Bi2O3/TiO2復(fù)合納米顆粒的可見光光催化性能

楊 娟李建通 繆 娟

(河南理工大學(xué)理化學(xué)院，焦作 454003)

Bi2O3/TiO2復(fù)合納米顆粒的可見光光催化性能

楊 娟＊李建通 繆 娟

(河南理工大學(xué)理化學(xué)院，焦作 454003)

采用溶膠與水熱相結(jié)合的方法合成了具有可見光光催化活性的復(fù)合納米顆粒Bi2O3/TiO2，并對其進(jìn)行了X射線衍射、透射電鏡、X射線光電子能譜、紫外-可見漫反射譜、紅外光譜、低溫N2吸附脫附及電子順磁共振分析。結(jié)果表明，復(fù)合少量的氧化鉍可顯著抑制TiO2由銳鈦礦到金紅石的相轉(zhuǎn)移過程，并將光吸收范圍擴(kuò)展到可見光區(qū)?？梢姽庹丈湎?λ＞420 nm)，利用電子順磁共振技術(shù)檢測到明顯的羥基自由基(·OH)信號。鉍的最佳摻雜量為Bi/Ti質(zhì)量比2.0%，適量鉍的摻入能顯著改善銳鈦礦TiO2的結(jié)晶度，抑制光生電子-空穴對的復(fù)合，提高光催化量子效率。通過可見光照射下，4-氯酚的降解實(shí)驗(yàn)測試Bi2O3/TiO2復(fù)合納米顆粒的可見光光催化活性。同時，利用氣-質(zhì)聯(lián)用儀對4-氯酚降解過程的中間產(chǎn)物進(jìn)行了測定，并提出可見光照射下的Bi2O3光敏化機(jī)理。

氧化鉍；TiO2；可見光；光催化；4-氯酚

Powdered titania have been proven to be excellent photocatalytic materials for degradation of organic pollutants under UV irradiation[1-2].However,the wide band gap of TiO2(anatase of 3.2 eV,rutile of 3.0 eV)limits the absorption wavelength to less than 387 nm,which is only 3%～5%of the sunlight energy.Therefore,thedevelopmentofvisible-lightphotocatalystsis indispensable to be able to utilize the major portion ofthe solar spectrum and to realize indoor application of photocatalysts.

Thus far,a lot of efforts have been devoted to modify the photocatalyst[3-5].Among the studies,an importantstrategytoextentthe lightabsorption property of TiO2is the formation of heterojunction between TiO2and a sensitizer semiconductor with a narrow bandgap[6-8].In the heterojunction structure,the sensitizer is excited by visible light irradiation,and some of the photogenerated electrons and holes will then be transferred to TiO2.Bi2O3,with a direct band gap 2.8 eV,thus will be able to absorb some portion of visible light(λ＜440 nm)and decompose the organic pollutants[9-10].But alone,its photocatalytic activity is very low,owing to the high electron-hole recombination rate in Bi2O3[11].On the other hand,Bi2O3can act as an effective photosensitizer and form the coupled semiconductor with TiO2.Rengaraj and Li[12]reported that Bi3+-TiO2could improve the photocatalytic reduction of nitrate in aqueous solution under UV illumination.Jing et al.[13]demonstrated that Bi2O3-compounded TiO2could improve the photocatalytic decomposition of dyes pollutant rhodamine B (RhB).Bian et al.[14]synthesized active Bi2O3/TiO2visible photocatalyst with ordered mesoporous structure and highly crystallized anatase by evaporation-induced self-assembly method.However,to the best of our knowledge,there has been no reports of systematic studies on effects of the bismuth content on the TiO2phase transformation and the photoinduced charge properties by ESR technique,together with their relationships with the enhanced photocatalytic activity and degradation approach of 4-CP under visible-light irradiation.

In the present work,we prepared Bi2O3/TiO2photocatalysts by sol-hydrothermal method with different contents of bismuth.The prepared materials were characterized by XRD,TEM,XPS,UV-Vis DRS,FTIR and ESR spectroscopy.The enhanced photocatalytic activity was tested in the degradation of 4-CP under visible illumination,which was chosen as probe molecule,due to its environmental importance as priority toxic pollutant[15].The promoting mechanism on the activity from the high anatase crystallinity,the optical response extent,the increasing surface OH group density and the effective photosensitizating effect of Bi2O3were examined.Meanwhile,by the examination of the intermediates with GC-MS,the photocatalytic mechanism and the possible approach of visible-light degradation for 4-CP were also discussed.

1 Experimental

1.1 Reagents and materials

Titanium tetra-n-butoxide(Ti(O-Bu)4)and bismuth nitrate with analytical grade were obtained from Aldrich Chemical Co.Glycolic acid,succinic acid,fumaric acid,malic acid,1,1,1,3,3,3-hexamethyldisilazane,Chlorotrimethylsilane and anhydrous pyridine were purchased from J&K chemical Ltd.4-CP,hydroquinone and all other chemicals were of analytical grade used without further purification.

1.2 Photocatalysts preparation

The Bi2O3/TiO2samples with different percentages of bismuth(0.5%,1%,2%,4%and 5%,(w/w))were prepared by sol-hydrothermal method,using Bi(NO3)3and Ti(O-Bu)4as precursors.In a typical process,10 mL of Ti(O-Bu)4was dissolved in 10 mL of ethanol by stirring vigorously to produce Ti(O-Bu)4-C2H5OH solution.Meanwhile,10 mL of water,2 mL of 16 mol·L-1HNO3and the desired amount of Bi(NO3)3were added to another 40 mL of C2H5OH to form an ethanolnitric acid-water solution.Consequently,the Ti(O-Bu)4-C2H5OH solution was slowly added dropwise to the latter solution under vigorous stirring to carry out a hydrolysis.The obtained semitransparent solwas transferred to a 100 mL Teflon autoclave and kept at 140℃underauthigenicpressurefor6hfor hydrothermal treatment.Then,the autoclave was cooled to room temperature and the precipitates obtained were separated by centrifugation,washed thoroughly with deionized water and ethanol,dried at 90℃overnight,and calcined in air at 500 ℃ for 2 h.A TiO2sample was also prepared by the same procedure except without the addition of the bismuth precursor.

1.3 Photocatalyst characterization

The crystallographic properties were investigated by a Philips X′Pert PRO X-ray diffractometer usingCu Kα radiation(λ=0.15418 nm),in which an accelerating voltage of 40 kV and an emission current of 30 mA over the 2θ range of 10°～90°.The settings for XRD examination were as follows:divergence slit,1 mm;graphite monochromator;anti-scatterslit,2 mm;receiving slit,0.15 mm;scintillator detector.The particle size was estimated using the Scherrer equation.The morphologies were observed by a transmission electron microscopy (TEM,JEOL JEM-2010).N2adsorption-desorption isotherms were collected at 77 K by using Micromeritics ASAP 2020 Surface Area&Pore Size Analyzer.IR spectrum was recorded as KBr pellets on Bruker Fourier transform infrared(FTIR)spectrometer.The ultraviolet-visible diffuse reflectance spectra(UV-Vis DRS)of the samples in the wavelength range 250～750 nm were recorded using a spectrophotometer (Hitachi U-3010),with BaSO4as a reference.Surface electronic states were analyzed by X-ray photoelectron spectroscopy (XPS,Axis Ultra,Kratos analytical Ltd.)with Al Kα X-ray source.All binding energies were calibrated by using the contaminant carbon(C1s 284.6 eV)as a reference.The electron spin resonance (ESR)signals of radicals trapped by 3,4-Dihydro-2,2-dimethyl-2H-pyrrole 1-oxide(DMPO,CAS No:[3317-61-1])were detected at ambient temperature on a Bruker (E 500)spectrometer.The irradiation source was the same as used in the degradation of 4-CP.The settings for the ESR spectrometer were as follows:center field,3480 G;sweep width,100 G;microwave frequency,9.64 GHz;modulation frequency,100 kHz;power,10.05 mW.

1.4 Photocatalytic reaction

The photocatalytic degradation of4-CP was carried out at 25℃in an 75 mL self-designed glass photochemical reactor containing 0.050 g of catalyst and 50 mL of 1.0×10-4mol·L-14-CP aqueous solution.Prior to photoreaction,the suspension was magnetically stirred in dark for 30 min to establish an adsorption/desorption equilibrium.The suspension was vertically irradiated from the top by a 300 W Xenon lamp(Changtuo Instrumental Corporation of Beijing)at constantstirringspeed.AlltheUV lightswith wavelength shorter than 420 nm were removed by a glass filter(JB-420).At the given time intervals,the analytical samples were taken from the suspension and immediately centrifuged at 4 000 r·min-1for 10 min,then filtrate through a 0.22 μm Millipore filter to remove particles.The filtrate was analyzed by HPLC for the degree of 4-CP degradation.

The concentrations of 4-CP were measured by HPLC using an Agilent 1200 HPLC with a diode-array detector(G1315C)and a 1200 series binary pump.An Intersil ODS-3C-18,5 μm 4.6 ×250 mm column was used.Substances were routinely quantified from their absorbance at 280 nm.The eluent was 60%aqueous methanol and 40%phosphate buffer solution(0.1%,V/V).GC-MS data were obtained on an Agilent 6890 gas chromatograph using a 25 m 0.20 mm×0.33 μm DB-5 column,coupled with an Aglient 5985 mass spectrometer.The temperature program was as follows:at 50℃,hold time=6.5 min;from 50 to 200 ℃,rate=10℃·min-1.The injector port was set for split operation at 250℃.The samples after irradiation were filtered,and the filtrate was then concentrated by a rotary evaporator and freeze-dried overnight.The residue was finally redissolved in 0.1 mL anhydrous pyridine,followed by the addition of 0.1 mL hexamethyldisilazane and 0.05 mL of chlorotrimethylsilane[16].The silylated sample was further analyzed by GC-MS.

Total organic carbon was measured by a Tekmar Dohrmann Apollo 9000 TOC analyzer.The concentration of the chloride ions produced was determined using a chloride ion selective electrode.The K2HPO4was used for the buffer solution and to adjust the ionic strength.

2 Results and discussion

2.1 XRD,TEM and XPS characterization

XRD peaks at 2θ=25.28°and 2θ=27.40°are often taken as the characteristic peaks of anatase(101)and rutile(110)crystal phase,respectively.Fig.1 shows the XRD patterns of pure TiO2and modified samples with different bismuth contents.The percentage of anatase in the samples can be estimated from the respective integrated XRD peak intensities using the quality factor ratio of anatase to rutile (1.265),and the crystal sizescan also be calculated using the Scherrer equation[17].

From Fig.1,it can be seen that pure TiO2have significant diffraction peaks representing the characteristic of anatase phase around 2θ of 25.2°,37.9°,47.8°,53.8°,55.0°,62.1°,62.7°,68.8°,70.3°and 75.1°,respectively.However,about 19.6%of rutile was also detected,implying that there is some phase transformation in the present experimental conditions.Compared with pure TiO2,the modified TiO2with 0.5%or 1.0%bismuth exhibits lower rutile characteristic peak.These two samples contained about 12.4%and 5.5%rutile phase.When the bismuth content increases to 2.0%,or more than 2.0%,no rutile phase is detected in the bismuth-compounded TiO2samples.Theseresults demonstrate that the surface-modification with Bi can inhibiteffectively the phase transformation from anatase to rutile,which is favorable to the improvement of the anatase crystallinity.The high crystallization degree of anatase facilitates the rapid transfer of photoelectrons from bulk to the surface,which could effectively inhibit the recombination between photoelectrons and holes,leading to enhanced photocatalytic quantum efficiency[18].However,the crystallization degree and sizes of Bi2O3/TiO2decrease slightly with the increase of bismuth contents,as mainly evidenced by the intensity and the full width at the half maximum(FWHM)value of their characteristic XRD peaks.The reason may be that the presence of bismuth disturbs the crystallization process during calcination[19].

TEM images of TiO2nanoparticles uncompounded(A)and compounded with 2.0%Bi(B)are shown in Fig.2.The dispersion of TiO2nanoparticles is markedly improved by compounding Bi.It can be also seen that the both samples display similar spherical form,with the particle size of 20～25 nm and 10～15 nm,respectively,demonstrating that compounding Bi can inhibit the growth of TiO2nanoparticles.Additionally,individual particles sizes in Fig.2 are comparable with those obtained by the Scherrer equation (Table 1),which demonstrates the particles are mainly mono-disperse and non-agglomerate.

The XPS spectrum of 2.0%Bi-modified TiO2and the high-resolution XPS spectrum of Bi4f are shown in Fig.3.The peaks centered at 158.6 and 163.9 eV could be assigned to Bi4f7/2and Bi4f5/2region[20].The presence of Bi2O3exerts no significant influence on the XPS spectra in either the Ti2p or O1s orbitals.Moreover,the XRD peaks of Bi-compounded TiO2do not shift much compared with bare TiO2.These results demonstratethat the Bi2O3is present mainly as a separate phase,which is ascribed to the larger size of Bi atom(103 pm)than that of Ti atom(61 pm)[12].

2.2 Optical absorption properties of photocatalysts

The surface hydroxyl groups on titania have been recognized to play an importantrole on the photocatalytic reaction.Fig.4 shows the FTIR spectra of different TiO2samples diluted and pressed in KBr dics.The strong and broad IR band of curve a and b between 400～850 cm-1correspond to the Ti-O stretching vibration modes in crystal TiO2[21].With the increase in bismuth content,the additional peak around 489 cm-1appears due to the vibrations from Bi-O bonds[22],as displayed in curve c,d,e and f.The IR peak at 1 630 cm-1is ascribed to the bending vibration of O-H bonds of adsorbed water strongly bound to the catalyst surface[23-24].The broad absorption peaks near 3400 cm-1are attributed to the stretching mode of O-H bond,which is related to water molecules and crystal surface hydrogen bonding.Obviously,as the bismuth content of modified TiO2samples increases,the amount of surface hydroxylgradually increases.The largersurface hydroxyl group density will lead to the enhancement of the photocatalytic activity.Because the larger surface hydroxyl group can interact with photogenerated holes,giving bettercharge transferand inhibiting the recombination of electron-hole pairs.

As shown in Fig.5,the UV-Vis DRS spectra demonstrate that the pure TiO2displays no significant absorbance in the visible region due to the big energy gap (3.2 eV).With the introduction of Bi ions,the absorption edge shifts towards longer wavelengths(400～600 nm).The absorbance of Bi2O3/TiO2has similar intensity with the Bi content from 0.5%～2.0%.Meanwhile,further increase of the Bi content is bene-ficial to the light absorbance.The absorbance of Bi2O3/TiO2increases with Bi content,suggesting that the spectral response in the visible region mainly results from Bi2O3photosensitization[9].Briefly,the Bi2O3photo sensitizer with narrow energy gap (2.8 eV)could be easily activated by visible lights and induce photoelec-trons and holes.The photo-holes in bismuth oxide could easily transfer from the valence band (VB)of Bi2O3to the neighboring VB of TiO2[25].Thus,the Bi2O3-TiO2heterojunctions formed in the composite TiO2could effectively inhibit the recombination between photoelectrons and holes,leading to the strong response in visible area.

2.3 ESR signal analysis of DMPO-·OH

Spin-trapping ESR technique was employed to identify the possible short-lived reactive oxygen species involved in the photocatalytic systems.For this study,all the ESR spectra were recorded by the same irradiation as used in the photocatalytic degradation using DMPO as the radical trapping agent,and the ESR signals at different irradiation time are shown in Fig.6.

It can be seen from Fig.6,no ESR signals are observed when the photocatalysis is performed in the dark in the presence of catalyst and DMPO.Under visible light illumination,it is evident that in the pure TiO2system,no signal(1∶2∶2∶1 signals)of the DMPO-·OH radical adducts is observed during the degradation process (Fig.6A).Whereas,the generation of·OH species is confirmed by ESR technique when irradiated with visible light for the 2.0%Bi-TiO2system(Fig.6B)[26].The results may reveal why 2.0% Bi-TiO2exhibits much higher activity than bare TiO2.Moreover,the intensity of the peaks further increases with the increase of irradiation time and reaches stable state in 15 min,therefore the intensity of DMPO-·OH adduct peak produced in 20 min irradiation is similar to that in 15 min irradiation.

2.4 Photocatalytic degradation of 4-chlorophenol

In order to evaluate the photocatalytic activity of the prepared catalysts and find out the optimum content of Bi species,a set of experiments for 4-CP degradation under visible-light irradiation was carried out in and the results are shown in Fig.7A.The pure TiO2is rather inefficient since it could not be activated by visible lights due to a big energy band gap (3.2 eV).Modification of TiO2with Bi2O3results in abrupt increase of the photocatalytic activity owing to the Bi2O3-photosensitization.It is found that pseudo-firstorderkinetics is obeyed for the photocatalytic degradation of 4-CP.Therefore,the apparent first order kinetic Eq.(1)is used to fit the experimental data in Fig.7A.

Where kappis the apparent rate constant,C is the concentration of 4-CP remaining in the solution at irradiation time of t,and C0is the initial concentrationat t＝0.The variation in ln(C0/C)as a function of irradiation time are given in Fig.7B.The calculated data are given in Table 1.

The results ofFig.7B and Table 1 show that the effectiveness of the catalyst is strongly dependent on the amount of dopant ions.The 4-CP degradation efficiency after 7 h follows the order:2.0%Bi-TiO2＞4.0%Bi-TiO2＞ 5.0%Bi-TiO2＞ 1.0%Bi-TiO2＞ 0.5%Bi-TiO2.The experimental results are also related to BET specific surface area of Bi-modified TiO2.For instance,the BET specific surface area of 2.0%Bi-TiO2is 130 m2·g-1,which is much higher than 33 m2·g-1of bare TiO2.The larger specific surface area provides larger contact area and will lead to higher photo-degradation efficiency.Among the Bi-compounded TiO2,2.0%(wt)Bi-TiO2catalyst exhibits the highest activity under visible illumination.However,very high Bi content(＞2.0%)is harmful for the photocatalytic activity because of the agglomeration of the Bi2O3particles.The high Bi contents facilitates charge transport and reduces charge recombination,the large nanoparticles may act as the centers of electron-hole recombination and reduce quantum efficiency[27].

2.5 Mineralization and dechlorination

From an application perspective,analysis of degradation products is useful to estimate the efficiency of the photocatalytic technique,and it also may help reveal details of the chemical process taking place during the degradation and mineralization.To identify the intermediates of 4-CP degradation,GC-MS analysis was used.The unfunctionalized degradation mixture is not suitable for GC-MS analysis,so the mixtures were silylated with TMS groups.The GC-MS results demonstrate the hydroxylated intermediates,such as catechol,hydroquinone,4-chlorocatecholand 4-chlororesorcinol,were firstly generated during the photodegradation of 4-CP.The primary products mainly involves the addition of HO·to aromatic ring and substitution of chlorine by HO·.Subsequently,under the effect of HO·radicals,the hydroxylated intermediates were further oxidated and resulted in the formation of a series of low molecular weight carboxylic acids through the cleavage of benzene rings,which were also analyzed by GC-MS.The aliphatic intermediates are mainly dicarboxylic acids and substitutional dicarboxylic acids,such as oxalic acid,glycolic acid,malonic acid,maleic acid,succinic acid,fumaric acid,tartronic acid,malic acid and tartaric acid.In most instances,these structural assignments were confirmed with samples of authentic material that was processed in the same way that showing the same chromatographic and MS behavior.However,other reasonable pathways also maybe exist to get to these compounds.

Meanwhile,during the photocatalytic degradation of 4-CP,the attack of HO·to 4-CP may replace chlorine atoms and produced organic dicarboxylic acids before complete mineralization.To examine the extent of mineralization of 4-CP under visible light illumination,both removal yield of TOC and the quantity of inorganic chloride ions released were determined.

Temporal changes of TOC and variations in the concentration of Cl-are shown in Fig.8.The initial 4-CP contains 13.9 mg·L-1of TOC.After the adsorption of 4-CP on the 2.0%Bi-TiO2surface,the TOC values in the supernatants drop to 12.6 mg·L-1.The rate of TOC reduction is remarkably slower than that of 4-CP.About 62%of TOC still remains after 13 h irradiation when the release of Cl-occurrs to a greater extent during the degradation of4-CP.The maximum extentof dechlorination is ca.76%(1.52×10-4mol·L-1),which is close to the theoretical quantity of about 1.60 ×10-4mol·L-1(the quantity of 4-CP degradation).It can be concluded from this result that dechlorination of 4-CP is completed but about half of 4-CP is mineralized intoCO2and H2O.

2.6 Cyclic experiments

Based on the above results,one could conclude that 2.0%Bi modified-TiO2exhibit the highest activity under visible irradiation.Besides the high activity,the 2.0%Bi-TiO2also displays strong durability.As shown in Fig.9,only 3%decrease in activity is observed even after being used repetitively for 8 times,which demonstrates that this catalyst is quite stable during liquid-phase photocatalytic degradation.

2.7 Proposed mechanism and possible degradation pathway

In the absence of Bi2O3,the titania cannot be directly excited by visible light.Modification of TiO2with Bi2O3could prevent phase transition from anatase to rutile and lead to the strong spectral response in visible region,as indicated in Fig.1 and Fig.5.The abrupt increase of the photocatalytic activity of 4-CP degradation ascribes the Bi2O3-photosensitization.Briefly,the Bi2O3photosensitizer with narrow energy gap (2.8 eV)could be easily activated by visible light and induce photoelectrons and holes.In the absence of TiO2,these electrons and holes might recombine rapidly,leading to the quenching of spectral response.

In Bi2O3/TiO2system,the heterojunctions formed in the composite catalyst would promote the photogenerated holes in bismuth oxide to be transferred to the upper lying valence bands of titania,because the valence band of Bi2O3is lower than that of titania(as shown in Fig.10).The process is thermodynamically feasible[28].Therefore,the recombination between photoelectrons and holes could be effectively inhibited and much more holes are captured to generate hydroxyl radicals and/or further induce photocatalytic reactions.Accordingly,the distinct difference of ESR signals observed between the 2.0%Bi-modified TiO2and pure TiO2dispersions is understandable.As a result,the photocatalytic activity of Bi2O3/TiO2composite photocatalyst enhances a lot compared to the pure TiO2.Based on the identification of intermediate products,the degradative process of 4-CP firstly undergoes the hydroxylation or dechlorination reaction induced by active hydroxyl radicals.After that,these hydroxylated intermediates are oxidated and a series of dicarboxylic acids or substitutional dicarboxylic acids are generated.

3 Conclusions

Bi2O3/TiO2composite photocatalyst was synthesized by the sol-hydrothermal method and characterized by XRD,TEM,XPS,FTIR,UV-Vis DRS and ESR techniques.The promoted activity of such Bi2O3/TiO2mainly derives from the high anatase crystallinity,the optical response extent and the strong photosensitizing effect of Bi2O3.The enhanced photocatalytic activity of thematerialwasevaluated on the visible light photodegradation of 4-CP.TOC analysis shows that the mineralization of 4-CP over Bi2O3/TiO2photocatalyst is feasible.The analyses of degradation intermediates by GC-MS and the ESR signals reveal the possible pathways during the 4-CP photodegradation.

Acknowledgements:We are grateful to key Lab for Special Functional Materials,Ministry of Education,Henan University for the XPS and TEM measurement.

References:

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[1]Hoffmann M R,Martin S T,Choi W,et al.Chem.Rev.,1995,95:69-96

[2]Fujishima A,Rao T N,Tryk D A.J.Photochem.Photobiol.C:Rev.,2000,1:1-21

[3]ZHANG Xia(張霞),MENG Hao(孟皓),CAO Xiang-Hui(曹向會).Chinese J.Inorg.Chem.(Wuji Huaxue Xuebao),2009,25(11):1947-1952

[4]REN Ling(任凌),YANG Fa-Da(楊發(fā)達(dá)),ZHANG Yuan-Ming(張淵明),et al.Chinese J.Inorg.Chem.(Wuji Huaxue Xuebao),2008,24(4):541-546

[5]Kisch H,Sakthivel S,Janczarek M,et al.J.Phys.Chem.C,2007,111:11445-11449

[6]Paola A D,Palmisano L,Venezia A M,et al.J.Phys.Chem.B,1999,103:8236-8244

[7]Zhang H,Ouyang S,Li Z,et al.J.Phys.Chem.Solids,2006,67:2501-2505

[9]Bessekhouad Y,Robert D,Weber J.Catal.Today,2005,101:315-321

[10]Zhang L S,Wang W Z,Yang J,et al.Appl.Catal.A,2006,308:105-110

[11]Fox M A,Dulay M T.Chem.Rev.,1993,93:341-357

[12]Rengaraj S,Li X Z.Chemosphere,2007,66:930-938

[13]Wang J,Jing L Q,Xue L P,et al.J.Hazard.Mater.,2008,160:208-212

[14]Bian Z F,Zhu J,Wang S H,et al.J.Phys.Chem.C,2008,112:6258-6262

[15]Marc P T,Verónica G M,Miguel A B,et al.Appl.Catal.B,2004,47:219-256

[16]YANG Juan(楊娟),DAI Jun(戴俊),MIAO Juan(繆娟),et al.Acta Chim.Sinica(Huaxue Xuebao),2009,67(17):1973-1980

[17]Dohnal V,Fenclova D.J.Chem.Eng.Data,1995,40:478-483

[18]Zhang Q H,Gao L,Guo J K.Appl.Catal.B,2000,26:207-216

[19]Zhang J,Li M J,Feng Z C,et al.J.Phys.Chem.B,2006,110:927-935

[20]Schuhl Y,Baussart H,Delobel R,et al.J.Chem.Soc.Faraday Trans.,1983,79:2055-2061

[21]Lin Y H,Wang D J,Zhao Q D,et al.J.Phys.Chem.B,2004,108:3202-3206

[22]Dimitrov V,Dimitriev Y,Montenero A.J.Non-Cryst.Solids,1994,180:51-54

[23]Jing L Q,Fu H G,Wang B Q,et al.Appl.Catal.B,2006,62:282-291

[24]Zhang M H,Shi L Y,Yuan S,et al.J.Colloid Interf.Sci.,2009,330:113-118

[25]Gujar T P,Shinde V R,Lokhande C D.Mater.Res.Bull.,2006,41:1558-1564

[26]Zhao J,Wu T,Wu K,et al.Environ.Sci.Technol.,1998,32:2394-2400

[27]Xin J H,Zhang S M,Qi G D.React.Kinet.Catal.Lett.,2005,86:291-298

[28]Ao Y H,Xu J J,Fu D G,et al.Sep.Purif.Technol.,2008,61:436-441

Visible Light Photocatalytic Performance of Bi2O3/TiO2Nanocomposite Particles

YANG Juan＊LI Jian-Tong MIAO Juan
(Department of Physics and Chemistry,Henan Polytechnic University,Jiaozuo,Henan 454003,China)

Visible-light photoactive Bi2O3/TiO2catalysts were prepared by sol-hydrothermal process.The as-prepared samples were characterized by XRD,TEM,XPS,UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS),FTIR,N2adsorption-desorption and ESR.Compounding with low amounts of Bi2O3could effectively inhibit the phase transformation from anatase to rutile.UV-Vis DRS showed an extension of light absorption into the visible region.ESR results indicated that the active species(·OH)was generated with visible illumination (λ＞420 nm).It was found that the optimal dosage of bismuth was 2.0wt%.Proper amount of bismuth species compounded on the TiO2surface could improve the anatase crystallinity,which could inhibit the recombination between photoelectrons and holes,leading to enhanced photocatalytic quantum efficiency.Meanwhile,the enhanced visible-light activity was tested by the photocatalytic degradation of 4-chlorophenol(4-CP).Furthermore,the generated intermediates were identified using gas chromatograph-mass spectrometer and Bi2O3-photosensitization mechanism under visible light illumination was proposed.

bismuth oxide;TiO2;visible light;photocatalysis;4-chlorophenol

O643.3；O614.41

A

1001-4861(2011)03-0547-09

2010-10-08。收修改稿日期：2010-11-25。

國家自然科學(xué)基金(No.51074067)，河南省教育廳自然科學(xué)基金(No.2010B150009)資助項(xiàng)目。

＊通訊聯(lián)系人。E-mail：yangjuan0302@yahoo.cn