Insight into the catalytic mechanism of γ-Fe2O3/ZnFe2O4 for hydrogen peroxide activation under visible light.

Magnetic γ-Fe2O3 supported on mesoporous ZnFe2O4 was synthesized by impregnation and deposition-precipitation methods. The obtained γ-Fe2O3/ZnFe2O4 was found to be an effective catalyst for the degradation and mineralization of Orange II with H2O2 under visible light irradiation, which can be attributed to the enhanced production of OH and particularly O2-. The catalytic mechanism of γ-Fe2O3/ZnFe2O4 for H2O2 activation and the degradation pathway of Orange II were investigated. The result indicates that the loaded γ-Fe2O3 could capture the electrons in the conductive band of ZnFe2O4, thus promoting the formation of O2- from the reaction between H2O2 and holes. Meanwhile, the formed Fe2+ and electrons could react with H2O2 to produce OH. According to the results of liquid chromatography-mass spectrometry, electron paramagnetic resonance and scavenger experiments, Orange II should be mainly degraded by O2- but not OH due to the destruction of azo bond, while its intermediates were further mineralized by O2- and OH.