A novel and high-performance double Z-scheme photocatalyst ZnO-SnO₂-Zn₂SnO₄ for effective removal of the biological toxicity of antibiotics

Visible light-responsive tetradecahedral ZnO-SnO₂-Zn₂SnO₄ photocatalysts possessing double Z-scheme mechanism were prepared via a hydrothermal pathway and subsequent annealing treatment. Due to its enhanced optical absorption ability and effective charge separation, the sample with a Zn/Sn atom ratio of 3:2 (Z32) exhibited superior degradation of the antibiotics ciprofloxacin and sulfamonomethoxine under visible light irradiation and also degraded bisphenol A. Furthermore, five-cycle experiments confirmed that Z32 also exhibited satisfactory photostability. The trapping experiment and electron spin resonance data demonstrated that both OH and O₂^- play important roles in the photocatalytic system, where electron transfer coincides with the double Z-scheme mechanism. Photo-generated electrons in the conduction band (CB) of ZnO can transfer to the valence band (VB) of Zn₂SnO₄, while electrons in the CB of SnO₂ transfer to the VB of ZnO, as a result of the intimate-contact, chemically-bound interface. Therefore, the reduction and oxidation reactions occur at higher reduction and oxidation potentials, producing reactions that can successfully eliminate the biotoxicity of antibiotics to Escherichia coli DH5a after photocatalytic degradation by Z32.