Removal Effect And Mechanism Of Nano-Zerovalent Copper On Enrofloxacin In Fenton-like System

In recent years,due to the needs of social development,antibiotics have been widely used in medical,animal husbandry,aquaculture and agriculture.The concentration of antibiotics in the water environment has also attracted more and more attention.Enrofloxacin?ENR?and sulfamethoxazole?SMZ?are two typical antibiotics which are used to prevent and treat various diseases in animals and humans.Because these two antibiotics are not easily degraded in the water environment and can last longer under low light conditions,they are often detected in surface water,drinking water,wastewater and other aquatic environments.Therefore,research on how to effectively remove ENR and SMZ has become a research hotspot.Molecular oxygen?O₂?is a green,inexpensive oxidant,but due to the stability of O₂,the removal effect of ENR and SMZ is not high.This paper explored the enhancement effect of nano-zero copper?n ZVC?as a catalyst on the oxidative degradation of ENR and SMZ by O₂,and studied the oxidative effect of its reaction mechanism and common factors on the removal rate of ENR and SMZ activated by n ZVC.At the same time,enrofloxacin was used as the representative to study its reaction path in the n ZVC/O₂ system.The usability of the n ZVC/O₂ system is evaluated by the total copper content in the system.The research results showed that ENR was almost not degraded in the absence of n ZVC,but when n ZVC was present in the system,the degradation rate of ENR increased significantly.The increase of n ZVC dosage and higher reaction temperature could promote the degradation of enrofloxacin.The lower p H value??3.96?could promote the degradation of ENR,while under strong alkaline?p H=10.96?conditions,the n ZVC/O₂ system could hardly remove ENR.Under the condition of 15?,initial p H=3,and n ZVC dosage of 0.50 g·L^-1,the removal rate of enrofloxacin could reach 99%in 60 min.At the same time,the intermediate products of ENR in the degradation process were explored by high performance liquid chromatography tandem time-of-flight mass spectrometer,and it was revealed that the degradation of ENR can be mainly achieved by decarboxylation,hydroxyl substitution,quinolinone and piperazine ring cleavage.The results show that the n ZVC/O₂ system oxidizes enrofloxacin to open the quinolone ring and undergoes further oxidation,deamination,dehydrogenation,and decyclopropane until the ENR was fully mineralized.Among them,the piperazine ring and the carboxyl group were the main sites in the degradation process.Oxidation of-COOH on the piperazine ring and substitution by-OH were the main pathways,which leads to ENR being mineralized and converted to CO₂,H₂O and NO₃^-.This study also found that the n ZVC/O₂ system had a good degradation effect on SMZ.The increase of n ZVC dosage,acidic conditions and higher reaction temperature could promote the degradation of SMZ.However,under neutral and alkaline conditions,SMZ hardly degrades.The copper ion dissolution test showed that the total copper content in the solution was 0.52mg·L^-1,at 20?,initial p H=3,and the dosage of n ZVC was 0.50 g·L^-1 after 60 min,which was less than the specified 1 mg·L^-1.indicating the availability of the n ZVC/O₂ system.