research article photocatalytic oxidation of gaseous

Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2013 Article ID 890240 6 pageshttpdxdoiorg1011552013890240

Research ArticlePhotocatalytic Oxidation of Gaseous Benzene under185 nm UV Irradiation

Haibao Huang12 Xinguo Ye1 Huiling Huang1 Peng Hu1

Lu Zhang1 and Dennis Y C Leung3

1 School of Environmental Science and Engineering Sun Yat-Sen University Guangzhou 510275 China2Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology Guangzhou 510275 China3Department of Mechanical Engineering The University of Hong Kong Pokfulam Road Hong Kong

Correspondence should be addressed to Haibao Huang seabao8gmailcom and Dennis Y C Leung ycleunghkuhk

Received 19 July 2013 Accepted 11 August 2013

Academic Editor Guisheng Li

Copyright copy 2013 Haibao Huang 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

Benzene is a toxic air pollutant and causes great harm to human being Photocatalytic oxidation (PCO) has been frequently studiedfor benzene removal however its PCO efficiency is still very low and the photocatalysts are easy to be deactivated To improvethe efficiency and stability of PCO UV lamps with partial 185 nm UV irradiation were used to activate photocatalysts (denotedas 185-PCO) Cobalt modified TiO

2(Co-TiO

2) was developed to improve the PCO activity and eliminate ozone generated from

185 nm UV irradiation Results show that benzene removal efficiency of PCO with 254 nm UV irradiation (denoted as 254-PCO)is only 21 while it was greatly increased to 515 in 185-PCO 185-PCO exhibited superior capacity for benzene oxidation In the185-PCO process much ozone was left in case of TiO

2as photocatalysts while it can be nearly eliminated by 1 Co-TiO

2

1 Introduction

With the rapid development of economy and the increase inpopulation massive volatile organic compounds (VOCs) aredischarged from both industry (such as chemical petro-chemical painting and coating factories) and human activ-ities [1 2] VOCs not only do great harm to the health ofhuman being but also cause serious damage to the atmo-spheric environment They can lead to atmospheric com-pound pollution and haze The haze weather which lastedfor a long time in many cities of China in early 2013 hadcausedmuch trouble to local people It is of great significanceto control VOCs pollution

Benzene is a representative VOC It is very toxic and car-cinogenic Benzene is hard to be destructed by conventionaltechnology due to its benzene ring The methods of benzeneremoval include conventional ways such as adsorption [3 4]catalytic combustion [5] and biological degradation [6] andemerging ways such as nonthermal plasma [7] and photo-catalysis [8ndash10] However the application of these methods isgreatly limited due to their inherent drawbacks such as highcost deactivation and byproducts [11ndash14]

PCO is one of the fastest developed technologies forVOCs control The most widely used UV sources in PCOare 254 nm and 365 nm UV lamp However the conven-tional PCO process has disadvantages such as photocatalystdeactivation recombination of electron-hole pair and lowefficiency [15] In order to improve the efficiency and stabilityof PCO UV lamps with partial 185 nm UV irradiation(denoted as 185-PCO) were used to activate photocatalysts[16ndash18] 185 nmUV lamps cannot only irradiate photocatalystbut also generate active oxidants such as ∙O ∙OH and ozoneThey are also facile cheap and energy efficient Previousstudy showed that the toluene removal of 185-PCO is 7times higher than that of PCO under 254 nm UV irradiation(denoted as 254-PCO) and no obvious deactivation wasobserved in the former [19] However massive ozone wasresidual at the outlet of photocatalytic reactor since TiO

2

had poor activity towards ozone decomposition Ozone is abyproduct and it is harmful to the environment and the healthof human being meanwhile it is a strong oxidant and can beused to enhance the oxidation of pollutants

Cobalt is a commonly used metal not only for TiO2dop-

ing but also as an active component of ozone decomposition

2 International Journal of Photoenergy

minus

+

Gas distributing system Analysis system

To airZero air generatorThermometer

Valve

GC

Ozone analyzer

Humidometer

Mass flowcontroller Water

Benzene buffer

UV lamps

Power

Seal

Photocatalyst

Glass container

Photocatalyst

Support ring

Benzene PCO system Detailed PCO reactor

Quartz glass tube

Gas flow

Figure 1 Schematic diagram of experimental setup

agent In this study cobalt modified TiO2(Co-TiO

2) was

developed to improve the PCO activity and eliminate ozonegenerated from 185 nm irradiation Benzene was selectedas representative VOC and its oxidation performance iscompared between 185-PCO and 254-PCO Results showthat Co-TiO

2can simultaneously increase benzene removal

and ozone decomposition in 185-PCO 185-PCO presents anefficient economic simple and stable process for benzeneremoval

2 Experimental Sections

21 Preparation of Photocatalysts TiO2was prepared by sol-

gel method using tetrabutyl titanate as the precursor absolutealcohol as the solution and HCl as the inhibitor respectivelyThe preparation procedure is as follows cobalt acetate wasadded into the mixture of 50mL absolute alcohol and 17mLtetrabutyl titanate and mixed for 30min forming solution AAnother mixture B containing 18mL absolute alcohol 1mLHCl and 3mL deionized water was dropwise added intosolution A under intensive stirring The stirring was stoppedtill the gelatin was formed The gelatin was aged for 12 h andthen dried at 120∘C for 6 h The dry powder was followed bycalcinations at 550∘C for 4 h Thus cobalt doped TiO

2was

produced Pure TiO2was fabricated by similar processes for

the preparation of Co-TiO2except that no cobalt acetate was

introduced during the synthesis The catalysts were grindedinto 40ndash60 mesh before use

22 Catalytic Activity Test The experimental setup and PCOreactor were shown in Figure 1 The catalytic activity test

system was composed of 3 parts gas distribution benzenePCO and gas analysis systemThe gas from zero air generatoris dry air free of CO CO

2 and hydrocarbon It was used

for bubble water and benzene liquid to generate waterand benzene vapor respectively The benzene concentrationhumidity and gas flow can be regulated by themass flow con-trollers (S49 Horibametron) A 05 Lmin gas flow of 50 ppmbenzene concentration and 50 humidity was introducedinto benzene PCO reactor The reactor is a glass cylindercontainer with an effective volume of 05 L in which a quartzglass tube was located in the centre and two UV lamps (4WSungreen) were fixed in both sides of the tube with a distanceof 8mm The detailed PCO reactor is shown in Figure 1A solid rod of 8mm diameter was placed in the center ofthe quartz glass tube with 13 cm id and the photocatalystswas loaded in the space between the rod and glass tubeBy this way the photocatalysts have more chances to beirradiated by UV light The UV lamps were turned on for30min for thewarming-up of systembefore reaction and datarecordingThe gaseous benzene entered into the reactor fromthe bottom of glass tube and left from the top The benzeneand ozone concentrations of effluent were monitored bygas chromatography (GC) equipped with a FID (GC9790IIFuli) and ozone analyzer (Model 202 2B Technology) onlinerespectively

23 Catalyst Characterization BET surface areas of the sam-ples were measured by N

2adsorption-desorption isotherms

at 77K using Quadrasorb SI instrument Prior to the mea-surement the samples were degassed at 573K for 2 h Themorphology of photocatalysts was obtained with scanningelectron microscopy (SEM) (JSM-6330F JEOL) operated at

International Journal of Photoenergy 3

Table 1 BET surface area of photocatalysts

Samples BET surface area m2g Particle size nmP25 554 290TiO2 966 105Co-TiO2 269 349

beam energy of 200 kV XRD patterns were collected with aPanalytical Empyrean X-ray powder diffractometer operatedat 35 kV and 25mA using Cu K 120572 (120582 = 15418 A) radiationThe intensity data were collected in a 2120579 range from 20∘ to80∘

3 Results and Discussion

31 Characterization Figure 2 shows the XRD spectra of thesynthesized TiO

2and Co-TiO

2as well as the commercial

TiO2(P25 Degussa) The nanocrystalline anatase structure

was confirmed by (101) (004) (200) (105) and (204) diffrac-tion peaks [20] The XRD patterns of anatase have a mainpeak at 2120579 = 252∘ corresponding to the 101 plane (JCPDS 21-1272) while themain peaks of rutile and brookite phases are at2120579 = 274

∘ (110 plane) and 2120579 = 308∘ (121 plane) respectivelyTherefore rutile and brookite phases have not been detectedon the synthesized TiO

2and Co-TiO

2 They exhibit very

similar shape of diffractive peaks of the crystal planes TheXRD patterns did not show any Co phase indicating thatCo ions uniformly dispersed among the anatase crystallitesUnlike the synthesized TiO

2 weak peaks of rutile phase can

be observed on P25 (Figure 1) The average particle size ofTiO2was estimated by applying the Scherrer equation (119863 =

119870120582120573 cos 120579) on the anatase and rutile diffraction peaks (themost intense peaks for each sample) where 119863 is the crystalsize of the catalyst 120582 is the X-ray wavelength (154 A) 120573 is thefull width at half maximum (FWHM) of the catalyst (radian)119870 = 089 and 120579 is the diffraction angle [21] The averagecrystal sizes of TiO

2 1 Co-TiO

2 and P25 were calculated

to be around 105 nm 349 nm and 290 nm respectivelyas shown in Table 1 Compared with P25 the synthesizedTiO2can greatly reduce the particle size however the doping

of cobalt triggered the aggregation of particle during thesynthesis process leading to the increase in particle size

This observation is consistent with the results of BETsurface area and the observation of SEM images The BETsurface area of TiO

2 1 Co-TiO

2and P25 is 966 269 and

554m2g respectively TiO2with the smallest particle size

has the largest BET surface areaSEMmicrograph of TiO

2 1 Co-TiO

2 and P25 nanopar-

ticles is shown in Figure 3 This image shows uniform smallparticles which are coherent together on the TiO

2and P25

however the particles of 1 Co-TiO2got aggregated The

results agree well with the results of XRD pattern and BETsurface area

32 Catalytic Activity Test Figure 4 compared benzeneremoval efficiency in PCO processes with 185 nm and 254 nmUV irradiation It can be found that it is very low in case

20 30 40 50 60 70 800

5000

10000

15000

20000

25000

(b)

(c)

(a)

A

R RutileA Anatase

RRR

AAAAA

A

Inte

nsity

(cps

)

P25

1 Co-2120579 (∘)

TiO2

TiO2

Figure 2 XRD spectra of photocatalysts (a) P25 (b) TiO2 and

(c) 1 Co-TiO2

of 254-PCO process Benzene removal efficiency is onlyabout 2 It is well known that benzene is very difficultto be destructed due to its stable 120587-bonding Moreover theintermediates from benzene PCO can lead to the seriousdeactivation of photocatalysts [22] However benzene con-version was greatly increased to about 50 under 185 nmUVirradiation and no obvious deactivation was observed afterreaction for 3 h Among 3 tested samples Co-TiO

2obtained

the highest benzene removal efficiency of 515 followed byP25 (502) and TiO

2(457) Benzene removal efficiency

of 185-PCO is over 20 times than that of 254-PCO 185-PCOis a very complex process in which 185 nm UV lamp notonly acted as the irradiation light of photocatalysis but alsogenerated reactive oxidants such as ∙O ∙OH and ozone Thereaction processes for the formation of reactive oxidants areas follows [23]

H2O + h] 997888rarr ∙H + ∙OH

O2+ h] 997888rarr 2 ∙O

∙O +H2O 997888rarr 2 ∙OH

∙O +O2997888rarr O

3

(1)

In order to clarify the contribution of 185 nm irradiationthe photocatalysts were removed from the reactor The newprocess is photolysis It can be found that benzene removalefficiency reached 38 under 185 nm irradiation alone185 nm photolysis contributes much to benzene oxidation inthe 185-PCO process The sum of benzene removal efficiencydue to PCO and 185 nm photolysis is about 40 whichis approximately 10 smaller than that of 185-PCO Thisindicated that other factors were also involved in benzeneoxidation in the 185-PCO process besides photolysis andPCO As we know ozone can be abundantly generatedfrom 185 nm UV irradiation The ozone concentration is138 ppm in the absence of photocatalysts Ozone is strong


(a) P25 (b) TiO2

(c) 1 Co-TiO2

Figure 3 SEM images of photocatalysts (a) P25 (b) TiO2 and (c) 1 Co-TiO

2

oxidant Although it cannot directly oxidize benzene it canbe decomposed into more active oxygen species with the aidof catalysts [24]

O3+

lowast997888rarr O

2+Olowast

Olowast +O3997888rarr O

2+O2

lowast

O2

lowast997888rarr O

2+

lowast

(2)

lowast represents the catalytic active sites

33 Ozone Decomposition 185-PCO exhibitedmore superiorcapacity for benzene oxidation than 254-PCO Howeverozone is another important concern besides benzene removalsince it is a toxic byproduct Although 3 tested samples hadsimilar benzene removal efficiency since 185 nmUV photoly-sis contributed to a large proportion of benzene removal theyhad entirely different activity toward ozone decompositionAs shown in Figure 5 the ozone concentration at outlet of185-PCO reactor after reaction for 25 h was 119 ppm in caseof the synthesized TiO

2 and it was dropped to 584 ppm

in case of P25 Although the synthesized TiO2had higher

BET surface area than that of P25 its capacity for ozonedecomposition is worse than that of the latter It was reported

0

10

20

30

40

50

Benz

ene r

emov

al effi

cien

cy (

)

P25

185nm + photocatalyst254nm + photocatalyst185nm

1 Co-TiO2TiO2

Figure 4 Benzene removal efficiency in different processes

that higher BET surface area should be helpful for ozonedecomposition [25] The difference between synthesizedTiO2and commercial P25 is that the former is pure anatase


0 20 40 60 80 100 120 140 160

0

20

40

60

80

100

120

Ozo

ne co

ncen

trat

ion

at o

utle

t (pp

m)

Time (min)

P25

1 Co-TiO2

TiO2

Figure 5 Ozone concentration at outlet of 185-PCO reactor withdifferent photocatalysts

40

45

50

55

3 Co2 Co1 Co05 Co

Rem

oval

effici

ency

of b

enze

ne (

)

01 Co

Figure 6 Effect of Co loading amount on benzene removal

TiO2while P25 contained some rutile TiO

2besides anatase

one A previous study showed that TiO2with partial rutile

had better capacity for ozone decomposition than that of pureanatase TiO

2[26] As for Co-TiO

2 ozone can be completely

eliminated Cobalt is a very active component for ozonedecomposition Co doped TiO

2exhibited superior activity

toward ozone elimination In comprehensive view of benzeneremoval and ozone decomposition Co-TiO

2exhibited the

best performance among the 3 tested samples

34 Effect of Co Doping In order to study the effect of Codoping 01 05 1 2 and 3 Co-TiO

2were prepared

and tested in 185-PCO process The results after reaction for150min are shown in Figure 6 Benzene removal efficiency isonly 476 in case of 01 Co-TiO

2 As the increase in Co

loading benzene removal efficiency was increased to 515in case of 1 Co-TiO

2and 524 in case of 3 Co-TiO

2

0

10

20

30

40

50

60

70

80

3 Co2 Co05 Co 1 Co01 Co

O3

conc

entr

atio

n at

the o

utle

t (pp

m)

Figure 7 Effect of Co loading amount on ozone concentration atthe outlet

Figure 7 shows the effect of cobalt loading amount onozone concentration at the outlet after reaction for 150minIn case of Co doping amount lower than 1 the ozoneconcentration at the outlet was dropped with the increase inCo loading As for 01 Co doping the ozone concentrationis 795 ppm while it was decreased to nearly zero in caseof 1 Co doping The increase in Co doping can providemore catalytic active sites for ozone decompositionHoweverthe ozone concentration at the outlet was increased withfurther increase in Co doping Too much Co doping is notbeneficial to ozone decomposition since Co probably getsaggregated and blocks themicropore of TiO

2Thiswill reduce

the catalytic active sites and BET surface area leading toworse activities toward ozone decomposition

4 Conclusion

To improve the efficiency and stability of PCO 185-PCO wasused to activate photocatalysts Co-TiO

2was developed to

improve the PCO activity and eliminate the ozone generatedfrom 185 nm UV irradiation Results show that benzeneremoval efficiency of PCOwith 254-PCO is only 21while itwas greatly increased to 515 in the 185-PCOprocess 185 nmUV irradiation can generate much reactive oxygen speciessuch as ∙O ∙OH and ozone which can jointly enhancebenzene oxidation together with PCO In 185-PCO muchozone is left in case of TiO

2as photocatalysts while it can be

completely eliminated by 1Co-TiO2 185-PCO is an efficient

and promising process for benzene removal

Acknowledgments

The authors gratefully acknowledge the financial supportfrom Research Fund for the Doctoral Program of HigherEducation of China (no 20120172120039) the NationalNature Science Foundation of China (no 51208207) theResearch Fund Program of Guangdong Provincial Key Labo-ratory of Environmental Pollution Control and RemediationTechnology (no 2013K0001) and the Fundamental ResearchFunds for the Central Universities (no 13lgzd03)


References

[1] R Atkinson ldquoAtmospheric chemistry of VOCs and NOxrdquoAtmospheric Environment vol 34 no 12ndash14 pp 2063ndash21012000

[2] S Zuo F Liu J Tong and C Qi ldquoComplete oxidation of ben-zene with cobalt oxide and ceria using the mesoporous supportSBA-16rdquo Applied Catalysis A vol 467 pp 1ndash6 2013

[3] A A M Daifullah and B S Girgis ldquoImpact of surface charac-teristics of activated carbon on adsorption of BTEXrdquo Colloidsand Surfaces A vol 214 no 1ndash3 pp 181ndash193 2003

[4] M Farhadian D Duchez C Vachelard and C Larroche ldquoBTXfemoval from polluted water through bioleaching processesrdquoApplied Biochemistry and Biotechnology vol 151 no 2-3 pp295ndash306 2008

[5] L Wang V D Vien K Suzuki M Sakurai and H KameyamaldquoPreparation of anodised aluminium catalysts by an electrolysissupporting method for VOC catalytic combustionrdquo Journal ofChemical Engineering of Japan vol 38 no 2 pp 106ndash112 2005

[6] G Darracq A Couvert C Couriol E Dumont A AmraneandP LeCloirec ldquoActivated sludge acclimation for hydrophobicVOC removal in a two-phase partitioning reactorrdquo Water Airand Soil Pollution vol 223 no 6 pp 3117ndash3124 2012

[7] M Kang B-J Kim S M Cho et al ldquoDecomposition of tolueneusing an atmospheric pressure plasmaTiO

2catalytic systemrdquo

Journal of Molecular Catalysis A vol 180 no 1-2 pp 125ndash1322002

[8] T-C Pan H-C Chen G-T Pan and C-M Huang ldquoPhoto-catalytic oxidation of gaseous isopropanol using visible-lightactive silver vanadatesSBA-15 compositerdquo International Journalof Photoenergy vol 2012 Article ID 314361 8 pages 2012

[9] F-L Cao J-G Wang F-J Lv et al ldquoPhotocatalytic oxidationof toluene to benzaldehyde over anatase TiO

2hollow spheres

with exposed 001 facetsrdquo Catalysis Communications vol 12 no11 pp 946ndash950 2011

[10] A Kachina S Preis G C Lluellas and J Kallas ldquoGas-phaseand aqueous photocatalytic oxidation of methylamine thereaction pathwaysrdquo International Journal of Photoenergy vol2007 Article ID 32524 6 pages 2007

[11] S K Agarwal and J J Spivey ldquoEconomic effects of catalystdeactivation during VOC oxidationrdquo Environmental Progressvol 12 pp 182ndash185 1993

[12] MDDriessen TMMiller andVHGrassian ldquoPhotocatalyticoxidation of trichloroethylene on zinc oxide characterization ofsurface-bound and gas-phase products and intermediates withFT-IR spectroscopyrdquo Journal of Molecular Catalysis A vol 131no 1ndash3 pp 149ndash156 1998

[13] M Kosusko ldquoCatalytic oxidation of groundwater strippingemissionsrdquo Environmental Progress vol 7 no 2 pp 136ndash1421988

[14] J JeongK SekiguchiW Lee andK Sakamoto ldquoPhotodegrada-tion of gaseous volatile organic compounds (VOCs) using TiO

2

photoirradiated by an ozone-producing UV lamp decompo-sition characteristics identification of by-products and water-soluble organic intermediatesrdquo Journal of Photochemistry andPhotobiology A vol 169 no 3 pp 279ndash287 2005

[15] H B Huang andD Y C Leung ldquoVacuumultraviolet-irradiatedphotocatalysis advanced process for toluene abatementrdquo Jour-nal of Environmental Engineering vol 137 no 11 pp 996ndash10012011

[16] J Jeong K Sekiguchi and K Sakamoto ldquoPhotochemical andphotocatalytic degradation of gaseous toluene using short-wavelength UV irradiation with TiO

2catalyst comparison of

three UV sourcesrdquo Chemosphere vol 57 no 7 pp 663ndash6712004

[17] L Yang Z Liu J Shi Y Zhang H Hu and W ShangguanldquoDegradation of indoor gaseous formaldehyde by hybrid VUVand TiO

2UV processesrdquo Separation and Purification Technol-

ogy vol 54 no 2 pp 204ndash211 2007[18] P Zhang J Liu and Z Zhang ldquoVUV photocatalytic degrada-

tion of toluene in the gas phaserdquo Chemistry Letters vol 33 no10 Article ID CL-040801 pp 1242ndash1243 2004

[19] H Huang D Y C Leung G Li M K H Leung and X FuldquoPhotocatalytic destruction of air pollutants with vacuumultraviolet (VUV) irradiationrdquo Catalysis Today vol 175 no 1pp 310ndash315 2011

[20] Y Xie S H Heo S H Yoo G Ali and S O Cho ldquoSynthesis andphotocatalytic activity of anatase TiO

2nanoparticles-coated

carbon nanotubesrdquo Nanoscale Research Letters vol 5 no 3 pp603ndash607 2010

[21] M Hamadanian A Reisi-Vanani and A Majedi ldquoPreparationand characterization of S-doped TiO

2nanoparticles effect

of calcination temperature and evaluation of photocatalyticactivityrdquo Materials Chemistry and Physics vol 116 no 2-3 pp376ndash382 2009

[22] H Yuzawa J Kumagai and H Yoshida ldquoReaction mechanismof aromatic ring amination of benzene and substituted benzenesby aqueous ammonia over platinum-loaded titanium oxidephotocatalystrdquoThe Journal of Physical Chemistry C vol 117 pp11047ndash11058 2013

[23] T Alapi and A Dombi ldquoDirect VUV photolysis of chlorinatedmethanes and their mixtures in an oxygen stream using anozone producing low-pressure mercury vapour lamprdquo Chemo-sphere vol 67 no 4 pp 693ndash701 2007

[24] W Li G V Gibbs and S T Oyama ldquoMechanism of ozonedecomposition on amanganese oxide catalystmdash1 In situ Ramanspectroscopy and Ab initio molecular orbital calculationsrdquoJournal of the American Chemical Society vol 120 no 35 pp9041ndash9046 1998

[25] H Huang D Ye and X Guan ldquoThe simultaneous catalyticremoval of VOCs andO

3in a post-plasmardquoCatalysis Today vol

139 no 1-2 pp 43ndash48 2008[26] H Yin J Xie Q Yang and C Yin ldquoMechanism of ozone de-

composition on the surface of metal oxiderdquo Chemical Researchand Application vol 15 pp 1ndash5 2003

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


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


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


minus

+

Gas distributing system Analysis system

To airZero air generatorThermometer

Valve

GC

Ozone analyzer

Humidometer

Mass flowcontroller Water

Benzene buffer

UV lamps

Power

Seal

Photocatalyst

Glass container

Photocatalyst

Support ring

Benzene PCO system Detailed PCO reactor

Quartz glass tube

Gas flow

Figure 1 Schematic diagram of experimental setup

agent In this study cobalt modified TiO2(Co-TiO

2) was

developed to improve the PCO activity and eliminate ozonegenerated from 185 nm irradiation Benzene was selectedas representative VOC and its oxidation performance iscompared between 185-PCO and 254-PCO Results showthat Co-TiO

2can simultaneously increase benzene removal

and ozone decomposition in 185-PCO 185-PCO presents anefficient economic simple and stable process for benzeneremoval

2 Experimental Sections

21 Preparation of Photocatalysts TiO2was prepared by sol-

gel method using tetrabutyl titanate as the precursor absolutealcohol as the solution and HCl as the inhibitor respectivelyThe preparation procedure is as follows cobalt acetate wasadded into the mixture of 50mL absolute alcohol and 17mLtetrabutyl titanate and mixed for 30min forming solution AAnother mixture B containing 18mL absolute alcohol 1mLHCl and 3mL deionized water was dropwise added intosolution A under intensive stirring The stirring was stoppedtill the gelatin was formed The gelatin was aged for 12 h andthen dried at 120∘C for 6 h The dry powder was followed bycalcinations at 550∘C for 4 h Thus cobalt doped TiO

2was

produced Pure TiO2was fabricated by similar processes for

the preparation of Co-TiO2except that no cobalt acetate was

introduced during the synthesis The catalysts were grindedinto 40ndash60 mesh before use

22 Catalytic Activity Test The experimental setup and PCOreactor were shown in Figure 1 The catalytic activity test

system was composed of 3 parts gas distribution benzenePCO and gas analysis systemThe gas from zero air generatoris dry air free of CO CO

2 and hydrocarbon It was used

for bubble water and benzene liquid to generate waterand benzene vapor respectively The benzene concentrationhumidity and gas flow can be regulated by themass flow con-trollers (S49 Horibametron) A 05 Lmin gas flow of 50 ppmbenzene concentration and 50 humidity was introducedinto benzene PCO reactor The reactor is a glass cylindercontainer with an effective volume of 05 L in which a quartzglass tube was located in the centre and two UV lamps (4WSungreen) were fixed in both sides of the tube with a distanceof 8mm The detailed PCO reactor is shown in Figure 1A solid rod of 8mm diameter was placed in the center ofthe quartz glass tube with 13 cm id and the photocatalystswas loaded in the space between the rod and glass tubeBy this way the photocatalysts have more chances to beirradiated by UV light The UV lamps were turned on for30min for thewarming-up of systembefore reaction and datarecordingThe gaseous benzene entered into the reactor fromthe bottom of glass tube and left from the top The benzeneand ozone concentrations of effluent were monitored bygas chromatography (GC) equipped with a FID (GC9790IIFuli) and ozone analyzer (Model 202 2B Technology) onlinerespectively

23 Catalyst Characterization BET surface areas of the sam-ples were measured by N

2adsorption-desorption isotherms

at 77K using Quadrasorb SI instrument Prior to the mea-surement the samples were degassed at 573K for 2 h Themorphology of photocatalysts was obtained with scanningelectron microscopy (SEM) (JSM-6330F JEOL) operated at







2and Co-TiO





2and Co-TiO

2 They exhibit very





2 1 Co-TiO





2 1 Co-TiO

2and P25 is 966 269 and



2 1 Co-TiO

2 and P25 nanopar-


2and P25




20 30 40 50 60 70 800

5000

10000

15000

20000

25000

(b)

(c)

(a)

A

R RutileA Anatase

RRR

AAAAA

A

Inte

nsity

(cps

)

P25

1 Co-2120579 (∘)

TiO2

TiO2


(c) 1 Co-TiO2


2obtained




H2O + h] 997888rarr ∙H + ∙OH

O2+ h] 997888rarr 2 ∙O

∙O +H2O 997888rarr 2 ∙OH

∙O +O2997888rarr O

3

(1)



(a) P25 (b) TiO2

(c) 1 Co-TiO2


2


O3+

lowast997888rarr O

2+Olowast


2+O2

lowast

O2

lowast997888rarr O

2+

lowast

(2)






0

10

20

30

40

50

Benz

ene r

emov

al effi

cien

cy (

)

P25


1 Co-TiO2TiO2




0 20 40 60 80 100 120 140 160

0

20

40

60

80

100

120

Ozo

ne co

ncen

trat

ion

at o

utle

t (pp

m)

Time (min)

P25

1 Co-TiO2

TiO2


40

45

50

55

3 Co2 Co1 Co05 Co

Rem

oval

effici

ency

of b

enze

ne (

)

01 Co



2besides anatase



2[26] As for Co-TiO





2exhibited the



2were prepared





2

0

10

20

30

40

50

60

70

80


O3

conc

entr

atio

n at

the o

utle

t (pp

m)



2Thiswill reduce


4 Conclusion


2was developed to





Acknowledgments



References












2hollow spheres







2

































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of







2and Co-TiO





2and Co-TiO

2 They exhibit very





2 1 Co-TiO





2 1 Co-TiO

2and P25 is 966 269 and



2 1 Co-TiO

2 and P25 nanopar-


2and P25




20 30 40 50 60 70 800

5000

10000

15000

20000

25000

(b)

(c)

(a)

A

R RutileA Anatase

RRR

AAAAA

A

Inte

nsity

(cps

)

P25

1 Co-2120579 (∘)

TiO2

TiO2


(c) 1 Co-TiO2


2obtained




H2O + h] 997888rarr ∙H + ∙OH

O2+ h] 997888rarr 2 ∙O

∙O +H2O 997888rarr 2 ∙OH

∙O +O2997888rarr O

3

(1)



(a) P25 (b) TiO2

(c) 1 Co-TiO2


2


O3+

lowast997888rarr O

2+Olowast


2+O2

lowast

O2

lowast997888rarr O

2+

lowast

(2)






0

10

20

30

40

50

Benz

ene r

emov

al effi

cien

cy (

)

P25


1 Co-TiO2TiO2




0 20 40 60 80 100 120 140 160

0

20

40

60

80

100

120

Ozo

ne co

ncen

trat

ion

at o

utle

t (pp

m)

Time (min)

P25

1 Co-TiO2

TiO2


40

45

50

55

3 Co2 Co1 Co05 Co

Rem

oval

effici

ency

of b

enze

ne (

)

01 Co



2besides anatase



2[26] As for Co-TiO





2exhibited the



2were prepared





2

0

10

20

30

40

50

60

70

80


O3

conc

entr

atio

n at

the o

utle

t (pp

m)



2Thiswill reduce


4 Conclusion


2was developed to





Acknowledgments



References












2hollow spheres







2

































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


(a) P25 (b) TiO2

(c) 1 Co-TiO2


2


O3+

lowast997888rarr O

2+Olowast


2+O2

lowast

O2

lowast997888rarr O

2+

lowast

(2)






0

10

20

30

40

50

Benz

ene r

emov

al effi

cien

cy (

)

P25


1 Co-TiO2TiO2




0 20 40 60 80 100 120 140 160

0

20

40

60

80

100

120

Ozo

ne co

ncen

trat

ion

at o

utle

t (pp

m)

Time (min)

P25

1 Co-TiO2

TiO2


40

45

50

55

3 Co2 Co1 Co05 Co

Rem

oval

effici

ency

of b

enze

ne (

)

01 Co



2besides anatase



2[26] As for Co-TiO





2exhibited the



2were prepared





2

0

10

20

30

40

50

60

70

80


O3

conc

entr

atio

n at

the o

utle

t (pp

m)



2Thiswill reduce


4 Conclusion


2was developed to





Acknowledgments



References












2hollow spheres







2

































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0 20 40 60 80 100 120 140 160

0

20

40

60

80

100

120

Ozo

ne co

ncen

trat

ion

at o

utle

t (pp

m)

Time (min)

P25

1 Co-TiO2

TiO2


40

45

50

55

3 Co2 Co1 Co05 Co

Rem

oval

effici

ency

of b

enze

ne (

)

01 Co



2besides anatase



2[26] As for Co-TiO





2exhibited the



2were prepared





2

0

10

20

30

40

50

60

70

80


O3

conc

entr

atio

n at

the o

utle

t (pp

m)



2Thiswill reduce


4 Conclusion


2was developed to





Acknowledgments



References












2hollow spheres







2

































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


References












2hollow spheres







2

































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

research article photocatalytic oxidation of gaseous

Documents