Efficient Degradation Of Enrofloxacin And Diazepam In Typical Aquaculture Water By Nanoscale-Zero-Valent Copper

With the continuous growth of population and rapid development of industry and agriculture,the demand for various drug compounds has expanded by leaps and bounds.In recent years,antibiotics and other animal drugs have been misused in animal husbandry and aquaculture,resulting in serious pollution of farmed water bodies.Enrofloxacin（ENR）is a veterinary broad-spectrum antibacterial drug,widely used to treat skin infections and respiratory tract infections in animals.Diazepam（DZP）is a psychotropic drug that acts as a sedative and is illegally added to feed and in the transportation of aquatic products to keep fish fresh.ENR and DZP in farmed water bodies pose serious hazards to aquatic ecosystems and aquatic product safety.Research on how to remove these two contaminants from farmed water bodies has become an urgent problem.Nanoscale zero-valent copper（nZVC）has high reactivity and can achieve efficient removal of pollutants.In this study,we selected ENR and DZP as typical pollutants in cultured water,investigated the degradation and oxidation mechanism of nZVC/O₂ and nZVC/PDS oxidation systems for ENR and DZP,respectively,and analyzed their transformation products.The degradation of ENR by the nZVC/O₂ system was achieved by in situ activation of molecular oxygen（O₂）for efficient degradation.The degradation performance of nZVC/O₂was investigated by the influencing factors of initial pH,reaction temperature,and nZVC dosing amount.The results showed that nZVC was able to remove 99.51%of ENR from the water column under an aerobic atmosphere at the reaction temperature of 35℃,initial pH=3,and nZVC dosage of 0.5 g/L.The coexistence of inorganic anions showed that Cl^-enhanced the degradation of ENR by stabilizing Cu⁺,while humic acid slightly inhibited the degradation of ENR by competing with ENR for·OH,slightly inhibiting the degradation of ENR by the system.Mechanistic analysis showed that·OH was the main active species in the nZVC/O₂ system,and the conversion between Cu⁺and Cu²⁺played a key role in the formation of-OH.ENR degradation pathway was achieved through hydroxylation on the quinolone and piperazine rings,and ring-opening cleavage deoxydeamination after hydroxylation of the piperazine ring.The nZVC/PDS system degrades the DZP process by activating the peroxydisulfate（PDS）in solution to achieve effective degradation.Without the addition of nZVC,only 15.03%of the DZP solution was removed in 60 min at 25℃,pH=9,and[PDS]₀=2.0 mM.In contrast to the case without the addition of nZVC,the addition of nZVC achieved a 5.4-fold improvement in degradation efficiency.In addition,the DZP degradation rate was faster under acidic conditions,while higher degradation efficiency was achieved under neutral and alkaline conditions.Inorganic interference experiments showed that NO₃^-,SO₄^2-and humic acid had little effect on the system degradation of DZP,while the presence of Cl^-and H₂PO₄^-significantly reduced the system degradation of PDS.Twenty DZP transformation products were identified by high-resolution time-of-flight mass spectrometry（QTOF-MS）,and the mechanism study showed that DZP was oxidized by hydroxylation on the benzodiazepine ring,and the ring was gradually opened by demethylation and decarbonylation to form a six-membered ring after rearrangement.In this study,nZVC was used as a catalyst to achieve the removal of hard-to-degrade organic pollutants from water bodies,which provides a theoretical basis for the removal of animal drugs from farmed water bodies.