Photocatalytic H2 generation from spinels ZnFe2O4, ZnFeGaO4 and ZnGa2O4

The three spinels ZnFe2O4, ZnFeGaO4 and ZnGa2O4 were synthesised by conventional solid state reaction method. ZnFeGaO4 has unit cell parameter between the parent spinels and shows appreciable absorption in visible light range with a band gap ∼1.9 eV. Photocatalytic experiments show that ZnFeGaO4 has a reasonable hydrogen production rate (∼9 μmol h−1/g catalyst) under visible light irradiation (λ ≥ 420 nm) but exhibits an improved performance (hydrogen production rate ∼971 μmol h−1/g catalyst) compared with parent ZnFe2O4 compound (hydrogen production rate ∼861 μmol h−1/g catalyst) under full range irradiation (λ ≥ 250 nm). The photo-electrodes prepared by electrophoretic deposition of spinel powders onto the fluorine doped tin oxide glass showed a clear impedance response under irradiation. Introducing Ga into the ZnFe2O4 structure seems to enhance the light absorbance in the UV region and modify the electronic structure which accounts for the improved photocatalytic activity.

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► A series of spinels ZnFe2O4, ZnFeGaO4 and ZnGa2O4 were synthesised.
► Inverse occupancy in the spinel structure between Zn and Fe or Ga is very small.
► Light absorption in the visible region is controlled by Fe in the structure.
► Ga in the structure helps to improve the light absorption in the UV region.
► ZnFeGaO4 shows an improved photoactivity in either UV or visible irradiation.