Research Article LiNbO Coating on Concrete Surface: A New ...downloads.hindawi.com/journals/tswj/2013/686497.pdf · Schematic diagram is shown in Figure . is is a chal- ... and their

Hindawi Publishing CorporationThe Scientific World JournalVolume 2013 Article ID 686497 6 pageshttpdxdoiorg1011552013686497

Research ArticleLiNbO3 Coating on Concrete Surface A New andEnvironmentally Friendly Route for Artificial Photosynthesis

Ranjit K Nath12 M F M Zain1 and Abdul Amir H Kadhum2

1 Sustainable Construction Materials and Building Systems (SUCOMBS) Research Group Faculty of Engineering andBuilt Environment Universiti Kebangsaan Malaysia 43600 Bangi Malaysia

2 Department of Chemical amp Process Engineering Faculty of Engineering and Built Environment Universiti Kebangsaan Malaysia43600 Bangi Malaysia

Correspondence should be addressed to Ranjit K Nath rkn chemyahoocom

Received 27 September 2013 Accepted 30 October 2013

Academic Editors Y Hara and Y Kang

Copyright copy 2013 Ranjit K Nath et al This 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

The addition of a photocatalyst to ordinary buildingmaterials such as concrete creates environmentally friendly materials by whichair pollution or pollution of the surface can be diminished The use of LiNbO

3photocatalyst in concrete material would be more

beneficial since it can produce artificial photosynthesis in concrete In these research photoassisted solid-gas phases reductionof carbon dioxide (artificial photosynthesis) was performed using a photocatalyst LiNbO

3 coated on concrete surface under

illumination ofUV-visible or sunlight and showed that LiNbO3achieved high conversion ofCO

2into products despite the low levels

of band-gap light available The high reaction efficiency of LiNbO3is explained by its strong remnant polarization (70120583Ccm2)

allowing a longer lifetime of photoinduced carriers as well as an alternative reaction pathway Due to the ease of usage and goodphotocatalytic efficiency the research work done showed its potential application in pollution prevention

1 Introduction

In the last two centuries fossil fuels and the cheap energyhave been provided for energy in the industrial development[1] The excessive use of fossil fuels has produced CO

2in

the earthrsquos atmosphere which is one of the responsible forgreenhouse effect [2] The effect of increasing atmosphericcarbon dioxide is directly linked to global warming [3] Thereduction of CO

2by the process of artificial photosynthesis is

believed to be one of the alternatives that emits oxygen usingatmospheric CO

2and water in presence of photocatalyst [2]

Artificial photosynthesis was investigated by using avariety of approaches [4] like replication of the chemicalreactions that take place in plants [5] and concerted effortsusing ruthenium complexes and structures as an organic dye[6] to sensitize wide band-gap semiconductors in presenceof visible light [7] In this process a semiconductor is usedas a photocatalyst that can absorb light and using thisenergy it can chemically convert CO

2and water into formic

acid and oxygen [8 9] In this work we describe artificial

photosynthesis taking place on photocatalyst LiNbO3coated

on concrete surface by producing formic acid and oxygen

2 Approach to Artificial Photosynthesis

The goal of artificial photosynthesis is to mimic the greenplants and other photosynthetic organisms that use sunlightto make valuable substances [10] In natural photosynthesisthe first step is water splitting in which proton is generatedand O

2is released using solar energy [11] The second step

is the Calvin cycle in which CO2is reduced to hydrocarbons

[4] Schematic diagram is shown in Figure 1 This is a chal-lenging goal because success requires integration of multiplechemical functions in stable chemical architecture

21 Catalyst for CO2Reduction To perform artificial pho-

tosynthesis the photocatalyst must be able to drive thereduction of CO

2and ideally the oxidation of water [12]

To achieve this the reaction potentials must be inside the

2 The Scientific World Journal

Surface 1

D

H++

H++

Surface 2

CatRed

lowast

Clowast Catox

1

2H2O

1

4O2

1

2CO2

1

2HCOOH

eminus eminus eminus eminus

h

Figure 1 Schematic diagram illustrating the photoelectrochemical reaction between CO2and H

2O to give HCOOH and O

2initiated by

excitation and photoinjection in presence of photocatalyst

2

0

1

3

Vb 048V Eg 320 eV

Potentials of REDOX couples

V versus

SHE

minus4

minus3

minus2

minus1

CO2HCOOHCO2HCHO

H2OO2

LiNbO3 TiO2

Eg 378 eV

Vb 27V

Cb minus050V

Cb minus330V

CO2CO2minus

CO2CO2minus

2

Figure 2 Bandpositions of LiNbO3andTiO

2versus SHE in relation

to the redox reactions of artificial photosynthesis [7]

band edges of the photocatalyst [13] Besides many testedsemiconductors (ZnO Fe

2O3 CdS ZnS and TiO

2) LiNbO

3

can quickly reduce CO2more than others [14ndash16]

Figure 2 compares the potential of the valence and con-duction bands of LiNbO

3andmostly used photocatalyst TiO

2

in relation to the cell potential of the conversion of CO2[17]

This figure shows that in TiO2valence band holes can oxidize

water and conduction band electrons cannot reduce CO2

to CO2

minus due to low energy than required Table 1 LiNbO3

drives the reaction of CO2and water to formic acid but

the valence band holes do not oxidize water directly [8]This is due to its valence band and conduction band energylevel The valence and conduction band energy of LiNbO

3

are 048 v and minus330 v Conduction band electrons of LiNbO3

can reduce CO2to CO

2

minus due to high energy and valenceband holes oxidize water by physisorbing due to its strongremnant polarization [8]The reaction step of LiNbO

3allows

a different reaction pathway because of its highly reducingconduction band electrons [7]

Table 1 Key reaction of artificial photosynthesis with redox poten-tial [10]

Reactions E∘ V versus SHECO2 + eminus rarr CO

2

minusminus190

CO2 + 2eminus rarr CO2

2minusminus145

CO2 + 2eminus + 2H+rarr HCOOH minus022

2H2O rarr O2 + 4H+ + 4eminus 123H2O rarr ∙OH + H+ + eminus 210

22 Water Oxidation Catalyst for Artificial PhotosynthesisWater oxidation is a more complex chemical reaction thanproton reduction In natural photosynthesis the oxygen-evolving complex performs this reaction by accumulatingreducing equivalents (electrons) in a manganese-calciumcluster within photosystem II (PS II) and then delivers themto water molecules [18] with the resulting production ofmolecular oxygen and protons

2H2O 997888rarr O

2+ 4H+ + 4eminus (1)

Without a catalyst (natural or artificial) this reaction isvery endothermic and it requires high temperatures (at least2500K) [19] Many metal oxides have been found to havewater oxidation catalytic activity [20 21] especially thosefrom relatively abundant transitional metals but these metaloxides suffer from low turnover frequency and slow electrontransfer properties and their mechanism of action is hard todecipher and adjust [8]

Remnant polarization of LiNbO3allows this process at

different reaction pathway that leads to a charge occurringon the interface [22] This charge interacts with species incontact with the surface producing a tightly bound layer[23ndash25] that changes the nature of bonding in physisorbedmaterials In the case of water LiNbO

3will physisorb a tight

layer of molecules [26]The valence band location of LiNbO3

(048V versus SHE) is unable to oxidize water directly thephysisorbed water appears to prevent any further reactionson the surface of the catalyst [27] In the gas-solid reactionthere is more CO

2available and bound on the surface of the

LiNbO3[8] This bound CO

2reacts with photoexcited holes

and electrons in the LiNbO3and produces reactive species

that react with H2O to form end products [10] One such

The Scientific World Journal 3

Figure 3 LiNbO3coated concrete slab in reaction chamber

species is CO2

minus that reacts with water to produce formic acidand oxygen

H2O + CO

2

minus997888rarr HCOOH + 1

2O2+ eminus (2)

The physisorption of molecules on ferroelectric surfaces[27] affects the localization of electrons in the molecule andthe bond angles This condition allows for easier injectionor removal of electrons than that in less chemically strainedsystems

3 Materials and Methods

31 Materials Ordinary portland cement sand and stoneaggregate are used to prepare the concrete sample commer-cially available in Malaysia In this research locally availablecoarse river sand and stone aggregate of 10mm size wereused The specific gravity of sand and aggregate used in thisresearch is 263 and 265 respectively The LiNbO

3powder

CAS 12031-63-9 and CO2from Sigma-Aldrich were used as

the photocatalyst in this study

32 Sample Proportions The concrete samples were fabri-cated in steel moulds with internal dimensions of 20 times10 times 5 cm3 Cement sand and stone aggregate are mixedthoroughly with a mix ratio of 1 2 4 and water cementratio of 05 and poured into the steel mould Then thecompaction was done by putting the steel moulds on amechanical vibrating tableThe surface of concrete was madesmoothening with a glass plate The concrete samples wereremoved from the moulds after 24 hours and putted intowater for 28 days for proper curing After curing sampleswere allowed to dry in the air for a few hours Dried samplewas then coated with 075mm LiNbO

3paste

33 Equipment and Experimental Procedure The central partof the experimental setup used is a reaction chamber allowinga sample of size 20times10times5 cm3 to be fixed All structural partsinside the box are to allow laminar flow of the gas along thesample surface and to make sure of the uniform distributionof CO

2gas The reaction chamber was tested in experiments

under reaction conditions before use and found to be airtight and nonreactive under prolonged UV irradiation Afluorescent lamp of wavelengths 366 nm was used to supply

0

20

40

60

80

100

5001000150020002500300035004000

Tran

smitt

ance

()

Wavenumbers (cmminus1)

O-H

C-OC = O

Figure 4 FT-IR spectra of water sample taken from reactionchamber after one day

10

30

50

70

90

110

130

150

170

0 05 1 15 2 25 3 35 4 45 5 55 6

Peak

hei

ght (

mAu

)

Retention time (min)

2705

minus10

Figure 5 HPLC of sample taken from reaction chamber

photoirradiation to activate the photocatalyst Two types ofsensors were used to control the temperature and humidityFigure 3 shows the illustration of the reaction chamber andthe test setup for artificial photosynthesis LiNbO

3coated

concrete block is placed in the reaction chamber A reservoirof 30mL of distilled water was then added in a tray beforefilling it with CO

2gas to create a 30 70 mix with air An

irradiation was carried out using a UV lamp or by naturalsunlight after irradiation the vessel was allowed to cool andsamples were collected from the water reservoir for analysis

4 Results and Discussion

41 FT-IR Analyses FT-IR analyses were carried out withBio-Rad FTS-185 (Digilab) equipment usingAttenuated TotalReflexion (ATR) unit The spectra were usually recorded inthe range of 4000ndash400 cmminus1 with 2 cmminus1 resolution and 32scans were collected each time

Band assignments report available in literature arededucted from spectra performed in diffuse reflectance Inthe present work spectra acquisition is performed in ATRA shift of about 3 wave number units is noted in spectra(Figure 4)


Table 2 FT-IR characterization of sample

Band assignments Sample after one day (cmminus1) Sample after two days (cmminus1) Sample after three days (cmminus1)OndashH 34012 s b 34023 s b 34017 s bC=O 16443 s 16452 s 16448 sCndashO 6871 w 6853 w 6807 w

(a) (b)

(c) (d)

Figure 6 (a) SEM photomicrograph of the LiNbO3before photocatalytic reaction on the specimenrsquos surface (b) SEM photomicrograph of

the LiNbO3before photocatalytic reaction on the specimenrsquos surface (c) SEM photomicrograph of the LiNbO

3after photocatalytic reaction

on the specimenrsquos surface (d) SEM photomicrograph of the LiNbO3after photocatalytic reaction on the specimenrsquos surface

Nevertheless the band assignments are in close agree-ment with those previously reported [28ndash30] The FT-IRdata for band assignments are presented in Table 2 Thebroad bands at 34012 cmminus1 34023 cmminus1 and 34017 cmminus1are due to the stretching OndashH bond from HCOOH Theasymmetric stretching bands at 16443 cmminus1 16452 cmminus1and 16448 cmminus1 are due to C=O bond in HCOOHThe widebands at 6871 cmminus1 6853 cmminus1 and 6807 cmminus1 are due to CndashO bond in HCOOH

42 HPLC Analyses TheHPLC of sample was performed onZORBAXECLIPS C18 150mm times 46mm 5120583with a flow rate06mLmin keeping column temperature at 40∘C

The mobile phase consisted of 20mM H2SO4in ace-

tonitrile and detection of formic acid was performed byinjecting 20 120583L of sample solution into a UV detector ofwavelength 220 nm The retention time (119877

119905) of main peak

was 26min under these conditions [31] The main peak ofstandard formic acid solution appears at the retention time(119877119905) 269min For comparison with the standard solution

spectrum of sample solution was taken at the same condi-tions Each spectrum (Figure 5) gives the peak at the sameretention time that indicates the presence of HCOOH

43 SEM Observations Figures 6(a) and 6(b) illustrated thescanning electronmicroscope (SEM)photomicrographof theLiNbO

3before photocatalytic reaction on the specimenrsquos sur-

faceThemorphology of the particles is round and systematicstructure particles This is due to the carbonation of concretethat enhances the possibility of artificial photosynthesis Onthe other handmicrostructure of LiNbO

3particles is changed

after the photocatalytic reaction The SEM photomicrographof the LiNbO

3after photocatalytic reaction on the specimenrsquos

surface is shown in Figures 6(c) and 6(d) Larger anddarker agglomerates were appeared the microstructure ofLiNbO

3 A net decrease in porosity is also observed pores

are progressively filled due to the carbonation of concretematerial that increases the contact of CO

2with photocatalyst

44 EDX Analyses Chemical composition change wasexpected from energy-dispersive X-ray (EDX) analysisFigure 7 represents EDX analysis performed before and afterphotocatalytic reaction on specimens surface Twenty punc-tual analyses are performed for each area Expected changeof chemical composition is observed Figure shows that thereis an increase in the amount of oxygen after photocatalyticreaction


2751

7349

3255

7324

0

10

20

30

40

50

60

70

80

046 23

Mol

ecul

e by

wei

ght (

)


Before photocatalytic reactionAfter photocatalytic reaction

Oxygen

NbLi

Figure 7 EDX analysis performed before and after photocatalyticreaction on specimens surface

The amounts of O and NbL are 2751 and 7349 byweight before photocatalytic reaction and the amounts of Oand NbL are 3255 and 7324 by weight after photocatalyticreaction which indicates the occurrence of artificial photo-synthesis on specimensrsquo surface

5 Conclusions

This paper focuses on the application of LiNbO3as photocat-

alytic material in concrete blocks The addition of LiNbO3in

buildingmaterials adds an additional property to the concreteby creating artificial photosynthesis which is the best wayto convert CO

2into O

2and HCOOH and simultaneously

reduce global CO2level This work demonstrates the impact

of the photocatalytic reactions and shows LiNbO3to be

an exciting new material for use as a photocatalyst inconstruction

Acknowledgments

The work is financed by ZamalahInstitutional Scholarshipprovided from the Universiti Kebangsaan Malaysia and theMinistry of Higher Education of Malaysia The first authorexpresses honest appreciation to Chittagong University ofEngineeringampTechnology (CUET) Chittagong Bangladeshfor providing leave for this research

References

[1] A B Robinson N E Robinson and A Soon ldquoEnvironmentalEffects of Increased Atmospheric Carbon Dioxiderdquo Journal ofAmerican Physicians and Surgeons vol 12 pp 79ndash90 2007

[2] W Lee C Liao M Tsai C Huang C Jeffrey and S Wu ldquoAnovel twin reactor for CO

2photoreduction to mimic artificial

photosynthesisrdquo Applied Catalysis B vol 132-133 pp 445ndash4512013

[3] R K Nath M F M Zain and A A H Kadhum ldquoPhotoca-talysismdasha novel approach for solving various environmentaland disinfection problems a brief reviewrdquo Journal of AppliedSciences Research vol 8 no 8 pp 4147ndash4155 2012

[4] O Ozcan F Yukruk E U Akkaya andD Uner ldquoDye sensitizedartificial photosynthesis in the gas phase over thin and thickTiO2films under UV and visible light irradiationrdquo Applied

Catalysis B vol 71 no 3-4 pp 291ndash297 2007[5] G Ibram ldquoConversion of carbon dioxide to methanol using

solar energymdasha brief reviewrdquo Materials Sciences and Applica-tions vol 2 pp 1407ndash1415 2011

[6] M R Hoffmann S T Martin W Choi and D W BahnemannldquoEnvironmental applications of semiconductor photocatalysisrdquoChemical Reviews vol 95 no 1 pp 69ndash96 1995

[7] R K Nath M FM Zain and A A H Kadhum ldquoNewMaterialLiNbO

3for photocatalytically improvement of indoor airmdashan

overviewrdquo Advances in Natural and Applied Sciences vol 6 no7 pp 1030ndash1035 2012

[8] M Stock and S Dunn ldquoLiNbO3mdasha polar material for solid-gas

artificial photosynthesisrdquo Ferroelectrics vol 419 no 1 pp 9ndash132011

[9] C H Ao and S C Lee ldquoIndoor air purification by photocatalystTiO2immobilized on an activated carbon filter installed in an

air cleanerrdquoChemical Engineering Science vol 60 no 1 pp 103ndash109 2005

[10] M Stock and S Dunn ldquoLiNbO3mdasha new material for artifi-

cial photosynthesisrdquo IEEE Transactions on Ultrasonics Ferro-electrics and Frequency Control vol 58 no 9 pp 1988ndash19932011

[11] L Casser A Beeldens N Pimpineli and G L Guerrini ldquoPho-tocatalysis of cementitious materialsrdquo in International RILEMSymposium on Photocatalysis Environment and ConstructionMaterials pp 131ndash145 Florence Italy October 2007

[12] M Carraro A Sartorel F M Toma et al ldquoArtificial photosyn-thesis challenges water oxidation at nanostructured interfacesrdquoTopics in Current Chemistry vol 303 pp 121ndash150 2011

[13] J-MHerrmann ldquoHeterogeneous photocatalysis state of the artand present applicationsrdquoTopics in Catalysis vol 34 no 1ndash4 pp49ndash65 2005

[14] G Seshadri C Lin and A B Bocarsly ldquoA new homogeneouselectrocatalyst for the reduction of carbon dioxide to methanolat low overpotentialrdquo Journal of Electroanalytical Chemistry vol372 no 1-2 pp 145ndash150 1994

[15] P K J Robertson ldquoSemiconductor photocatalysis an envi-ronmentally acceptable alternative production technique andeffluent treatment processrdquo Journal of Cleaner Production vol4 no 3-4 pp 203ndash212 1996

[16] W-C Yang B J Rodriguez A Gruverman and R J NemanichldquoPolarization-dependent electron affinity of LiNbO

3surfacesrdquo

Applied Physics Letters vol 85 no 12 pp 2316ndash2318 2004[17] J H Alstrum-Acevedo M K Brennaman and T J Meyer

ldquoChemical approaches to artificial photosynthesisrdquo InorganicChemistry vol 44 no 20 pp 6802ndash6827 2005

[18] V Balzani A Credi and M Venturi Photoinduced ChargeSeparation and Solar Energy Conversion in Molecular Devicesand Machines A Journey Into the Nanoworld Wiley-VCHWeinheim Germany 2003

[19] J O Bockris B Dandapani D Cocke and J GhoroghchianldquoOn the splitting of waterrdquo International Journal of HydrogenEnergy vol 10 no 3 pp 179ndash201 1985


[20] Y Chapuis D Klvana C Guy and J Kirchnerova ldquoPhotocat-alytic oxidation of volatile organic compounds using fluorescentvisible lightrdquo Journal of the Air amp Waste Management Associa-tion vol 52 no 7 pp 845ndash854 2002

[21] L Cao Z Gao S L Suib T N Obee S O Hay and J D Frei-haut ldquoPhotocatalytic oxidation of toluene on nanoscale TiO

2

catalysts studies of deactivation and regenerationrdquo Journal ofCatalysis vol 196 no 2 pp 253ndash261 2000

[22] M-J Choi andD-H Cho ldquoResearch activities on the utilizationof carbon dioxide in Koreardquo CleanmdashSoil Air Water vol 36 no5-6 pp 426ndash432 2008

[23] R Prasad and P Singh ldquoA review on CO oxidation over copperchromite catalystrdquo Catalysis Reviews Science and Engineeringvol 54 no 2 pp 224ndash279 2012

[24] M C J Bradford and M A Vannice ldquoCO2reforming of CH

4rdquo

Catalysis Reviews Science and Engineering vol 41 no 1 pp 1ndash42 1999

[25] J Zhao and X Yang ldquoPhotocatalytic oxidation for indoor airpurification a literature reviewrdquo Building and Environment vol38 no 5 pp 645ndash654 2003

[26] AHarhira LGuilbert P Bourson andHRinnert ldquoDecay timeof polaron photoluminescence in congruent lithium niobaterdquoPhysica Status Solidi (C) vol 4 no 3 pp 926ndash929 2007

[27] D Li M H Zhao J Garra et al ldquoDirect in situ determinationof the polarization dependence of physisorption on ferroelectricsurfacesrdquo Nature Materials vol 7 no 6 pp 473ndash477 2008

[28] J Arana C Garriga I Cabo J M Dona-Rodrıguez OGonzalez-Dıaz J A Herrera-Melian and J Perez-Pena ldquoFTIRstudy of formic acid interactionwith TiO

2and TiO

2dopedwith

Pd and Cu in photocatalytic processesrdquoApplied Surface Sciencevol 239 no 1 pp 60ndash71 2004

[29] H A Al-Hosney S Carlos-Cuellar J Baltrusaitis and V HGrassian ldquoHeterogeneous uptake and reactivity of formic acidon calcium carbonate particles a Knudsen cell reactor FTIRand SEM studyrdquo Physical Chemistry Chemical Physics vol 7 no20 pp 3587ndash3595 2005

[30] M Ibrahim A Nada and D E Kamal ldquoDensity functionaltheory and FTIR spectroscopic study of carboxyl grouprdquo IndianJournal of Pure amp Applied Physics vol 43 no 12 pp 911ndash9172005

[31] A K Mubeen S Sukumar P Vikas K Nanidkumar andB Sadanandam ldquoA validated NPmdashHPLC method for thedetermination of formic acid in pharmaceutical excipientimidureardquo International Journal of Pharmaceutical and Biomed-ical Research vol 2 no 3 pp 140ndash144 2011

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Active and Passive Electronic Components

Control Scienceand Engineering

Journal of



RotatingMachinery


Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design



Shock and Vibration


Civil EngineeringAdvances in

Acoustics and VibrationAdvances in



Electrical and Computer Engineering

Journal of

Advances inOptoElectronics


Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of


Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks



Surface 1

D

H++

H++

Surface 2

CatRed

lowast

Clowast Catox

1

2H2O

1

4O2

1

2CO2

1

2HCOOH

eminus eminus eminus eminus

h

Figure 1 Schematic diagram illustrating the photoelectrochemical reaction between CO2and H

2O to give HCOOH and O

2initiated by

excitation and photoinjection in presence of photocatalyst

2

0

1

3

Vb 048V Eg 320 eV

Potentials of REDOX couples

V versus

SHE

minus4

minus3

minus2

minus1

CO2HCOOHCO2HCHO

H2OO2

LiNbO3 TiO2

Eg 378 eV

Vb 27V

Cb minus050V

Cb minus330V

CO2CO2minus

CO2CO2minus

2

Figure 2 Bandpositions of LiNbO3andTiO

2versus SHE in relation

to the redox reactions of artificial photosynthesis [7]

band edges of the photocatalyst [13] Besides many testedsemiconductors (ZnO Fe

2O3 CdS ZnS and TiO

2) LiNbO

3

can quickly reduce CO2more than others [14ndash16]

Figure 2 compares the potential of the valence and con-duction bands of LiNbO

3andmostly used photocatalyst TiO

2

in relation to the cell potential of the conversion of CO2[17]

This figure shows that in TiO2valence band holes can oxidize

water and conduction band electrons cannot reduce CO2

to CO2

minus due to low energy than required Table 1 LiNbO3

drives the reaction of CO2and water to formic acid but

the valence band holes do not oxidize water directly [8]This is due to its valence band and conduction band energylevel The valence and conduction band energy of LiNbO

3

are 048 v and minus330 v Conduction band electrons of LiNbO3

can reduce CO2to CO

2

minus due to high energy and valenceband holes oxidize water by physisorbing due to its strongremnant polarization [8]The reaction step of LiNbO

3allows

a different reaction pathway because of its highly reducingconduction band electrons [7]

Table 1 Key reaction of artificial photosynthesis with redox poten-tial [10]

Reactions E∘ V versus SHECO2 + eminus rarr CO

2

minusminus190

CO2 + 2eminus rarr CO2

2minusminus145

CO2 + 2eminus + 2H+rarr HCOOH minus022

2H2O rarr O2 + 4H+ + 4eminus 123H2O rarr ∙OH + H+ + eminus 210

22 Water Oxidation Catalyst for Artificial PhotosynthesisWater oxidation is a more complex chemical reaction thanproton reduction In natural photosynthesis the oxygen-evolving complex performs this reaction by accumulatingreducing equivalents (electrons) in a manganese-calciumcluster within photosystem II (PS II) and then delivers themto water molecules [18] with the resulting production ofmolecular oxygen and protons

2H2O 997888rarr O

2+ 4H+ + 4eminus (1)

Without a catalyst (natural or artificial) this reaction isvery endothermic and it requires high temperatures (at least2500K) [19] Many metal oxides have been found to havewater oxidation catalytic activity [20 21] especially thosefrom relatively abundant transitional metals but these metaloxides suffer from low turnover frequency and slow electrontransfer properties and their mechanism of action is hard todecipher and adjust [8]

Remnant polarization of LiNbO3allows this process at

different reaction pathway that leads to a charge occurringon the interface [22] This charge interacts with species incontact with the surface producing a tightly bound layer[23ndash25] that changes the nature of bonding in physisorbedmaterials In the case of water LiNbO

3will physisorb a tight

layer of molecules [26]The valence band location of LiNbO3

(048V versus SHE) is unable to oxidize water directly thephysisorbed water appears to prevent any further reactionson the surface of the catalyst [27] In the gas-solid reactionthere is more CO

2available and bound on the surface of the

LiNbO3[8] This bound CO

2reacts with photoexcited holes

and electrons in the LiNbO3and produces reactive species

that react with H2O to form end products [10] One such



species is CO2


H2O + CO

2


2O2+ eminus (2)




3powder




3paste




0

20

40

60

80

100

5001000150020002500300035004000

Tran

smitt

ance

()


O-H

C-OC = O


10

30

50

70

90

110

130

150

170

0 05 1 15 2 25 3 35 4 45 5 55 6

Peak

hei

ght (

mAu

)


2705

minus10



3coated










(a) (b)

(c) (d)





















2with photocatalyst



2751

7349

3255

7324

0

10

20

30

40

50

60

70

80

046 23

Mol

ecul

e by

wei

ght (

)



Oxygen

NbLi



5 Conclusions




2into O





Acknowledgments


References

























3surfacesrdquo








2





4rdquo






2and TiO

2dopedwith







RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











species is CO2


H2O + CO

2


2O2+ eminus (2)




3powder




3paste




0

20

40

60

80

100

5001000150020002500300035004000

Tran

smitt

ance

()


O-H

C-OC = O


10

30

50

70

90

110

130

150

170

0 05 1 15 2 25 3 35 4 45 5 55 6

Peak

hei

ght (

mAu

)


2705

minus10



3coated










(a) (b)

(c) (d)





















2with photocatalyst



2751

7349

3255

7324

0

10

20

30

40

50

60

70

80

046 23

Mol

ecul

e by

wei

ght (

)



Oxygen

NbLi



5 Conclusions




2into O





Acknowledgments


References

























3surfacesrdquo








2





4rdquo






2and TiO

2dopedwith







RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation












(a) (b)

(c) (d)





















2with photocatalyst



2751

7349

3255

7324

0

10

20

30

40

50

60

70

80

046 23

Mol

ecul

e by

wei

ght (

)



Oxygen

NbLi



5 Conclusions




2into O





Acknowledgments


References

























3surfacesrdquo








2





4rdquo






2and TiO

2dopedwith







RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










2751

7349

3255

7324

0

10

20

30

40

50

60

70

80

046 23

Mol

ecul

e by

wei

ght (

)



Oxygen

NbLi



5 Conclusions




2into O





Acknowledgments


References

























3surfacesrdquo








2





4rdquo






2and TiO

2dopedwith







RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation












2





4rdquo






2and TiO

2dopedwith







RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









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