Nano-CuOx for ciprofloxacin effective removal via wet peroxide oxidation catalysis and its practical application in wastewater

Using Cu(NO3)2·3H2O as active material and citric acid (CA) as complexing agent, heterogeneous catalyst nano-CuOx was prepared by sol-gel method. The catalytic wet peroxide oxidation (CWPO) reaction system was established accordingly. The system was used to treat ciprofloxacin (CIP) in simulated wastewater and real wastewater. The effects of the molar ratio of metal salt to CA, calcination temperature, H2O2 dosage, reaction temperature, and catalyst dosage on the physicochemical structure and the properties of CWPO were investigated. The results showed that when the molar ratio of CA to metal salt (Cu(NO3)2·3H2O) was 1.8, the calcination temperature was 500 °C, the concentration of H2O2 was 10 mmol · L–1, the reaction temperature was 95 °C, and the dosage of catalyst was 1 g · L–1, CWPO system has the best degradation effect on CIP. At thses optical conditions, the removal rate reached 86.8%, chemical oxygen demand (COD) removal rate reached 54.9%, and the recycling rate of the catalyst was very good. The refractory organics in actual pharmaceutical wastewater could be oxidized by this system as well, and the COD removal rate reaches 47%. The degradation mechanism of CIP showed that the main functions of the CWPO system were ·O2– and ·OH radicals. The possible degradation pathways were determined by ion chromatography to be intermediate products generated from piperazine ring cleavage, defluorination, decarboxylation, and quinoline hydroxylation of CIP. The catalyzing mechanism was investigated in detail; some useful information was obtained in this work.