Study On Preparation Of Fe₃O₄-CeO_x/AC@ZrO₂ And Its Performance For Catalytic Ozonation Of Tetracycline Hydrochloride

With the development of the medical industry,a large number of antibiotics have been used to treat human diseases.Tetracycline is one of the common antibiotics,which has been frequently detected in surface water in recent years,posing a serious threat to water and human environment.Catalytic ozonation based on advanced oxidation technology（AOPs）and gradually become the primary choice and research focus for the treatment of refractory organic compounds in sewage in recent years,compared with the traditional wastewater treatment and other advanced oxidation technology,catalytic ozonation of widely applicable conditions,degradation products was clean,and there will be no secondary pollution in the treatment process."metal oxide+carbon"was used to successfully synthesize Fe₃O₄-Ce O_x/AC,and then in order to improve the catalytic effect and protect the stability of catalytic core and structure,prepared Fe₃O₄-Ce O_x/AC@Zr O₂ core-shell catalyst.Using tetracycline hydrochloride（TC）as the target pollutant,the catalytic performance of the above two catalysts in the degradation of tetracycline hydrochloride in ozonation system was investigated respectively.The main research results are:（1）The catalyst Fe₃O₄-Ce O_x/AC was prepared by hydrothermal method and impregnation calcination.The calcination temperature was 600℃and the calcination time was 3 h.It was found that when the initial p H of solution was 5 and dosage was 0.2 g·L^-1,the catalyst has the best catalytic effect.When the initial concentration of tetracycline hydrochloride was 20 mg·L^-1 and the dosage of ozone was 4 mg·L^-1·min^-1,the removal rate of tetracycline hydrochloride was more than 99%within 10 min,the reaction rate is about twice as fast as ozonation The removal rate of TOC was 38%within 90 min,which was18%higher than that of ozonation.And the catalytic activity and low metal leaching rate can still be maintained after the continuous test for 90 min.The catalyst was characterized by various means.The morphology and structure of the catalyst were observed by SEM.The changes of specific surface area and pore volume before metal loading on the catalyst were mastered by BET.The valence state and distribution of metal oxides on the catalyst were known by XPS.Through this series of characterizations,it was proved that the metal oxide was successfully loaded and the catalyst preparation was completed.（2）On the basis of the catalyst Fe₃O₄-Ce O_x/AC,the concentration of cerium salt in the impregnation solution was increased,and the catalyst Fe₃O₄-Ce O_x/AC@Zr O₂ was prepared by hydrolyzing Zr OCl₂·8H₂O.When the initial p H of solution was 7 and dosage was 0.2g·L^-1,the catalyst has the best catalytic effect.When the initial concentration of tetracycline hydrochloride was 20 mg·L^-1 and the dosage of ozone was 4 mg·L^-1·min^-1,the removal rate of tetracycline hydrochloride could reach more than 99%within 10 min,the reaction rate constant increased by 0.289 compared with that of single ozonation,and the TOC removal rate reached 44%within 90 min,which increased by 24%compared with ozonation.The rate constant of mineralization reaction increased from 0.0023 to 0.0061.After 90 min of continuous experiment,the catalyst still maintained a high catalytic activity.ICP was used to detect the new catalyst with increased cerium concentration.It was found that the addition of Zr O₂ shell on the catalyst greatly reduced the metal leaching rate of the catalyst.Using a variety of means such as SEM,XPS of the catalyst,characterized by SEM to observe the changes of surface morphology of catalyst after adding Zr O₂ shell,confirmed by XRF catalyst on the element type and content of each element on the catalyst by XPS understanding the information such as the valence state change and distribution proportion,through XRD understanding of core-shell catalyst crystal structure,FTIR was used to detect the types of functional groups on the catalyst and the changes of functional groups after the experiment.The preparation of Fe₃O₄-Ce O_x/AC@Zr O₂ core-shell catalyst has been proved successfully.（3）The quenching experiment confirmed that·OH played a catalytic role in the system.In order to confirm the existence of·OH,EPR was used to detect·OH in the system,and the catalytic mechanism was explored to speculate that there are three main ways for the formation of·OH:one is the direct oxidation and decomposition of ozone to form;The other is the polyvalent metal interaction on the catalyst,in which the low-valent metal will react with ozone and H⁺and be oxidized to the form of a higher valence state,in this process,·OH and oxygen are generated.Third,the escape of lattice oxygen on the metal oxide during the preparation process of the catalyst leads to the formation of oxygen vacancies on the surface of the catalyst,and the combined action of the oxygen vacancies with O₃ and OH^-produces·OH.