Separation And Anti-fouling Performance Of The Modified PTFE Prous Membrane

Membrane separation technology has the advantages of green environmental protection,low cost,high efficiency,no secondary pollution,etc.,and has received extensive attention in the fields of dyeing wastewater and sewage treatment.However,problems such as inevitable membrane fouling during the separation process limit the development of membrane technology.Polytetrafluoroethylene?PTFE?membranes can be used in harsh separation environments due to their high chemical stability,resistance to acid,alkali and high temperature,etc.But their hydrophobicity results in poor wetting properties and anti-fouling properties on the membrane surface,limiting the large-scale application of PTFE membranes in the field of water treatment.In this paper,the PTFE porous membrane was hydrophilically modified to improve separation and anti-fouling performance of the membrane.The PTFE membrane was firstly modified with fluorocarbon surfactant?QS?solution.The surface structure,morphology,wettability and fouling behavior to humic acid?HA?and lysozyme?LYS?aqueous solution of membranes modified by different content QS were studied.On this basis,XDLVO theory was used to investigate the contribution of interface free energy to the contamination of PTFE membranes modified by different content QS.The fouling mechanism of humic acid?HA?and lysozyme?LYS?to PTFE membranes modified by different content QS were analyzed.Finally,by linearly fitting the trend of hydrophilic PTFE membrane modified with different QS content and the interface free energy calculated by XDLVO theory,the consistency between the membrane fouling of the actual filtration process and XDLVO theoretical analysis was verified.The results showed that when the QS content was 0.8wt%,the surface water contact angle of the hydrophilic modified PTFE membrane was 2.1°,which was super hydrophilic.The results of membrane filtration experiments showed that the QS hydrophilic modified PTFE membrane helped to reduce the flux decline rate during membrane filtration.When the superhydrophilic PTFE membrane modified by 0.8wt%QS filtered HA or LYS aqueous solution,the rate of decline in flux was the slowest throughout the process.The theoretical analysis of XDLVO showed that QS was beneficial to enhance the interfacial interaction between PTFE membrane surface and foulants.The interface free energy between QS modified superhydrophilic PTFE membrane and HA or LYS was the largest,which was greater than 34.151 and6.863mJ/m²,respectively,showing the membrane had the best anti-fouling performance.The fouling trend and interfacial free energy of hydrophilic modified PTFE membrane with different QS content were linearly fitted,and the correlation coefficient was greater than 0.902,which proved the consistency between membrane filtration and XDLVO analysis.In order to improve the separation performance of PTFE microfiltration membrane,PEI/PVP-PTFE loose nanofiltration membrane was prepared by the PTFE membrane modified with polyelectrolyte polyethyleneimine?PEI?/polyvinylpyrrolidone?PVP?.The surface structure,morphology and wettability of PEI/PVP-PTFE loose nanofiltration membrane were studied.The nanofiltration separation and desalination performance of the prepared PEI/PVP-PTFE loose nanofiltration membrane on chrome black T,congo red and evans blue aqueous solution were investigated.And the long-term stability,acid and alkali resistance and anti-fouling properties of PEI/PVP-PTFE loose nanofiltration membrane prepared under optimal conditions were studied.The membrane prepared under optimal conditions had a water contact angle of 8.7°and showed hydrophilicity.The prepared PEI/PVP-PTFE loose nanofiltration membrane can effectively separate the aqueous solutions of chrome black T,congo red and evans blue dyes.The rejection rate was greater than 92.8%,and the flux was greater than200.3L·m^-2·h^-1·MPa^-1.In addition,the optimum membrane was continuously operated in 10.0ppm evans blue and congo red aqueous solution for more than 80h showing good stability.The prepared PEI/PVP-PTFE loose nanofiltration membrane was kept at146.2L·m^-2·h^-1·MPa^-1 for 30h in a 10ppm evans blue aqueous solution containing 3.0wt%HCl.The rejection rate remained at 85.3%,indicating good acid resistance.The prepared PEI/PVP-PTFE loose nanofiltration membrane separated 10.0ppm chrome black T,congo red,and evans blue aqueous solution containing 100ppm of sodium chloride and flux was greater than 193.4L·m^-2·h^-1·MPa^-1.The dye rejection rate was greater than 91.3%and the rejection rate for sodium chloride was less than 13.4%,showing good dye desalination effect.And continuous operating for 60hours in evans blue and congo red aqueous solution containing sodium chloride,the stability performance of dye desalination was good.The HA or LYS were selected as typical foulants to study the anti-fouling performance of PEI/PVP-PTFE loose nanofiltration membrane.The results showed that the flux retention of membranes was 87.2%and70.4%after five cycles.Theoretical analysis of XDLVO showed that compared with the PTFE original membrane,the PEI/PVP-PTFE loose nanofiltration membrane had greatly improved anti-fouling performance.