Research On The Construction And Performance Of Anti-fouling Thin-layer Composite Polyamide Membrane

Thin-film composite?TFC?polyamide?PA?membrane is a breakthrough in the field of membrane separation due to its unique asymmetric structure and excellent perm-selectivity.TFC membranes have been widely used in both the pressure-driven membrane processes,like reverse osmosis?RO?and nanofiltration?NF?,and the osmotic-driven separation processes,like forward osmosis?FO?process.However,membrane fouling,which generally causes a reduction of separation efficiency and increases the operation cost,is still a main obstacle of restricting the further application of TFC membranes.In this work,the research progress of TFC membrane fouling in the pressure-driven and osmotic-driven membrane process were reviewed and discussed.The TFC membrane surface modification of the dense PA active layer and the microporous support layer were proposed and investigated.The antifouling properties of the TFC membranes in the two different membrane processes were improved without sacrificing their perm-selectivity.The major research focuses on the following:?1?Fabrication of antifouling TFC NF membrane via in-situ surface grafting of PEI followed by zwitterionic modificationA zwitterion-modified TFC NF membrane?NF-ZPEI?was fabricated through grafting the hydrophilic branched polyethyleneimine?PEI?onto the PA layer,followed by in-situ quaternization.Results show that the formation of zwitterions on the polyamide layer dramatically improved the surface hydrophilicity without affecting the thickness and surface morphology of the polyamide layer.The NF tests present that the NF-ZPEI membrane exhibited the enhanced water permeability 11.6%higher than the control sample?NF-PA?,and the excellent selectivity to mono-divalent salt ion.Thanks to the formation of hydration layer and the steric hindrance of the zwitterionic PEI branches,the NF-ZPEI membrane possessed an improved antifouling property regardless of the charge property of the foulant,and achieved a suppressed flux decline rate?FDR?of 21.8%and 40.2%during the fouling process by bovine serum albumin?BSA?and lysozyme?LYZ?,respectively,which were much lower than those of the pristine membrane?33.5%&68.9%?.Moreover,the corresponding flux recovery rates?FRRs?of NF-ZPEI membrane were 86.2%and 91.9%,higher than the values of the pristine membrane.?2?Fabrication of the TFC FO membrane with sandwich-like CNTs-coated support to simultaneously improve the perm-selectivity and antifouling propertyThe sandwich-like carbon nanotubes?CNTs?-coated composite support was successfully prepared through the deposition of CNTs on both sides of the polyethersulfone?PES?microfiltration?MF?membrane for the fabrication of high flux and antifouling TFC FO membrane.The CNTs top layer facilitated the formation of polyamide layer.The CNTs back layer provided an antifouling surface for the prevention of foulants adsorption and intrusion into the PES support.Results demonstrate that the CNTs back layer exhibited the superior rejection towards BSA??98%?and the enhanced hydrophilicity.Compared with the control sample,the water permeability coefficient?A value?of the TFC FO membrane having the sandwich-like CNTs-coated support?TFC-M?were increased by 29.3%,meanwhile,and the structural parameter?S value?was decreased by 20.0%.Furthermore,the TFC-M membrane exhibited excellent perm-selectivity with the water flux J_w of 35.66 Lm^-2h^-1 and the reverse salt flux J_s of 1.42 gm^-2h^-1 when tested in the membrane orientation of the active layer facing to a draw solution?AL-DS?of 1 M Na Cl.Dynamic BSA fouling experiments confirm that the FDR of the TFC-M membrane was decreased by 17.1%,compared with the TFC FO membrane without the CNTs back layer.Aiming to improve the antifouling property of the TFC membrane for different membrane processes,two kinds of TFC membranes were fabricated in this work through zwitterionic surface modification of the PA layer and rational design of the support layer.The transport properties and the antifouling properties of these TFC membranes were comprehensively investigated.Our work shines a light on the structure design and performance optimization of the high-performance TFC membrane having the enhanced flux and antifouling properties.