Modification Of MOFs And Their Performance In The Degradation Of Organic Pollutants By Advanced Oxidation Process

With the development of human society,environmental problems have emerged in recent years,with the quality of the atmosphere and the environment of water bodies being particularly polluted.Advanced oxidation was used as a low-cost,high-efficiency and environmentally friendly method for environmental pollution control and remediation technologies,especially photocatalysis and photo-Fenton technology.To date,the semiconductor materials used in this field have suffered from low photogenerated carrier yields,fast compounding and poor stability,so there was an urgent need to develop catalysts with better performance.Metal-organic frameworks（MOFs）had the advantages of porosity,high specific surface area and easy adjustment of pore size,but they also generally had problems such as large forbidden band width,low efficiency of photogenerated charge separation and weak light absorption ability,and their application prospects were still limited.Therefore,there was a need to modify them to obtain materials with higher catalytic activity.The use of MOFs as a sacrificial template or precursor material,the design and preparation of porous-derived MOFs composites with controlled morphology;or the construction of heterojunctions using MOFs in combination with other semiconductor materials were known to be feasible strategies.This not only broadened the visible light response but also improved the photoexcited carrier separation efficiency,which was necessary to enhance the catalytic performance.In this paper,a series of novel and highly efficient catalysts were designed and synthesised using MOFs as the main material,derived by high-temperature calcination and the construction of heterojunctions to evaluate the catalytic activity and investigate the possible degradation mechanism using formaldehyde as a gaseous volatile organic pollutant（VOCs）and the broad-spectrum antibiotic ciprofloxacin（CIP）as a liquid-phase pollutant.Details of the study are as follows:1.Ti-based MOF NH₂-MIL-125 was synthesized by solvothermal method and the complexes made by grinding inorganic sulphur powder with it were calcined at high temperature to obtain S/N co-doped Ti O₂ with most surface oxygen vacancies and retaining the morphology of MOFs（TNSx,x is the calcination temperature）.To demonstrate the presence of S and N doping and oxygen vacancies,the crystal structure and morphological characteristics of the prepared materials were analyzed using XRD,Raman,FTIR,SEM,TEM,XPS,XRF and other characterization methods.Under xenon lamp irradiation,there was 98.00%removal of HCHO after 150 min and good cycling stability and structural stability after 5 cycles.The best photogenerated electron and hole separation efficiency of the prepared composites was also determined by PL and TRPL characterisation.Based on the degradation results,electrochemical means,EPR tests and in-situ IR means,the role of·OH and·O₂^-was elucidated and the possible mechanism was discussed in depth.2.MIL-88B（Fe）/Bi₄O₅Br₂ composites were prepared by solvent thermal method by preparing spun Fe based MOF MIL-88B（Fe）and sheet assembled nano-spheres Bi₄O₅Br₂,and the two were compounded by ball milling method.The structure,the morphology and composition of surface functional groups of the prepared materials were revealed by various characterisation means.The degradation of ciprofloxacin（CIP）by the MIL-88B（Fe）/Bi₄O₅Br₂ composites was significantly enhanced in the photo-Fenton system.It was verified that the composite BM41 with a 1:4 mass ratio of MIL-88B（Fe）to Bi₄O₅Br₂ had the best photo-Fenton performance,with a CIP degradation rate of 94.05%within90 min under visible light irradiation.The effects of catalyst dosage,initial p H and inorganic anions on the photo-Fenton system were also investigated.The results of PL,EIS and instantaneous photocurrent tests demonstrated that BM41has a faster photogenerated electron transfer rate and thus has superior photocatalytic activity.Finally,the generation of·OH,·O₂^-,and h⁺in the system jointly contribute to the removal of pollutants as demonstrated by radical capture experiments and EPR tests,and the mechanism of efficient degradation of organic pollutants by MIL-88B（Fe）/Bi₄O₅Br₂ photo-Fenton is proposed.This research work opens new avenues for the application of Fe-based MOF as a non-homogeneous photo-Fenton catalyst in environmental remediation.