Photocatalytic H2 production from spinels ZnGa2−xCrxO4 (0≤x≤2) solid solutions

Solid solutions of ZnGa 2− x Cr x O 4 (0≤ x ≤2) were successfully prepared by solid state reactions . Introducing Cr into ZnGa 2 O 4 crystal structure significantly improves its light absorption and greatly enhances its photocatalytic activity . An optimized Cr content ( x =1.5 for ZnGa 0.5 Cr 1.5 O 4 ) was found for the solid solutions with the highest photocatalytic hydrogen production rate (~775   μmol/h). Compositional analysis suggests there is a strong enrichment of Cr at the surface of sample ZnGa 0.5 Cr 1.5 O 4 compared with other samples. Theoretical calculations suggest their electronic structures involve spin-polarized conduction band (CB) and valence band (VB) that are mainly composed of Cr 3 d orbitals. The highest photocatalytic activity observed in ZnGa 0.5 Cr 1.5 O 4 is probably due to the higher Cr content at the surface that favors the Cr 3 d orbital overlapping.