Research On The Preparation And Performacne Of Functional Separation Membranes By Radiation Induced Direct Crosslinking

Due to the advantages of green,high efficiency and energy saving,membrane separation technology has been widely used in many fields,such as chemical production,pharmaceutical engineering and environmental protection.As the core of membrane separation technology,the performance of the membrane is the key to determine the production efficiency and application scope in membrane separation projects.However,with the development of membrane separation technology,conventional membranes have been unble to meet the needs of expanding applications.Therefore,the research of high-performance functional membranes has become an important prerequisite for the further development of membrane separation technology.In general,the study of high-performance membranes is mainly from three aspects,including the improvement of membrane structure,the development of new membrane materials and the modification of membranes.For polymer membranes,the membrane modification is the most common,feasible and effective technical route.Membrane modification includes physical modification(such as blending,coating,doping,etc.)and chemical modification(such as surface grafting,crosslinking,etc.).Among them,chemical modification means that the founctional components are firmly connected with membranes via covalent bonds,endowing the membrane with durable and stable functionalization.The radiation induced graft polymerization(RIGP)is an important method for the chemical modification of polymer membranes,because of convenient operation,high efficiency,mild reaction condition and wide application.Nevertheless,RIGP is often performed using vinyl monomers or macromers as modifiers,which are costly and unsuitable to obtain,thus hindering the application in polymer membrane modification.In contrast,radiation induced direct crosslinking(RIDC),as another important way in polymer radiation,has been neglected so far for polymer membrane functionalization.Herein,this paper is devoted to studying the feasibility of the modification and construction of polymer membranes through RIDC technology,and to evaluate the performances of the modified membranes.(1)Functionalization of polymer membranes by RIDC.First,the poly(vinyl alcohol)(PVA)gel was constructed on the membrane surface and pores inner surface of poly(vinylidene fluoride)(PVDF)membranes via RIDC,realizing the three-dimensional(3D)modification of the membrane.The results of FTIR,XPS and solid state NMR proved the formation of covalent bonds between PVA gel layer and PVDF membranes,and the order of factors affected the PVA loading on PVDF membrane is as follow:PVA concentration>absorbed dose>dose rate.In addition,the water flux of modified PVDF membranes was decreased with the increase of PVA loading,while the retention performance shows the opposite trend.The PVDF microfiltration membrane was transformed into ultrafiltration membrane after the modification in high PVA loading.Moreover,in the study on the versatility of RIDC,poly(vinyl pyrrolidone)(PVP),sodium alginate(SA)and poly(ethylene glycol)(PEG)were successfully covalently anchored on PVDF membranes.It was found that the crosslinking ability of modifiers under radiation is an important factor for its modification on the PVDF membrane.On the basis of the above research,we further explored the performances of PVDF/PVA hybrid membranes prepared under low absorbed dose(17 k Gy)and high absorbed dose(200 k Gy)for separating oil-in-water emulsion and anti-protein pollution,respectively.In the separation of oil-in-water emulsions,the PVDF/PVA hybrid membranes(17 k Gy)has good hydrophilicity,underwater superoleophobicity and excellent oil adhesion resistance.The modified PVDF membrane not only exhibits good permeation flux(?6.9×10² L m^-2 h^-1 bar^-1),high water flux recovery(?98%)and excellent oil rejection(?99.5%)through cross-flow filtration under ultra-low pressure(0.084 bar),but also can separate a variety of oil-in-water emulsions and shows excellent anti-pollution performance for high viscosity oils.In the anti-protein contamination test,the PVDF/PVA hybrid membranes(200 k Gy)shows high water flux recovery(>95%)and ultra-low irreversible pollution rates(<5%)of bovine serum albumin(BSA)and lysozyme.Even through multiple cycles,it still has a good flux recovery(?85%).Moreover,the covalently anchored PVA gel endows the PVDF membrane with good chemical resistance in acidic,alkaline and Na Cl O solution.(2)Preparation of MWNTs-based membranes by RIDC and its application in oil-in-water emulsion separation.Based on the previous work,the multi-walled carbon nanotubes(MWNTs)was modified by PVA chains through RIDC.FT-IR,¹H-NMR and TEM results demonstrated that PVA chains were successfully covalently connected onto MWNTs,which exhibited excellent dispersibility and stability in aqueous solution.Furthermore,the bucky papers(BP)were facilely constructed by depositing the modified MWNTs on cellulose acetate(CA)membranes by vacuum filtration,which showed great hydrophilicity and underwater superoleophobicity.The obtained BP membranes were used to separate various oil-in-water emulsions and exhibited high filtration flux and oil rejection.Moreover,even in the long time cycle separation of high viscosity engine oil-in-water emulsion,the BP membrane still maintained the high water flux recovery(>86.5%)and oil rejection(>99.4%).(3)Preparation of GO-based membrane by RIDC and its application in acid recovery via diffusion dialysis.The graphene oxide(GO)and PVA hybrid membranes(r AGO)were prepared by combining RIDC and vacuum-assisted self-assembly.High-energy rays not only initiated the reduction of GO sheets,but also formed covalent bonds between PVA chains and GO sheets.The XRD result showed that there were two regions in r AGO membrane,including the GO sheets intercalated by PVA chains and tightly stacked reduced GO sheets.This unique structure of r AGO membrane could effectively inhibit the penetration of metal ions while allowing the transport of H⁺due to the steric hindrance of PVA and size exclusion of reduced GO sheets.Furthermore,in the recovery of low-concentration acid(0.1 M)from a series of metal ion solutions by DD process,the H⁺dialysis coefficients(U_H)of the r AGO membrane were around 5(10^-3m h^-1),reached the level of commercial anion exchange membrane(DF-120).Meanwhile,the obtained separation factor(S_H+/Fe2+)of r AGO membrane was 233.6,achieving the selective separation of H⁺and metal ions in acid recovery.