Experimental Study On Photodegradation Mechanism Of Fluconazole In The Fe(?)- Mixed Carboxylate System

The antibiotics used in a large number of fields such as medical care,animal husbandry,agriculture and food industry enter the ecological environment through various means,causing harm to aquatic animals and plants and humans,and will lead to the emergence of drug-resistant bacterial flora.Traditional water treatment methods have lower removal efficiency of antibiotics,so the removal of antibiotics has attracted extensive attention of researchers.There are trivalent iron?Fe????,oxalic acid?ox?,and citrate?cit?in natural water bodies.Fe???can form higher photoactivity complexes with carboxylates such as ox and cit,and generate the reactive species such as^·OH,HO₂^·,O₂^·-under the light,which can effectively degrade the refractory organic pollutants.In this dissertation,the typical triazole antifungal antibiotic fluconazole?FLC?was studied to investigate the photodegradation kinetics and degradation mechanism of FLC in Fe???-cit-ox mixed carboxylic acids.The synergistic effect of the dicarboxylic acid system on the degradation of FLC was explored.Using terephthalic acid?TPA?as a molecular probe,we determined the steady state concentration of^·OH under different conditions of the Fe???-cit-ox complex system.We learned more about the reaction mechanism of the Fe???-cit-ox complex system,and optimized reaction conditions.By comparison with the FLC photodegradation rate constant,we further explored the synergistic effect of dicarboxylic acids with the primary conclusions as following,?1?In this experiment,non-fluorescent TPA was used as a molecular probe,which reacts with^·OH to generate hTPA with fluorescence,and hTPA was measured with a fluorescence spectrophotometer to calculate indirectly the steady state concentration of^·OH.The hTPA concentration and fluorescence intensity show a good linear relationship,indicating a reliable method for the determination of the steady state concentration of^·OH.?2?In Fe???-cit,Fe???-ox complex systems,^·OH steady state concentration is related to pH and initial concentration of cit.In Fe???-cit system,the steady-state concentration of^·OH is higher under weak acidic conditions,and the steady-state concentration of^·OH increases with the increase of the initial citrate concentration at fixed pH.In the Fe???-ox system,the steady-state concentration of^·OH decreases with increasing pH.[^·OH]_ss increases with the initial concentration of ox when the pH is the same.Compared with Fe???-cit complex system,Fe???-ox complex system has higher photoactivity under acidic conditions.?3?In Fe???-cit-ox complex system,the steady-state concentration of^·OH is related to the pH and the initial citrate concentration.Compared with Fe???-cit complex system and Fe???-ox complex system alone,the steady state concentration of^·OH in the mixed carboxylic acid system is greatly improved.Under weak acidic conditions,the steady-state concentration of^·OH is higher and there is better synergistic effect in near neutral conditions.Under acidic conditions,the system has no synergistic effect.At alkaline pH?pH 7.0-8.0?,the increase of ox concentration can increase the synergistic effect of Fe???-cit-ox complex system.?4?In the Fe???-cit system,the photodegradation effect of fluconazole was related to pH and citrate concentration.When the initial concentration of citric acid was constant,the photodegradation efficiency of FLC followed the order pH8.0<3.0<7.0<4.0<6.0<5.0<5.5.When the initial concentration of citrate was constant,the photodegradation rate constant of FLC was the highest at pH 5.5.At a certain pH,the higher initial citrate concentration,the higher photodegradation rate constant of fluconazole.In the Fe???-ox system,when the pH value is fixed,the higher initial concentration of oxalate,the higher photodegradation rate constant of fluconazole.When the concentration of oxalate was fixed,the photodegradation effect of fluconazole was better under acid conditions,and the order was pH8.0<7.0<6.0<5.5<5.0<3.0<4.0,which corresponds to the order of the steady state concentration of^·OH.?5?In the Fe???-cit-ox complex system,the photodegradation effect of fluconazole was related to the pH value and the initial concentration of carboxylic acid.The photodegradation rate constant was highest at pH 5.0 under different initial concentration of the five groups of carboxylic acids.With the same pH value and initial concentration of cit,the higher the initial concentration of ox,the higher the photodegradation rate constant of fluconazole,corresponding to the results of the steady state concentration of^·OH.?6?In Fe???-cit-ox complex system,ox and cit have a synergistic effect on the degradation of FLC under certain conditions.When the initial concentration of citric acid was 50?M and the oxalic acid concentration varied from 50 to 500?M,a synergistic effect was observed under near neutral conditions.In contrast,under acidic conditions?pH3.0-5.0?with the ox concentration from 50 to 500?M,there is no synergistic effect on the photodegradation of FLC.Under near neutral conditions,an increase in the initial concentration of ox can increase the synergistic effect when the pH is the same.?7?By LC-MS,the photodegradation products of FLC by Fe???-cit-ox complex system were analysed,and a possible degradation pathway of FLC in this system was proposed.The resulting^·OH first replaces fluorine on the benzene ring and then oxidizes two five-membered nitrogen-containing heterocycles.This paper investigates the steady-state concentration of Fe???-cit-ox mixed carboxylic acid system at different pH and carboxylic acid concentrations.FLC was selected as the target pollutant to study its photodegradation kinetics and reaction mechanism in mixed carboxylic acid system.The synergistic effect of Fe???-cit-ox mixed carboxylic acid system was discussed under different conditions.This finding suggests the potential application of Fe???-cit-ox mixed carboxylic acid in the wastewater treatment.