Photocatalytic CO2 reduction using water as an electron donor by a powdered Z-scheme system consisting of metal sulfide and an RGO–TiO2 composite

Abstract

CuGaS₂, (AgInS₂)_x–(ZnS)_2−2x, Ag₂ZnGeS₄, Ni- or Pb-doped ZnS, (ZnS)_0.9–(CuCl)_0.1, and ZnGa_0.5In_1.5S₄ showed activities for CO₂ reduction to form CO and/or HCOOH in an aqueous solution containing K₂SO₃ and Na₂S as electron donors under visible light irradiation. Among them, CuGaS₂ and Ni-doped ZnS photocatalysts showed relatively high activities for CO and HCOOH formation, respectively. CuGaS₂ was applied in a powdered Z-scheme system combining with reduced graphene oxide (RGO)-incorporated TiO₂ as an O₂-evolving photocatalyst. The powdered Z-scheme system produced CO from CO₂ in addition to H₂ and O₂ due to water splitting. Oxygen evolution with an almost stoichiometric amount indicates that water was consumed as an electron donor in the Z-schematic CO₂ reduction. Thus, we successfully demonstrated CO₂ reduction of artificial photosynthesis using a simple Z-scheme system in which two kinds of photocatalyst powders (CuGaS₂ and an RGO–TiO₂ composite) were only dispersed in water under 1 atm of CO₂.