ZnGa(2-x)In(x)S4 (0 ≤ x ≤ 0.4) and Zn(1-2y)(CuGa)(y)Ga(1.7)In(0.3)S4 (0.1 ≤ y ≤ 0.2): optimize visible light photocatalytic H2 evolution by fine modulation of band structures.

ABSTRACT

Band structure engineering is an efficient technique to develop desired semiconductor photocatalysts, which was usually carried out through isovalent or aliovalent ionic substitutions. Starting from a UV-activated catalyst ZnGa2S4, we successfully exploited good visible light photocatalysts for H2 evolution by In(3+)-to-Ga(3+) and (Cu(+)/Ga(3+))-to-Zn(2+) substitutions. First, the bandgap of ZnGa2-xInxS4 (0 ≤ x ≤ 0.4) decreased from 3.36 to 3.04 eV by lowering the conduction band position. Second, Zn1-2y(CuGa)yGa1.7In0.3S4 (y = 0.1, 0.15, 0.2) provided a further and significant red-shift of the photon absorption to ∼500 nm by raising the valence band maximum and barely losing the overpotential to water reduction. Zn0.7Cu0.15Ga1.85In0.3S4 possessed the highest H2 evolution rate under pure visible light irradiation using S(2-) and SO3(2-) as sacrificial reagents (386 µmol/h/g for the noble-metal-free sample and 629 µmol/h/g for the one loaded with 0.5 wt % Ru), while the binary hosts ZnGa2S4 and ZnIn2S4 (synthesized using the same procedure) show 0 and 27.9 µmol/h/g, respectively. The optimal apparent quantum yield reached to 7.9% at 500 nm by tuning the composition to Zn0.6Cu0.2Ga1.9In0.3S4 (loaded with 0.5 wt % Ru).