Preparation Of MOF Membrane And Its Application In The Removal Of Heavy Metal Ions

The large amount of heavy metal ions in sewage poses a great threat to humans and the natural environment,because heavy metal ions are not biodegradable.Once they enter the human body directly through the biological chain or drinking water,they will cause irreversible damage to the human body.Therefore,how to efficiently and quickly remove heavy metal ions will be a challenging subject.Metal organic frameworks(MOFs),porous frameworks formed by the coordination of metal ions or metal clusters with organic ligands,have attracted widespread attention in recent years.Due to the characteristics of MOFs materials,such as ultra-high specific surface area,adjustable pore structure,and easy functionalization,they are widely used in gas separation,catalysis,drug loading,sensing and other fields.A large number of studies have proved the advantages of MOFs materials in the removal of heavy metal ions.However,it also faces many problems.The difficulty of processing,separation and recovery of MOFs powder materials and potential secondary pollution restrict the development of MOFs materials in the field of sewage treatment.Based on this,the strategy of MOF membrane was proposed,hoping to avoid the disadvantage of powder materials by changing the existing form of MOFs materials.On the basis of maintaining the structure and characteristics of MOFs powder materials,MOF membrane introduces membrane performance,which will be more conducive to the application of MOF membrane in the removal of heavy metal ions.In this paper,two kinds of MOF membranes were prepared by two easy to operate methods and their applications in the removal of heavy metal ions were investigated.1.A series of substrate-supported MOF membranes were prepared by a simple in-situ solvothermal method.Under solvothermal conditions,Zr-DMBD MOF can be obtained through coordinated connection of zirconium ion with 2,5-dimercaptoterephthalic acid(H₂DMBD).The mercapto functional group introduced on the MOF ligand can achieve the adsorption and removal of mercury ions through coordination with mercury ions.Filter paper was selected as the substrate,and Zr-DMBD MOF particles were grown on the filter paper to obtain MOF membrane,which was called Zr-DMBD filter membrane.X-ray diffraction(XRD),scanning electron microscopy(SEM),infrared(FT-IR)and other tests have proved the successful preparation of Zr-DMBD filter membrane.In the process of preparing filter membrane,it was found that the use of template trifluoroacetic acid(TFA)could effectively regulate the growth process of MOF particles.Under the guidance of filter paper substrate,more MOF particles grew on the filter paper.The mercury ion adsorption experiments were carried out with the prepared Zr-DMBD filter membrane.It was found that the prepared Zr-DMBD filter membrane has a good removal ability for mercury ions,97.8%of mercury ions in the solution can be removed within a few minutes,and it has good selectivity and stability.2.The self-supporting MOF membrane was prepared by the method of post-synthesis polymerization.The copolymerization process of NH₂-Ui O-66 and monomer methyl methacrylate(MMA)successfully chemically grafted the polymer polymethyl methacrylate(PMMA)on NH₂-Ui O-66 to obtain MOF polymer powder material,denoted as NH₂-Ui O-66-PMMA.The chemical interaction between the MOF material and the polymer can effectively improve the compatibility of the two,thereby preparing a continuous and defect-free MOF membrane.NH₂-Ui O-66-PMMA membrane was prepared by evaporation-induced interface assembly method on the water surface.The results of X-ray diffraction(XRD),scanning electron microscopy(SEM)and infrared(FT-IR)tests show that the NH₂-Ui O-66-PMMA membrane is successfully prepared.The prepared NH₂-Ui O-66-PMMA membrane has a good ability to remove lead ions.