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

Abstract

The BiOIO3/Bi2WO6 binary catalyst was prepared by hydrothermal method, and a Bi0/I−-BiOIO3/Bi2WO6 all-solid-state Z-scheme heterojunction composite catalyst with Bi0 deposition and I-doping was prepared by further reducing it with NaBH4 as reducing agent. When the content of BiOIO3 is 20 wt% and n(NaBH4): n(BiOIO3 + Bi2WO6) = 0.3, Bi0/I−-BiOIO3/Bi2WO6 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 Bi2WO6 and pure BiOIO3, respectively. The characterization results show that the main reasons for the improvement of the activity of Bi0/I−-BiOIO3/Bi2WO6 are the formation of heterojunction in the catalyst, the surface plasmon resonance (SPR) effect generated by Bi0 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 Bi0/I−-BiOIO3/Bi2WO6 were proposed. Finally, the electron transfer mechanism of Bi0/I−-BiOIO3/Bi2WO6 all-solid-state Z-scheme heterojunction was proposed based on the test results of Tauc-plot curve and M–S curve.