Preparation And Properties Of Magnetic Carbon Nanotube-modified Polyvinyl Chloride-based Composite Nanofiltration Membranes

In this paper,the magnetic ferroferric oxide/oxidized multi-walled carbon nanotubes(Fe₃O₄/o-MWCNTs)composite particles synthesized by the chemical coprecipitation method was used as additives to prepare magnetic carbon nanotube modified polyvinyl chloride porous support membrane(Fe₃O₄/o-MWCNTs/PVC)with high porosity and hydrophilicity through the magnetic field assisted non-solvent induced phase separation method(NIPS).Then the ultra-thin polyamide(PA)layer was constructed on the surface of the modified porous support membrane by the interfacial polymerization method to prepare the PA/Fe₃O₄/o-MWCNTs/PVC composite nanofiltration membrane.The surface enrichment behavior of magnetic nanoparticles under magnetic field assisted conditions and their effects on the structure and performance of porous support membrane and ultra-thin separation layer were studied,and the comprehensive performance of composite nanofiltration membranes was optimized.Fe₃O₄/o-MWCNTs composite nanoparticles with excellent hydrophilicity and superparamagnetism synthesized by chemical co-precipitation method were used as additives and PVC was used as the membrane-forming polymer.Fe₃O₄/o-MWCNTs/PVC membrane was prepared by NIPS under the magnetic field.The effect of the addition of magnetic Fe₃O₄/o-MWCNTs and its directional migration under the magnetic field on the structure and performance of the Fe₃O₄/o-MWCNTs/PVC porous membrane were investigated.The results showed that the addition of hydrophilic Fe₃O₄/o-MWCNTs nanoparticles and its directional migration to the membrane surface under the action of magnetic field promoted the double diffusion and microphase separation processes in the membrane formation process,which simultaneously increased the membrane porosity,hydrophilicity,pure water flux and bovine serum albumin(BSA)rejection ratio.The Fe₃O₄/o-MWCNTs/PVC porous membrane prepared under the action of magnetic field exhibited higher pure water flux(400 L·m^-2·h^-1)and outstanding BSA rejection ratio(89%),which were 60%and 117%higher than the PVC pristine membrane.Take Fe₃O₄/o-MWCNTs/PVC porous membrane assisted by magnetic field as support membrane,and anhydrous piperazine(PIP)aqueous phase solution mixed with compound acid binding agent triethylamine(TEA)and camphorsulfonic acid(CSA),and trimesoyl chloride(TMC)oil phase solution were configured,respectively.Then the PA/Fe₃O₄/o-MWCNTs/PVC composite nanofiltration membrane was prepared by interfacial polymerization.The effect of the magnetic carbon nanotube modified PVC porous support membrane on the surface chargeability,PA layer thickness,mechanical properties,pressure resistance and permeability of the composite nanofiltration membrane were investigated.The results indicated that the composite nanofiltration membrane prepared by the Fe₃O₄/o-MWCNTs/PVC porous support membrane obtained under the magnetic field emerged smaller roughness,thinner PA layer,larger pore size,excellent mechanical properties and better pressure resistance.The prepared composite nanofiltration membranes presented excellent divalent salts rejection,and the rejection ratio of Mg SO₄and Na₂SO₄ were above 95%and 93%,respectively.The permeation flux of PA/Fe₃O₄/o-MWCNTs/PVC composite nanofiltration membrane prepared by Fe₃O₄/o-MWCNTs/PVC porous support membrane under the magnetic field was the best,which could reach 35.4 L·m^-2·h^-1.