Enhanced photocatalytic hydrogen-production performance of graphene-Zn(x)Cd(1-x)S 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 (H2) energy. In this study, high-efficiency visible-light-driven photocatalytic H2 production without the assistance of precious-metal cocatalysts was achieved on graphene-Zn(x)Cd(1-x)S composites with controlled compositions. The graphene-Zn(x)Cd(1-x)S 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 Zn(x)Cd(1-x)S and in situ growth of Zn(x)Cd(1-x)S nanoparticles on graphene nanosheets. Such a scenario results in abundant and intimate interfacial contact between graphene and Zn(x)Cd(1-x)S nanoparticles, efficient transfer of the photogenerated charge carriers, and enhanced photocatalytic activity for H2 production. The highest H2-production rate of 1.06 mmol  h(-1)  g(-1) was achieved on a graphene-Zn0.5Cd0.5S composite photocatalyst with a graphene content of 0.5 wt %, and the apparent quantum efficiency was 1.98 % [corrected] at 420 nm. In comparison, the graphene-Zn(x)Cd(1-x)S composite photocatalyst prepared by using an inorganic S source such as Na2S exhibited much lower activity for photocatalytic H2 production. In this case, homogeneous nucleation of Zn(x)Cd(1-x)S 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 H2 production.