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

CuGaS, (AgInS)-(ZnS), AgZnGeS, Ni- or Pb-doped ZnS, (ZnS)-(CuCl), and ZnGaInS showed activities for CO reduction to form CO and/or HCOOH in an aqueous solution containing KSO and NaS as electron donors under visible light irradiation. Among them, CuGaS and Ni-doped ZnS photocatalysts showed relatively high activities for CO and HCOOH formation, respectively. CuGaS was applied in a powdered Z-scheme system combining with reduced graphene oxide (RGO)-incorporated TiO as an O-evolving photocatalyst. The powdered Z-scheme system produced CO from CO in addition to H and O 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 reduction. Thus, we successfully demonstrated CO reduction of artificial photosynthesis using a simple Z-scheme system in which two kinds of photocatalyst powders (CuGaS and an RGO-TiO composite) were only dispersed in water under 1 atm of CO.