Study On The Decomplexation Of Heavy Metal Complexes By Electro-assisted Metal-organic Frameworks Materials Catalytic Activation Of Peroxydisulfate

The heavy metals complexes are structurally stable heavy metal pollutants formed by the complexation of heavy metal ions and organic ligands,mainly from heavy metal industries such as the electroplating industry,printing and dyeing industry,etc.Heavy metal complexes have both biotoxicity,high water solubility and refractory biodegradability,and can exist stably in a wide pH range.It is difficult to completely remove them by existing water treatment processes,which seriously threatens ecological security and human health.The development of high-efficiency treatment technology for water bodies containing heavy metal complexes is an important proposition in the field of water pollution control and water environmental protection.In this study,Fe-MOF and Ce-doped modified Fe-MOF were prepared and used as heterogeneous catalysts for electrocatalytic activation of peroxodisulfate（PDS）.And the EC/MOF/PDS system was constructed to break the complex to degrade the heavy metal-EDTA complex.The effect,key influencing factors and mechanism of EC/MOF/PDS system on Cu-EDTA decomplexation were mainly explored.The specific conclusions obtained are as follows:（1）The Fe-MOF catalytic was prepared by a simple and rapid microwave method,and its morphology,structure and composition of Fe-MOF were analyzed by SEM,FT-IR,XRD and BET.The EC/Fe-MOF/PDS system was constructed for the degradation of Cu-EDTA complexes.In this process,the contribution of each part in the EC/Fe-MOF/PDS system was studied using combining the characterization and the degradation performance of different systems.The performance of the EC/Fe-MOF/PDS system was investigated by changing the reaction conditions such as the amount of catalyst,PDS concentration,pH,current density,and electrolyte concentration.Finally,the stability of the constructed catalytic system was investigated.The results show that:The Fe-MOF prepared in this study has a spindle structure with polycrystalline aggregate growth,good crystal crystallization,rich functional groups,large specific surface area and pore size structure,which can provide sites for the degradation of organic pollutants.XPS characterization showed that the ratio of Fe（Ⅱ）/Fe（Ⅲ）on Fe-MOF increased from 0.003 to 0.121 after the reaction,and the EC/Fe-MOF/PDS system also achieved complete degradation of Cu-EDTA at 100 min.It shows that the electric assist accelerates the redox cycle,thereby improving the catalytic performance.With the increased cycles,the removal efficiency increased significantly,and the pseudo-first-order kinetic constant k value of the system increased from 4.15×10^-2min^-1in the first cycle to 7.28×10^-2min^-1in the fifth cycle.It is indicated by XPS and EDS characterization that Cu（0）/Cu（Ⅰ）/Cu（Ⅱ）is formed on the surface of the catalytic material after the reaction.Due to the continuous deposition of Cu species on the surface of the MOF,Cu（0）/Cu（Ⅰ）/Cu（Ⅱ）on the catalyst was finally obtained.the redox of the Cu（0）/Cu（Ⅰ）/Cu（Ⅱ）couple on the catalyst participates in the activation of PDS,which makes the degradation performance of the catalyst significantly enhanced.The intermediate products of the reaction process were studied by FT-ICR-MS technology,and it was proposed that Cu-EDTA was gradually decomposed into small molecular substances and inorganic substances through the decarboxylation/deamination process.Electron spin resonance（ESR）and radical quenching experiments confirmed that sulfate radical(SO₄^·-)and hydroxyl radical（HO^·）in EC+Fe-MOF+PDS system play an important role in the degradation of Cu-EDTA complexes.In addition,the EC/Fe-MOF/PDS system also showed good performance for the degradation of other heavy metal-EDTA complexes,which could be completely degraded within 100 min.（2）The Fe-MOF was modified by Ce doping,and the preparation conditions were optimized by adjusting the Ce doping amount and metal-organic ligand ratio.When the ratio of the two metals is Fe:Ce=5:4 and the metal-organic ligand ratio is M:TA=10:8,the EC+Ce/Fe-MOF+PDS system has the best catalytic effect,the Cu-EDTA complex can be completely removed within 50 min and the pseudo-first-order kinetic constant k value is0.138 min^-1.The BET,FT-IR and XRD characterization methods were used to analyze the morphology,structure and composition differences after doping,and it was confirmed that the doping of Ce led to the generation of more ligand defects,and also increased the pore size and specific surface area of the material,increasing the catalyst.Electrochemical characterization proved that Ce doping improved the catalytic performance of MOF materials.The experimental results show that Ce/Fe-MOF contains oxygen vacancies.The EPR experiments and free-radical quenching experiments show that the active component of EC+Ce/Fe-MOF+PDS system is synergistically promoted by oxygen vacancies,Fe²⁺/Fe³⁺,Ce³⁺/Ce⁴⁺.