Accelerating antibiotic degradation by integrating tertiary magnetic ZnFe2O4/BiVO4/rGO heterojunction with ozone-nanobubbles

Abstract

In this study, ZnFe2O4, BiVO4, and ZnFe2O4/BiVO4/rGO materials were synthesized using the hydrothermal method in mild conditions to study the oxytetracycline (OTC) degradation process. The results on surface morphology, functional group, structure, and optical and electrochemical characteristics revealed that ZnFe2O4/BiVO4/rGO were successfully prepared with high purity and good distribution of chemical elements. The impact of different parameters like pH, catalyst load, reaction time, initial OTC concentration, and the presence of ozone-nanobubbles on the OTC degradation efficiency was systematically examined to obtain optimal treatment conditions. Synergic effects between ozone-nanobubbles and ZnFe2O4/BiVO4/rGO heterojunction led to an enhancement of over 20 % of OTC degradation yield. The OTC degradation reached 96.3 % within 100 min at optimal conditions (pH 7.0, [Cat.] = 0.5 g/L, and [OTC] = 20 mg/L). The combination of ZnFe2O4 and BiVO4 allowed to benefit from the generation of both effective electrons and holes, which enhanced the generation rate of both superoxide and hydroxyl radicals responsible for degrading the pollutant in water while rGO sheets contributed to slowing down the recombination rate between electrons and holes and improving the photocatalytic activities of the ZnFe2O4/BiVO4/rGO. Liquid chromatography-mass spectrometry (LC-MS) analyses were deployed to figure out intermediate substances and possible degradation pathways of the OTC degradation process. The ZnFe2O4/BiVO4/rGO heterojunction exhibited a pretty good durability and stability, and was easily recovered with the aid of a magnet. The toxicity of the by-products was significantly declined compared to the OTC antibiotic.