Preparation And Properties Of Porous Material Doped Polyamide Nanofiltration Membrane And Environmental Applications

Nanofiltration（NF）,as a pressure-driven membrane separation technology,can effectively separate divalent/polyvalent ions and organic molecules in the range of 200-1000 Da,and has wide application prospect in the fields of seawater desalination,wastewater treatment,and organic solvent treatment.At present,the main NF membranes on the market are polyamide（PA）thin film composite（TFC）membranes prepared by interfacial polymerization.However,PA TFC membrane has always been faced with the"trade-off"effect between permeation flux and rejection,that is,the membrane flux and rejection are mutually restricted,and it is difficult to improve simultaneously.Doping nanomaterials into PA selective layers to prepare thin film nanocomposite（TFN）membranes is expected to overcome the“trade-off”effect and improve the separation performance of nanofiltration membranes.However,the commonly used nanomaterials often have problems such as uneven dispersion and easy stacking.In view of these problems,this study proposes some effective solutions as follows:（1）Two-dimensional MXene nanosheets and three-dimensional accordion-like MXene（AMXene）particles containing two-dimensional nanochannels were assembled on porous substrates by vacuum assisted method,and then embedded into PA selective layer through interfacial polymerization.The experimental results show that,compared with the horizontal two-dimensional nanochannels formed by stacking of MXene nanosheets,the two-dimensional channels in randomly oriented AMXene give water a shorter transport path,making the membrane permeation flux reach to 24.1 L m^-2 h^-1bar^-1,which is 210%of that of the control membrane without AMXene.Meanwhile,its Na₂SO₄ rejection is 97.1%.In addition,this AMxene membrane also showed excellent performance in long-term stability tests.（2）A TFN-Zn O membrane containing Zn O nanoparticles was firstly prepared by interfacial polymerization method,and then the Zn O was in situ transformed into metal-organic framework ZIF-8 by reaction with 2-methylimidazole to prepare a TFN-ZIF-8membrane.Scanning electron microscopy and transmission electron microscopy characterization clearly revealed that ZIF-8 crystals with well-defined structure were uniformly dispersed in the PA layer.The pure water flux of TFN-ZIF-8 membrane is20.4 L m^-2 h^-1 bar^-1,which is 423%higher than that of TFC membrane as the control.Meanwhile,the rejection of Na₂SO₄ of the TFN-ZIF-8 membrane is 97.4%.（3）By adding Zn O nanoparticles into the polyimide（PI）casting solution,the base membrane containing Zn O was prepared and further crosslinked by hexadidiamine to get the Zn O/PI membrane.Then this Zn O/PI membrane was immersed in a solution containing 2-methylimidazole to grow ZIF-8 nanoparticles on its surface in situ.Finally,（PA/ZIF-8）/PI membrane was prepared by interfacial polymerization and used for solvent resistant nanofiltration.The results show that the nanofiltration membrane has a uniformly dispersed ZIF-8 intermediate layer,and the permeation flux of ethanol is1.6 L m^-2 h^-1 bar^-1,which is 510%of that of the control TFC membrane.Meanwhile,that membrane also maintain the high organic dye rejection:the rejection of Rose Bengal is 99.5%.In addition,the separation performance of TFN nanofiltration membrane for different organic dye wastewater and the reasons for its enhancement were also studied in detail.