S

Ja

Nb

a

ARRAA

KPBTHM

1

taagieHf

ttSvdtsahsloa

0d

Applied Surface Science 257 (2011) 7381–7386

Contents lists available at ScienceDirect

Applied Surface Science

journa l homepage: www.e lsev ier .com/ locate /apsusc

tudy on highly visible light active Bi-doped TiO2 composite hollow sphere

ingjing Xua,∗, Mindong Chena, Degang Fub

Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, College of Environmental Science and Engineering,anjing University of Information Science & Technology, Nanjing 210044, ChinaState Key Laboratory of Bioelectronics, Southeast University, Nanjing 210096, China

r t i c l e i n f o

rticle history:eceived 26 September 2010eceived in revised form 28 January 2011ccepted 8 February 2011

a b s t r a c t

Bi-doped hollow titania spheres were prepared using carbon spheres as template and Bi-doped titaniananoparticles as building blocks. The Bi-doped titania nanoparticles were synthesized at low tempera-ture. The prepared hollow spheres were characterized by X-ray diffraction (XRD), transmission electronmicroscope (TEM), UV–vis diffuse reflectance spectrum (DRS) and X-ray photoelectron spectroscopy

vailable online 16 March 2011

eywords:hotocatalysisi-dopeditania

(XPS). The effects of Bi content on the physical structure and photocatalytic activity of doped hollowtitania sphere samples were investigated. Results showed that there was an optimal Bi-doped content(4%) for the photocatalytic degradation of methylene blue (MB).

© 2011 Elsevier B.V. All rights reserved.

ollow spheresethylene blue

. Introduction

Heterogeneous semiconductor photocatalytic process is one ofhe advanced oxidation technologies. It has received extensivettention for over two decades for purifying contaminated waternd air [1–6]. Among different semiconductors, titanium dioxide isenerally recognized as the most promising photocatalyst due tots biological and chemical inertness, strong oxidizing power, costffectiveness, long-term stability and environment friendly [1,2].owever, the performance of titania needs to be further enhanced

or practical application, due to its low quantum efficiency.Therefore, numerous works have been focused on enhancing

he photocatalytic performance by different ways. The first one iso couple titania with other semiconductors (such as CdS, ZnO, andiO2) [7–10] or with materials have large surface area (such as acti-ated carbon and mesoporous silica) [11–15], the second way is toope titania with metal ions such as Ag, Pt, and Au [16–20]. Thehird way is to prepare nano titania with different morphologiesuch as nanowires [21,22], nanotubes [23,24], nanorods [25,26]nd so on. Recently, fabrication of titania hollow microspheresas also attracted enormous attention because of their low den-

ity, large surface area, good surface permeability as well as highight-harvesting efficiencies [27]. On the other hand, for the sakef efficient utilization of sunlight, the technology of enlarging thebsorption scope of TiO2 appears as an appealing challenge. There-

∗ Corresponding author.E-mail address: xujj@seu.edu.cn (J. Xu).

169-4332/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.apsusc.2011.02.030

fore, the developing of new generation photocatalysts is important.Wang et al. investigated the preparation and photocatalytic activ-ity of lanthanide ions doped titania hollow sphere [28–30], and thedoped hollow spheres showed high photocatalytic activity undervisible light irradiation. However, to the best of our knowledge,there is no work focused on the preparation and phtocatalytic activ-ity of Bi-doped TiO2 composite hollow sphere.

Therefore, in the present work, we find a way for the preparationof Bi-doped TiO2 composite hollow sphere. Then, we studied theirphotocatalytic activity on decomposition of methylene blue (MB)in aqueous solution.

2. Experiment

2.1. Preparation of carbon spheres

The synthesis of colloidal carbon spheres is as following way,12 g of glucose was dissolved in 80 mL water to form a clear solution.The solution was then sealed in a 100 mL Teflon-lined autoclave andmaintained at 180 ◦C for 3 h. The samples were then centrifuged,washed by water and ethanol for several cycles, respectively. Theobtained carbon spheres were then dried at 80 ◦C for 4 h undervacuum.

2.2. Preparation of Bi-doped titania

Bi -doped titania was prepared as follows: 25 mL Ti (OBu)4diluted with 8 mL (i-PrOH) was dropwise added into aqueous solu-tion dissolved with definite bismuth nitrate, whose acidity was

7 e Science 257 (2011) 7381–7386

arwtmp

2

sstctwphr

2

Bm0wwN4paowcwpto

2

tm2mawb(

3

3

lsc4bts

visible light region enhanced as the doping content increased. Thisproperty would induce high photocatalytic activity to as-preparedsamples under visible light irradiation.

Quantitative XPS analysis is investigated on Bi-H-TiO2-3, and thetypical full survey spectrum is shown in Fig. 4(a). From the figure,

Table 1Different parameters of Bi-H-TiO2-1–Bi-H-TiO2-4.

Samples PWHMH Crystallite size (nm) Apparent rate constant(min−1)

382 J. Xu et al. / Applied Surfac

djusted with HNO3 (pH = 2.5). Then, the solution was kept undereflux condition (around 75 ◦C) for 24 h. Finally, Bi-doped TiO2 solas obtained after PrOH and n-butyl alcohol were removed from

he solution in a rotatory evaporator under vacuum. In our experi-ent, four samples with Bi atom percent of 1%, 2%, 4% and 6% were

repared.

.3. Preparation of Bi-doped hollow titania spheres (Bi-H-TiO2)

0.15 g carbon spheres were added into 30 mL Bi-doped titaniaol prepared by above mentioned method. The suspension wastirred for 6 h under vacuum condition. Then the solids were cen-rifuged, washed by water for 3 times. Thus, Bi-doped titania coatedarbon spheres were obtained. In order to produce Bi-doped hollowitania spheres of anatase, the titania-carbon composite particlesere calcined at 500 ◦C for 4 h in the air. Then the obtained sam-les were defined as Bi-H-TiO2-1–Bi-H-TiO2-4 for Bi-doped titaniaollow spheres with bismuth ion percent of 1%, 2%, 4% and 6%,espectively.

.4. Photocatalytic activity

In order to investigate the photocatalytic activity of as-preparedi-doped hollow titania spheres, degradation experiments ofethylene blue (MB) were studied under visible light irradiation.

.1 g of samples was dispersed into a 100 mL MB aqueous solution,hich initial dye concentration is 1 × 10−5 M and then irradiatedith a 250 W halogen lamp (Instrumental Corporation of Beijingormal University, with a light filter cutting off the light below00 nm) under continuous stirring. Before the irradiation, the sus-ension was maintained in the dark for 1 h to reach completedsorption–desorption equilibrium. The blank experiment with-ut catalysts was also investigated, and the value can be neglectedith less than 1.0% of conversion after 2 h illumination. The con-

entration of MB was determined by UV–vis spectra. Furthermore,e investigated the photocatalytic activity of the as-prepared sam-les under UV light irradiation. Under UV light, all conditions arehe same with that of visible light except the initial concentrationf MB (2 × 10−5 M).

.5. Characterization

The structure properties were determined by X-ray diffrac-ometer (XD-3A, Shimadazu Corporation, Japan) using graphite

onochromatic copper radiation (Cu–K�) at 40 kV, 30 mA over the� range 20–80◦. The morphologies were characterized by trans-ission electron microscopy (TEM, Hitachi, H-7650). The UV–vis

bsorption spectra of the hollow titania spheres were observedith Shimadzu UV-2100 equipped with an integrating sphere. The

inding energy was identified by X-ray photoelectron spectroscopyXPS) with Mg-K� radiation (ESCALB MK-II).

. Results and discussion

.1. Characterization of the samples

The phase structures of the as prepared Bi-doped titania hol-ow spheres were investigated by XRD method and the results arehown in Fig. 1. It can be seen that all samples exhibit only the

haracteristic peaks of anatase phase (major peaks: 25.4◦, 38.0◦,8.0◦, 54.7◦). No crystalline phase ascribed to bismuth oxides cane found since that the Bi content is below the detection limits ofhe XRD instrument, or the Bi species are dispersed well on theurface of titania nanoparticles. The average crystallite sizes can be

Fig. 1. XRD patterns of Bi-H-TiO2-1–Bi-H-TiO2-4.

calculated by applying the Debye–Scherrer formula on the anatase(1 0 1) diffraction peaks: [31]

D = K�

ˇ cos �(1)

where D is the crystalline size, � the wavelength of X-ray radia-tion (0.1541 nm), K the constant usually taken as 0.89, and ˇ isthe peak width (in radians) at half-maximum height (PWHMH)after subtraction of equipment broadening, 2� = 25.4◦ for anatasephase titania. From the figure we can see that the peak of 25.4◦

become wider and the intensity of this characterized peak becomelower as the doping amount of Bi ion increases. Therefore, wecan predict that the crystal size of the different samples wouldbecome smaller as the doping amount of Bi ion increases. The dataof PWHMH and the calculated average particle size are listed inTable 1. From the table, we can see that the size of the titania crys-tallites become smaller with the doping amount of Bi ion increases.It illustrates that Bi doping suppresses the crystallite growth ofanatase titania. This is because the adsorption of Bi species on thesurface of titania inhibits crystallites growth of titania nanoparti-cles. Fig. 2 shows the typical image of Bi-H-TiO2-2, it can be seenthat there is a strong contrast between the edges and centers,which indicates that the hollow structure of titania spheres hasbeen formed, though the samples didn’t show good monodisperseproperties.

To study the optical absorption properties of as-preparedsamples, UV–visible diffuse reflectance spectra in the range of200–750 nm were investigated, and the results are shown in Fig. 3.It can be seen that modification of titania with bismuth significantlyaffected the light absorption property of the photocatalysts. A redshift for Bi-H-TiO2 samples appears when compared to pure tita-nia (about 380 nm). Furthermore, we can see that the absorption in

Visible light UV light

Bi-H-TiO2-1 0.0086 16.7 0.009 0.021Bi-H-TiO2-2 0.0089 16.0 0.011 0.028Bi-H-TiO2-3 0.0094 15.1 0.028 0.049Bi-H-TiO2-4 0.0133 10.7 0.013 0.032

J. Xu et al. / Applied Surface Science 257 (2011) 7381–7386 7383

wCtsbabtBrw3aT[u

the variations in ln(C0/C) as a function of UV light irradiation.

Fig. 2. TEM image of Bi-H-TiO2-3.

e can see that the sample contains Ti, O, Bi and C elements. Theelement can be ascribed to the adventitious hydrocarbon from

he XPS instrument itself. Fig. 4(b) shows the high-resolution XPSpectra of Bi 4f region. The peaks around 164.1 eV and 158.9 eV cane assigned to Bi 4f5/2 and Bi 4f7/2 region, respectively. The resultsre in good agreement with Shamaila et al. [32], who ascribed theseinding energy values to Bi2O3. Therefore, we can also concludehat all the Bi species in our sample were present in the form ofi2O3. Furthermore, we investigated the state of Ti and its high-esolution XPS spectrum is also shown in Fig. 4. From the figure,e can see that there are two peaks assigned to 2p 1/2 and 2p

/2 existed in Ti 2p orbital. The Ti 2p1/2 and 2p 3/2 are located

t the binding energies of about 464.2 and 458.5 eV, respectively.he result is in good agreement with the reported literature values32–34]. This result illustrates that the Ti oxidation state remainnchanged.

Fig. 3. The UV–vis diffuse reflectance spectra of Bi-H-TiO2-1–Bi-H-TiO2-4.

3.2. Photocatalytic activity

Photocatalytic activity of the Bi-doped titania hollow spheresamples was investigated by photodegradation effect of MB inaqueous solution under UV or visible illumination. Fig. 5(a) showsthe variation of MB concentration as irradiation time in the pres-ence of difference of different samples under visible light. Thedegradation percents of MB are 56.0%, 63.0%, 90.9% and 70.6% forBi-H-TiO2-1, Bi-H-TiO2-2, Bi-H-TiO2-3 and Bi-H-TiO2-4 under vis-ible light irradiation, respectively. Fig. 6(a) shows variation of MBconcentration as irradiation time in the presence of difference ofdifferent samples under visible light. The degradation percent of MBare 73.1.0%, 83.1%, 95.9% and 87.7% for Bi-H-TiO2-1, Bi-H-TiO2-2, Bi-H-TiO2-3 and Bi-H-TiO2-4 under UV light irradiation, respectively.

The photocatalytic degradation is supported to follow pseudofirst-order reaction kinetics in the studied concentration range. Andreaction kinetics has often been described in terms of Langmuir-Hinshelwood model, which can be expressed as follows:

−dC

dt= kr

KaC

1 + KaC(2)

where (−dC/dt) is the degradation rate of MB, C is the MB con-centration in the solution, t is reaction time, kr is a reaction rateconstant, and Ka is the adsorption coefficient of MB. KaC is negligi-ble when value of C is very small. As a result, Eq. (2) can be describesa first-order kinetics. Setting Eq. (2) at the initial conditions of thephotocatalytic procedure, when t = 0, C = C0, it can be described asfollows:

ln(

C0

C

)= kapp × t (3)

where kapp is the apparent rate constant, used as the basic kineticparameter for the different photocatalysts, since it enables oneto determine a photocatalytic activity independent of the pre-vious adsorption period in the dark, and the concentration ofremaining MB in the solution. The variations in ln(C0/C) as a func-tion of irradiation time are given in Fig. 5(b), and the obtainedapparent rate constants are listed in Table 1. We can see thatthe photocatalytic activity follows the following trend: Bi-H-TiO2-3 > Bi-H-TiO2-4 > Bi-H-TiO2-2 > Bi-H-TiO2-1. Fig. 6(b) also shows

The obtained apparent rate constants are listed in Table 1 too.The rapid degradation of the MB under visible light irradiationis mainly ascribed to the Bi-doping of TiO2. While under visiblelight, it is different from that of UV irradiation. Since the Bi ions

7384 J. Xu et al. / Applied Surface Science 257 (2011) 7381–7386

Fig. 4. (a) XPS survey spectrum of Bi-H-TiO2-3 and (b) High-resolution XPS spec-trum of Bi 4f region and high-resolution XPS spectrum of Ti 2p region of Bi-H-TiO2-3.

Fig. 5. (a) Variation of MB concentration against time under visible light irradiation

in the presence of Bi-H-TiO2-1–Bi-H-TiO2-4 and (b) linear transform ln(C0/C) = f(t) ofthe kinetic curves of MB disappearance for Bi-H-TiO2-1–Bi-H-TiO2-4 from Fig. 5(a).

doing may introduces structural defects in TiO2, and changes theband-gap energy (this point can be seen from the UV–visible dif-fuse reflectance spectra results). Thus, the excitation energy isexpanded from UV to visible light. As a result, the presence of Biions in TiO2 accelerates the interfacial electron transfer process,and induces better photocatalytic activity. However, in our studieddoping range, results from photocatalytic experiments are not con-sistent with that of UV–visible diffuse reflectance spectra analysis.That is, more doping amount of Bi lead to more red-shift, but nothigher photo-activity. This can be explained that, too much amountof Bi would form recombination centers, where photo-inducedcarriers could be captured. That leads to lower photocatalyticactivity. In our experiment, the optimal doping content of Biis 4%.

4-chlorophenol (4-CP) was also chosen as model molecule toinvestigate the visible light photocatalytic activity of the as pre-pared samples. The results are shown in Fig. 7, it can be seenthat most 4-CP are decomposed after 3 h irradiation. Furthermore,the photocatalytic degradation percents follow the same trend as

MB degradation (i.e. Bi-H-TiO2-3 > Bi-H-TiO2-4 > Bi-H-TiO2-2 > Bi-H-TiO2-1). The results illustrate that Bi-doping indeed inducedvisible light effective activity to titania.

J. Xu et al. / Applied Surface Scien

Fig. 6. (a) Variation of MB concentration against time under UV irradiation in thepresence of Bi-H-TiO2-1–Bi-H-TiO2-4 and (b) linear transform ln(C0/C) = f(t) of thekinetic curves of MB disappearance for Bi-H-TiO2-1–Bi-H-TiO2-4 from Fig. 6(a).

Fig. 7. Variation of 4-CP concentration against time under visible light irradiationin the presence of Bi-H-TiO2-1–Bi-H-TiO2-4.

[

[

[

[

[

[

[

[

[

[

[

ce 257 (2011) 7381–7386 7385

4. Conclusions

In summary, a method has been presented for preparation ofBi-doped anatase hollow TiO2 spheres. The doping Bi atoms inhibitthe grain growth. The absorbance spectra of Bi-doped samplesexhibited significant red-shift to visible region. The photocatalyticactivity of as-prepared hollow titania spheres with different Bi-doped content was determined by degradation of MB and 4-CPunder visible light irradiation. Results show that the obtainedBi-doped titania hollow sphere samples are all with high photo-catalytic activity under visible light. In the present work, it is foundthat the optimal Bi-doped content is 4%.

Acknowledgments

We are grateful for grants from Open Foundation of State KeyLaboratory of Hydrology-Water Resources and Hydraulic Engi-neering (No. 2010490511) and the project supported by NanjingUniversity of Information Science & Technology (20100348).

References

[1] A. Fujishima, T.N. Rao, D.A. Tryk, Titanium dioxide photocatalysis, J. Photochem.Photobiol. C 1 (2000) 1–21.

[2] J. Herrmann, Heterogeneous photocatalysis: fundamentals and applications tothe removal of various types of aqueous pollutants, Catal. Today 53 (1999)115–129.

[3] M.R. Hoffmann, S.T. Martin, W.Y. Choi, D.W. Bahnemann, Environmental appli-cations of semiconductor photocatalysis, Chem. Rev. 95 (1995) 69–96.

[4] C. Wang, Y.H. Ao, P.F. Wang, S.H. Zhang, J. Qian, J. Hou, A simple method forlarge-scale preparation of ZnS nanoribbon film and its photocatalytic activityfor dye degradation, Appl. Surf. Sci. 256 (2010) 4125–4128.

[5] C. Wang, Y.H. Ao, P.F. Wang, J. Hou, J. Qian, A facile method for the preparationof titania-coated magnetic porous silica and its photocatalytic activity underUV or visible light, Colloid Surf. A 360 (2010) 184–189.

[6] X.L. Fu, X.X. Wang, Z.X. Ding, D.Y.C. Leung, Z.Z. Zhang, J.L. Long, W.X. Zhang, Z.H.Li, X.Z. Fu, Hydroxide ZnSn(OH)6: a promising new photocatalyst for benzenedegradation, Appl. Catal. B 91 (2009) 67–72.

[7] X.M. Song, J.M. Wu, M. Yan, Distinct visible-light response of composite filmswith CdS electrodeposited on TiO2 nanorod and nanotube arrays, Electrochem.Commun. 11 (2009) 2203–2206.

[8] N. Wang, X.Y. Li, Y.X. Wang, Y. Hou, X.J. Zou, G.H. Chen, Synthesis ofZnO/TiO2 nanotube composite film by a two-step route, Mater. Lett. 62 (2008)3691–3693.

[9] J. Bennani, R. Dillert, T.M. Gesing, D. Bahnemann, Physical properties, stability,and photocatalytic activity of transparent TiO2/SiO2 films, Sep. Purif. Technol.67 (2009) 173–179.

10] P. Wihelm, D. Stephan, Photodegradation of rhodamine B in aqueous solutionvia SiO2@TiO2 nano-spheres, J. Photochem. Photobiol. A: Chem. 185 (2007)19–25.

11] A.M. Busuioc-Tomoiaga, M. Mertens, P. Cool, N. Bilba, E.F. Vansant, A simple wayto design highly active titania/mesoporous silica photocatalysts, Stud. Surf. Sci.Catal. 174 (2008) 377–380.

12] L.F. Velasco, J.B. Parra, C.O. Ania, Role of activated carbon features on the pho-tocatalytic degradation of phenol, Appl. Surf. Sci. 256 (2010) 4170–4174.

13] D.Q. Mo, D.Q. Ye, Surface study of composite photocatalyst based on plasmamodified activated carbon fibers with TiO2, Surf. Coat. Technol. 203 (2009)1154–1160.

14] T. Cordero, C. Duchamp, J.M. Chovelon, C. Ferronato, J. Matos, Influence of L-type activated carbons on photocatalytic activity of TiO2 in 4-chlorophenolphotodegradation, J. Photochem. Photobiol. A: Chem. 191 (2007) 122–131.

15] T. Cordero, C. Duchamp, J.M. Chovelon, C. Ferronato, J. Matos, Surface nano-aggregation and photocatalytic activity of TiO2 on H-type activated carbons,Appl. Catal. B: Environ. 73 (2007) 227–235.

16] M. Wen, L.M. Zhou, W.M. Guan, Y.Q. Li, J.M. Zhang, Formation and bioactiv-ity of porous titania containing nanostructured Ag, Appl. Surf. Sci. 256 (2010)4226–4230.

17] K. Nishijima, T. Fukahori, N. Murakami, T. Kamai, T. Tsubota, T. Ohno, Develop-ment of a titania nanotube (TNT) loaded site-selectively with Pt nanoparticlesand their photocatalytic activities, Appl. Catal. A: Gen. 337 (2008) 105–109.

18] L.A. Pretzer, P.J. Carlson, J.E. Boyd, The effect of Pt oxidation state and concen-tration on the photocatalytic removal of aqueous ammonia with Pt-modifiedtitania, J. Photochem. Photobiol. A: Chem. 200 (2008) 246–253.

19] Q. Zhao, M. Li, J.Y. Chu, T.S. Jiang, H.B. Yin, Preparation, characterization of Au (orPt)-loaded titania nanotubes and their photocatalytic activities for degradationof methyl orange, Appl. Surf. Sci. 255 (2009) 3773–3778.

20] Q. Kang, L.X. Yang, Q.Y. Cai, An electro-catalytic biosensor fabricated with Pt–Aunanoparticle-decorated titania nanotube array, Bioelectrochemistry 74 (2008)62–65.

7 e Scien

[

[

[

[

[

[

[

[

[

[

[

[

386 J. Xu et al. / Applied Surfac

21] R.H. Tao, J.M. Wu, H.X. Xue, X.M. Song, X. Pan, X.Q. Fang, X.D. Fang, S.Y. Dai, Anovel approach to titania nanowire arrays as photoanodes of back-illuminateddye-sensitized solar cells, J. Power Source 195 (2010) 2989–2995.

22] B.X. Wang, Y. Shi, D.F. Xue, Large aspect ratio titanate nanowire prepared bymonodispersed titania submicron sphere via simple wet-chemical reactions, J.Solid State Chem. 180 (2007) 1028–1037.

23] Y.M. Xiao, J.H. Wu, G.T. Yue, G.X. Xie, J.M. Lin, M.L. Huang, The preparationof titania nanotubes and its application in flexible dye-sensitized solar cells,Electrochim. Acta 55 (2010) 4573–4578.

24] Y. Hou, X.Y. Li, P. Liu, X.J. Zou, G.H. Chen, P.L. Yue, Fabrication and photo-electrocatalytic properties of highly oriented titania nanotube arrays with{1 0 1} crystal face, Sep. Purif. Technol. 67 (2009) 135–140.

25] H.G. Yu, J.G. Yu, B. Cheng, J. Lin, Synthesis, characterization and photocatalyticactivity of mesoporous titania nanorod/titanate nanotube composites, J. Haz-ard. Mater. 147 (2007) 581–587.

26] R.H. Tao, J.M. Wu, H.X. Xue, W.W. Dong, Z.H. Deng, X.D. Fang, Pulsed laserdeposition of titania on rutile nanorod arrays, Thin Solid Film 518 (2010)4191–4196.

27] J.G. Yu, S.W. Liu, H.G. Yu, Microstructures and photoactivity of meso-porous anatase hollow microspheres fabricated by fluoride-mediated self-transformation, J. Catal. 249 (2007) 59–66.

[

[

ce 257 (2011) 7381–7386

28] C. Wang, Y.H. Ao, P.F. Wang, J. Hou, J. Qian, S.H. Zhang, Preparation, character-ization, photocatalytic properties of titania hollow sphere doped with cerium,J. Hazard. Mater. 178 (2010) 517–521.

29] C. Wang, Y.H. Ao, P.F. Wang, J. Hou, J. Qian, Photocatalytic performance of Gdion modified titania porous hollow spheres under visible light, Mater. Lett. 64(2010) 1003–1006.

30] C. Wang, Y.H. Ao, P.F. Wang, J. Hou, J. Qian, Preparation, characterization andphotocatalytic activity of the neodymium-doped TiO2 hollow spheres, Appl.Surf. Sci. 257 (2010) 227–231.

31] Z.H. Zhang, M.F. Hossain, T. Arakawa, T. Takahashi, Facing-target sputteringdeposition of ZnO films with Pt ultra-thin layers for gas-phase photocatalyticapplication, J. Hazard. Mater. 176 (2010) 973–978.

32] S. Shamaila, A.K.L. Sajjad, F. Chen, J.L. Zhang, Study on highly visible light activeBi2O3 loaded ordered mesoporous titania, Appl. Catal. B: Environ. 94 (2010)272–280.

33] M. Kang, Y.R. Ko, M.K. Jeon, S.C. Lee, S.J. Choung, J.Y. Park, S. Kim, S.H. Choi,Characterization of Bi–TiO2 nanometer sized particle synthesized by solvother-mal method and CH3CHO decomposition in a plasma-photocatalytic system, J.Photochem. Photobio. A: Chem. 173 (2005) 128–136.

34] M. Srinivasan, T. White, Degradation of methylene blue by three-dimensionallyordered macroporous titania, Environ. Sci. Technol. 41 (2007) 4405–4409.