Study On The Performance And Mechanism Of Photocatalytic Degradation Of Tetracycline Hydrochloride And Reduction Of Hexavalent Chromium Based On MOFs-based Modified Material

With the rapid development of modern industry and agriculture,a large number of persistent organic pollutants and heavy metals enter the ecological environment,especially in the water environment,which was bound to pose a great threat to the survival and living environment of aquatic organisms and human beings.At present,in the removal of pollutants in the environment,most of the removal methods have the problems of high cost,easy to produce secondary pollution and unclear removal mechanism.In order to solve the scientific problems of high removal cost and unclear degradation mechanism,a variety of MOFs photocatalysts were used to investigate the influencing factors of photocatalytic degradation of pollutants and their photocatalytic degradation mechanism with tetracycline hydrochloride（TCH）and hexavalent chromium（Cr（VI））as target pollutants.The main results are as follows:（1）A MOF-based photocatalyst NH₂-MIL-101(Fe²⁺/Fe³⁺)with new morphology and mixed metal valence was prepared by original flavor reduction method.In the novel MOF,Fe²⁺and Fe³⁺formed mixed-valence clusters,the performance of which was similar to that of biological enzymes,with Fe²⁺as the active centre and Fe³⁺as the high-valence metal ion.Fe³⁺in NH₂-MIL-101(Fe²⁺/Fe³⁺)was reduced to Fe²⁺,by ethylene glycol（EG）in situ and its structure is changed by controlling the content of EG,and the ratio of Fe²⁺to Fe³⁺was controlled,so as to further regulate the formation of different morphologies.The Fe²⁺/Fe³⁺redox-active centre can improve the migration and separation of photogenerated electron-hole pairs,which is the main factor for improving catalytic activity under simulated sunlight irradiation.The results show that NH₂-MIL-101(Fe²⁺/Fe³⁺)has higher ability of photocatalytic removal of TCH and Cr（VI）than pure NH₂-MIL-101（Fe）.Quenching experiments showed that·O₂^-,·OH and h⁺were involved in the degradation of TCH and the reduction of Cr（VI）.It can be predicted that adjusting the valence state and morphology of internal metal ions will be one of the ideal means to improve the photocatalytic performance of single semiconductors and provide a good theoretical basis for its wide application in practice.（2）A MOF（NH₂-MIL-125（Ti））with controllable oxygen vacancy defects was synthesized by heat treatment.The utilization of photogenerated free radicals can be improved by introducing oxygen vacancies.In addition,the ligands from the surface to the interior of the sample decarboxylated successively,resulting in the decrease of the specific surface area and the increase of micropores ratio and defect energy level.When the heat treatment time is 300 mins,NH₂-MIL-125（Ti）has a medium defect energy level,which is beneficial to the separation of photogenerated charge,has the highest photocatalytic activity,and achieves 100%removal rate of Cr（VI）within 2 h.The intermediate was identified by LC-MS,and the possible degradation pathway of TCH was obtained.It provides an optimization strategy of single semiconductor catalyst for photocatalytic degradation of organic pollution and heavy metal pollution.