Making use of the δ electrons in K4Mo2(SO4)4 for visible light induced photocatalytic hydrogen production

Quadruply bonded dimolybdenum complexes with a σ2π4δ2 electronic configuration for the ground state have rich metal-centered photochemistry. Earlier study showed that stoichiometric or less amount of molecular hydrogen was produced upon irradiation of ultraviolet light (λ = 254 nm) on K4Mo2(SO4)4 in sulfuric acid solution, which was attributed to the reductive capability of the ππ* excited state. In order to make use of the δ electrons for visible light induced photocatalytic hydrogen evolution, a multi-component heterogeneous photocatalytic system containing K4Mo2(SO4)4 photosensitizer, TiO2 electron relay and MoS2 co-catalyst is designed and tested. With ascorbic acid added as a sacrificial reagent, irradiation of artificial sunlight (AM 1.5) on the reaction in 5 M H2SO4 has produced molecular hydrogen of 13400 μmol g–1 (based on Mo2 complex), which is 30 times higher than the hydrogen yield obtained from reaction of bare K4Mo2(SO4)4 with H2SO4 by ultraviolet light irradiation. Further improvement of hy...