Degradation Of Levofloxacin By BiVO₄-Based Composite Photoanodes In A Photocatalytically Coupled PMS Activation System

Levofloxacin(LVF)is being used on a large scale in the treatment of human and animal diseases.However,due to its highly stable and incomplete metabolism,LVF residues are slowly accumulated in the ecological chain,posing a great threat to aquatic and terrestrial ecosystems.Therefore,there is an urgent need to develop efficient and low energy-consuming technologies for the degradation of levofloxacin.Photocatalysis(PEC)has been shown to be an efficient technology for the degradation of pollutants.Recently,researchers have developed a technique to degrade organic pollutants with PEC coupled with peroxymonosulfate(PMS)to achieve more efficient removal of organic pollutants from wastewater.In photocatalytic water treatment technology,the photocatalytic performance depends largely on the choice of photoanode,and bismuth vanadate(BiVO4)is often used as a photoanode material because of its narrow band gap(2.4 eV)and excellent photocatalytic performance.However,it also leads to excessive spontaneous recombination of photogenerated electron-hole pairs because of the narrow band gap and short hole diffusion length,which severely limits the application of BiVO4 in practice.Therefore,in this paper,a rational approach was taken to modify the BiVO4 material around its deficiencies.Meanwhile,PMS was introduced and a PMS-coupled photocatalytic degradation system was constructed for the degradation of levofloxacin.The main research of the thesis is as follows:1.Degradation of levofloxacin by CuFeO2/BiVO4 composite photoanodes in a photocatalytically coupled PMS-activated systemBiVO4 photoanodes and CuFeO2 powder materials were synthesized by electrodeposition and hydrothermal methods,respectively,and then CuFeO2/BiVO4 composite photoanodes were prepared by spin coating method.The materials were characterized by XRD,SEM,TEM,XPS,and UV-vis DRS for physical phase,morphology,valence,and light absorption properties,respectively.After that,the degradation performance of the composite photoanode was tested under the PMScoupled photocatalytic system using levofloxacin(LVF)as the degradation substrate,and the effect of different conditions on the degradation performance was investigated.It was found that the CuFeO2/BiVO4 composite photoanode degraded about 75%of LVF(15 ppm)within 30 min,which is a 45%improvement in degradation rate compared with the BiVO4 photoanode.In addition,the photoelectrochemical performance of the composite photoanode was tested,and it was confirmed that the loading of CuFeO2 and the introduction of PMS promoted the separation of photo-generated electrons and photo-generated holes,thus enhancing the degradation performance of the composite photoanode against LVF.Combined with the free radical burst experiments,h+,·OH,·O2·-and SO4·were found to be the main active species in the degradation of LVF.The cyclic stabilization experiments show that the CuFeO2/BiVO4 composite photoanode has excellent stability and degradation ability for different pollutants,which indicates that the material has broad prospects for practical applications.2.Degradation of levofloxacin by Co2(OH)3Cl/BiVO4 composite photoanodes in a photocatalytically coupled PMS-activated systemIn the second work,we introduced Co2(OH)3Cl,a cobalt-based solid solution material with a stronger activation capacity for PMS,to enhance the role of PMS in the degradation system.BiVO4 photoanodes and Co2(OH)3Cl powder materials were synthesized by electrodeposition and hydrothermal methods,respectively,and then Co2(OH)3Cl/BiVO4 composite photoanodes were prepared by spin coating method.The physical phase,morphology,valence and light absorption properties of the pure samples and composites were characterized by XRD,SEM,TEM,XPS,and UV-vis DRS,respectively.After that,the degradation performance of Co2(OH)3Cl/BiVO4 composite photoanode was tested under PMS-coupled photocatalytic system using levofloxacin(LVF)as the degradation substrate,and the effect of different conditions on the degradation performance was investigated.It was found that the Co2(OH)3Cl/BiVO4 composite photoanode degraded about 90%of LVF(15 ppm)within 30 min,which was 60%higher than that of BiVO4 photoanode and 15%higher than that of CuFeO2/BiVO4.In addition,the photoelectrochemical performance of the composite photoanode was tested,and it was confirmed that the loading of Co2(OH)3Cl and the introduction of PMS promoted the separation of photo-generated electrons and photo-generated holes.Combined with the free radical burst experiments,h+,OH,·O2-and SO4·-were found to be the main active species in the degradation of LVF.The cyclic stability experiments showed that the Co2(OH)3Cl/BiVO4 composite photoanode has good stability and degradation performance for different pollutants,which proved the feasibility of the composite in practical applications.