Norfloxacin Degradation In An Iron Oxide-Catalyzed Fenton-Like(UV/IO/Oxalate) System And The Quantum Chemical Calculation Study

Since the 21st century,the abuse of pharmaceuticals and personal care products?PPCPs?have greatly drawn people's attentions all over the world.Since the existence and accumulation of PPCPs have caused serious risks to the human health and the ecoenvironment,it is essential to develop green technologies of high efficiency for PPCPs treatment.In this study,heterogeneous photochemical iron oxide/oxalate system?UV/IO/Ox?was established for the degradation of norfloxacin?NOR?—a typical antibiotic pollutant,by the photochemical in-situ generated reactive oxygen specises?ROS?in the systems.The results are shown below:NOR can be efficiently degraded in the UV/Fe₃O₄/Ox,UV/?-Fe₂O₃/Ox,UV/?-Fe₂O₃/Ox and UV/?-FeOOH/Ox systems,the NOR degradation performance was greatly affected by the IO dosages,the Ox concentrations,the NOR concentrations and the initial pH.The different properties of the four iron oxides made the optimal conditions differ in the four systems.The results showed that hydroxyl radical?HO·?was the main ROS for NOR degradation,it could be generated both on the surface of the iron oxides and in the bulk solution,and both of which contributed to the NOR degradation.The catalytic activity of the iron oxide was well correlated with its surface properties,an iron oxide with more abundant single-?-OH?or double-coordinated??-OH?surface hydroxyl would possess higher catalytic activity.Take UV/Fe₃O₄/Ox system as the study object,the effect of Fe₃O₄ predissolution process on NOR degradation was investigated.In the predissolution process,the inner-sphere iron-Ox complex which formed on the surface of Fe₃O₄ could accelerate the formation dissolved iron-Ox complex.Both the surface-bounded and dissolved iron-Ox complex could be activated by the UV light to produce various ROS,thus remarkably improve the initial degradation rate of NOR.During the degradation process,the surface-bounded ROS could be transferred into the bulk solution during the reaction process,thus NOR was mainly degraded homogeneously in the bulk solution.The reaction mechanism in the UV/Fe₃O₄/Ox system was proposed.It mainly included homogeneous-heterogeneous iron cycle in the solid-water interface and a series of bulk radical reactions.Besides,complexation instead of photochemical reduction would be dominant during the whole dissolution process even under UV irradiation.The unstable crystal structure of Fe₃O₄induced by the UV irradiation would further weakening the surface Fe-O bonds and accelerating the complexation dissolution process.Under the attack of HO·,O₂^·?and CO₂^·?,NOR can be degraded though three pathways,i.e.,defluorination,the oxidative re-arrangements of the piperazine ringand CO₂^·–addition.The quantum chemical calculation study showed that the re-arrangements of the piperazine ring were caused by the attack of HO·.The addition reaction of CO₂^·–on the benzene ring led to the dissociation of F atom,and both HO·and CO₂^·–could lead to the transformation of ethyl.The reaction barriers of the intermediates formation reactions were not too high,and a considerable amount of reaction heat was released in the above reactions.Obviously,the quantum chemical calculation results were replenishes and furthers of the experimental results,and it further demonstrated that CO₂^·?was one of the main ROS that responsible for NOR degradation.