Environmentally friendly synthesis of S-scheme heterojunction UiO-66-NH2/Bi7O9I3 for promoted degradation of ciprofloxacin under visible light: DFT calculation, degradation mechanism and toxicity evaluation

Abstract

To efficiently improve electrical conductivity and inhibit the combination of electron-hole (e–/h+), a novel S-scheme heterojunction composite of UiO-66-NH2/Bi7O9I3 was successfully built via in situ construction of Bi7O9I3 onto UiO-66-NH2. Both characterizations and DFT calculation show that charge transfer path in the UiO-66-NH2/Bi7O9I3 conforms to S-scheme heterojunction mechanism, and the Internal Electric Field generated in the UiO-66-NH2/Bi7O9I3 not only motivates photogenerated electrons to directly transfer from conduction band in UiO-66-NH2 to valence band in Bi7O9I3, but also greatly reduce the recombination rate of e–/h+. The generation of hydroxyl, superoxide and holes radicals are certified directly by Electron Spin Resonance. As-synthetized catalysts can be easily motivated and show an outstanding photodegradation rate (96.9 %) toward ciprofloxacin. The degradation rate of UiO-66-NH2/Bi7O9I3 is much higher than that of both monomers. Moreover, both the degradation pathway of ciprofloxacin and toxicity evaluation of intermediates were discussed in detail. The present research provides a mild and feasible synthesis method of a S-scheme heterojunction with an excellent photocatalytic degradation capacity to pollutants.