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2008 Cetyltrimethylammoniumbromide (CTAB)-assisted hydrothermal of ZnIn2S4 for hydrogen production

Cetyltrimethylammoniumbromide (CTAB)-assisted hydrothermal synthesis of ZnIn 2S 4as an ef?cient

visible-light-driven photocatalyst for hydrogen production

Shaohua Shen,Liang Zhao,Liejin Guo *

State Key Laboratory of Multiphase Flow in Power Engineering,School of Energy and Power Engineering,Xi’an Jiaotong University,Xianning West Street 28#,Shaanxi 710049,PR China

a r t i c l e i n f o

Article history:Received 4April 2007Received in revised form 6May 2008

Accepted 11May 2008

Available online 16August 2008Keywords:ZnIn 2S 4

Visible-light-driven photocatalyst Hydrogen Hydrothermal

a b s t r a c t

A series of ZnIn 2S 4photocatalysts was synthesized via a cetyltrimethylammoniumbromide (CTAB)-assisted hydrothermal method.These ZnIn 2S 4products were characterized by X-ray diffraction (XRD),UV–visible absorption spectra (UV–vis)and scanning electron microscopy (FESEM).The effects of hydrothermal time and CTA

B on the crystal structures,morphologies and optical properties of ZnIn 2S 4products were discussed in detail.The photocatalytic activities of the as-prepared samples were evaluated by photocatalytic hydrogen production from water under visible-light irradiation.It was found that the photocatalytic activities of these ZnIn 2S 4products decreased with the hydrothermal time prolonging while increased with the amount of CTAB increasing.The highest quantum yield at 420nm of ZnIn 2S 4photocatalyst,which was prepared through the CTAB (9.6mmol)-assisted hydrothermal procedure for 1h,was determined to be 18.4%.The optimum amount of Pt loaded for the ZnIn 2S 4photocatalyst was about 1.0wt%,under the present photocatalytic system.

a2008International Association for Hydrogen Energy.Published by Elsevier Ltd.All rights

reserved.

1.Introduction

The photocatalysis of H 2O into H 2and O 2via aqueous suspensions of semiconductor powders has drawn increasing attention in recent years,as noted in several reviews [1–3].Numerous photocatalysts reportedly exhibit high photo-catalytic activities for hydrogen production from water,including NaTaO 3[4],Sr 2Nb 2O 7[5],La 2Ti 2O 7[6],La 4CaTi 5O 17[7],and K 2La 2Ti 3O 10[8].However,these oxide photocatalysts are only active under UV light,which occupies only 5%of the solar spectrum at the earth surface.Therefore,it is indis-pensable to develop a visible-light-driven photocatalyst,taking the solar spectrum into account.Recently,many efforts have been made to explore novel photocatalysts for water

splitting under visible light.Although different kinds of visible-light-driven photocatalysts [9–12]have been reported,the number of photocatalysts working in the visible-light region is limited and highly ef?cient photocatalysts have not been developed so far.

Sul?des,which have narrow band gaps and valence bands at relatively negative potentials compared to oxides,can be good candidates for visible-light-driven photocatalysts.However,sul?de photocatalysts such as CdS are not stable for water splitting,because photocorrosion will be induced when photogenerated holes oxidize the photocatalyst itself.Although incorporation of metal sul?des into interlayers [12]or mesoporous materials [13]was ef?cient for stabilizing the metal sul?des and producing hydrogen from water,the

*Corresponding author .Tel.:t862982663895;fax:t862982669033.E-mail address:lj-guo@https://www.sodocs.net/doc/0210071424.html, (L.

Guo).

A v a i l a b l e a t w w w.s c i e n c e d i r e c t.c o m

j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /h e

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photocatalytic ef?ciency was still low.Recently,several multicomponent sul?des have been reported to show high photocatalytic ef?ciency[14–16],informing that multicom-ponent sul?des may be a new class of ef?cient visible-light-driven photocatalysts.

Ternary sul?des ZnIn2S4,as the only member of the AB2X4 family semiconductor with a layered structure,has attracted far-ranging interests because of its potential applications in different?elds such as charge storage[17],thermoelectricity [18],photoconduction[19]and so on.In2003,Lei et al.[20] synthesized ZnIn2S4by a simple hydrothermal method and ?rstly treated ZnIn2S4as an ef?cient visible-light-driven photocatalyst for hydrogen production.In our previous research[21–23],ZnIn2S4also showed quite good photo-catalytic and photoelectrochemical properties.Thus,ZnIn2S4 turned to be a good candidate for hydrogen production from water under visible-light irradiation.In the present study,we synthesized a series of ZnIn2S4photocatalysts via a cetyl-trimethylammoniumbromide(CTAB)-assisted hydrothermal method.The effects of hydrothermal time and CTAB on the crystal structure,morphology,optical property and photo-catalytic activity of ZnIn2S4products were discussed in detail.

2.Experimental

2.1.Synthesis of ZnIn2S4

All chemicals are analytical grade and used as received without further puri?cation.ZnIn2S4products were prepared by a CTAB-assisted hydrothermal method[24].In a typical proce-dure,different amounts of cetyltrimethylammoniumbromide (CTAB),0.735g of ZnSO4$7H2O,1.615g of In(NO3)3$4H2O and a double excess of thioacetamide(TAA)were dissolved in50mL of distilled water.The mixed solution was then transferred into a70mL Te?on-lined autoclave.The autoclave was sealed and kept at160 C for different hours,and then cooled to room temperature naturally.A yellow precipitate was obtained, which was then?ltered and washed with absolute ethanol and distilled water for several times.After drying in vacuum at 80 C,ZnIn2S4was obtained,labeled as ZIS-x-y(x:amount of CTAB,0–9.6mmol;y:hydrothermal time,1–48h).

2.2.Characterization

The X-ray diffraction(XRD)patterns were obtained from a PANalytical X’pert MPD Pro diffractometer using Ni-?ltered Cu K a irradiation(wavelength1.5406A?)with the scanning step of 0.2 /s.The operation voltage and current were40kV and40mA, respectively.UV–visible absorption spectra of the samples were determined on a Hitachi U-4100UV–vis–near-IR spectropho-tometer with BaSO4as the reference.The scanning range was from300to700nm.The morphology of ZnIn2S4products was also characterized by a scanning electron microscope(JEOL JSM-6700FE),in which the accelerating voltage was5kV.

2.3.Evaluation of photocatalytic activity

Photocatalytic hydrogen evolution was performed in a side-irradiation Pyrex cell.A300-W Xe lamp was used as the light source,and the UV part of the light was removed by a cut-off ?lter(l>430nm).Hydrogen evolved was analyzed by an online thermal conductivity detector(TCD)gas chromato-graph(NaX zeolite column,nitrogen as a carrier gas).In all experiments,180mL of deionized water containing0.2g of catalyst and0.25M Na2SO3/0.35M Na2S mixed sacri?cial agent was added into the reaction cell.Here,sacri?cial agent was used to scavenge photogenerated holes.Nitrogen was purged through the cell before reaction to remove oxygen.Pt as a cocatalyst for the promotion of hydrogen evolution was photodeposited in situ on the photocatalyst from the precursor of H2PtCl6$6H2O.The temperature for all the pho-tocatalytic reactions was kept at35?5 C.Control experi-ments showed no appreciable H2evolution without irradiation or photocatalyst.Apparent quantum yields de?ned by Eq.(1)were measured using a420nm band-pass?lter and an irradiatometer.The energy conversion ef?ciency in the visible-light region(using300W Xe lamp combined with a430nm cut-off?lter)was determined by Eq.(2).

A:Q:Y:e%T?The number of reacted electrons

The number of incident photons

?100

?The number of evolved H2molecules?2?100

(1)

h C?

D G0

R P

E S A

(2)

In Eq.(2),D G0

is the standard Gibbs energy for the energy-storage reaction generating product H2,R P is the rate(mol sà1) of generation of H2in its standard state,E S is the incident visible-light irradiance(W mà2)and A is the irradiated area(m2).

3.Results and discussion

3.1.Structure characterization

The phase and crystallographic structure of the ZnIn2S4 products were determined by powder X-ray diffraction(XRD). Fig.1A(a–e)shows the XRD patterns of the ZnIn2S4products obtained through a CTAB(1.8mmol)-assisted hydrothermal route at160 C for1–48h(ZIS-1.8-y,y?1–48h),respectively. The XRD patterns of all the products present similar pro?les and all the diffraction peaks can be indexed to a hexagonal phase of ZnIn2S4(ICSD-JCPDS card No.01-072-0773,a?3.85A?, c?24.68A?).No other impurities such as ZnS,In2S3,oxides or organic compounds related to reactants were detected,indi-cating the phase-purity of ZnIn2S4.Moreover,the XRD patterns of ZIS-1.8-1(Fig.1A(a))indicate that the ZnIn2S4 product obtained by our synthesis method is of high phase-purity even in a very short time reaction.The apparently broadening of the peaks indicates that the products are composed of small nanocrystalline particles.It is noted that the position of peak(006)is shifted slightly to higher angle with the hydrothermal time increasing,as shown in Fig.1B, which results in the decreasing of d(006)space.This may be due to the more compact layered structure of the ZnIn2S4 products synthesized via a longer time hydrothermal reac-tion,as the ZnIn2S4products possess a layered structure along the c-axis,as shown in Fig.3.That is to say,hydrothermal time

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could affect the crystal structure of ZnIn 2S 4products prepared under the present synthetic condition.

Fig.2A gives out the XRD patterns of ZnIn 2S 4products hydrothermally prepared at 160 C for 1h with different amounts of CTAB in the synthetic condition (ZIS-x -1,x ?0–9.6mmol).Fig.2A (a)shows the XRD pattern of ZnIn 2S 4products obtained under hydrothermal condition without CTAB,while Fig.2A (b–e)are the spectra of CTAB-assisted ZnIn 2S 4samples.Despite of different amounts of CTAB,the diffraction peaks of all the samples can also be indexed to a pure hexagonal phase of ZnIn 2S 4.However,the corre-sponding intensities of a few diffraction peaks among the products are dissimilar in some cases.For example,the peaks of (104)and (108)are discernible in ZnIn 2S 4prepared without CTAB (ZIS-0-1),while these peaks are not visible for the other ZnIn 2S 4products synthesized under CTAB-assisted hydro-thermal condition.This dissimilarity may be attributed to the difference in their microstructures.Moreover,by checking the

position of peak (006)shown in Fig.2B,one can easily ?nd that this peak would shift to low angle with the addition of CTAB in the synthesis procedure,and even further shift to lower angle with the amount of CTAB increasing.The same phenomena can be found in the XRD patterns of the ZnIn 2S 4products in previous literature [24].This means that CTAB would insert into the layered crystal structure and expand the interlayer space along the c -axis of the ZnIn 2S 4products during the hydrothermal synthetic process.Such shift of peak (006)predicts that the crystal structure of ZnIn 2S 4products can be also affected by the addition of different amounts of CTAB in the hydrothermal condition.

As a consequence,ZnIn 2S 4products with pure hexagonal phase could be easily synthesized under present hydro-thermal condition,but the hydrothermal time and CTAB amount would affect the crystal structures of the obtained

10203040506070

800

500100015002000250030003500400045005000

550060006500

e d c b (213)(202)

(1012)

(112)

(108)

(104)

(102)

a: ZIS-0-1b: ZIS-0.7-1c: ZIS-1.8-1 d: ZIS-4.5-1e: ZIS-9.6-1

I n t e n s i t y / a .u .

2 Theta / degree

(006)

I n t e n s i t y / a .u .

2 Theta / degree

a b c d e A

Fig.2–XRD patterns of ZnIn 2S 4products synthesized by hydrothermal method with different amounts of CTAB for assistance:(a)0mmol;(b)0.7mmol;(c)1.8mmol;(d)4.5mmol;(e)9.6mmol.

20304050607080

0500100015002000250030003500400045005000

5500600065007000e d c b (213)

(202)

(1012)

(112)

(108)

(102)

I n t e n s i t y / a .u .

2 Theta / degree

a: ZIS-1.8-1b: ZIS-1.8-6c: ZIS-1.8-12d: ZIS-1.8-24e: ZIS-1.8-48

(006)

1516171819202122232425

I n t e n s i t y / a .u .

2 Theta / degree

b c d e

Fig.1–XRD patterns of ZnIn 2S 4products synthesized by hydrothermal method for different times:(a)1h;(b)6h;(c)12h;(d)24h;(e)48h.

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ZnIn 2S 4products.Shift of peak (006)in the XRD patterns means different d (006)spaces of ZnIn 2S 4.Fig.3shows the crystal structure of the layered ZnIn 2S 4,in which the stacking of atoms along the c -axis is in a repeated sequence of S-Zn-S-In-S-In-S [25].The cell parameters of ZnIn 2S 4are

a ?

b ?3.85A

?,c ?24.68A ?.As we know,the d (006)space is consistent with one sixth of the lattice constant along the c -axis of the ZnIn 2S 4structure.Thus,it can be concluded that the hydrothermal time and CTAB amount would affect the c -axis growth of ZnIn 2S 4.

3.2.Morphology

The representative FESEM images of ZnIn 2S 4products obtained through a hydrothermal route for 1–48h (ZIS-1.8-y ,y ?1–48h)are shown in Fig.4,indicating the hydrothermal time made a great effect on the morphologies of ZnIn 2S 4products.Fig.4A,B gives out the morphology of ZnIn 2S 4synthesized by a 1-h hydrothermal procedure.Interestingly,the ZnIn 2S 4crystallites self-organized into microspheres comprising of numerous ZnIn 2S 4petals.Under the reported condition,the ZnIn 2S 4microspheres were quite uniform with diameters ranging from 1to 2m m.Similar morphology has been observed in CdIn 2S 4by Kale et al.[26].With the hydro-thermal time prolonging,ZnIn 2S 4still presented to be uniform microspheres with diameters of 1to 2m m (ZIS-1.8-6in Fig.4C,D and ZIS-1.8-12in Fig.4E,F),which were also comprised of numerous petals.However,when the hydrothermal route was kept for 24h,the obtained ZnIn 2S 4product (ZIS-1.8-24)mainly presented to be microclusters (Fig.4G,H).For the ZnIn 2S 4product obtained through a 48-h hydrothermal reaction (ZIS-

1.8-48),a mixture of different morphologies,including microclusters and micro?owers,was observed.Both micro-clusters and micro?owers were organized from ZnIn 2S 4petals (shown in Fig.4I).However,the petals in micro?owers were constructed by a large number of nanoparticles –the sizes of the nanoparticles were quite uniform and about 100nm (shown in Fig .4J).The observed morphology changing with the processing time indicated that the ZnIn 2S 4crystallites could easily self-organize into numerous ZnIn 2S 4petals and further aggregate to microspheres,however,the longer hydrothermal time would hinder the assemblage of ZnIn 2S 4microspheres,and ZnIn 2S 4crystallites would develop to be larger nanoparticles.Such an important effect of hydro-thermal time on the morphology,observed ?rstly for the ZnIn 2S 4photocatalyst,has not been reported hitherto.

Fig.5shows the FESEM images of ZnIn 2S 4products synthesized in hydrothermal condition with the assistance of different amounts of CTAB (ZIS-x -1,x ?0–9.6mmol).All these ZnIn 2S 4products presented to be similar microspheres comprising of numerous ZnIn 2S 4petals.Without CTAB,the obtained ZnIn 2S 4microphere (ZIS-0-1)was quite open and puffy,the gap between petals was observed in the range of 200–600nm (Fig.5B)and the petals were slightly curved.For the CTAB-assisted ZnIn 2S 4products,the gap between petals was in the range of 100–200nm,suggesting the more compact and dense microsphere-like morphology as compared to ZIS-0-1.Additionally,it was found that the petals of CTAB-assisted ZnIn 2S 4products (ZIS-x -1,x ?0.7–9.6mmol)were much more curved than those of ZIS-0-1,that is to say,the curvature of the petals was further accelerated by the assistance of CTAB under the reported hydrothermal condition.However,the reason and detailed mechanism for such morphology differ-ence of ZnIn 2S 4products are not yet well understood.

3.3.Optical properties

Fig.6(a–e)shows the UV–vis diffuse re?ectance spectra of ZnIn 2S 4products obtained through a hydrothermal route for 1–48h (ZIS-1.8-y ,y ?1–48h),respectively.These ZnIn 2S 4products show almost the same absorption pro?le with absorption edge at about 510nm.The band gap of these ZnIn 2S 4products was determined to be 2.43eV.The steep shape of the visible edge and the strong absorption in the visible region also reveal that the absorption band of ZnIn 2S 4is ascribed to the transition from the valence band to the conduction band [16],but not due to the transition from the metal impurity level to the conduction band [27,28].Thus,the steep absorption edge reveals single phase ZnIn 2S 4,which is in good agreement with our XRD results.

The effects of CTAB on the optical properties of ZnIn 2S 4products are demonstrated in Fig.7.The absorption edge of obtained ZnIn 2S 4product without the assistance of CTAB (ZIS-0-1)was at 540nm,while the CTAB-assisted ZnIn 2S 4products (ZIS-x -1,x ?0.7–9.6mmol)presented the approximating absorption edge at 510nm.The slight shift of absorption edge for CTAB-assisted samples may be due to the small crystallite size and different particle morphology [29].The band gaps of ZIS-0-1and CTAB-assisted ZnIn 2S 4were determined to be 2.30and 2.43eV,

respectively.

Fig.3–The crystal structure of layered ZnIn 2S 4.

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Fig.4–FESEM images of ZnIn 2S 4products synthesized by hydrothermal method for different times:(A,B)1h;(C,D)6h;(E,F)12h;(G,H)24h;(I,J)48h.

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Fig.5–FESEM images of ZnIn 2S 4products synthesized by hydrothermal method with different amounts of CTAB for assistance:(A,B)0mmol;(C,D)0.7mmol;(E,F)1.8mmol;(G,H)4.5mmol;(I,J)9.6mmol.

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3.4.Photocatalytic activity

Photocatalytic hydrogen productions over various obtained ZnIn 2S 4photocatalysts were evaluated.Control experiments showed no appreciable hydrogen evolution without irradia-tion or photocatalyst.To improve the photocatalytic activity of hydrogen evolution,Pt as a cocatalyst should be loaded on the photocatalyst to provide active sites for hydrogen production [30–32].

3.4.1.Effect of hydrothermal time

As discussed above,the hydrothermal time made important effects on the crystal structures and morphologies of ZnIn 2S 4products.Photocatalytic hydrogen productions over ZIS-1.8-y

(y ?1–48h)photocatalysts are given in Figs.8and 9.During the 15-h photocatalytic reaction process,these ZnIn 2S 4pho-tocatalysts showed quite stable photocatalytic activities for hydrogen evolution under visible-light irradiation,the rates of hydrogen evolution were determined to be 91.65,72.56,66.51,51.58and 22.49m mol h à1for ZIS-1.8-1,ZIS-1.8-6,ZIS-1.8-12,ZIS-1.8-24and ZIS-1.8-48,respectively.With the hydro-thermal time prolonging,the photocatalytic activities of ZIS-1.8-y (y ?1–48h)photocatalysts decreased,as shown in Fig.9.Table 1gives out the crystal structure parameters,rates of hydrogen production and quantum yields of various ZnIn 2S 4photocatalysts.According to the data in Table 1,we can observe that the longer hydrothermal time results in the smaller d (006)spaces and hence lower photocatalytic activi-ties of hydrogen production over ZIS-1.8-y (y ?1–48h)

0300

600900

1200

1500

Reaction time / h

H y d r o g e n E v o l u t i o n / μm o l

Fig.8–Hydrogen evolution over ZnIn 2S 4photocatalysts synthesized by hydrothermal method for different times:(a)1h;(b)6h;(c)12h;(d)24h;(e)48h.

0.00.2

0.4

0.6

0.8

1.0

1.2

A b s / a .u .

Wavelength / nm

Fig.7–UV–vis spectra of ZnIn 2S 4products synthesized by hydrothermal method with different amounts of CTAB for assistance:(a)0mmol;(b)0.7mmol;(c)1.8mmol;(d)4.5mmol;(e)9.6mmol.

300

400

500

600

700

0.00.20.4

0.6

0.8

1.0

1.2

A b s / a .u .

Wavelength / nm

Fig.6–UV–vis spectra of ZnIn 2S 4products synthesized by hydrothermal method for different times:(a)1h;(b)6h;(c)12h;(d)24h;(e)48h.

100

Hydrothermal time / h

R a t e o f h y d r o g e n e v o l u t i o n / μm o l ?h -1

Fig.9–Rates of hydrogen evolution over ZnIn 2S 4

photocatalysts synthesized by hydrothermal method for different times.

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photocatalysts.Fig.10A shows the relationship between d spaces of peak (006)and quantum yields of ZIS-1.8-y (y ?1–48h)photocatalysts.The photocatalytic activities of ZIS-1.8-y (y ?1–48h)photocatalysts increase with the d (006)space increasing,which may be due that the increasing d (006)space could promote the photogenerated charge separation in ZnIn 2S 4photocatalysts.In the hexagonal structure of ZnIn 2S 4,the atoms are arranged in layers at six equally separated levels along the c -axis.Each of Zn ion is in a tetrahedral environment of four S atoms (ZnS 4),In ions are in two envi-ronments,octahedral environment of six S atoms (InS 6)and tetrahedral environment of four S atoms (InS 4).The unit cell of

crystal structure is c ?24.68A

?,thus the d (006)space should be determined to be 4.11A

?,according to the ZnIn 2S 4crystal structure (Fig.3).The XRD results revealed that the d (006)space increased with hydrothermal time shortening,implying the increasing extent of distortion in ZnIn 2S 4structure.The correlation between the photocatalytic activity and the structure distortion has so far been reported for some metal oxide photocatalysts [33–36].It has been demonstrated that the metal oxides consisting of distorted structure unit with dipole moment are photocatalytically active for water decomposition,whereas distortion-free oxides exhibited negligible activity.Thus,it can be deduced that the distortion of ZnIn 2S 4structure with dipole moment is also associated to the photocatalytic activity,as the internal ?elds due to the dipole moment are considered to be useful for electron-hole separation upon photoexcitation [37].

On the other hand,hydrothermal time has a great in?u-ence on the morphologies of ZnIn 2S 4photocatalysts prepared in the reported synthetic condition,and then the different morphologies of ZIS-1.8-y (y ?1–48h)photocatalysts could be another factor affecting the photocatalytic activity.ZIS-1.8-y (y =1–12h)photocatalysts with microsphere-like morphology have the higher photocatalytic activities,as compared to ZIS-1.8-y (y ?24–48h)photocatalysts,which present micro-clusters instead of microspheres.That is to say,the micro-sphere morphology would be advantageous to improve the photocatalytic activity of ZnIn 2S 4photocatalyst in some extent.

3.4.2.Effect of CTAB assistance

Fig.11makes it clear that the photocatalytic activities of ZnIn 2S 4photocatalysts can be ef?ciently enhanced when synthesized under the assistance of CTAB in the reported synthetic condition.However,as the amount of CTAB further increased,the photocatalytic activity increased but slowly.Table 1gives out the crystal structure parameters,rates of hydrogen production and quantum yields of the ZIS-x -1(x ?0–9.6mmol)photocatalysts.As discussed on the ZIS-1.8-y (y ?1–48h)photocatalysts (Fig.10A),a similar relationship between d (006)spaces and quantum yields was observed for the ZIS-x -1(x ?0–9.6mmol)photocatalysts (Fig.10B).Fig.10B proves again that the increasing d (006)space as one key factor could improve the photocatalytic activity of ZnIn 2S 4photocatalyst.

The UV–vis spectra show that the band gaps of ZnIn 2S 4photocatalysts were enlarged under the assistance of CTAB in the hydrothermal condition.It is commonly accepted that a larger band gap energy corresponds to a more powerful

4.26 4.28 4.30 4.32 4.34 4.36 4.38 4.40 4.42 4.44 4.46

681012141618

Q u a n t u m y i e l d / %

d (006) / ?

8101214161820

Q u a n t u m y i e l d / %

d (006) / ?

A B Fig.10–Relationship between d (006)spaces and quantum yields of ZnIn 2S 4photocatalysts synthesized by

hydrothermal method (A)for different times,and (B)with different amounts of CTAB for assistance.

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redox capability [38,39].Since the CTAB-assisted ZnIn 2S 4photocatalysts (ZIS-x -1,x ?0.7–9.6mmol)have larger band gaps than the ZIS-0-1photocatalysts,their reducing abilities should be stronger,which results in the higher photocatalytic activity of CTAB-assisted ZnIn 2S 4photocatalysts as compared to the ZIS-0-1photocatalyst.

3.4.3.Effect of Pt loaded

In order to optimize the amount of Pt loaded,different amounts of Pt were photodeposited on the ZIS-1.8-1photo-catalyst.Fig.12shows the photocatalytic rates of hydrogen production over Pt-loaded ZIS-1.8-1photocatalysts.The rate of naked ZIS-1.8-1photocatalyst was only 10m mol h à1.As Pt was loaded,the rate of hydrogen production increased greatly.In particular,the 1.0wt%Pt-loaded ZIS-1.8-1photocatalyst shows a 11-fold increase of hydrogen production as compared

to the naked ZIS-1.8-1photocatalyst,and the hydrogen production rate amounts to 110m mol h à1.While the amount of Pt further increased,the rate of hydrogen production could be hardly enhanced,and even decreased when 3.0wt%Pt was loaded on the ZIS-1.8-1photocatalyst.Thus,it can be concluded that the optimum amount of Pt loaded is about 1.0wt%for the ZnIn 2S 4photocatalyst,under the present photocatalytic system.

Conclusions

A series of ZnIn 2S 4as ef?cient visible-light-driven photo-catalysts for hydrogen production has been prepared via a CTAB-assisted hydrothermal method.In the reported synthetic condition,the hydrothermal time and the amount of CTA

B have important effects on the crystal structures,morphologies,optical properties and photocatalytic activities of the obtained ZnIn 2S 4photocatalysts.

(1)With hydrothermal time prolonging,the d (006)space of

ZnIn 2S 4is reduced and the microsphere-like morphology of ZnIn 2S 4is destroyed,and hence the photocatalytic activities of ZnIn 2S 4photocatalysts are lowered markedly.(2)With the assistance of CTAB in the hydrothermal condi-tion,the photocatalytic activity of obtained ZnIn 2S 4can be improved ef?ciently as compared to the ZnIn 2S 4synthe-sized without CTAB.As the amount of CTAB increases,the d (006)space of ZnIn 2S 4increases correspondingly.The band gap of obtained ZnIn 2S 4photocatalyst can also be enlarged in the CTAB-assisted hydrothermal condition.(3)For the obtained ZnIn 2S 4photocatalyst,the optimum

amount of Pt loaded is about 1.0wt%,under the present photocatalytic system.

Acknowledgement

The authors gratefully acknowledge the ?nancial supports of the National Natural Science Foundation of China (No.50521604)and National Basic Research Program of China (No.2003CB214500).

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020*********

120140R a t e o f H 2 e v o l u t i o n / μm o l ?h -1

Amount of Pt / wt%

Fig.12–Rates of hydrogen evolution over ZnIn 2S 4

photocatalysts with different amounts of Pt loaded.

100

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Amount of CTAB / mmol

Fig.11–Rates of hydrogen evolution over ZnIn 2S 4

photocatalysts synthesized by hydrothermal method with different amounts of CTAB for assistance.

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2008 Cetyltrimethylammoniumbromide (CTAB)-assisted hydrothermal of ZnIn2S4 for hydrogen production

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