Bi0/I− co-modified BiOIO3/Bi2WO6 Z-scheme heterojunction catalysts for degradation of antibiotics under visible light: Mechanism, optimization and pathway

The BiOIO 3 /Bi 2 WO 6 binary catalyst was prepared by hydrothermal method, and a Bi 0 /I − -BiOIO 3 /Bi 2 WO 6 all-solid-state Z-scheme heterojunction composite catalyst with Bi 0 deposition and I-doping was prepared by further reducing it with NaBH 4 as reducing agent. When the content of BiOIO 3 is 20 wt% and n(NaBH 4 ): n(BiOIO 3  + Bi 2 WO 6 ) = 0.3, Bi 0 /I − -BiOIO 3 /Bi 2 WO 6 has the best photocatalytic activity. Under the optimized reaction conditions (catalyst dosage 1.0 g/L, antibiotic initial concentration 20 mg/L), the degradation efficiency of oxytetracycline (OTC) reached 83.56 % after 60 min reaction under visible light, and its pseudo-first-order reaction rate constant was 0.02431 min −1 , which was 2.56 times and 3.94 times that of pure Bi 2 WO 6 and pure BiOIO 3 , respectively. The characterization results show that the main reasons for the improvement of the activity of Bi 0 /I − -BiOIO 3 /Bi 2 WO 6 are the formation of heterojunction in the catalyst, the surface plasmon resonance (SPR) effect generated by Bi 0 and the impurity energy level introduced by I-doping, which jointly promote the separation of photogenerated electron-hole pairs (e − -h + ) in the catalyst and enhance the absorption capacity of the catalyst to visible light. The intermediates produced during the reaction were analyzed by high performance liquid chromatography-mass spectrometry (HPLC-MS). Two possible pathways for the degradation of OTC by Bi 0 /I − -BiOIO 3 /Bi 2 WO 6 were proposed. Finally, the electron transfer mechanism of Bi 0 /I − -BiOIO 3 /Bi 2 WO 6 all-solid-state Z-scheme heterojunction was proposed based on the test results of Tauc-plot curve and M–S curve.