Preparation And Separation Performance Of ZIFs/PES Composite Membranes

Polyethersulfone（PES）is a typical polymer membrane material with thermal stability and chemical inertness.Zeolite imidazole frameworks（ZIFs）have aqueous solution stability.In this paper,ZIFs and PES were combined to prepare ZIFs/PES membrane for the separation of dyes and heavy metal ions.Firstly,the prepared ZIF-67 nanoparticles were blended in the PES membrane,and the chemical composition and morphology of the membrane were characterized by Fourier transform infrared spectroscopy（FTIR）,scanning electron microscopy（SEM）and X-ray diffraction（XRD）.The results showed that ZIF-67 nanoparticles were loaded on the surface of the substrate and inside the pores.In addition,contact angle and water flux experiments showed that the hydrophilicity and permeability of the blend membrane were significantly improved after adding ZIF-67 nanoparticles.The blend membrane was used for dye separation,and it was found that the dye retention rate and adsorption performance were significantly improved.The retention rate of Congo red（CR）and Rhodamine B（Rh B）was99.8%and 23.4%,respectively.In addition,the blend membrane was used for the separation of tungstate ions（W（VI））with a retention rate of 50%.Therefore,blending ZIF-67nanoparticles in PES membrane can significantly improve the performance of the membrane.Then,based on the synthesis of ZIF-8 nanoparticles,ZIF-8/CS@PES composite membrane was prepared by compounding with chitosan（CS）.The chemical composition,morphology,structure,surface properties and permeability of the composite membrane were tested by FTIR,XRD,SEM,AFM,contact angle and water flux.The membrane was used for the separation of CR,Rh B and W（VI）,and its thermodynamic（Langmuir and Freundlich adsorption isotherms）and kinetic（quasi-first-order and quasi-second-order kinetics）behaviors were studied.The results showed that the adsorption of CR,Rh B and W（VI）on ZIF-8/CS@PES composite membrane was monolayer chemical adsorption,and the adsorption mechanism was mainly charge exclusion,hydrogen bonding and metal coordination.Finally,based on the synthesis of Zn/Co-ZIF bimetallic nanoparticles,Zn/Co-ZIF@PES blend membrane was prepared.NH₂-Zn/Co-ZIF nanoparticles were synthesized by amino modification of Zn/Co-ZIF nanoparticles,and NH₂-Zn/Co-ZIF@PES blend membrane was prepared.The chemical composition,morphology,structure,surface properties and permeability of the blend membrane were characterized by FTIR,XRD,SEM,contact angle and water flux,and they were used for dye treatment and W（VI）separation.The results showed that blending Zn/Co-ZIF or NH₂-Zn/Co-ZIF nanoparticles in PES membrane could significantly improve the hydrophilicity,permeability,dye and W（VI）removal rate of the blend membrane.When the addition amount of nanoparticles was 0.4wt%,the rejection rates of CR and W（VI）were 99.8%and 63.1%,respectively,indicating that the separation performance of the blend membrane was significantly improved.