Comparison of TiO2 and ZnO catalysts for heterogenous photocatalytic removal of vancomycin B

Continuous input into the aquatic ecosystem and persistent structures have created concern of antibiotics, primarily due to the potential for the development of antimicrobial resistance. Degradation kinetics and mineralization of vancomycin B (VAN-B) by photocatalysis using TiO2 and ZnO nanoparticles was monitored at natural pH conditions. Photocatalysis (PC) efficiency was followed by means of UV absorbance, total organic carbon (TOC), and HPLC results to better monitor degradation of VAN-B itself. Experiments were run for two initial VAN-B concentrations (20-50 mgL(-1)) and using two catalysts TiO2 and ZnO at different concentrations (0.1 and 0.5 gL(-1)) in a multi-lamp batch reactor system (200 mL water volume). Furthermore, a set of toxicity tests with Daphnia magna was performed to evaluate the potential toxicity of oxidation by-products of VAN-B. Formation of intermediates such as chlorides and nitrates were monitored. A rapid VAN-B degradation was observed in ZnO-PC system (85% to 70% at 10 min), while total mineralization was observed to be relatively slower than TiO2-PC system (59% to 73% at 90 min). Treatment efficiency and mechanism of degradation directly affected the rate of transformation and by-products formation that gave rise to toxicity in the treated samples.