Ternary photocatalyst Bi5O7I/Bi2O2CO3/Ag2CO3 with double Z-scheme heterojunction for the degradation of levofloxacin under visible light: Practical application and DFT calculation

A novel double Z-scheme heterojunction Bi ₅O ₇I/Bi ₂O ₂CO ₃/Ag ₂CO ₃ was constructed by a simple hydrothermal calcination and one-step in-situ growth technique, demonstrating efficient levofloxacin degradation (86.9 % in 60 min). The degradation rates of the system are 1.5, 4.1, 1.3 and 1.4 times faster than those of pure Bi ₅O ₇I, Bi ₂O ₂CO ₃, Ag ₂CO ₃ and binary Bi ₅O ₇I/Bi ₂O ₂CO ₃, respectively. The method enhances the photocatalyst performance through improving the separation efficiency of electron-hole pairs (e ^-/h ⁺) and the production of various free radicals in the double Z-scheme system. The generation of hydroxyl radicals (•OH), superoxide radicals (•O ₂ ^–) and holes (h ⁺) species were directly confirmed by Electron Spin Resonance test, and their contributions on the degradation of Levofloxacin follow the order of h ⁺ > •OH > •O ₂ ^–. The band structure, density of states, work function and potential sites of contaminant vulnerability in the material were determined by Density Functional Theory (DFT), which provides additional evidence for the formation of double Z-scheme heterojunction. Besides, the degradation experiment was conducted with four real surface water bodies, including lake water, river water, tap water and effluent of sewage treatment plant. The results show that the degradation rate for Levofloxacin reaches 60∼80 %. Moreover, Levofloxacin and its intermediate products were identified and their toxicity was predicted with Quantitative Structure-Activity Relationship (QSAR) modelling, which can be useful in the future for the actual design of a double Z-scheme heterojunction photocatalyst to efficiently remove pollutants under visible light irradiation.