Water-salt Transport Of Hydrophilized Polyethersulfone

Polymer-based desalination membrane processes(such as reverse osmosis(RO)and nanofiltration(NF))have been extensively developed.As the mainstream commercial polyamide reverse osmosis membrane,the thin-layer composite layer has shortcomings such as poor pollution resistance and poor chlorine resistance,which limit its application and long-term performance.Sulfonated polyethersulfone has been proven to be a reverse osmosis/nanofiltration membrane material with excellent chlorine resistance,however its desalination performance is not comparable to that of commercial polyamide membranes.Based on this,we prepared hydrophilic polyethersulfone with controllable content of carboxyl,amino and zwitterion hydrophilic side groups by thiol-ene click chemistry reaction.The water/salt mass transfer properties of the hydrophilized polyethersulfone membrane were studied based on the solution-diffusion theory,which provided theoretical guidance for the preparation of good chlorine-resistant desalting membrane.The results show that:(1)The ~1H NMR spectrum proved that BPES with different double bond content was successfully synthesized,and its molecular weight decreased with the increase of the proportion of ally-containing monomers,which may be related to the low reactivity of diallyl bisphenol sulfur.Three sulfhydryl-containing small molecules(TGA,DL-CYSAH and DMAET)were bonded to BPES through the thiol-ene click chemistry reaction.As the content of double bonds in BPES increasesd,the content of small molecules increased.The water contact angles of the membranes after the hydrophilization modification were significantly reduced.As the content of small molecules increased,the water contact angle of the membrane gradually decreased.BPES-g-CYSAH exhibited the most excellent hydrophilic,owing to DL-CYSAH containing two hydrophilic groups;(2)The water uptake of BPES-g-DMAET membrane increased with the increased of the content of tertiary amine groups,which may be due to the increased free volume caused by the relative looser polymer chains packing with the presence of the bulky tertiary amine groups.The water uptake of BPES-g-CYSAH membranes and BPES-g-TGA membranes first increased and then decreased with the increase of small molecule content.This was because the increase of polar groups led to the enhancement of interaction between molecular chains,thus decreasing free volume;(3)With the increase of hydrophilic groups,the water permeability and diffusion coefficients of BPES-g-TGA and PES-g-DMAET membranes increased,while the water permeability and diffusion coefficients of zwitterionic BPES-g-CYSAH membranes increased first and then decreased,which was mainly related to the self-association of DL-CYSAH zwitterionic groups;(4)As the water partition coefficient increased,the salt partition coefficient of the hydrophilic modified BPES membrane increased slightly,but the salt diffusion coefficient did not change significantly,this was because the polar hydrophilic BPES inhibits the diffusion of salt ions.After hydrophilization modification,the water/salt solubility selectivity,water/salt diffusion selectivity and water/salt permeation selectivity of BPES membrane were increased,especially the water/salt permeation selectivity of BPES-g-CYSAH membrane exceeded the upper limit of Robeson.Hydrophilic modification can regulate the water and salt transport properties of the polyethersulfone membrane,which is expected to prepare desalination membranes with high water flux and rejection.