M-substituted (M = Co, Ni and Cu) zinc ferrite photo-catalysts for hydrogen production by water photo-reduction

• A0.2Zn0.8Fe2O4 was synthesized by co-precipitation method.
• A0.2Zn0.8Fe2O4 was used as heterogeneous photo-catalyst for hydrogen production.
• Co0.2Zn0.8Fe2O4 was highly efficient to produce hydrogen under visible light irradiation.

A0.2Zn0.8Fe2O4 ferrites with A = Co, Ni and Cu were successfully prepared by co-precipitation followed by annealing at 650 °C. They were characterized by using XRD, EDX, BET, FTIR, RDS, electrical conductivity, Current-Potential, Mott–Schottky and Nyquist techniques and their photo-catalytic properties were evaluated in hydrogen production through water photo-reduction. XRD revealed the formation of cubic ferrospinel structures with particle sizes in the nano-range. BET surface areas of the ternary spinels were higher than that of the binary ZnFe2O4. The electrical conductivities of A0.2Zn0.8Fe2O4 were found to obey the Arrhenius law with activation energies of conduction between 0.17 and 0.31 eV. They were found to be n-type semiconductors with narrow band gap. The photo-catalytic results for hydrogen production indicated that the Co substitution dramatically enhances the catalytic activity of ZnFe2O4. This substituted zinc ferrite shows the highest photo-catalytic activity under visible light irradiation, which varies as follows: Co0.2Zn0.8Fe2O4 >> Ni0.2Zn0.8Fe2O4 > ZnFe2O4 > Cu0.2Zn0.8Fe2O4.