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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...

The use of graphene to enhance the efficiency of photocatalysts has attracted much attention. This is because of the unique optical and electrical properties of the two-dimensional (2-D) material. This review is focused on the recent significant advances in the fabrication and applications of graphenebased hybrid photocatalysts. The synthetic strategies for the composite semiconductor photocatalysts are described. The applications of the new materials in the degradation of pollutants, photocatalytic hydrogen evolution and antibacterial systems are presented. The challenges and opportunities for the future development of graphene-based photocatalysts are also discussed.

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A facile one-step microwave-assisted chemical method has been successfully used for the synthesis of Cu2O/reduced graphene oxide (RGO) composites. Photocatalytic CO2 reduction was then investigated on the junction under ambient conditions. The RGO coating dramatically increases Cu2O activity for CO2 photoreduction to result in a nearly six times higher activity than the optimized Cu2O and 50 times higher activity than the Cu2O/RuOx junction in the 20th hour. Furthermore, an apparent initial quantum yield of approximately 0.34 % at 400 nm has been achieved by the Cu2O/RGO junction for CO2 photoreduction. The photocurrent of the junction is nearly double that of the blank Cu2O photocathode. The improved activity together with the enhanced stability of Cu2O is attributed to the efficient charge separation and transfer to RGO as well as the protection function of RGO, which was proved by XRD, SEM, TEM, X-ray photoelectron spectroscopy, photo-electrochemical, photoluminescence, and impedance characterizations. This study further presents useful information for other photocatalyst modification for efficient CO2 reduction without the need for a noble-metal co-catalyst.

Photocatalysis provides a cost effective method for both renewable energy synthesis and environmental purification. Photocatalytic activity is dominated by the material design strategy and synthesis methods. Here, for the first time, we report very mild and effective photo-deposition procedures for the synthesis of novel Fe2 O3 -TiO2 nanocomposites. Their photocatalytic activities have been found to be dramatically enhanced for both contaminant decomposition and photoelectrochemical water splitting. When used to decompose a model contaminant herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D), monitored by both UV/Vis and total organic carbon (TOC) analysis, 10% Fe-TiO2 -H2 O displayed a remarkable enhancement of more than 200 % in the kinetics of complete mineralisation in comparison to the commercial material P25 TiO2 photocatalyst. Furthermore, the photocurrent is nearly double that of P25. The mechanism for this improvement in activity was determined using density functional theory (DFT) and photoluminescence. These approaches ultimately reveal that the photoelectron transfer is from TiO2 to Fe2 O3 . This favours O2 reduction which is the rate-determining step in photocatalytic environmental purification. This in situ charge separation also allows for facile migration of holes from the valence band of TiO2 to the surface for the expected oxidation reactions, leading to higher photocurrent and better photocatalytic activity.

Co-catalyst loading provides an effective way to enhance the efficiency of photocatalysts for solar hydrogen production. From a sustainability point of view, it has immense scientific and technological values to explore more efficient co-catalytic systems by using multi-cocatalysts, because of potential synergetic effects between different components. Herein, the feasibility of using Ti3C2 MXene nanoparticles and Pt nanoclusters as dual co-catalysts to enhance the photoactivity of g-C3N4 for H2 production was investigated. Due to the improved electrical conductivity and increased reactive sites for photoreduction reactions, Ti3C2 and Pt co-modified photocatalysts exhibited a high photocatalytic hydrogen production activity of 5.1 mmol h-1 g-1. Compared to g-C3N4/Ti3C2 and g-C3N4/Pt, the 3- and 5-fold increased photoactivity demonstrated great potential of Ti3C2 MXene nanoparticles to construct high-performance photocatalysts. The synergetic effects between Ti3C2 and Pt were fundamentally investigated, indicating that the specific transfer of electrons not only contributed to the inhibited recombination of charge carriers but also resulted in good stability of heterostructured photocatalysts. Our results have demonstrated an approach worthy for the design and fabrication of high-efficiency heterostructures with superior photoactivity for hydrogen energy production.

Although possessing high activity for solar hydrogen production, exploring robust Cu 2 O-based photocatalysts remains a challenging task due to its intrinsic drawback of susceptible oxidation. Herein, we present a strategy to stabilize Cu 2 O by modulating the exposed facets and structural defects of TiO 2 . Both experimental characterizations and theoretical calculations proved that surface oxygen vacancies in 101-faceted TiO 2 could create conducting channels for denoting electrons to Cu 2 O, mimicking the Z-scheme charge transfer in natural photosynthesis. Due to the defect-enhanced charge separation and the effective scavenging of oxidative holes in Cu 2 O, Cu 2 O/TiO 2 heterostructures with exposed {101} facets and oxygen vacancies exhibited 251-fold increased activity for solar water splitting, together with unpredicted photostability. In contrast, defect-induced isolated states in the bulk of 001faceted TiO 2 led to the formation of Type II Cu 2 O/TiO 2 junction with moderate photoactivity and poor stability. Thus, our work not only provides insights into the facet-and defect-dependent interfacial mechanism in heterostructured nanocatalysts but also opens up a promising avenue for developing high-performance noble-metal-free photocatalysts for energy conversion applications.