ZnGa2S4 with a 3.4 eV band gap and defect chalcopyrite structure showed photocatalytic activity for hydrogen evolution from an aqueous solution containing SO32- and S2- as electron donors under ultraviolet-light irradiation. Cosubstitution of Cu(I) with Ga(III) for Zn(II) sites in ZnGa2S4 gave visiblelight response. The photocatalytic activities of Zn1-2x(CuGa)(x)Ga2S4 (x = 0.15-0.50) depended on the value x of the composition. Pd(0.5 wt%)-loaded Zn-0.4(CuGa)(0.3)Ga2S4 (x = 0.3) showed the highest activity with 15% of an apparent quantum yield at 420 nm. The dependence of the photocatalytic activity on the composition was due to the balance among the number of absorbed photons for photocatalytic reaction, the mobilities of electron and hole at conduction and valence bands, and the conduction band level affecting the driving force for reducing water to hydrogen. Pd(0.5 wt%)-loaded Zn-0.4(CuGa)(0.3)Ga2S4 and Rh(0.5 wt%)-loaded CuGa5S8 (x = 0.5) were active for solar hydrogen production using a solar simulator. (C) 2013 Elsevier Inc. All rights reserved.