Modification Strategy Of Iron-based Metal Framework MIL-53(Fe) For Photo-Fenton Degradation Of Aqueous Tetracycline Hydrochloride

Recently,as a new type of advanced oxidation process(AOP),photo-Fenton technology has been widely used to degrade various organic pollutants in water due to its strong oxidizing ability,high efficiency reaction rate,and environmental friendliness.The photocatalysis-based Fenton technology combines the advantages of photocatalysis and the traditional Fenton process,that is,the introduction of photocatalysis can effectively accelerate the cycle of high-valent metal ions Fe(Ⅲ)and low-valent metal ions Fe(Ⅱ).More active materials are produced on the surface of the catalyst,which greatly improves its catalytic activity.Therefore,the preparation of high-performance catalysts has become the key to determining the performance of photo-Fenton.As the most common iron-based metal organic framework(MOF),MIL-53(Fe)has an adjustable mesoporous structure and uniformly dispersed iron metal active sites.At the same time,dense iron oxide clusters can effectively absorb visible light,so it is light Ideal for Fenton catalysts.However,MIL-53(Fe)alone has a high photo-generated charge and hole recombination rate and limited light absorption capacity,resulting in a reduction in the number of electrons that can be effectively used,which greatly limits the reduction of Fe(Ⅲ)to Fe(Ⅱ)rate.Therefore,a modification strategy is still needed to improve the photo-Fenton performance of MIL-53(Fe).Studies have shown that MOF modification based on heterojunctions and functional groups can effectively increase the light absorption range of the catalyst and the separation of photogenerated carriers.In this paper,flaky BiOI and Cl functional groups were used as the means of heterojunction modification and functional modification respectively,and MIL-53(Fe)/BiOI and Cl-MIL-53(Fe)catalyst,and in-depth study of its performance and mechanism through characterization tests and theoretical calculations,the results show that:1.The characterization results confirmed the structure and composition of the MIL-53(Fe)/BiOI heterojunction.The modification of the heterojunction promotes the separation of charge carriers,and the photogenerated electrons accelerate the Fe(II)/Fe(III)cycle.The MIL-53(Fe)/BiOI composite material has the effect of tetracycline(TCH)under the photo-Fenton system.The degradation is significantly improved.The TCH removal efficiency of MIL-53(Fe)/BiOI-60 can reach 86.21%within 14 minutes,which is much higher than that of MIL-53(Fe)(60.30%)and BiOI(53.51%)alone.In addition,singlet oxygen and h~+have been shown to be the main active substances that degrade tetracycline.2.The characterization results and first-principles theoretical calculations confirm that the Cl functional group modification maintains the skeleton structure of the original MIL-53(Fe),and 2Cl-MIL-53(Fe)can generate more photogenerated electrons and holes,and due to the delocalization of chlorine atoms,the recombination of electrons and holes can be reduced and the migration of carriers can be improved.This not only improves the photocatalytic performance of MIL-53(Fe),but also accelerates the cycle rate of Fe(Ⅲ)and Fe(Ⅱ).In addition,the introduction of Cl functional group also increases the electron cloud density on the surface of Fe atoms in the active center and enhances its catalytic activity.2Cl-MIL-53(Fe)can effectively remove 82.3%of tetracycline within 16 minutes,and the reaction rate is3.8 times that of the original MIL-53(Fe).At the same time,2Cl-MIL-53(Fe)also shows a strong p H tolerance(2.6-11.8)and good recyclability and stability.In this paper,we have successfully improved the photo-Fenton catalytic performance of the iron-based metal-organic framework MIL-53(Fe)through these two methods,and explored the path of charge transport in the MIL-53(Fe)/BiOI composite and the reason for the improvement of catalytic performance.More innovatively,in the experiment of Cl functional group modification,we first studied the influence of halogen on the energy band structure of metal organic framework MIL-53(Fe),and the chemical environment of the ferrite clusters in MIL-53(Fe)was analyzed through theoretical calculations,and the reason why the modification of the Cl functional group improved the performance of MIL-53(Fe)optical Fenton was explained in more detail.This research work provides a new idea for iron-based MOF as a heterogeneous photo-Fenton catalyst to degrade pollutants in water,and provides a new direction for the design of efficient,environmentally friendly and durable photo-Fenton catalysts.