TiO2 nanotubes incorporated with CdS for photocatalytic hydrogen production from splitting water under visible light irradiation

international journal of hydrogen energy 35 (2010) 7073–7079

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TiO2 nanotubes incorporated with CdS for photocatalytic hydrogen production from splitting water under visible light irradiation Caolong Li a,b, Jian Yuan a, Bingyan Han a, Li Jiang a, Wenfeng Shangguan a,* a b

Research Center for Combustion and Environment Technology, Shanghai Jiao Tong University, Shanghai 200240, PR China Department of Applied Chemistry, Kunming University of Science and Technology, Kunming 650093, Yunnan, PR China

article info

abstract

Article history:

The CdS/TiO2 composites were synthesized using titanate nanotubes (TiO2NTs) with

Received 18 November 2009

different pore diameters as the precursor by simple ion change and followed by sulfuri-

Received in revised form

zation process at a moderate temperature. Some of results obtained from XRD, TEM, BET,

31 December 2009

UV–vis and PL analysis confirmed that cadmium sulfide nanoparticles (CdSNPs) incorpo-

Accepted 5 January 2010

rated into the titanium dioxide nanotubes. The photocatalytic production of H2 was

Available online 1 February 2010

remarkably enhanced when CdS nanoparticles was incorporated into TiO2NTs. The apparent quantum yield for hydrogen production reached about 43.4% under visible light

Keywords:

around l ¼ 420 nm. The high activity might be attributed to the following reasons: (1) the

Hydrogen production

quantum size effect and homogeneous distribution of CdSNPs; (2) the synergetic effects

Photocatalysis

between CdS particles and TiO2NTs, viz., the potential gradient at the interface between

CdS/TiO2

CdSNPs and TiO2NTs.

Nanotube

1.

ª 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Introduction

Photocatalytic water splitting over semiconductors is an effective and attractive method for converting solar energy into clean and renewable hydrogen fuel. Since water splitting over TiO2 photoelectrode was firstly reported by Fujishima and Honda in 1972 [1], many kinds of materials and derivatives are known to either catalyze overall water splitting or cause water oxidation or reduction in the presence of external redox agents [2]. However, up to now, TiO2 is still one of the most widely used photocatalysts due to it’s exceptional optical and electronic properties, strong oxidizing power, non-toxicity, chemical stability, and low cost [3]. Combining the properties of TiO2 nanoparticles with the open mesoporous morphology and high specific surface of layered titanates, titanate nanotubes (TiO2NTs) have also received

much attention in past 10 years [4,5]. The researches mainly focused on the synthesis of these nanotubes and their possible applications as substrate to be decorated with different active catalysts [6–8]. Crystalline cadmium sulfide (CdS) has smaller bandgap energy (2.42 eV) and can be used to induce photocatalytic water decomposition under visible light irradiation [9]. It is discovered that, by controlling the particle sizes, microstructure of CdS or by combining with some other layer compound or solid porous material, such as mesoporous silica [10,11], titanosilicate zeolite [11], titanate nanotubes [8] or layered metal oxides [12–15], some novel physical and chemical properties of CdS could be attained. The transportation of photogenerated carries between the energy band of CdS and TiO2NTs could prevent the recombination of charges and improve the photocatalysis activity [16]. Xiao reported [8] that

* Corresponding author. E-mail address: [email protected] (W. Shangguan). 0360-3199/$ – see front matter ª 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2010.01.008

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CdS nanoparticles decorated with titanate nanotubes was effective for the degradation of RhB, suggesting that combining CdS particles and TiO2NTs might result in synergetic effects in the photocatalytic reaction. We had reported [17] the successful preparation of CdS-intercalated metal compounds only by simple ion change and followed by sulfurization process, and indicated that the photocatalytic activity for hydrogen evolution of CdS-intercalated nanocomposites was superior to simple CdS and the physical mixture of CdS with metal oxides. However, it was found that H2 evolution on these photocatalysts resulted mainly from UV-light and less from visible light, although the absorption edge of the CdS-intercalated nanocomposites extended up to 550 nm [17]. Aim to make use of visible light and enhance the quantum efficiencies of photocatalytic reaction, we synthesized CdS/ TiO2NT composites with CdS inside or outside TiO2NTs starting from different pore diameter TiO2NTs and then by simple ion change and followed by sulfurization process at a moderate temperature for CdS incorporation. The prepared CdS/TiO2NT composites were characterized by XPS, XRD, TEM, BET, PL, and UV–vis absorption. H2 production through photocatalytic water splitting on the CdS/TiO2NT composite catalysts was investigated and discussed.

CdS/TiO2NT composites were prepared by ultrasonic stirring 500 mg of TiO2NTs-1 and TiO2NTs-2 in 50 ml of Cd(CH3COO)2 aqueous solution (0.2 M) at 50  C for 18 h, followed by rinsing with water and depositing in deionized water for 24 h, respectively. Then the obtained white titanate/Cd2þ nanotubes were dispersed in thiourea (NH2CSNH2) solution (0.2 M) at room temperature for 20 min and at 70  C for another 120 min with stirring. After thorough washing, depositing in deionized water for 24 h then drying at 90  C, light-yellow CdS/ TiO2NT composites (named as CdSTNT-1 and CdSTNT-2) were obtained [8,19]. ICP monitored that the CdSTNT-1 and CdSTNT-2 contains 13.44 wt% CdS and 8.32 wt% CdS, respectively. In addition, the physical mixture of 20 wt% neat CdS þ 80 wt% TiO2NTs-1 was used as a reference photocatalyst. For in situ photo-deposition of Pt onto various catalysts, as-synthesized neat CdS, the physical mixture, CdSTNT-1 and CdSTNT-2 were impregnated with an appropriate volume of aqueous solution containing a desirable amount of H2PtCl6$6H2O (1 mg ml1 Pt) and ethanol. The solutions were then illuminated for 5 h with visible light (l  420 nm), filtered and then dried in oven. The materials were used as the photocatalysts of water splitting.

2.2.

2.

Experimental

2.1.

Preparation of photocatalysts

The neat CdS photocatalyst was prepared by a precipitation method. A stoichiometric amount of 50 ml Cd(CH3COO)2 aqueous solution (0.2 M) was added drop-by-drop to thiourea (NH2CSNH2) solution (0.2 M) at room temperature and stirred at 70  C for 120 min. After thorough washing, deposited in deionized water for 24 h then dried at 90  C. Light-yellow CdS powders were obtained. Titanate nanotube [18] was synthesized with commercial Degussa P25 powder as starting material. 2 g P25 was added into 50 ml of 10 M NaOH solution to form a suspension. The suspension was placed in a Teflon-lined autoclave and heated at 160  C for 24 h. After cooled in air, the resultant precipitate was centrifugal separated at a speed of 10 000 rpm, thoroughly washed with 0.1 M HCl aqueous solution and subsequent distilled water for several times until the PH value of the eluate reached around 7. At last, the collected white powder was dried in an oven at 70  C overnight. It was denoted as TiO2NTs-1. For comparison, the following method was also used for preparing TiO2NTs. 4 ml tetrabutyl tianate was dropwise added to 50 ml of 10 M NaOH solution under stirring about 30 min. After stirring for half an hour, the suspended solution was transferred into a Teflon-lined autoclave and placed at 160  C for 24 h. After cooled naturally in air, the mixture was centrifuged at a speed of 10 000 rpm and the precipitates were collected. The white powder was thoroughly washed with 0.1 M HCl aqueous solution and distilled water. This operation was repeated until the washing water showed the PH value of 7. Lastly, the powder was dried 70  C. Nanotube prepared by this method was denoted as TiO2NTs-2.

Characterization

The UV–visible absorption was measured by using a UV–vis spectrophotometer (TU1901, China). The specific surface area was determined by the Brunauer–Emmett–Teller (BET) method at 77 K. Nitrogen adsorption–desorption isotherms were measured on a Quantachrome NOVA1000 Sorptomatic apparatus. Elemental Analysis was carried out on an Iris Advantage 1000 inductively coupled plasma analyzer (ICP). The XRD patterns were obtained with a Bruker D8 advance diffractometer using CuKa radiation. The transmission electron microscopy (TEM) measurements were conducted using a JEM-2010. The photoluminescence (PL) spectra were checked by using LS 50B (Perkin Elmer, Inc., USA).

2.3.

Photocatalytic reaction procedures

Photocatalytic hydrogen evolution was performed in a 300 ml top-irradiation Quartz or Pyrex cell at room temperature. The effective irradiation area for the cell is 28.26 cm2. The reaction cell was connected to a vacuum system, and the hydrogen evolved was analyzed by a thermal conductivity detector (TCD) gas chromatograph (China; GC-9200, MS-5A zeolite column, argon as a carrier gas). A 300 W Xe lamp was used as the light source, and the UV part of the light was removed by a cutoff filter (l  420 nm) when the process was carried out under visible light irradiation. Apparent quantum yields defined by equation (1) were measured using a 420 nm bandpass filter and an irradiatometer [9]. In the experiment, the irradiation power after the band-pass filter was determined to be 5.0 mW/cm2. A:Q:Y:ð%Þ ¼ ¼

number of reacted electrons  100 number of incident photons number of evolved H2 molecules  2  100 number of incident photons

(1)

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3.

Results and discussion

3.1.

X-ray diffraction

25000

The XRD patterns of the precursor Degussa P25, synthesized nanotubes, neat CdS and CdS/TiO2NT composites were shown in Fig. 1. Peaks marked ‘A’, ‘R’ and ‘O’ in Fig. 1 correspond to anatase phase, rutile and orthorhombic system of titanate respectively. The CdS/TiO2NT composites and TiO2NTs exhibit well-crystallized orthorhombic system, indicating that tube-like material was synthesized. Moreover, no diffraction peaks corresponding to anatase, rutile or brookite were observed. These results were in accordant with earlier reported results [20,21]. The transition of crystalline phase from anatase and rutile TiO2 to the orthorhombic system took place readily in the hydrothermal processes because titanate nanostructures possess large surface area and more defects. The peaks of the XRD profile are all quite broad, suggesting the small nanometer size dimensions of the tubes. TiO2NTs diffraction peaks could be detected on the XRD pattern of CdS/ TNT composites, while CdS diffraction peaks were not observed. It may be due to the formation of amorphous CdS or small size CdS particles, or the CdS incorporated into titanate nanotubes could not be irradiated by X-ray.

3.2.

XPS spectra

The chemical composition of sample CdSTNT-1 and the valence states of various species were determined by X-ray photoelectron spectroscopy. For the XPS spectra shown in Fig. 2, only peaks assigned to Cd, S, Ti, O and C electrons were identified. Carbon peak may originate from absorbed organic groups or molecules. XPS results confirmed that CdS were

O

O

O

A B C D A RA R

R

A

E

R

F 10

20

30

40

50

60

2θ / degree Fig. 1 – XRD patterns of the (A) CdSTNT-1, (B) TiO2NTs-1, (C) CdSTNT-2, (D) TiO2NTs-2, (E) P25 and (F) neat CdS. (O: orthorhombic, A: anatase and R: rutile).

Intensity (a.u)

20000 15000

O1s Ti2p

10000

Cd3d C1s

5000

S2p 0 1000

800

600

400

200

0

Binding Energy (eV) Fig. 2 – XPS spectra of CdSTNT-1 nanocomposite.

successfully incorporated with TiO2NTs of 3.55 wt% for CdSTNT-1. Compared with the ICP results referred above, the XPS result showed the lower amount of CdS. It may be due to that some CdS were incorporated into the TiO2NTs.

3.3.

Surface area and pore volume analysis

Specific surface areas of the samples were determined from the nitrogen absorption data measured at liquid nitrogen temperature using Brunauer–Emmett–Teller technique. Nitrogen adsorption/desorption isotherms and pore size distribution for the samples are presented in Fig. 3. The N2 isotherms for TiO2NTs-1 and CdSTNT-1 are typically BDDT Type III isotherm with a large type H3 hysteresis hoop [22] and a large uptake is observed when close to saturation pressure, where capillary condensation in the large voids among the aggregates of nanotubes starts. However, the N2 isotherms for TiO2NTs-2 and CdSTNT-2 were a type III isotherm with a large type H1 hysteresis hoop, indicating that they have even aperture distribution and regular shape of pore canal [22]. At the same time, the CdSTNT-1 isotherms was lower than TiO2NTs-1. And the BET surface area decreased from 346 m2/g of TiO2NT-1 to 287 m2/g of CdSTNT-1. This also happened for TiO2NTs-2 (320 m2/g) and CdSTNT-2 (230 m2/g). The above results indicated that the incorporation processes decreased the BET surface area and pore volume of TiO2NTs samples simultaneously, due to the covering of the CdS on the outside surface of TiO2NT-1 or on the inner wall of TiO2NTs-1. It could be concluded from BJH analysis (Fig. 3b) that the pore size distributions strongly depended on the methods of preparation of nanotubes. The TiO2NTs-1 sample showed trimodal mesopore size distributions, i.e., smaller mesopores with pore diameters of 3.0–4.0 nm and larger mesopores with pore diameters about 10–20 nm. While for CdSTNT-1, the pore volume decreased and the pore diameters shifted from about 10–20 nm to a smaller pore size distributions center about 7–9 nm, while the smaller mesopores with pore diameters of 3.0–4.0 nm remained unchanged. It may be due to that CdSNPs could incorporate into the TiO2NTs with bigger pores. However, TiO2NTs-2 and CdSTNT-2 showed uniform pores with the pore size distributions centered at 6 nm. The

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B

TiO2NT-1 CdSTNT-1 TiO2NT-2 CdSTNT-2

600 500

Dv(d)[cm3/g]

Va/cm3(STP)g-1

A

400 300 200 100 0 0.0

0.2

0.4

0.6

0.8

1.0

P/P0

0.015 0.014 0.013 0.012 0.011 0.010 0.009 0.008 0.007 0.006 0.005 0.004 0.003 0.002 0.001 0.000

TiO2NT-1 CdSTNT-1 TiO2NT-2 CdSTNT-2

10

100

1000

Dr/A

Fig. 3 – (A) Nitrogen adsorption/desorption isotherm, (B) corresponding BJH pore size distribution.

CdSTNT-2 pore size distributions center had no shift to the smaller scale. It may be due to that CdS was covered on outside surface of TiO2NT-2.

3.4.

Electron microscopic studies

Fig. 4 shows the TEM images of as-prepared TiO2NTs-1, TiO2NTs-2 and CdSTNT-1, CdSTNT-2 nanocomposites. The titanate nanotubes fabricated from commercial P25 were tubular materials with the length of several microns and the

diameter about 10–25 nm (Fig. 4A). The nanotubes possess a hollow inner pore with open tube ends, displaying disorder orientation. The diameter of the CdS nanoparticles incorporated into the TiO2NTs-1 was about 3w5 nm (Fig. 4C) and the image demonstrates that the CdS particles with more homogeneous dispersion and smaller size can be obtained inside the hollow cavity more easily than those particles formed outside or on the surface of TiO2NTs-1. The surface structures of concave shape might contribute to the formation of a ‘‘nest’’ on the inner surface of tubes. This structure

Fig. 4 – TEM images of samples (A) TiO2NTs-1, (B) TiO2NTs-2, (C) CdSTNT-1, (D) CdSTNT-2.

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promoted a uniform distribution of the small CdS particles which were strongly associated with the ‘‘nest’’, and restrained the aggregating and growing of these particles. Fig. 4B shows the TEM images of the titanate nanotubes fabricated from the tetrabutyl tianate. The tubular TiO2NTs-2 photocatalysts with the length about 50 nm and the diameter about 5 nm showed uniform pores. For the CdSTNT-2 photocatalyst in Fig. 4D, the CdS nanoparticles was not incorporated into the TiO2NTs-2. The regions of circle 1 and circle 2 may be CdS particles aggregated and grew into larger particles on the outside surface of TiO2NTs-2. This was consistent with the BET results.

titanate nanotubes [24]. In all cases, it could also be observed that the PL peaks were at the same position except the change of PL peak intensity between 510 nm and 625 nm and two emission peaks which appeared at around 525 nm and 580 nm. The high-energy band E1 may be attributed to near band edge emission arising from the recombination of CdS excitations, whereas the red-shift of the band E2 compared to the absorption spectrum is generally assigned to the excitations bound to ionized donors and/or the shallow trapped electron-hole pairs, showing the intrinsic character and the surface defects of the different morphologies CdS crystals, especially from the defects of the grain surface [25]. On the other hand, the fluorescence intensity in Fig. 5B suggests that the order of the photogenerated electron-hole recombination is as follows: CdSTNT-1 < CdSTNT-2. It might be concluded that the homogeneous distribution of CdS nanoparticles on the inner wall of TiO2NTs will result in the quick transference of the electrons into the surface of TiO2NTs in the CdSTNT-1. Consequently, the high production of H2 is generated.

3.5. Optical absorption and photoluminescence spectroscopy studies Fig. 5 A shows the UV–vis diffuse reflectance spectrum of CdSTNT-1 and CdSTNT-2. The spectra of CdS/TiO2NT composite photocatalysts showed an overlap of the spectra coming from CdSNPs and TiO2NTs. The spectra absorption from the 300–360 nm contributed by TiO2NTs was within ultraviolet region as shown in region I. The absorption band edge was extended to the visible region in region II by a small plateau from 360 to 420 nm, indicating that the absorption of TiO2NTs can be sensitized with CdSNPs. The above results suggested that the CdS/TiO2NT composites could be a promising visible light photocatalyst. Owing to the homogeneous distribution of CdS particles about 3w5 nm attached on the inner wall of TiO2NTs, the absorption band edge of CdSTNT-1 was also slight blue-shift compared to that of CdSTNT-2. It is well known that, absorption intensity has a linear correlation with amount of absorption materials. Reversely, in this system, the absorption intensity of CdSTNT-1 (ICP: 13.44 wt% CdS) is lower than that of CdSTNT-2 (ICP: 8.32 wt% CdS), which further demonstrated that the CdS nanoparticles incorporated into the TiO2NTs-1. The CdS/TiO2NT composites can emit visible light at room temperature with excitation wavelength 398 nm. Fig. 5B shows photoluminescence (PL) spectra of CdSTNT-1 and CdSTNT-2, which demonstrate the interactions between CdSNPs and TiO2NTs. The results suggested that CdSTNT-1 and CdSTNT-2 share an emission band between 450 and 500 nm, which is assigned to the oxygen vacancies at various energies during the process of preparation [23]. Ma et al. have also reported the presence of oxygen vacancies in undoped

3.6.

Photocatalytic hydrogen production

The photocatalytic activity over various Pt-loaded catalysts for hydrogen production is shown in Fig. 6 A. The reaction was performed with an aqueous solution containing 0.35 M Na2SO3 and 0.25 M Na2S as sacrificial reagents under visible light irradiation (l  420 nm). The photocatalytic processes are presented as follows. The first main reaction is the photoinduced reaction on the semiconductor:  
hv420 nm CdSNP=TiO2 NT þ hv ƒƒƒƒƒƒƒƒ ƒ! CdSNP hþ =TiO2 NT e

The second reaction is the reduction of protons in the solution to hydrogen by photoelectrons and the holes are consumed to oxidize sulfide ion to elemental sulfur:
TiO2 NT 2e þ 2H2 O/H2 þ 2OH

(3)

 2 þ þ SO2 3 þ 2OH þ 2h /SO4 þ 2H

(4)

S2 þ 2hþ /S Or S2 2

(5)

Otherwise, the elemental sulfur is converted to soluble thiosulfate ion by a reaction with the sulfite ion:

A 100

B

E2

E1

PL Intensity (a.u.)

Refectance

80

60

40

CdSTNT-1

CdSTNT-2

CdSTNT-1

20

CdSTNT-2 0 300

400

500

wavelength /nm

600

(2)

700

500

550

wavelength /nm

Fig. 5 – (A) UV–visible diffuse reflectance spectra, (B) PL spectra.

600

650

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The average of hydrogen evolution (μmol / h)

500 450 400 350 300 250 200

The amount of hydrogen evolution ( μmol)

international journal of hydrogen energy 35 (2010) 7073–7079

B

5000

A

(a)

(a)

4000

3000

2000

(b) (c)

1000

(d) 0 0

2

4

6

8

(c) 100

10

12

14

16

Time / h

150

(b)

(d)

50 0

Fig. 6 – (A) The average rate of H2 evolution and (B) the amount of H2 evolved vs irradiation time in 10 ml 0.35 M Na2SO3, 10 ml 0.25 M Na2S and 5 ml 0.1 mg/ml Pt H2PtCl6$6H2O aqueous solution; 300-W Xe lamp; l ‡ 420 nm on various photocatalysts: (a) CdSTNT-1; (b) CdSTNT-2; (c) the physical mixture of 20 wt% CdS D 80 wt% TiO2NT-1; (d) a neat CdS powder. Photocatalyst: 0.15 g.

S þ SO2 3 /S2 O3

(6)

For CdSTNT-1 photocatalyst, in which CdS was incorporated into the TiO2NTs-1, it was observed that the average rate of hydrogen evolution was equal to 402 mmol/h, which was about one order of magnitude higher compared to that obtained from neat CdS, and was 3.8 times and 3.4 times compared to that of the physical mixture of 20 wt% CdS þ 80 wt% TiO2NTs-1 and CdSTNT-2, respectively. The apparent quantum yields at 420 nm wavelength on CdSTNT-1 attained at about 43.4%. From these results, it can be concluded that incorporation of CdSNPs into titanate nanotubes may act as an important role for hydrogen production. The time courses of hydrogen production were showed in Fig. 6B. CdSTNT-1 photocatalyst showed linear increase and highest hydrogen production during the whole photocatalytic reactions and the total amounts of H2 produced after the continuous 13 h reaction were 5118 mmol. The hydrogen evolution rates of CdSTNT-2 were a slight lower than CdSTNT1 at the beginning of reaction. While it underwent a rapid decrease of photocatalytic activity after reaction for 4 h, the hydrogen evolution rates is about one order of magnitude lower, compared to that obtained from initial hydrogen evolution rates. It is explained that CdS distributed on outside surface of TiO2NT-2 may play the role of catalysis at the beginning of reaction. During the proceeding of photocatalytic reaction, CdS lost its activity due to the photo-corrosion process. However, for CdSTNT-1, the consecutive photocatalytic activity under the experiment condition implied the stability against photo-corrosion of CdS growth inside TiO2NT. Possible reasons for the superior photocatalytic activity of the CdSTNT-1 hetero-structure photocatalyst were small size and homogeneous distribution of CdS particles which were synthesized on the inner wall of TiO2NTs. These CdS particles will contribute to an efficient electron-hole pairs separation and the electrons fast transport. Moreover, in such system, the distance that the photoinduced holes and electrons have

to diffuse before reaching the interface decreased. Because of the decreased distance, the holes and electrons can be effectively captured by the electrolyte in the solution [13]. The same phenomenon was also reported in previous study [14,17]. Furthermore, interfacial area between TiO2NTs and CdSNPs particles was enlarged due to the larger surface area and the concave shape of inner wall of TiO2NTs, while the contact area decreased in outside surface of TiO2NTs which has a convex shape. This might result from the easy formation of the potential gradient at the interface between CdSNPs and TiO2NTs. Park [26] also reported similar theory of potential gradient. In addition, the flat band potential of the components, the photocatalytic performance of the couple is also related to the geometry of the particles, the surface contact between particles and the particles size [27]. In this study, the promotion effect of the CdS incorporated into the TiO2NTs compounds may result from the formation of micro heterojunctions between the CdS nanoparticles which are inside of the tube and the TiO2NTs. The conduction bands of TiO2NTs and CdSNPs were suitably disposed for electrons transfer, which cause electrons transfer from the CB of CdSNPs to that of TiO2NTs when CdSNPs is excited by visible light. Thus, the recombination between the electrons and the holes was effectively depressed. From the discussion above, it might be concluded that there is a synergetic effect between TiO2NTs and CdSNPs. The holes remain in CdSNPs and react with hole scavengers of sulfide and sulfite ions. In sum, it can be concluded that in order to operate more efficiently for this system, the size and homogeneous distribution of individual compound and close contact between two compounds both play important roles.

4.

Conclusions

The CdS/TiO2NTs composite photocatalyst, in which CdS with homogeneous distribution was incorporated inside the TiO2NTs, has been successfully fabricated to develop a highly active photocatalyst for hydrogen production from water containing sulfide and sulfite ions as hole scavengers under visible light irradiation. The apparent quantum yield was quite high for hydrogen production in the experimental condition, which resulted from a synergetic effect of CdS particles and TiO2NTs. The potential gradient at the interface between CdSNPs and TiO2NTs helped to facilitate the diffusion of photoelectrons generated from CdS particles toward TiO2NTs, and led to high photocatalytic activity of hydrogen production. The prepared catalyst in this study is found to be feasible and attractive for use in further design and preparation of other photocatalytic water splitting materials.

Acknowledgements The study was supported by the National Key Basic Research and Development Program (No. 2009CB220000) and the National High Technology Research and Development Program of China (2007AA05Z155).

international journal of hydrogen energy 35 (2010) 7073–7079

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