Preparation Of Composite Nanofiltration Membrane Based On Pre-deposited MOFs And Study On PPCPs Remova

Pharmaceutical and personal care products（PPCPs）are organic micropollutants widely found in wastewater,including pharmaceuticals and clean products.They are highly toxic and bioaccumulative,which pose a potential threat to human and ecological environment.Nanofiltration is considered to be an effective technology for the removal of PPCPs from water,but it is not satisfying for the removal of neutral and hydrophobic small molecules.Recently,metal-organic frameworks（MOFs）have been widely used in the modification of nanofiltration membrane due to their strong chemical stability,adjustability and organic compatibility.In this paper,two kinds of MOFs,polyethyleneimine（PEI）modified ZIF-8 and UiO-66-NH₂,modified with polyethyleneimine（PEI）,were respectively pre deposited on the surface of polyacrylonitrile（PAN）based membranes.The details are as follows.（1）PEI-modified ZIF-8 nanocrystals were self-assembled into hydrophilic star-shaped particles（ZIF-8-PEI）.The ZIF-8-PEI particles supported the cross-sectional profile of the PA layer,increasing the roughness of the PA layer and the permeation area.In addition,the hydrophilic and stellate structure of the ZIF-8-PEI distributed on the PAN membranes adsorbed more aqueous piperazine（PIP）solution and a regular tent-like and reticulated PA flim with increased effective membrane surface area and additional water transport channels were formed after the interfacial polymerization.At a ZIF-8-PEI loading mass of 1.27 mg·cm^-2,the water permeance of the TFN membrane was 18.55 L·m^-2·h^-1·bar^-1 which increased by a 79%compared to the TFC membrane,while the retention of SO₄^2-was maintained at 93.4%.In addition,the enhanced surface hydrophilicity of the TFN membrane and the hydrophilicity of the ZIF-8-PEI reduced the interaction between the hydrophobic PPCPs and the PA layer;therefore,the retention rates of methyl paraben,propyl paraben,bisphenol A,were respectively41.7%,26.8%,54.8%,higher than TFC membranes.（2）By pre-deposition of UiO-66-NH2 onto the surface of the base film.The hydrophilic UiO-66-NH₂ distributed on the substrate induced a hydrophilic membrane surface and interfacial hydrophilic channels,thus improving the mass transfer resistance of hydrophobic PPCPs.On the other hand,the covalent bonding between amine groups of UiO-66-NH₂ and TMC rendered the MOF crystals to be stably fixed in the formed PA layer,which significantly improved of the interfacial stability and avoided the generation of non-selective defects.At a UiO-66-NH₂loading of 10.83μg cm^-2,the water permeance of the TFN membrane was 25.83 L·m^-2·h^-1·bar^-1,115%higher than that of TFC membrane,and Na₂SO₄ retention was 96.1%.The retention rates of methyl p-hydroxybenzoate,propyl p-hydroxybenzoate,bisphenol A and benzyl p-hydroxybenzoate were respectively 49.5%,66.9%,74.5%and 85.2%,much higher than those of the TFC membrane.Moreover,the water/PPCPs selectivity was increased by up to 5 times compared to the TFC membrane.This work provided useful ideas for the preparation of highly efficient nanofiltration membranes for the enhanced removal of hydrophobic PPCPs from wastewater.