Ultrasonic degradation of tetracycline combining peroxymonosulfate and BiVO₄ microspheres

Tetracycline (TC) has received widespread attention due to the negative impacts of the drug abuse on ecological system and human health. Sonodegradation coupled with catalyst has proven to be an efficient method to treating TC. In this paper, BiVO4 microspheres synthesized by hydrothermal method and peroxymonosulfate (PMS) were used as sonocatalysts. Comparison of the degradation experiments revealed that combination of BiVO4/PMS with ultrasound (US) resulted in the highest degradation rate of TC, and the synergistic factor was calculated to be 6.17, which indicates a very significant synergistic effect. Effects of many factors, such as US power, BiVO4 concentration, dosage of PMS, initial TC concentration and matrix ion, on tetracycline degradation were investigated, and the operating parameters were optimized by response surface methodology, which predicted that TC degradation rate could reach 91.4 % after 60 min by setting initial TC concentration of 20 mg/L, BiVO4 concentration of 1.156 g/L, PMS dosage of 2.331 mM, and US power of 419 W. Active species analysis verified that radicals, such as center dot OH, SO4 center dot-, h(+) and O-2(center dot-), were the primary contributors to TC removal, and ultrasonic cavitation plays a key role in sonocatalysis. The TC degradation rate only decreased by 1.6 % after four reuses of BiVO4. Moreover, the intermediate of TC degradation was detected using a liquid chromatograph-mass spectrometer (LC-MS), and the degradation pathway revealed that deamination, decarbonization and ring-opening reaction eventually result in the decomposition of TC. This work proposes a method for an efficient degradation of TC in waste water.