Catalysis Today 249 (2015) 5962

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Catalysis Today

j our na l ho me page: www.elsev ier .com/ locate /ca t tod

Carbonized polyacrylonitrile bers for the catalytoxalic a

Alexandr , JoManuel FLaboratory of C rsity oPortugal

a r t i c l

Article history:Received 13 AReceived in re17 December 2Accepted 28 DAvailable onlin

Keywords:Catalytic ozonPolyacrylonitrNitrogen-containing groupsSurface chemistryOxalic acid

which asses00 Ctrogele an

1. Introdu

Catalyticwater pollumaterials, scarbon nanas ozonatioural properan importathe case of bon materispecies cap[2,18]. Furthadsorption face reactiois originateTherefore, telectron-wifunctional g

CorresponE-mail add

juliana.sousa@(M.F.R. Pereira

http://dx.doi.o0920-5861/ ction

ozonation has emerged as a powerful treatment oftants, even for refractory organic compounds. Carbonuch as activated carbon [115], carbon xerogels [16] andotubes [1722], have shown to be promising materialsn catalysts. Some studies have reported that their text-ties and, mainly, the chemical surface properties playnt role in their performance as ozonation catalysts. Inthe surface chemistry, it is well known that basic car-als favor the formation of hydroxyl radicals, which areable to quickly react with organic pollutants in solutionermore, the basicity of the carbon materials favors the

of those organic compounds and their oxidation by sur-ns [2,4,18]. The basic character of the carbon materialsd by a high density of electrons on the basal planes.his basicity could be promoted removing oxygenatedthdrawing groups and/or introducing some convenientroups, such as different nitrogenated groups (pyridines,

ding author: Tel.: +351 225 084 871; fax: +351 225 081 449.resses: agg@fe.up.pt (A.G. Gonc alves), ext12035@fe.up.pt (J. Moreira),fe.up.pt (J.P.S. Sousa), jlg@fe.up.pt (J.L. Figueiredo), fpereira@fe.up.pt), jjmo@fe.up.pt (J.J.M. rfo).

pyridones and pyrroles), which contribute to the increase of theelectronic density on the material surface [23].

Nitrogen-containing groups can be introduced after preparationof carbon materials or during the material synthesis by severaltreatments. Among them, nitric acid oxidation, reaction of sur-face carboxyl groups with diamine compounds, and treatmentat high temperatures with ammonia, ammonia-air, or ammonia-steam mixtures are commonly used [24]. Various types of carbonmaterials with incorporated nitrogen (carbon xerogels [25], carbonnanotubes [26] and activated carbons [27,28]) have been tested incatalytic ozonation. These studies have reported that the presenceof nitrogenated groups on the surface of carbon materials improvestheir catalytic performance.

Adequate carbon materials having nitrogenated groups canbe synthesized by carbonization of nitrogen-containing precur-sors, like polymers with nitrogen in their structure. This is thecase of polyacrylonitrile (PAN) bers, produced by polymeriza-tion from acrylonitrile and vinyl acetate monomers, which containhigh amounts of nitrogen [29]. In this approach, chemical treat-ments for the introduction of nitrogenated groups are not required,decreasing the cost and time consumed for the synthesis of carbonmaterials enriched with nitrogen.

Therefore, this work aims to carbonize textile polyacrylonitrilebers at different temperatures and expose then to 10 h of activa-tion in order to test them as catalysts in the ozonation of oxalic

rg/10.1016/j.cattod.2014.12.0452015 Elsevier B.V. All rights reserved.cid

a G. Gonc alves , Jssica Moreira, Juliana P.S. Sousa.R. Pereira, Jos J.M. rfoatalysis and Materials Associate Laboratory LSRE/LCM, Faculty of Engineering, Unive

e i n f o

ugust 2014vised form014ecember 2014e 25 January 2015

ationile bers

a b s t r a c t

Textile polyacrylonitrile (PAN) bers, and activated during 10 h in order todegradation The ber carbonized at 8mainly, the high concentration of nicarbonization of PAN bers is a simpactivity in ozonation processesic ozonation of

s L. Figueiredo,

f Porto, Rua Dr. Roberto Frias, 4200-465 Porto,

contain nitrogen, were carbonized at different temperaturess their performance as ozonation catalysts in the oxalic acid

shows the best performance due to its basic character and,n surface groups, particularly N-pyridinic (N6) groups. Thed effective method to prepare materials with good catalytic

2015 Elsevier B.V. All rights reserved.

60 A.G. Gonc alves et al. / Catalysis Today 249 (2015) 5962

acid, which is a common nal oxidation product of several organicpollutants and is refractory to single ozonation.

2. Experimental

2.1. Prepara

The matfrom textilwhich werelogical Cen(CITEVE).

Pre-treaoriginal b1 C min1 uand the nathen carbondesired tem1 h [30]. Thmance as osample thatat 800 C). Tperature agow to a COeach samplcarbonizati10 h).

2.2. Charac

The texBrunauerEadsorption NOVA 4200

The surfized by temquantify thspectroscop(Altamira In(25 cm3 mintemperaturof CO and a DymaxioXPS analysa monochr15 kV (90 Wa pass enervey.

Elementmodel EA 1

2.3. Kinetic

The ozoscale reactojacket. Ozongenerator. Titored withwas removsium iodidewas lled wacid, at natfrom Sigmawater withcatalytic ozduced in th

Table 1Textural properties of the prepared samples.

Sample SBET (m2 g1) Vpore (cm3 g1) S /= pore (m2 g1)

FI 800 C 0 hC 10C 0 hC 0 h

w ra (50m, inrativsamerfois wugedximremerelated by8].

ults

arac

textrbonper

tura area

anain acord

decoic-Nolic-ted t, rela

theoundpresn tholutsent

origed, inoun

totalion o

amoas ue of o

in T is ladicapect850

pero 800 C, the oxygenated surface groups present are mainlyl and basic groups like carbonyls/quinones [31], which haveive effect on the ozonation process [2,4,18]. The increase ofization temperatures or the activation lead to a decrease inount of CO-releasing groups.tion of materials

erials to be used as ozonation catalysts were preparede PAN bers (FISIVON) supplied by FISIPE, Portugal,

subsequently knitted in the facilities of the Techno-tre for the Textile and Clothing Industries of Portugal

tment of the bers was carried out by heating 5 g of theers up to 300 C in a tubular reactor. A heating rate ofnder a constant air/N2 ow of 85 cm3 min1 was used,l temperature was maintained for 2 h. The bers wereized by raising the temperature at 5 C min1 up to theperature (800, 850 or 900 C), which was maintained fore study of the effect of the ber activation in its perfor-zonation catalyst was carried out using the carbonized

presented the highest catalytic activity (i.e. carbonizedhus, further activation was obtained by raising the tem-ain at 15 C min1 to 800 C, but then switching the N22 ow for a specic time [29]. The reference given to

e indicates carbon ber (FI) as well as the respectiveon temperature (800900 C) and activation time (0 or

terization

tural characterization of the materials, namely themmettTeller (BET) surface area, was based on the N2isotherms, determined at 196 C with a Quantachromee apparatus.ace chemistry of the prepared samples was character-perature programmed desorption (TPD), in order to

e oxygenated groups [31], and by X-ray photoelectrony (XPS). TPD analyses were performed in an AMI-200struments) apparatus. Helium was used as carrier gas1) and the temperature was programmed from roome to 1100 C at a heating rate of 5 C min1 The amountsCO2 released from the samples were monitored withn mass spectrometer (Ametek Process Instruments).es were performed in a Kratos AXIS Ultra HSA usingomatic Al K X-ray source (1486.7 eV), operating at), in FAT mode (Fixed Analyser Transmission), withgy of 40 eV for regions of interest and 80 eV for sur-

al analysis was performed in a Carlo Erba instrument,108.

experiments

nation experiments were carried out in a laboratoryr (ca. 1 L) equipped with agitation and a circulatione was produced from pure oxygen in a BMT 802X ozonehe concentration of ozone in the gas phase was mon-

a BMT 964 ozone analyzer. Ozone leaving the reactored in a series of gas washing bottles lled with potas-

(KI) solution. In each ozonation experiment the reactorith 700 mL of a solution containing 1 mM of oxalic

ural pH (approximately 3). Oxalic acid was purchasedAldrich. All solutions were prepared with ultrapure

a resistivity of 18.2 m cm at room temperature. Inonation experiments, 100 mg of catalyst was intro-e reactor. The experiments were performed at constant

FI 800FI 850FI 900

gas otration200 rpcompain the were panalyscentrifthe mameasumum followence [1

3. Res

3.1. Ch

TheThe cathe temthe texsurface

XPSto obtaing. Accan bepyridinto pyrrattribu403 eVever, inwere fto the (N-Q) odeconvare pre

Theexpectgen amas the reduct

Thethe arecentagshowngroupsCO2, inthe resand FI the temequal tneutraa positcarbonthe am

A.G. Gonc alves et al. / Catalysis Today 249 (2015) 5962 61

410

FI_850C

Inte

nsity

(a. u

.)

B. E. (eV)410 40 5 40 0 39 5

FI_9 00C_ 0h

Inte

nsity

(a. u

.)

410 40 5 40 0 39 5B. E. (e V)

FI_800C_0h

Inte

nsity

(a. u

.)

410

FI_800

Inte

nsity

(a. u

.)

Fig. 1. N1s XPS spectra for the prepared s

Table 2Chemical characterization of the prepared samples.

Sample N6 N-Q Ntotal, XPS (%, m/m) Ntotal, EA (%

FI 800 C 0 h 0.3 FI 800 C 10 0.2 FI 850 C 0 h 0.3 FI 900 C 0 h 0.2

3.2. Kinetic

In the prpH (approxbers was iit has beenucts from oozonation iin Fig. 2. Beafter 360 mlysts. Ozonathere is no

The adsodetermined

Fig. 2. Evoluti(3) during siadsorption (C0

ts do ande remed sa

iny of t

evalowinB.E. (eV) (%, m/m) B.E. (eV) (%, m/m)

398.6 4.6 400.9 4.6 9.2 13.7 h 398.5 2.3 401.2 3.4 5.7 10.3

398.6 1.9 401.3 4.3 6.2 12.5 398.8 2.6 401.1 3.3 5.9 10.8

experiments

esent study, the ozonation of oxalic acid, at the naturalimately 3), in the presence of the carbonized or activatednvestigated. This carboxylic acid was selected because

identied among the most common oxidation prod-rganic pollutants degradation and is refractory to singlen references [4,18,35]. The kinetic results are depicted

catalysFig. 2),that thprepar

Theactivitcan bethe folsides the degradation prole, the oxalic acid removalin of reaction was the value used to compare the cata-tion of oxalic acid leads directly to mineralization, i.e.

formation of organic intermediates.rption capacity of the samples towards oxalic acid was. The results indicated that adsorption on the prepared

on of the dimensionless concentration of oxalic acid at natural pHngle ozonation, ozonation catalyzed by the prepared samples and= 1 mM, catalyst = 0.14 g L1).

(see Fig. 2).not directlyworst perfointermediahave similable for all ooxalic acid.seems to dcentration obetter is its(see Fig. 3)face groups[2,4,18]. Necarbonizedsince they aby increasining the numinuence okinetic resucompared. presents beactivated samay be maoxalic acid this trend isample leadThese resulB. E. (eV)405 400 395

_0h

405 40 0 39 5B. E. (eV)

C_10h

amples.

, m/m) CO (mol g1) CO2 (mol g1) CO/CO2 mO%

4687 174 26.9 15.31009 92 11.0 3.43400 138 24.7 11.11359 87 15.7 4.5

es not contribute to the removal of oxalic acid (see can therefore be neglected. Thus, it can be considered

oval of oxalic acid in the presence of ozone and themples mainly occurs by catalytic ozonation.uence of carbonization temperature in the catalytiche carbonized PAN bers for ozonation of oxalic acidluated by comparison of the catalytic performance ofg samples: FI 800 C 0 h, FI 850 C 0 h and FI 900 C 0 h It can be veried that the activity of these materials is related to the temperature of carbonization, since thermance was obtained with the ber carbonized at thete temperature (850 C). The non-activated materialsr textural properties, since the surface area is negligi-f them, but different performances in the oxidation of

In this context, the presence of pyridinic groups (N6)ecisively inuences the catalysis: the higher the con-f N6 groups on the surface of carbonized samples, the

performance. However, this correlation is not strong probably because the basic oxygen-containing sur-

present also play a role in the catalytic mechanismvertheless, the presence of pyridinic groups (N6) on

bers contributes positively to the oxalic acid removal,re Lewis bases inducing basicity at the carbon surfaceg the electron density [23,36] and, therefore, increas-ber of active sites for ozonation. In order to assess the

f the activation in the performance of the materials, thelts obtained with FI 800 C 0 h and FI 800 C 10 h wereFig. 2 shows that the activated sample (FI 800 C 10 h)tter performance for oxalic acid removal than the non-mple (FI 800 C 0 h) in the beginning of reaction, whichinly justied by its high specic surface area, whereand molecular ozone can adsorb and react. However,s inverted after 120 min and, thus, the non-activateds to a faster removal of oxalic acid from the solution.ts indicate that the specic surface area of the studied

62 A.G. Gonc alves et al. / Catalysis Today 249 (2015) 5962

1.5 2.0 2. 5 3. 0 3. 5 4. 0 4. 5 5.075

80

85

90

95

100X o

xalic

aci

d (%

)

N6 groups (%)

R = 0.8906

Fig. 3. Oxalic acid conversion after 360 min of reaction vs. N6 content of carbonizedsamples (FI 800 C 0 h, FI 850 C 0 h and FI 900 C 0 h).

materials has not the most important role in the ozonation ofoxalic acid, suggesting again that the reaction is mainly favored bythe presence of nitrogenated groups and basic oxygenated surfacegroups (CO-releasing groups).

4. Conclus

PAN bbonized at 10 h. The pacid degrad

The inuparison of cThe presenpyridinic (N

The actiincreased tstressing thsurface gro

The berthe removahigh concen

The carbto prepare mprocesses.

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Carbonized polyacrylonitrile fibers for the catalytic ozonation of oxalic acid1 Introduction2 Experimental2.1 Preparation of materials2.2 Characterization2.3 Kinetic experiments

3 Results and discussion3.1 Characterization of catalysts3.2 Kinetic experiments

4 ConclusionsReferences