Development of Z-Scheme Photocatalyst Systems Combining Nonmetal Oxide Materials for Water Splitting under Visible Light Irradiation: (CuGa)0.5ZnS2 as a H2-Evolving Photocatalyst and TaON as an O2-Evolving Photocatalyst

Abstract

Water splitting under visible light irradiation using a Z-scheme system combining nonmetal oxides of TaON and (CuGa)_0.5ZnS₂ is demonstrated. The key factors lie in coloading with Ir and CoO_x cocatalysts on TaON and using reduced graphene oxide (RGO) as a solid-state electron mediator. Ir is loaded by an impregnation method, while CoO_x is loaded by either impregnation or photodeposition methods. Loaded Ir boosts the electron migration from TaON to RGO, and loaded CoO_x works as an active site for O₂ evolution. Photocatalytic reduction of graphene oxide to RGO accompanied by simultaneous oxidation of Co²⁺ ions to CoO_x over Ir-loaded TaON is the optimum process for the formation of an RGO-(CoO_x/Ir/TaON) composite.