Enhanced Photocatalytic Hydrogen-Production Performance of Graphene-ZnxCd1-xS Composites by Using an Organic S Source

In response to the increasing concerns over energy and environmental sustainability, photocatalytic water-splitting technology has attracted broad attention for its application in directly converting solar energy to valuable hydrogen (H-2) energy. In this study, high-efficiency visible-light-driven photocatalytic H-2 production without the assistance of precious-metal cocatalysts was achieved on graphene-ZnxCd1-xS composites with controlled compositions. The graphene-ZnxCd1-xS composites were for the first time fabricated by a one-step hydrothermal method with thiourea as an organic S source. It was found that thiourea facilitates heterogeneous nucleation of ZnxCd1-xS and in situ growth of ZnxCd1-xS nanoparticles on graphene nanosheets. Such a scenario results in abundant and intimate interfacial contact between graphene and ZnxCd1-xS nanoparticles, efficient transfer of the photogenerated charge carriers, and enhanced photocatalytic activity for H-2 production. The highest H-2-production rate of 1.06mmolh(-1)g(-1) was achieved on a graphene-Zn0.5Cd0.5S composite photocatalyst with a graphene content of 0.5wt%, and the apparent quantum efficiency was 19.8% at 420nm. In comparison, the graphene-ZnxCd1-xS composite photocatalyst prepared by using an inorganic S source such as Na2S exhibited much lower activity for photocatalytic H-2 production. In this case, homogeneous nucleation of ZnxCd1-xS becomes predominant and results in insufficient and loose contact with the graphene backbone through weak van der Waals forces and a large particle size. This study highlights the significance of the choice of S source in the design and fabrication of advanced graphene-based sulfide photocatalytic materials with enhanced activity for photocatalytic H-2 production.