Study On Polyvinylidene Fluoride Ultrafiltration Membrane Modified By Hydrophilic Carbon Nanomaterials(GO/AGQDs)

In order to improve permeability,anti-fouling performance of polymer-matrix membrane as well as endow it with new functions,carbon nanomaterials have been widely used in the hydrophilic modification of polymer-matrix membrane.However,there are few reports on the migration behavior,distribution and immobilization strategy of carbon nanomaterials in polymer-matrix membrane.In this paper,the distribution and migration mechanism of graphene oxide(GO)in polyvinylidene fluoride(PVDF)matrix membrane were firstly studied by physical blending.Then,the immobilization strategy of amino acid functionalized carbon quantum dots(AGQDs)on the surface of PVDF membrane was studied by chemical grafting.Through these two different modification methods,hydrophilic carbon nanomaterials can be enriched on the membrane surface to enhance the selective permeability and anti-fouling performance of PVDF ultrafiltration membrane.The detailed results are as followed:(1)GO were prepared by modified Hummers method and a series of characterization were conducted to prove its successful synthesis.Then,three kinds of polyvinylpyrrolidone(PVP)with different molecular weights(PVPK17,PVPK30,PVPK90)were used as the pore former and GO were used as hydrophilic nanomaterial to prepare PVDF/GO mixed matrix membrane by phased inversion methods.The migration behavior and distribution of GO in PVDF mixed matrix membrane as well as the microstructures and performance of modified membranes were investigated.Compared with K17(9 kDa)and K30(50 kDa)with the relatively lower MW,K90 with higher MW(1400 kDa)promoted more GO to migrate toward the membrane surface due to the strong hydrogen bonding interactions between K90 and GO.On the contrary,K17 and K30 favored more GO embedded within PVDF matrix nanocomposite membranes due to the weak interactions between K17/K30 and GO.As a result,the PMGK90 membrane incorporating PVPK90 and GO possessed the superior water permeability(694.3 LMH·bar-1)with the lowest water contact angle(66.85°)and the maximum surface free energy(51.16 mJ/m2).Moreover,the PMGK90 membrane exhibited the excellent antifouling performance in 8 types of experimental membranes with minimum BSA adsorption(21.47 μg/cm2),higher flux recovery rate(89%)and the lowest irreversible fouling(11%)resulted from the synergetic effects of PVPK90 and GO that contribute GO to migrating to the membrane surface.Therefore,the migration and distribution of GO in PVDF membrane matrix could be regulated by PVP with different molecular weight,which provides a facile approach to improve the separation performance of PVDF mixed matrix membrane(2)AGQDs were prepared by hydrothermal method using citric acid as carbon source and aspartic acid as functionalized agent,and its successful synthesis was proved by a series of characterization.Then,three types of amines with different molecular weight(EDA,PEIL,PEIH)were used to modify the surface of PVDF membrane by Michael addition reaction,and then AGQDs were fixed on the surface of PVDF membrane by amination reaction.Compared with PEIL and EDA,PEIH with higher molecular weight has larger steric hindrance,which makes AGQDs grafting reaction more likely to occur on the surface of the membrane rather than inside the membrane pore.Therefore,more AGQDs were grafted and fixed on the surface of PVDF-PEIH-AGQDs membrane.The water contact angle of PVDF-PEIH-AGQDs membrane was 50.7°,the water flux reached 197.14 LMH,and the flux recovery rate after being fouled by lysozyme and BSA was 93.50%and 74.00%respectively,showing the best comprehensive performance in prepared 7 types of experimental membranes.