no 4 pp 423ndash440 1995

[40] S W Jo B S Kwak K M Kim et al ldquoEffectively CO2

photoreduction toCH4by the synergistic effects of Ca andTi on

Ca-loaded TiSiMCM-41 mesoporous photocatalytic systemsrdquoApplied Surface Science vol 355 pp 891ndash901 2015

[41] J Y Do Y Im B S Kwak J-Y Kim and M Kang ldquoDramaticCO2photoreduction with H

2O vapors for CH

4production

using the TiO2(bottom)FendashTiO

2(top) double-layered filmsrdquo

Chemical Engineering Journal vol 275 pp 288ndash297 2015[42] M Tahir andN SaidinaAmin ldquoPhotocatalytic reduction of car-

bon dioxide with water vapors over montmorillonite modifiedTiO2nanocompositesrdquo Applied Catalysis B Environmental vol

142-143 pp 512ndash522 2013[43] Y Kohno H Hayashi S Takenaka T Tanaka T Funabiki

and S Yoshida ldquoPhoto-enhanced reduction of carbon dioxidewith hydrogen over RhTiO

2rdquo Journal of Photochemistry and

Photobiology A Chemistry vol 126 no 1ndash3 pp 117ndash123 1999[44] M Subrahmanyam S Kaneco and N Alonso-Vante ldquoA screen-

ing for the photo reduction of carbon dioxide supported onmetal oxide catalysts for C

1-C3selectivityrdquo Applied Catalysis B

Environmental vol 23 no 2-3 pp 169ndash174 1999[45] S S Tan L Zou and E Hu ldquoKinetic modelling for photosyn-

thesis of hydrogen and methane through catalytic reduction ofcarbon dioxide with water vapourrdquo Catalysis Today vol 131 no1ndash4 pp 125ndash129 2008

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

International Journal of Photoenergy 9

3104930075

20974

7123 74016450

TiO2basalt fiberBasalt fiber

50 100 150 200 250 300 3500Time (s)

minus50

0

50

100

150

200

250

300

350

Curr

ent (

mA

cm

2)

50mol Cu-TiO2basalt fiber50mol Ni-TiO2basalt fiber

50mol Fe-TiO2basalt fiber50mol Co-TiO2basalt fiber

Figure 9 Photocurrent responses of the pure basalt fiber and50mol M-TiO

2basalt fiber films when the light source was

switched on and off

after 8 h Generally CH4production from CO

2reduction

with H2O can be divided into the following three subpro-

cesses [41] proton production from H2O photodecompo-

sition CO radical production from CO2photo cleavage

and methane production from photosynthesis between theCO radical and proton The photogenerated electrons onthe photocatalysts by UV-radiation induce CO

2reduction

to produce CO2radicals whereas the holes react with the

adsorbed H2Omolecules to perform oxidationThe interme-

diate photogenerated species undergo different reactions toproduce CO CH

3OH andCH

4The production of CH

4from

methyl radicals (∙CH3) was confirmed which are dependent

directly on the formation of the intermediate product CO[42] As shown in this figure almost no methane wasobserved when only the lamp was turned on On the otherhand the amounts of CO and O

2generation increased and

a small amount of hydrogen was observed This means thatthe light does not induce photoreduction processes aloneOn the other hand there are different product distributionsaccording to the loaded metal species excessive methane isgenerated over the catalysts loaded with Ni and Co and thequantities of CO and CH

3OH gases are increased over the

catalysts loaded with Cu and Fe The M-TiO2basalt fiber

films showed higher CH4production from CO

2photoreduc-

tion than the pure basalt fiber and TiO2basalt fiber films

700 120583mol gcatminus1 Lminus1 CH

4was emitted over the pure basalt

fiber film suggesting that it contains a small amount of TiO2

On the other hand CH4production was 1121 120583mol gcat

minus1 Lminus1over the TiO

2basalt fiber film In contrast the maximum

Lamp turned on only

TiO2basalt fiberBasalt fiber

1 2 3 4 5 6 7 80Time (h)

0

50

100

150

200

250

300

350

400

Met

hane

yie

ld (120583

mol

g-c

atlowast

L)

50mol Cu-TiO2basalt fiber50mol Ni-TiO2basalt fiber

50mol Fe-TiO2basalt fiber50mol Co-TiO2basalt fiber

Figure 10 Photoreduction abilities of CO2with H

2O vapor to CH

4

over the pure basalt fiber film and 50mol M-TiO2basalt fiber

films after 8 h

CH4yields over the 50mol Co-TiO

2basalt fiber and Ni-

TiO2basalt fiber films were 3605 and 3073 120583mol gcat

minus1 Lminus1respectively The differences in yields were attributed to theirband-gaps electron-hole recombination tendencies and thegas adsorption abilities of the 50mol M-TiO

2basalt fiber

films In particular this study confirmed that the 50molCo-TiO

2particles show synergistic performance when the

basalt fiber is mixedThe reduction ofCO

2requires amultiple electron transfer

and leads to production of a variety of products dependingon the number of transferred electrons which determinethe final oxidation state of the carbon atom The standardredox potentials of the CO

2reduction half-reactions vary

from CO2HCOOH [43] to CO

2CH4[44] CO

2adsorbed

on a photocatalyst surface can be reduced to ∙CO2

minus anionradical which can react withH+ and eminus for formingHCOOHor HCOOminus or which can go to the postulated disproportion-ation reaction of two ∙CO

2

minus anion radicals into CO (afterall to be C radical) and CO

3

2minus to react with H radical Thisstudy seems to follow the latter Scheme 1 presents a modelfor CO

2photoreduction over the M-TiO

2basalt fiber films

based on the relationships between the optical propertiesof the photocatalysts and the catalytic activities Photonexcitation in M-TiO

2over the M-TiO

2basalt fiber films

will begin rapidly because M-TiO2has a shorter band-gap

than pure TiO2 and the excited electrons can be transferred

efficiently to CO2molecules In addition CO

2molecules

are adsorbed preferentially and easily on the basalt fibersurface The positive holes on the valance band of M-TiO

2

can be trapped byH2Ospecies and transferred toOH radicals

and protons The protons obtained are transformed to H

10 International Journal of Photoenergy

O

Basalt fiberFTO glass

FTO glass

H2

CO2

Basalt fiber (i) More CO2 adsorption good

H2O

∙H

∙CO2minus

+ ∙H rarr ∙CHrarr ∙CH2 rarr ∙CH3 rarr CH4

Reduction CO2 + eminus rarr ∙CO2minus

h+

eminus

h+

eminus

pasteM-TiO2basalt fiber

M-TiO2

ldquoMetal incorporatedrdquoUV light

decreaseTiO2 M-TiO2 M-TiO2

(i) Easy electron transfer(ii) Water (H2O) adsorption goodM-TiO2

Oxidation H2O + h+ rarr ∙OH + H+ H+ + O2997888rarr

Scheme 1 Model for CH4production from the photoreduction of CO

2with H

2O vapor over the M-TiO

2basalt fiber films

radicals by electrons and the H radicals then react with Cand CO radicals formed from the reduction of CO

2

minus overM-TiO

2 particularly over Co- or Ni-TiO

2semiconductors

resulting methane production [45] The mixed films ofbasalt fibers and M-TiO

2can also promote the separation

of photogenerated electron-hole pairs (eminush+) on M-TiO2

Therefore the synergetic effects of the basalt fibers and M-TiO2in the M-TiO

2basalt fiber films achieved higher CO

2

reduction efficiency

4 Conclusions

The 50mol M (Fe- Co- Ni- and Cu-) incorporated TiO2

photocatalysts obtained by the solvothermal method werecoated densely with basalt fibers on a Pyrex plate usinga squeeze technique and applied to the photoreduction ofCO2to CH

4 The CO

2adsorption abilities were improved

over the basalt fiber and CH4generation was enhanced

dramatically over 50mol M-TiO2basalt fiber films with

a threefold higher yield compared to the pure basalt fiberand TiO

2basalt fiber films In particular the photoreduction

of CO2with H

2O revealed a remarkable increase in CH

4

generation over the 50mol Co-TiO2basalt fiber film to

3605 120583mol gcatminus1sdotLminus1 after an 8 h reaction

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

This research was supported by ceramic fiber commercialcenter project of Korea Institute of Ceramic Engineeringamp Technology (KICET) funded by the Ministry of TradeIndustry amp Energy (MOTIE)

References

[1] M Tahir and N S Amin ldquoIndium-doped TiO2nanoparticles

for photocatalytic CO2reduction with H

2O vapors to CH

4rdquo

Applied Catalysis B Environmental vol 162 pp 98ndash109 2015[2] B S Kwak andM Kang ldquoPhotocatalytic reduction of CO

2with

H2O using perovskite Ca

119909Ti119910O3rdquo Applied Surface Science vol

337 pp 138ndash144 2015[3] C Fletcher Y Jiang and R Amal ldquoProduction of formic acid

from CO2reduction by means of potassium borohydride at

ambient conditionsrdquo Chemical Engineering Science vol 137 pp301ndash307 2015

[4] G Mahmodi S Sharifnia M Madani and V VatanpourldquoPhotoreduction of carbon dioxide in the presence of H

2 H2O

and CH4over TiO

2and ZnO photocatalystsrdquo Solar Energy vol

97 pp 186ndash194 2013[5] J Albo A Saez J Solla-Gullon V Montiel and A Irabien

ldquoProduction of methanol from CO2electroreduction at Cu

2O

and Cu2OZnO-based electrodes in aqueous solutionrdquo Applied

Catalysis B Environmental vol 176-177 pp 709ndash717 2015[6] P Akhter M Hussain G Saracco and N Russo ldquoNew nanos-

tructured silica incorporated with isolated Ti material for the

International Journal of Photoenergy 11

photocatalytic conversion of CO2to fuelsrdquo Nanoscale Research

Letters vol 9 article 158 2014[7] M Anpo ldquoPhotocatalytic reduction of CO

2with H

2O on

highly dispersed Ti-oxide catalysts as a model of artificialphotosynthesisrdquo Journal of CO

2Utilization vol 1 pp 8ndash17 2013

[8] H Abdullah M R Khan M Pudukudy Z Yaakob and NA Ismail ldquoCeO

2-TiO2as a visible light active catalyst for the

photoreduction ofCO2tomethanolrdquo Journal of Rare Earths vol

33 no 11 pp 1155ndash1161 2015[9] O Ola and M Mercedes Maroto-Valer ldquoReview of material

design and reactor engineering on TiO2photocatalysis for

CO2reductionrdquo Journal of Photochemistry and Photobiology C

Photochemistry Reviews vol 24 pp 16ndash42 2015[10] X Zhang L Wang Q Du Z Wang S Ma and M Yu

ldquoPhotocatalytic CO2reduction over B

4CC3N4with internal

electric field under visible light irradiationrdquo Journal of Colloidand Interface Science vol 464 pp 89ndash95 2016

[11] R Gusain P Kumar O P Sharma S L Jain and O PKhatri ldquoReduced graphene oxide-CuO nanocomposites forphotocatalytic conversion of CO

2into methanol under visible

light irradiationrdquo Applied Catalysis B Environmental vol 181pp 352ndash362 2016

[12] N M Nursam X Wang and R A Caruso ldquoHigh-throughputsynthesis and screening of titania-based photocatalystsrdquo ACSCombinatorial Science vol 17 no 10 pp 548ndash569 2015

[13] M V Dozzi S Marzorati M Longhi M Coduri L Artigliaand E Selli ldquoPhotocatalytic activity of TiO

2-WO3mixed oxides

in relation to electron transfer efficiencyrdquo Applied Catalysis BEnvironmental vol 186 pp 157ndash165 2016

[14] Y Qu and X Duan ldquoProgress challenge and perspective ofheterogeneous photocatalystsrdquo Chemical Society Reviews vol42 no 7 pp 2568ndash2580 2013

[15] J C Colmenares R Luque J M Campelo F Colmenares ZKarpinski and A A Romero ldquoNanostructured photocatalystsand their applications in the photocatalytic transformation oflignocellulosic biomass an overviewrdquo Materials vol 2 no 4pp 2228ndash2258 2009

[16] M Kitano M Matsuoka M Ueshima and M Anpo ldquoRecentdevelopments in titanium oxide-based photocatalystsrdquo AppliedCatalysis A General vol 325 no 1 pp 1ndash14 2007

[17] P Silija Z Yaakob V Suraja N N Binitha and Z S Akmal ldquoAnenthusiastic glance in to the visible responsive photocatalystsfor energy production and pollutant removal with specialemphasis on titaniardquo International Journal of Photoenergy vol2012 Article ID 503839 19 pages 2012

[18] H Xu S Ouyang L Liu P Reunchan N Umezawa and JYe ldquoRecent advances in TiO

2-based photocatalysisrdquo Journal of

Materials Chemistry A vol 2 no 32 pp 12642ndash12661 2014[19] Z He J Tang J Shen J Chen and S Song ldquoEnhancement of

photocatalytic reduction of CO2to CH

4over TiO

2nanosheets

by modifying with sulfuric acidrdquo Applied Surface Science vol364 pp 416ndash427 2016

[20] O Ola and M M Maroto-Valer ldquoTransition metal oxide basedTiO2nanoparticles for visible light induced CO

2photoreduc-

tionrdquo Applied Catalysis A General vol 502 pp 114ndash121 2015[21] D Eder ldquoCarbon nanotube-inorganic hybridsrdquo Chemical

Reviews vol 110 no 3 pp 1348ndash1385 2010[22] L Zhang R JamalQ ZhaoMWang andTAbdiryim ldquoPrepa-

ration of PEDOTGO PEDOTMnO2 and PEDOTGOMnO

2

nanocomposites and their application in catalytic degradationof methylene bluerdquo Nanoscale Research Letters vol 10 p 1482015

[23] M Urbanski A Lapko and A Garbacz ldquoInvestigation onconcrete beams reinforced with basalt rebars as an effectivealternative of conventional RC structuresrdquo Procedia Engineer-ing vol 57 pp 1183ndash1191 2013

[24] S A Chernyak E V Suslova A V Egorov L Lu S V Savilovand V V Lunin ldquoNew hybrid CNT-alumina supports for Co-based Fischer-Tropsch catalystsrdquo Fuel Processing Technologyvol 140 pp 267ndash275 2015

[25] K Shimura T Miyazawa T Hanaoka and S Hirata ldquoFischerndashTropsch synthesis over alumina supported bimetallic CondashNicatalyst effect of impregnation sequence and solutionrdquo Journalof Molecular Catalysis A Chemical vol 407 pp 15ndash24 2015

[26] F Fazlollahi M Sarkari A Zare A A Mirzaei and HAtashi ldquoDevelopment of a kinetic model for Fischer-Tropschsynthesis over CoNiAl

2O3catalystrdquo Journal of Industrial and

Engineering Chemistry vol 18 no 4 pp 1223ndash1232 2012[27] J Zhao W Xing Y Li and K Lu ldquoSolvothermal synthesis and

visible light absorption of anatase TiO2rdquo Materials Letters vol

145 pp 332ndash335 2015[28] S Liu J Yu and M Jaroniec ldquoAnatase TiO

2with dominant

high-energy 001 facets Synthesis properties and applicationsrdquoChemistry of Materials vol 23 no 18 pp 4085ndash4093 2011

[29] T Ungar ldquoMicrostructural parameters from X-ray diffractionpeak broadeningrdquo Scripta Materialia vol 51 no 8 pp 777ndash7812004

[30] A W Burton K Ong T Rea and I Y Chan ldquoOn the esti-mation of average crystallite size of zeolites from the Scherrerequation a critical evaluation of its application to zeolites withone-dimensional pore systemsrdquo Microporous and MesoporousMaterials vol 117 no 1-2 pp 75ndash90 2009

[31] A Jaroenworaluck N Pijarn N Kosachan and R StevensldquoNanocomposite TiO

2ndashSiO2gel for UV absorptionrdquo Chemical

Engineering Journal vol 181-182 pp 45ndash55 2012[32] J I Pena-Flores A F Palomec-Garfias C Marquez-Beltran

E Sanchez-Mora E Gomez-Barojas and F Perez-RodrıguezldquoFe effect on the optical properties of TiO

2Fe2O3nanostruc-

tured composites supported on SiO2microsphere assembliesrdquo

Nanoscale Research Letters vol 9 article 499 2014[33] D Kim Y Im K M Jeong S-M Park M-H Um and M

Kang ldquoEnhanced 2-chorophenol photodecomposition usingnano-sized Mn-incorporated TiO

2powders prepared by a

solvothermal methodrdquo Bulletin of the Korean Chemical Societyvol 35 no 8 pp 2295ndash2298 2014

[34] C C Huang C C Wu K Knight and D W Hewak ldquoOpticalproperties of CVD grown amorphous Ge-Sb-S thin filmsrdquoJournal of Non-Crystalline Solids vol 356 no 4-5 pp 281ndash2852010

[35] J Kim J S Lee and M Kang ldquoSynthesis of nanoporousstructured SnO

2and its photocatalytic ability for bisphenol a

destructionrdquo Bulletin of the Korean Chemical Society vol 32 no5 pp 1715ndash1720 2011

[36] M Thommes ldquoPhysical adsorption characterization ofnanoporous materialsrdquo Chemie Ingenieur Technik vol 82 no 7pp 1059ndash1073 2010

[37] A A Gribb and J F Banfield ldquoParticle size effects on trans-formation kinetics and phase stability in nanocrystalline TiO

2rdquo

American Mineralogist vol 82 no 7-8 pp 717ndash728 1997[38] S-H Nam S-J Cho C-K Jung et al ldquoComparison of

hydrophilic properties of TiO2thin films prepared by solndashgel

method and reactive magnetron sputtering systemrdquo Thin SolidFilms vol 519 no 20 pp 6944ndash6950 2011

12 International Journal of Photoenergy

[39] H G Feichtinger K Grochenig and T Strohmer ldquoEffi-cient numerical methods in non-uniform sampling theoryrdquoNumerische Mathematik vol 69 no 4 pp 423ndash440 1995

[40] S W Jo B S Kwak K M Kim et al ldquoEffectively CO2

photoreduction toCH4by the synergistic effects of Ca andTi on

Ca-loaded TiSiMCM-41 mesoporous photocatalytic systemsrdquoApplied Surface Science vol 355 pp 891ndash901 2015

[41] J Y Do Y Im B S Kwak J-Y Kim and M Kang ldquoDramaticCO2photoreduction with H

2O vapors for CH

4production

using the TiO2(bottom)FendashTiO

2(top) double-layered filmsrdquo

Chemical Engineering Journal vol 275 pp 288ndash297 2015[42] M Tahir andN SaidinaAmin ldquoPhotocatalytic reduction of car-

bon dioxide with water vapors over montmorillonite modifiedTiO2nanocompositesrdquo Applied Catalysis B Environmental vol

142-143 pp 512ndash522 2013[43] Y Kohno H Hayashi S Takenaka T Tanaka T Funabiki

and S Yoshida ldquoPhoto-enhanced reduction of carbon dioxidewith hydrogen over RhTiO

2rdquo Journal of Photochemistry and

Photobiology A Chemistry vol 126 no 1ndash3 pp 117ndash123 1999[44] M Subrahmanyam S Kaneco and N Alonso-Vante ldquoA screen-

ing for the photo reduction of carbon dioxide supported onmetal oxide catalysts for C

1-C3selectivityrdquo Applied Catalysis B

Environmental vol 23 no 2-3 pp 169ndash174 1999[45] S S Tan L Zou and E Hu ldquoKinetic modelling for photosyn-

thesis of hydrogen and methane through catalytic reduction ofcarbon dioxide with water vapourrdquo Catalysis Today vol 131 no1ndash4 pp 125ndash129 2008

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

10 International Journal of Photoenergy

O

Basalt fiberFTO glass

FTO glass

H2

CO2

Basalt fiber (i) More CO2 adsorption good

H2O

∙H

∙CO2minus

+ ∙H rarr ∙CHrarr ∙CH2 rarr ∙CH3 rarr CH4

Reduction CO2 + eminus rarr ∙CO2minus

h+

eminus

h+

eminus

pasteM-TiO2basalt fiber

M-TiO2

ldquoMetal incorporatedrdquoUV light

decreaseTiO2 M-TiO2 M-TiO2

(i) Easy electron transfer(ii) Water (H2O) adsorption goodM-TiO2

Oxidation H2O + h+ rarr ∙OH + H+ H+ + O2997888rarr

Scheme 1 Model for CH4production from the photoreduction of CO

2with H

2O vapor over the M-TiO

2basalt fiber films

radicals by electrons and the H radicals then react with Cand CO radicals formed from the reduction of CO

2

minus overM-TiO

2 particularly over Co- or Ni-TiO

2semiconductors

resulting methane production [45] The mixed films ofbasalt fibers and M-TiO

2can also promote the separation

of photogenerated electron-hole pairs (eminush+) on M-TiO2

Therefore the synergetic effects of the basalt fibers and M-TiO2in the M-TiO

2basalt fiber films achieved higher CO

2

reduction efficiency

4 Conclusions

The 50mol M (Fe- Co- Ni- and Cu-) incorporated TiO2

photocatalysts obtained by the solvothermal method werecoated densely with basalt fibers on a Pyrex plate usinga squeeze technique and applied to the photoreduction ofCO2to CH

4 The CO

2adsorption abilities were improved

over the basalt fiber and CH4generation was enhanced

dramatically over 50mol M-TiO2basalt fiber films with

a threefold higher yield compared to the pure basalt fiberand TiO

2basalt fiber films In particular the photoreduction

of CO2with H

2O revealed a remarkable increase in CH

4

generation over the 50mol Co-TiO2basalt fiber film to

3605 120583mol gcatminus1sdotLminus1 after an 8 h reaction

Competing Interests

The authors declare that they have no competing interests

Acknowledgments

This research was supported by ceramic fiber commercialcenter project of Korea Institute of Ceramic Engineeringamp Technology (KICET) funded by the Ministry of TradeIndustry amp Energy (MOTIE)

References

[1] M Tahir and N S Amin ldquoIndium-doped TiO2nanoparticles

for photocatalytic CO2reduction with H

2O vapors to CH

4rdquo

Applied Catalysis B Environmental vol 162 pp 98ndash109 2015[2] B S Kwak andM Kang ldquoPhotocatalytic reduction of CO

2with

H2O using perovskite Ca

119909Ti119910O3rdquo Applied Surface Science vol

337 pp 138ndash144 2015[3] C Fletcher Y Jiang and R Amal ldquoProduction of formic acid

from CO2reduction by means of potassium borohydride at

ambient conditionsrdquo Chemical Engineering Science vol 137 pp301ndash307 2015

[4] G Mahmodi S Sharifnia M Madani and V VatanpourldquoPhotoreduction of carbon dioxide in the presence of H

2 H2O

and CH4over TiO

2and ZnO photocatalystsrdquo Solar Energy vol

97 pp 186ndash194 2013[5] J Albo A Saez J Solla-Gullon V Montiel and A Irabien

ldquoProduction of methanol from CO2electroreduction at Cu

2O

and Cu2OZnO-based electrodes in aqueous solutionrdquo Applied

Catalysis B Environmental vol 176-177 pp 709ndash717 2015[6] P Akhter M Hussain G Saracco and N Russo ldquoNew nanos-

tructured silica incorporated with isolated Ti material for the

International Journal of Photoenergy 11

photocatalytic conversion of CO2to fuelsrdquo Nanoscale Research

Letters vol 9 article 158 2014[7] M Anpo ldquoPhotocatalytic reduction of CO

2with H

2O on

highly dispersed Ti-oxide catalysts as a model of artificialphotosynthesisrdquo Journal of CO

2Utilization vol 1 pp 8ndash17 2013

[8] H Abdullah M R Khan M Pudukudy Z Yaakob and NA Ismail ldquoCeO

2-TiO2as a visible light active catalyst for the

photoreduction ofCO2tomethanolrdquo Journal of Rare Earths vol

33 no 11 pp 1155ndash1161 2015[9] O Ola and M Mercedes Maroto-Valer ldquoReview of material

design and reactor engineering on TiO2photocatalysis for

CO2reductionrdquo Journal of Photochemistry and Photobiology C

Photochemistry Reviews vol 24 pp 16ndash42 2015[10] X Zhang L Wang Q Du Z Wang S Ma and M Yu

ldquoPhotocatalytic CO2reduction over B

4CC3N4with internal

electric field under visible light irradiationrdquo Journal of Colloidand Interface Science vol 464 pp 89ndash95 2016

[11] R Gusain P Kumar O P Sharma S L Jain and O PKhatri ldquoReduced graphene oxide-CuO nanocomposites forphotocatalytic conversion of CO

2into methanol under visible

light irradiationrdquo Applied Catalysis B Environmental vol 181pp 352ndash362 2016

[12] N M Nursam X Wang and R A Caruso ldquoHigh-throughputsynthesis and screening of titania-based photocatalystsrdquo ACSCombinatorial Science vol 17 no 10 pp 548ndash569 2015

[13] M V Dozzi S Marzorati M Longhi M Coduri L Artigliaand E Selli ldquoPhotocatalytic activity of TiO

2-WO3mixed oxides

in relation to electron transfer efficiencyrdquo Applied Catalysis BEnvironmental vol 186 pp 157ndash165 2016

[14] Y Qu and X Duan ldquoProgress challenge and perspective ofheterogeneous photocatalystsrdquo Chemical Society Reviews vol42 no 7 pp 2568ndash2580 2013

[15] J C Colmenares R Luque J M Campelo F Colmenares ZKarpinski and A A Romero ldquoNanostructured photocatalystsand their applications in the photocatalytic transformation oflignocellulosic biomass an overviewrdquo Materials vol 2 no 4pp 2228ndash2258 2009

[16] M Kitano M Matsuoka M Ueshima and M Anpo ldquoRecentdevelopments in titanium oxide-based photocatalystsrdquo AppliedCatalysis A General vol 325 no 1 pp 1ndash14 2007

[17] P Silija Z Yaakob V Suraja N N Binitha and Z S Akmal ldquoAnenthusiastic glance in to the visible responsive photocatalystsfor energy production and pollutant removal with specialemphasis on titaniardquo International Journal of Photoenergy vol2012 Article ID 503839 19 pages 2012

[18] H Xu S Ouyang L Liu P Reunchan N Umezawa and JYe ldquoRecent advances in TiO

2-based photocatalysisrdquo Journal of

Materials Chemistry A vol 2 no 32 pp 12642ndash12661 2014[19] Z He J Tang J Shen J Chen and S Song ldquoEnhancement of

photocatalytic reduction of CO2to CH

4over TiO

2nanosheets

by modifying with sulfuric acidrdquo Applied Surface Science vol364 pp 416ndash427 2016

[20] O Ola and M M Maroto-Valer ldquoTransition metal oxide basedTiO2nanoparticles for visible light induced CO

2photoreduc-

tionrdquo Applied Catalysis A General vol 502 pp 114ndash121 2015[21] D Eder ldquoCarbon nanotube-inorganic hybridsrdquo Chemical

Reviews vol 110 no 3 pp 1348ndash1385 2010[22] L Zhang R JamalQ ZhaoMWang andTAbdiryim ldquoPrepa-

ration of PEDOTGO PEDOTMnO2 and PEDOTGOMnO

2

nanocomposites and their application in catalytic degradationof methylene bluerdquo Nanoscale Research Letters vol 10 p 1482015

[23] M Urbanski A Lapko and A Garbacz ldquoInvestigation onconcrete beams reinforced with basalt rebars as an effectivealternative of conventional RC structuresrdquo Procedia Engineer-ing vol 57 pp 1183ndash1191 2013

[24] S A Chernyak E V Suslova A V Egorov L Lu S V Savilovand V V Lunin ldquoNew hybrid CNT-alumina supports for Co-based Fischer-Tropsch catalystsrdquo Fuel Processing Technologyvol 140 pp 267ndash275 2015

[25] K Shimura T Miyazawa T Hanaoka and S Hirata ldquoFischerndashTropsch synthesis over alumina supported bimetallic CondashNicatalyst effect of impregnation sequence and solutionrdquo Journalof Molecular Catalysis A Chemical vol 407 pp 15ndash24 2015

[26] F Fazlollahi M Sarkari A Zare A A Mirzaei and HAtashi ldquoDevelopment of a kinetic model for Fischer-Tropschsynthesis over CoNiAl

2O3catalystrdquo Journal of Industrial and

Engineering Chemistry vol 18 no 4 pp 1223ndash1232 2012[27] J Zhao W Xing Y Li and K Lu ldquoSolvothermal synthesis and

visible light absorption of anatase TiO2rdquo Materials Letters vol

145 pp 332ndash335 2015[28] S Liu J Yu and M Jaroniec ldquoAnatase TiO

2with dominant

high-energy 001 facets Synthesis properties and applicationsrdquoChemistry of Materials vol 23 no 18 pp 4085ndash4093 2011

[29] T Ungar ldquoMicrostructural parameters from X-ray diffractionpeak broadeningrdquo Scripta Materialia vol 51 no 8 pp 777ndash7812004

[30] A W Burton K Ong T Rea and I Y Chan ldquoOn the esti-mation of average crystallite size of zeolites from the Scherrerequation a critical evaluation of its application to zeolites withone-dimensional pore systemsrdquo Microporous and MesoporousMaterials vol 117 no 1-2 pp 75ndash90 2009

[31] A Jaroenworaluck N Pijarn N Kosachan and R StevensldquoNanocomposite TiO

2ndashSiO2gel for UV absorptionrdquo Chemical

Engineering Journal vol 181-182 pp 45ndash55 2012[32] J I Pena-Flores A F Palomec-Garfias C Marquez-Beltran

E Sanchez-Mora E Gomez-Barojas and F Perez-RodrıguezldquoFe effect on the optical properties of TiO

2Fe2O3nanostruc-

tured composites supported on SiO2microsphere assembliesrdquo

Nanoscale Research Letters vol 9 article 499 2014[33] D Kim Y Im K M Jeong S-M Park M-H Um and M

Kang ldquoEnhanced 2-chorophenol photodecomposition usingnano-sized Mn-incorporated TiO

2powders prepared by a

solvothermal methodrdquo Bulletin of the Korean Chemical Societyvol 35 no 8 pp 2295ndash2298 2014

[34] C C Huang C C Wu K Knight and D W Hewak ldquoOpticalproperties of CVD grown amorphous Ge-Sb-S thin filmsrdquoJournal of Non-Crystalline Solids vol 356 no 4-5 pp 281ndash2852010

[35] J Kim J S Lee and M Kang ldquoSynthesis of nanoporousstructured SnO

2and its photocatalytic ability for bisphenol a

destructionrdquo Bulletin of the Korean Chemical Society vol 32 no5 pp 1715ndash1720 2011

[36] M Thommes ldquoPhysical adsorption characterization ofnanoporous materialsrdquo Chemie Ingenieur Technik vol 82 no 7pp 1059ndash1073 2010

[37] A A Gribb and J F Banfield ldquoParticle size effects on trans-formation kinetics and phase stability in nanocrystalline TiO

2rdquo

American Mineralogist vol 82 no 7-8 pp 717ndash728 1997[38] S-H Nam S-J Cho C-K Jung et al ldquoComparison of

hydrophilic properties of TiO2thin films prepared by solndashgel

method and reactive magnetron sputtering systemrdquo Thin SolidFilms vol 519 no 20 pp 6944ndash6950 2011

12 International Journal of Photoenergy

[39] H G Feichtinger K Grochenig and T Strohmer ldquoEffi-cient numerical methods in non-uniform sampling theoryrdquoNumerische Mathematik vol 69 no 4 pp 423ndash440 1995

[40] S W Jo B S Kwak K M Kim et al ldquoEffectively CO2

photoreduction toCH4by the synergistic effects of Ca andTi on

Ca-loaded TiSiMCM-41 mesoporous photocatalytic systemsrdquoApplied Surface Science vol 355 pp 891ndash901 2015

[41] J Y Do Y Im B S Kwak J-Y Kim and M Kang ldquoDramaticCO2photoreduction with H

2O vapors for CH

4production

using the TiO2(bottom)FendashTiO

2(top) double-layered filmsrdquo

Chemical Engineering Journal vol 275 pp 288ndash297 2015[42] M Tahir andN SaidinaAmin ldquoPhotocatalytic reduction of car-

bon dioxide with water vapors over montmorillonite modifiedTiO2nanocompositesrdquo Applied Catalysis B Environmental vol

142-143 pp 512ndash522 2013[43] Y Kohno H Hayashi S Takenaka T Tanaka T Funabiki

and S Yoshida ldquoPhoto-enhanced reduction of carbon dioxidewith hydrogen over RhTiO

2rdquo Journal of Photochemistry and

Photobiology A Chemistry vol 126 no 1ndash3 pp 117ndash123 1999[44] M Subrahmanyam S Kaneco and N Alonso-Vante ldquoA screen-

ing for the photo reduction of carbon dioxide supported onmetal oxide catalysts for C

1-C3selectivityrdquo Applied Catalysis B

Environmental vol 23 no 2-3 pp 169ndash174 1999[45] S S Tan L Zou and E Hu ldquoKinetic modelling for photosyn-

thesis of hydrogen and methane through catalytic reduction ofcarbon dioxide with water vapourrdquo Catalysis Today vol 131 no1ndash4 pp 125ndash129 2008

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

International Journal of Photoenergy 11

photocatalytic conversion of CO2to fuelsrdquo Nanoscale Research

Letters vol 9 article 158 2014[7] M Anpo ldquoPhotocatalytic reduction of CO

2with H

2O on

highly dispersed Ti-oxide catalysts as a model of artificialphotosynthesisrdquo Journal of CO

2Utilization vol 1 pp 8ndash17 2013

[8] H Abdullah M R Khan M Pudukudy Z Yaakob and NA Ismail ldquoCeO

2-TiO2as a visible light active catalyst for the

photoreduction ofCO2tomethanolrdquo Journal of Rare Earths vol

33 no 11 pp 1155ndash1161 2015[9] O Ola and M Mercedes Maroto-Valer ldquoReview of material

design and reactor engineering on TiO2photocatalysis for

CO2reductionrdquo Journal of Photochemistry and Photobiology C

Photochemistry Reviews vol 24 pp 16ndash42 2015[10] X Zhang L Wang Q Du Z Wang S Ma and M Yu

ldquoPhotocatalytic CO2reduction over B

4CC3N4with internal

electric field under visible light irradiationrdquo Journal of Colloidand Interface Science vol 464 pp 89ndash95 2016

[11] R Gusain P Kumar O P Sharma S L Jain and O PKhatri ldquoReduced graphene oxide-CuO nanocomposites forphotocatalytic conversion of CO

2into methanol under visible

light irradiationrdquo Applied Catalysis B Environmental vol 181pp 352ndash362 2016

[12] N M Nursam X Wang and R A Caruso ldquoHigh-throughputsynthesis and screening of titania-based photocatalystsrdquo ACSCombinatorial Science vol 17 no 10 pp 548ndash569 2015

[13] M V Dozzi S Marzorati M Longhi M Coduri L Artigliaand E Selli ldquoPhotocatalytic activity of TiO

2-WO3mixed oxides

in relation to electron transfer efficiencyrdquo Applied Catalysis BEnvironmental vol 186 pp 157ndash165 2016

[14] Y Qu and X Duan ldquoProgress challenge and perspective ofheterogeneous photocatalystsrdquo Chemical Society Reviews vol42 no 7 pp 2568ndash2580 2013

[15] J C Colmenares R Luque J M Campelo F Colmenares ZKarpinski and A A Romero ldquoNanostructured photocatalystsand their applications in the photocatalytic transformation oflignocellulosic biomass an overviewrdquo Materials vol 2 no 4pp 2228ndash2258 2009

[16] M Kitano M Matsuoka M Ueshima and M Anpo ldquoRecentdevelopments in titanium oxide-based photocatalystsrdquo AppliedCatalysis A General vol 325 no 1 pp 1ndash14 2007

[17] P Silija Z Yaakob V Suraja N N Binitha and Z S Akmal ldquoAnenthusiastic glance in to the visible responsive photocatalystsfor energy production and pollutant removal with specialemphasis on titaniardquo International Journal of Photoenergy vol2012 Article ID 503839 19 pages 2012

[18] H Xu S Ouyang L Liu P Reunchan N Umezawa and JYe ldquoRecent advances in TiO

2-based photocatalysisrdquo Journal of

Materials Chemistry A vol 2 no 32 pp 12642ndash12661 2014[19] Z He J Tang J Shen J Chen and S Song ldquoEnhancement of

photocatalytic reduction of CO2to CH

4over TiO

2nanosheets

by modifying with sulfuric acidrdquo Applied Surface Science vol364 pp 416ndash427 2016

[20] O Ola and M M Maroto-Valer ldquoTransition metal oxide basedTiO2nanoparticles for visible light induced CO

2photoreduc-

tionrdquo Applied Catalysis A General vol 502 pp 114ndash121 2015[21] D Eder ldquoCarbon nanotube-inorganic hybridsrdquo Chemical

Reviews vol 110 no 3 pp 1348ndash1385 2010[22] L Zhang R JamalQ ZhaoMWang andTAbdiryim ldquoPrepa-

ration of PEDOTGO PEDOTMnO2 and PEDOTGOMnO

2

nanocomposites and their application in catalytic degradationof methylene bluerdquo Nanoscale Research Letters vol 10 p 1482015

[23] M Urbanski A Lapko and A Garbacz ldquoInvestigation onconcrete beams reinforced with basalt rebars as an effectivealternative of conventional RC structuresrdquo Procedia Engineer-ing vol 57 pp 1183ndash1191 2013

[24] S A Chernyak E V Suslova A V Egorov L Lu S V Savilovand V V Lunin ldquoNew hybrid CNT-alumina supports for Co-based Fischer-Tropsch catalystsrdquo Fuel Processing Technologyvol 140 pp 267ndash275 2015

[25] K Shimura T Miyazawa T Hanaoka and S Hirata ldquoFischerndashTropsch synthesis over alumina supported bimetallic CondashNicatalyst effect of impregnation sequence and solutionrdquo Journalof Molecular Catalysis A Chemical vol 407 pp 15ndash24 2015

[26] F Fazlollahi M Sarkari A Zare A A Mirzaei and HAtashi ldquoDevelopment of a kinetic model for Fischer-Tropschsynthesis over CoNiAl

2O3catalystrdquo Journal of Industrial and

Engineering Chemistry vol 18 no 4 pp 1223ndash1232 2012[27] J Zhao W Xing Y Li and K Lu ldquoSolvothermal synthesis and

visible light absorption of anatase TiO2rdquo Materials Letters vol

145 pp 332ndash335 2015[28] S Liu J Yu and M Jaroniec ldquoAnatase TiO

2with dominant

high-energy 001 facets Synthesis properties and applicationsrdquoChemistry of Materials vol 23 no 18 pp 4085ndash4093 2011

[29] T Ungar ldquoMicrostructural parameters from X-ray diffractionpeak broadeningrdquo Scripta Materialia vol 51 no 8 pp 777ndash7812004

[30] A W Burton K Ong T Rea and I Y Chan ldquoOn the esti-mation of average crystallite size of zeolites from the Scherrerequation a critical evaluation of its application to zeolites withone-dimensional pore systemsrdquo Microporous and MesoporousMaterials vol 117 no 1-2 pp 75ndash90 2009

[31] A Jaroenworaluck N Pijarn N Kosachan and R StevensldquoNanocomposite TiO

2ndashSiO2gel for UV absorptionrdquo Chemical

Engineering Journal vol 181-182 pp 45ndash55 2012[32] J I Pena-Flores A F Palomec-Garfias C Marquez-Beltran

E Sanchez-Mora E Gomez-Barojas and F Perez-RodrıguezldquoFe effect on the optical properties of TiO

2Fe2O3nanostruc-

tured composites supported on SiO2microsphere assembliesrdquo

Nanoscale Research Letters vol 9 article 499 2014[33] D Kim Y Im K M Jeong S-M Park M-H Um and M

Kang ldquoEnhanced 2-chorophenol photodecomposition usingnano-sized Mn-incorporated TiO

2powders prepared by a

solvothermal methodrdquo Bulletin of the Korean Chemical Societyvol 35 no 8 pp 2295ndash2298 2014

[34] C C Huang C C Wu K Knight and D W Hewak ldquoOpticalproperties of CVD grown amorphous Ge-Sb-S thin filmsrdquoJournal of Non-Crystalline Solids vol 356 no 4-5 pp 281ndash2852010

[35] J Kim J S Lee and M Kang ldquoSynthesis of nanoporousstructured SnO

2and its photocatalytic ability for bisphenol a

destructionrdquo Bulletin of the Korean Chemical Society vol 32 no5 pp 1715ndash1720 2011

[36] M Thommes ldquoPhysical adsorption characterization ofnanoporous materialsrdquo Chemie Ingenieur Technik vol 82 no 7pp 1059ndash1073 2010

[37] A A Gribb and J F Banfield ldquoParticle size effects on trans-formation kinetics and phase stability in nanocrystalline TiO

2rdquo

American Mineralogist vol 82 no 7-8 pp 717ndash728 1997[38] S-H Nam S-J Cho C-K Jung et al ldquoComparison of

hydrophilic properties of TiO2thin films prepared by solndashgel

method and reactive magnetron sputtering systemrdquo Thin SolidFilms vol 519 no 20 pp 6944ndash6950 2011

12 International Journal of Photoenergy

[39] H G Feichtinger K Grochenig and T Strohmer ldquoEffi-cient numerical methods in non-uniform sampling theoryrdquoNumerische Mathematik vol 69 no 4 pp 423ndash440 1995

[40] S W Jo B S Kwak K M Kim et al ldquoEffectively CO2

photoreduction toCH4by the synergistic effects of Ca andTi on

Ca-loaded TiSiMCM-41 mesoporous photocatalytic systemsrdquoApplied Surface Science vol 355 pp 891ndash901 2015

[41] J Y Do Y Im B S Kwak J-Y Kim and M Kang ldquoDramaticCO2photoreduction with H

2O vapors for CH

4production

using the TiO2(bottom)FendashTiO

2(top) double-layered filmsrdquo

Chemical Engineering Journal vol 275 pp 288ndash297 2015[42] M Tahir andN SaidinaAmin ldquoPhotocatalytic reduction of car-

bon dioxide with water vapors over montmorillonite modifiedTiO2nanocompositesrdquo Applied Catalysis B Environmental vol

142-143 pp 512ndash522 2013[43] Y Kohno H Hayashi S Takenaka T Tanaka T Funabiki

and S Yoshida ldquoPhoto-enhanced reduction of carbon dioxidewith hydrogen over RhTiO

2rdquo Journal of Photochemistry and

Photobiology A Chemistry vol 126 no 1ndash3 pp 117ndash123 1999[44] M Subrahmanyam S Kaneco and N Alonso-Vante ldquoA screen-

ing for the photo reduction of carbon dioxide supported onmetal oxide catalysts for C

1-C3selectivityrdquo Applied Catalysis B

Environmental vol 23 no 2-3 pp 169ndash174 1999[45] S S Tan L Zou and E Hu ldquoKinetic modelling for photosyn-

thesis of hydrogen and methane through catalytic reduction ofcarbon dioxide with water vapourrdquo Catalysis Today vol 131 no1ndash4 pp 125ndash129 2008

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

12 International Journal of Photoenergy

[39] H G Feichtinger K Grochenig and T Strohmer ldquoEffi-cient numerical methods in non-uniform sampling theoryrdquoNumerische Mathematik vol 69 no 4 pp 423ndash440 1995

[40] S W Jo B S Kwak K M Kim et al ldquoEffectively CO2

photoreduction toCH4by the synergistic effects of Ca andTi on

Ca-loaded TiSiMCM-41 mesoporous photocatalytic systemsrdquoApplied Surface Science vol 355 pp 891ndash901 2015

[41] J Y Do Y Im B S Kwak J-Y Kim and M Kang ldquoDramaticCO2photoreduction with H

2O vapors for CH

4production

using the TiO2(bottom)FendashTiO

2(top) double-layered filmsrdquo

Chemical Engineering Journal vol 275 pp 288ndash297 2015[42] M Tahir andN SaidinaAmin ldquoPhotocatalytic reduction of car-

bon dioxide with water vapors over montmorillonite modifiedTiO2nanocompositesrdquo Applied Catalysis B Environmental vol

142-143 pp 512ndash522 2013[43] Y Kohno H Hayashi S Takenaka T Tanaka T Funabiki

and S Yoshida ldquoPhoto-enhanced reduction of carbon dioxidewith hydrogen over RhTiO

2rdquo Journal of Photochemistry and

Photobiology A Chemistry vol 126 no 1ndash3 pp 117ndash123 1999[44] M Subrahmanyam S Kaneco and N Alonso-Vante ldquoA screen-

ing for the photo reduction of carbon dioxide supported onmetal oxide catalysts for C

1-C3selectivityrdquo Applied Catalysis B

Environmental vol 23 no 2-3 pp 169ndash174 1999[45] S S Tan L Zou and E Hu ldquoKinetic modelling for photosyn-

thesis of hydrogen and methane through catalytic reduction ofcarbon dioxide with water vapourrdquo Catalysis Today vol 131 no1ndash4 pp 125ndash129 2008

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chromatography Research International

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Applied ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Theoretical ChemistryJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Spectroscopy

Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Quantum Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Organic Chemistry International

ElectrochemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CatalystsJournal of