Study On Preparation And Performance Of Anti-fouling Composite Nanofiltration Membranes

Nanofiltration membranes had the characteristics of high separation efficiency and low energy consumption,and were widely used in seawater freshwater pretreatment,drinking water industry,food industry and other fields.However,membranes fouling occurs during the use of nanofiltration membranes,which will limit the large-scale application of nanofiltration membranes.Therefore,improving the anti-fouling performance of nanofiltration membranes were of great significance to the development of nanofiltration membranes.Therefore,improving the anti-fouling performance of nanofiltration membranes were of great significance to the development and application of nanofiltration membranesIn this paper,hydrophilically modified polytetrafluoroethylene(PTFE)flat membranes were used as the base membranes,polyethyleneimine(PEI)was used as the aqueous monomer,and trimesoyl chloride(TMC)was used as the oil phase monomer.The silane coupling agent(KH560)was used as the grafting monomer,and tetraethyl orthosilicate(TEOS)was used as the modifying monomer.The polyamide(PA)functional layer was firstly reacted by PEI and TMC,then KH560 was grafted on the PA functional layer,and finally the grafted PA functional layer was modified with TEOS to obtain PEI/TMC/KH560/TEOS composite nanofiltration.membranes.The properties of PEI/TMC/KH560/TEOS composite nanofiltration membranes were investigated by investigating the concentration of grafting monomer KH560,the grafting time of KH560,the concentration of modified monomer TEOS,the modification time of TEOS,the heat treatment temperature and the heat treatment time.The separation performance of PEI/TMC/KH560/TEOS composite nanofiltration membranes were studied,thus the optimum conditions for the preparation of PEI/TMC/KH560/TEOS composite nanofiltration membranes were obtained.Surface chemical structure,surface morphology of PEI/TMC/KH560/TEOS composite nanofiltration membranes were characterized by attenuated total reflectance Fourier transform infrared spectroscopy(ATR-FTIR),scanning electron microscopy(FE-SEM).The separation performance of PEI/TMC/KH560/TEOS composite nanofiltration membranes for four salt solutions(MgCl2,MgSO4,Na2SO4,NaCl),molecular weight cut off(MWCO)and pure water flux were tested by cross-flow filter;the anti-fouling performance of PEI/TMC/KH560/TEOS composite nanofiltration membranes were determined by using bovine serum albumin(BSA)and sodium dodecyl sulfate(SDS)as standard pollutants.Results are as follows:(1)During the preparation of PEI/TMC/KH560/TEOS composite nanofiltration membranes,with the increase of of KH560 concentration,the prolongation of grafting time,the increase of TEOS concentration,the prolongation of modification time,the increase of heat treatment or the prolongation of heat treatment time,the rejection rate of PEI/TMC/KH560/TEOS composite nanofiltration membranes increases first and then decreases,the permeate flux decreases first and then increases,and the anti-fouling performance first increases and then decreases.Considering the influence of various preparation conditions on membranes separation performance and anti-fouling performance,the optimum preparation conditions for preparing PEI/TMC/KH560/TEOS composite nanofiltration membranes are determined as follows:the concentration of KH560,grafting time,the concentration of TEOS(volume ratio)(TEOS:ethanol),modification time,the temperature of heat treatment,and the heat treatment time were 2 wt%,2 h,1:4,1 h,40? and 15 min,respectively.(2)Fourier infrared spectroscopy results show that KH560 was successfully grafted onto the membranes,and TEOS was successfully reacted with KH560 to form silica.The morphology of PEI/TMC/KH560/TEOS composite nanofiltration membranes were observed by field emission scanning electron microscopy.It was found that fine particles were formed on the surface of the prepared PEI/TMC/KH560/TEOS composite nanofiltration membranes.(3)The molecular weight cut-off of PEI/TMC/KH560/TEOS composite nanofiltration membranes is 480Da.With the pressure rising from 0.2MPa to 0.6MPa,and the pure water flux of the PEI/TMC/KH560/TEOS composite nanofiltration membranes increases from 0.63 L/m2-h to 2.48L/m2·h The rejection of the four kinds of salt solutions follow the orders:MgCl2>MgSO4>Na2SO4>NaCl.(4)KH560 was grafted on the PA functional layer,and the grafted PA functional layer was modified with TEOS.The prepared PEI/TMC/KH560/TEOS composite nanofiltration membranes had good anti-fouling performance.The steady-state flux reduction ratios of the PEI/TMC/KH560/TEOS composite nanofiltration membranes to BSA,SDS aqueous solutions were 29.5%and 35.1%,respectively,while for the PEI/TMC composite nanofiltration membranes,they were 31.2%and 52.8%,respectively.After physical cleaning,the flux of PEI/TMC/KH560/TEOS composite nanofiltration membranes and PEI/TMC composite nanofiltration membranes were recovered;when the pollutant is BSA,the flux recovery ratio(FRR)of the BSA-fouled membranes increased from 93.2%of the PEI/TMC composite nanofiltration membranes to 95.7%of the PEI/TMC/KH560/TEOS composite nanofiltration membranes;the FRR of SDS-fouled membranes increased from 83%of PEI/TMC composite nanofiltration membranes to 96.5%of the PEI/TMC/KH560/TEOS composite nanofiltration membranes.