Study On The Oxidative Degradation Of Amoxicillin In Water By CoFe₂O₄/UV Activated Persulfate

The use of antibiotics not only promotes the development of China’s medical industry,but also causes many negative effects.The threat of antibiotic pollution in water environment to China’s water quality safety is increasing.Amoxicillin,as one of the most commonly used broad-spectrum penicillin antibiotics,is widely used in medical and aquaculture industries.However,amoxicillin is difficult to be completely absorbed in organisms,and most of it is discharged into the water environment in the form of original activity or metabolites.Because the conventional water treatment process can not completely remove it,it is transmitted through the food chain.It causes potential harm and pollution to human and animal health and ecological environment.Among them,persulfate advanced oxidation technology is to activate persulfate to produce strong oxidizing sulfate radical（SO₄·^-）through certain activation methods.The free radical has the characteristics of high redox potential（2.5～3.1 V）,fast reaction rate,high selectivity,long half-life and so on.It is widely used in the degradation of various antibiotics in water environment.The activation system of transition metal ions is simple,the conditions are mild and the energy consumption is low.The activation of persulfate by ultraviolet（UV）irradiation has the advantages of high efficiency,high environmental protection and no secondary pollution.Both activation methods can effectively produce SO₄·^-.In this paper,amoxicillin was selected as the target organic compound of antibiotics,heterogeneous magnetic nano cobalt ferrite（CoFe₂O₄）catalyst was prepared to activate persulfate（PMS）to degrade amoxicillin.The effects of catalyst and oxidant dosage,initial concentration of amoxicillin,reaction temperature,initial pH value,and concentrations of HCO₃^-and Cl^-on the degradation of amoxicillin were investigated by single factor experiment.Secondly,the structural stability of CoFe₂O₄ after reuse was investigated by XRD and the dominant free radical of the reaction system was identified.The effects of different factors on the degradation of amoxicillin in UV/PMS system were studied.The mechanism and reaction principle of activation reaction were explored.The dominant free radicals in the system were revealed by free radical capture experiment.CoFe₂O₄ catalyst was applied in the UV catalytic reaction unit,and the degradation effect of amoxicillin in water by different single process and different combination process was comprehensively analyzed,which provided guidance for the promotion and application of the catalyst and the practical application of residual amoxicillin treatment.The main conclusions are as follows.（1）The solid phase catalyst was prepared by coprecipitation hydrothermal method.Combined with the removal effect of amoxicillin in CoFe₂O₄/PMS system,the magnetic nano CoFe₂O₄ catalyst was successfully prepared by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,energy dispersive X-ray spectroscopy（EDS）and vibrating sample magnetic strength analysis（VSM）.（2）Experiment setup 5 mmol·L^-1 of PMS,0.2 g·L^-1 of CoFe₂O₄,25°C of solution temperature,and no adjustment of initial pH value.After 90 minnites of reaction,the amoxicillin removal rate of 10 mg·L^-1 by CoFe₂O₄/PMS system reached 85.5%,and the corresponding quasi first order kinetic reaction constant was 2.15×10^-2 min^-1.The removal rates of CoFe₂O₄ and PMS were 7.4%and 4.0%respectively,which may be due to the limited amount of amoxicillin removal depending on the adsorption performance of catalyst particles or the oxidation performance of PMS.The results show that the removal of amoxicillin in this system is mainly due to the fact that the active components Fe²⁺and Co²⁺on the surface of organic pollutants can effectively activate the strong oxidation free radicals produced by persulfate.（3）In CoFe₂O₄/PMS system,the degradation efficiency of amoxicillin increased with the increase of catalyst and oxidant concentration,and decreased with the increase of initial amoxicillin concentration.With the increase of initial pH value,the degradation efficiency of amoxicillin increased first and then decreased.When pH value was 9,the degradation efficiency of CoFe₂O₄/PMS system was the best.When the temperature increased from 15℃to 35℃,the degradation efficiency of the reaction also increased.The degradation efficiency of amoxicillin first increased and then decreased with the increase of bicarbonate ion concentration,and the maximum degradation rate was achieved when the concentration was10 mmol·L^-1.The presence of chloride ion significantly inhibited the degradation of amoxicillin,and the effect of chloride ion on the degradation of amoxicillin was greater than that of bicarbonate ion.The catalytic activity and reusability of CoFe₂O₄ are still very high after four times of compound interest.Free radical capture experiments showed that the oxidative degradation of amoxicillin in CoFe₂O₄/PMS system depended on the combined action of SO₄·^-and HO·,but SO₄·^-played a leading role.（4）In UV/PMS system,the dosage of PMS was 0.5 mmol·L^-1,and the initial pH value was not adjusted.When the reaction time was 60 minnites,the removal rate of amoxicillin with initial concentration of 10 mg·L^-1 reached 90.3%.Compared with UV and PMS alone,the removal rate of amoxicillin in UV/PMS combined process is significantly higher.It may be that in PMS alone process,some persulfates are thermally activated to produce a small amount of SO₄·^-and degrade a small amount of amoxicillin.When treated by UV alone,part of amoxicillin was photodegradated due to the excitation of UV energy.（5）The initial concentration of amoxicillin inhibited the UV/PMS reaction.When the concentration of PMS was 0.5 mmol·L^-1,amoxicillin had the best degradation effect.When pH>9 and pH<7 is that the degradation efficiency of amoxicillin was not good.The presence of HCO₃^-and Cl^-also inhibited the degradation reaction,and the inhibition effect of HCO₃^-was more significant under the same conditions.The higher the concentration of humic acid,the stronger the inhibition.The degradation of amoxicillin was enhanced by SO₄·^-and HO·generated by UV/PMS process.According to the free radical capture experiment,SO₄·^-was indirectly proved to be the dominant free radical involved in the reaction.（6）Under the same conditions of control experiment,the removal rates of Amoxicillin by CoFe₂O₄/PMS system,UV/PMS system and CoFe₂O₄/UV/PMS system were 85.5%,90.3%and 84.0%,respectively.UV/PMS system had the best degradation effect,while CoFe₂O₄/PMS system and CoFe₂O₄/UV/PMS system had little difference.The degradation rate of the combined system was significantly higher than that of the UV/PMS system and CoFe₂O₄/PMS system within 30 minnites.both the UV activated PMS and the catalyst activated PMS produced SO₄·^-free radicals.The increase of the sources of free radicals accelerated the removal of amoxicillin.The free radical capture experiment indirectly proved that SO₄·^-was the dominant free radical in CoFe₂O₄/UV/PMS system.