Photocatalytic CO 2 reduction using water as an electron donor by a powdered Z-scheme system consisting of metal sulfide and an RGO–TiO 2 composite

CuGaS 2 , (AgInS 2 ) x –(ZnS) 2−2x , Ag 2 ZnGeS 4 , Ni- or Pb-doped ZnS, (ZnS) 0.9 –(CuCl) 0.1 , and ZnGa 0.5 In 1.5 S 4 showed activities for CO 2 reduction to form CO and/or HCOOH in an aqueous solution containing K 2 SO 3 and Na 2 S as electron donors under visible light irradiation. Among them, CuGaS 2 and Ni-doped ZnS photocatalysts showed relatively high activities for CO and HCOOH formation, respectively. CuGaS 2 was applied in a powdered Z -scheme system combining with reduced graphene oxide (RGO)-incorporated TiO 2 as an O 2 -evolving photocatalyst. The powdered Z -scheme system produced CO from CO 2 in addition to H 2 and O 2 due to water splitting. Oxygen evolution with an almost stoichiometric amount indicates that water was consumed as an electron donor in the Z -schematic CO 2 reduction. Thus, we successfully demonstrated CO 2 reduction of artificial photosynthesis using a simple Z -scheme system in which two kinds of photocatalyst powders (CuGaS 2 and an RGO–TiO 2 composite) were only dispersed in water under 1 atm of CO 2 .