Effect And Mechanism Of Photocatalytic Degradation Of Cu-EDTA By Fe-based MOFs

In recent years,with the continuous development of urban industrialization,the problem of water pollution in electroplating and printing and dyeing industries has become more and more serious.Heavy metal complexes have become a research hotspot due to their high toxicity and difficulty in degradation.The stability of heavy metal complexes is generally stronger than that of single heavy metal or organic pollutants.The removal of heavy metal complexes by traditional precipitation method requires a large number of precipitation auxiliaries due to the form of non-metal ions,and the cost is high.Because of the strong complexing ability of metal ions and chelating agents,the reaction conditions of ion exchange method are relatively strict and can not be applied well.As a typical advanced oxidation technology,photocatalytic degradation of heavy metal complexes has been widely studied due to its low energy consumption and high removal performance.Therefore,this paper proposed the use of iron-based MOFs materials to photocatalytic the degradation of heavy metal complexes in water.In the experiment,heavy metal complexes（Cu-EDTA）were used as the target pollutants to evaluate the degradation rules of two different iron-based MOFs materials in the photocatalytic system,and the possible degradation pathways were proposed.And through a series of characterization to analyze the reaction mechanism.To provide reference basis for the practical application of complexed heavy metal removal process in water,the main results are as follows:Firstly,MIL-53（Fe）prepared by solvothermal method can be effectively excited by ultraviolet light,and Cu-EDTA in water can be degraded through photocatalytic process,and MIL-53（Fe）-13 prepared at 13h has the best photocatalytic activity.The results showed that91%of Cu-EDTA was decompose within 60 min and 64%of Cu-EDTA was mineralized within 120 min under UV irradiation.The decomposition of Cu-EDTA is mainly driven by h⁺、·OH and ¹O₂ generated by MIL-53（Fe）.The degradation effect of Cu-EDTA under acidic conditions was better than that under neutral and alkaline conditions.The whole reaction process was combined with first-order reaction kinetics.With the increase of photocatalyst dosage,the photocatalytic removal effect increased first and then decreased slowly,and the degradation effect was the best when the dosage of 1g L^-1 was added.The photocatalytic decomposition of Cu-EDTA is accompanied by the removal of carbonyl group and hydroxyl group,and the generation of acetamide and other intermediate products,which are further degraded into glycine,acetic acid,oxalic acid,oxalic acid,and other small molecular organic acids in the presence of active substances.After three reuses of the photocatalyst,MIL-53（Fe）-13 could still degrade 70%Cu-EDTA within 120min under UV light.Secondly,after MIL-53（Fe）-13 is excited by ultraviolet light,the material will release Fe（III）into the system in the process of photocatalytic reaction,and the Fe（III）in the system will react with the photogenerated electrons generated after excitation to generate Fe（Ⅱ）,which effectively inhifies the recombination of photogenerated electrons and holes.The photocatalytic activity of MIL-53（Fe）-13 was maintained,and Fe（Ⅱ）could participate in Fenton-like reaction to promote the degradation of Cu-EDTA.At the same time,Fe（III）will undergo a REDOX reaction with Cu（II）generated by the disintegration of Cu-EDTA,and the generated Fe（Ⅱ）can also further promote the decomposition of pollutants.After photocatalytic reaction,Fe（III）will flocculate to form Fe（OH）_x and other flocculates.Meanwhile,flocculation co-precipitation will occur,which promotes the removal of Cu from the solution,and is conducive to better recovery of Cu from the wastewater of heavy metal complexes and reduction of heavy metal content in the water.Thirdly,modification of MIL-53（Fe）by doping Ag/AgCl can greatly improve the visible light responsiveness of photocatalytic materials.AAM-2 prepared by solvothermal method has the best photocatalytic activity when the metal content ratio is Fe:Ag=2:1.AAM-2 can decompose 97%of Cu-EDTA after 120 min photocatalytic reaction under visible light,and58%of Cu-EDTA can be mineralized within 120 min.The optimal dosage of AAM-2 for photocatalytic degradation of Cu-EDTA was 0.8 g L^-1.h⁺、·OH、¹O₂ and·O^2-were the main active substances for photocatalytic degradation.The results of five reutilization experiments show that the photocatalyst degradation efficiency of Cu-EDTA is still about 90%after five reutilization,and the modified Fe-based MOFs material has better practicability.