Sunlight-driven photodegradation of organic pollutants catalyzed by TiO 2 /(ZnS) x (CuInS 2 ) 1x nanocomposites† Yuhan Lin, a Fang Zhang, b Daocheng Pan, * a Hexing Li * b and Yunfeng Lu * c Received 28th January 2012, Accepted 7th March 2012 DOI: 10.1039/c2jm30540b TiO 2 /(ZnS) x (CuInS 2 ) 1x nanocomposites were prepared from oleic acid-capped TiO 2 nanocrystals and alloyed (ZnS) x (CuInS 2 ) 1x nanocrystals. Element mapping and transmission electron micros- copy (TEM) results suggested that the nanocomposites exhibit homogeneous composition with uniform mesoporous structure. High photocatalytic activities driven by simulated solar light were ach- ieved owning to their high surface area and efficient electron transfer from (ZnS) x (CuInS 2 ) 1x to TiO 2 . This work enables the synthesis of a large variety of photocatalysts from nanocrystal building blocks for various applications beyond photodegradation of organic pollutants. Photocatalytic degradation of organic pollutants has been a hot topic for the past two decades. 1–7 In this context, TiO 2 has been extensively investigated as a photocatalyst owing to its high activity, high stability, low cost, and non-toxicity. 7–14 However, TiO 2 possesses a high band gap (3.2 eV) with low utilization of solar irradiation; developing visible-light-driven photocatalysts therefore has been receiving a great deal of attention. 15,16 To date, much effort has been devoted to address this challenge, such as doping TiO 2 with metal cations (e.g., Cr 3+ , Ni 3+ ,V 5+ , Ce 3+ , and Fe 3+ ). 17–22 Nonetheless, as an indirect-band-gap semiconductor, TiO 2 exhibits low absorption coefficients in comparison with direct-band-gap semiconductors such as CdS, CdSe, Sb 2 S 3 and PbS. An alternative strategy is to synthesize the nanocomposites containing TiO 2 and narrow-band-gap semi- conductors, such as CdS, CdSe, PbS, Sb 2 S 3 , and WO 3 . 23–30 For such nanocomposites, photoelectrons generated from these narrow-band- gap semiconductors may be effectively transferred to the TiO 2 conduction band, which enables more effective hole–electron sepa- ration with less recombination. Using this strategy, highly effective photocatalysts may be constructed by integrating low fractions of narrow-band-gap semiconductors with TiO 2 ; however, most of the nanocomposites reported so far do contain toxic components, such as Cd 2+ , Pb 2+ , Sb 3+ , and Se 2 , 23,26,28,31–33 which may cause secondary pollution. Herein, we report the synthesis of visible-light-driven nano- composites of TiO 2 and (ZnS) x (CuInS 2 ) 1x using their nanocrystals as the building blocks. CuInS 2 nanocrystals possess a band gap of 1.5 eV and high absorption coefficients in the range 10 4 to 10 5 cm 1 . The band gaps of alloyed (ZnS) x (CuInS 2 ) 1x nanocrystals can be readily tuned from 1.5 to 3.7 eV by simply tailoring the ZnS/CuInS 2 ratios, 34 which enables effective utilization of visible light. Moreover, such alloyed (ZnS) x (CuInS 2 ) 1x nanocrystals do not contain the above-mentioned toxic elements, making them good candidates for photodegradation applications. Fig. 1 shows UV/vis absorption spectra and a photograph (inset) of oleic acid-capped TiO 2 (5 nm) and alloyed (ZnS) x (CuInS 2 ) 1x (6 nm) nanocrystals dissolved in toluene. With increasing CuInS 2 content, the alloyed (ZnS) x (CuInS 2 ) 1x nanocrystals change their color from green, orange, red to black. Consistently, the band-edge absorption of the (ZnS) x (CuInS 2 ) 1x nanocrystals gradually red shifts with increasing CuInS 2 ratio. The optical band gaps of the (ZnS) x (CuInS 2 ) 1x nanocrystals were calculated and are listed in Fig. 3. The TiO 2 /(ZnS) x (CuInS 2 ) 1x nanocomposites were obtained by simple mixing of an appropriate amount of TiO 2 and (ZnS) x (CuInS 2 ) 1x nanocrystals in toluene. Solvent evaporation created homogeneous mixtures of the nanocrystals capped with oleic Fig. 1 UV/vis absorption spectra of oleic acid-capped TiO 2 and (ZnS) x (CuInS 2 ) 1x nanocrystals with different ZnS to CuInS 2 ratios (inset: the photograph of TiO 2 and (ZnS) x (CuInS 2 ) 1x nanocrystals dissolved in toluene). a State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun 130022, China. E-mail: pan@ciac.jl.cn b The Education Ministry Key Lab of Resource Chemistry and Shanghai Key Laboratory of Rare Earth Functional Materials, Shanghai Normal University, Shanghai 200234, China. E-mail: HeXing-Li@shnu.edu.cn c Department of Chemical Engineering, University of California, Los Angeles, CA, USA 90095. E-mail: luucla@ucla.edu † Electronic supplementary information: Chemical composition, XRD, and the control experiments of TiO 2 /(ZnS) x (CuInS 2 ) 1x nanocomposites. See DOI: 10.1039/c2jm30540b This journal is ª The Royal Society of Chemistry 2012 J. Mater. Chem., 2012, 22, 8759–8763 | 8759 Dynamic Article Links C < Journal of Materials Chemistry Cite this: J. Mater. Chem., 2012, 22, 8759 www.rsc.org/materials COMMUNICATION Downloaded by Shanghai Normal University on 13 April 2012 Published on 13 March 2012 on http://pubs.rsc.org | doi:10.1039/C2JM30540B View Online / Journal Homepage / Table of Contents for this issue