Cu₂ZnSnS₄-Pt and Cu₂ZnSnS₄-Au Heterostructured Nanoparticles for Photocatalytic Water Splitting and Pollutant Degradation

Abstract

Cu 2 ZnSnS 4 , based on abundant and environmental friendly elements and with a direct band gap of 1.5 eV, is a main candidate material for solar energy conversion through both photovoltaics and photocatalysis. We detail here the synthesis of quasi-spherical Cu 2 ZnSnS 4 nanoparticles with unprecedented narrow size distributions. We further detail their use as seeds to produce CZTS-Au and CZTS-Pt heterostructured nanoparticles. Such heterostructured nanoparticles are shown to have excellent photocatalytic properties toward degradation of Rhodamine B and hydrogen generation by water splitting. C urrent functional nanomaterials must meet numerous very demanding properties that cannot be realized with a unique compound. Thus, the use heterostructured nanomaterials or nanocomposites is generally required in a wide range of applications. In such multiphase materials, not only the properties of the compounds but also those of their interface have a determinant influence over their performance. In particular, an efficient photocatalytic system requires an intimate interface between two phases, a light-absorbing semiconductor and a co-catalyst. Such hybrid materials can be produced with composition control at the nanometer scale through the direct growth in solution of one of the compounds from the surface of the other, which acts as a seed.1 Such direct growth of the heterostructured nanomaterial ensures a fast and efficient charge transfer between the two phases.Solar energy conversion to electricity or its storage in renewable fuels is a particularly interesting application requiring the development of high-performance, environmental friendly, and cost-effective heterostructured materials. While several semiconductors have been proposed to harvest sunlight, 2 Cu 2 ZnSnS 4 (CZTS) uniquely combines both outstanding optoelectronic properties, with a direct band gap energy of 1.5 eV, and a composition based on elements that abound in the Earth's crust. Such an environmental friendly and low-cost material has been demonstrated to be an excellent light absorber in photovoltaic devices and to have a large potential for photodegradation of pollutants and for photocatalytic generation of hydrogen and other value-added chemicals.3 CZTS and related quaternary nanocrystals can currently be produced by different procedures. 4 However, due to the difficulties in tuning the composition, phase, size, and shape of such complex materials, the preparation of CZTS-based heterostructures and particularly CZTS-metal hybrid nanoparticles has not yet been achieved.In the present work, we detail a procedure to produce colloidal CZTS-metal heterostructured nanoparticles with strongly electrically coupled interfaces. Au and Pt were the metals chosen due to their potential for plasmonic enhancement (Au) and a proper over-potential for hydrogen generation (Pt) (Scheme 1). Heterostructures were tested for photodegration of pollutants in solution using Rhodamine B as the model system, and for photocatalytic hydrogen generation from wate...

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