The Construction And Performance Of Zwitterionic Surfaces For Antifouling Ultrafiltration Membranes

Ultrafiltration(UF) membrane which is a pressure driven process has attracted an increasing attention due to its convenience, low cost, and energy saving. However, membrane fouling which lead to a decrease in flux and memebrane life has already been the major obstacle limiting the further use of ultrafiltration in industrial operations. Therefore, it is essential to take modification on membrane. Zwitterions have a special chemical structure, which bears an equimolar number of anions and cations, to form tight hydration layer by electrostatic interaction to inhibit the contact between the pollutant and membrane surfaces. It has been widely used in hydrophilic modification of UF, because its hydration ability is stronger than that of hydrogen bond. This study investigated the antifouling performance of UF which was introduced different zwitterions. The details in this paper were summarized as follows.Firstly, the aminated PVC membranes were prepared via in-situ amination with triethylenetetramine(TETA) in the casting solutions, which was a convenient and feasible method to modify polymer material for membrane fabrication. The introduction of amino groups not only enhanced the hydrophilic property of PVC membranes but also provided the active chemical sites on the membrane surfaces. The aminated PVC membranes were then immersed into the sodium chloroacetate solution to carry out quaternary amination reaction. The zwitterionic groups were formed on the PVC membrane surfaces and pore walls. The zwitterionic PVC membranes exhibited better permeability and fouling resistance ability than the initial PVC membrane. The corresponding resistances of membrane, cake formation, adsorption, and pore blocking were calculated to explore the membrane fouling mechanism.Secondly, the branched polyethyleneimine(PEI) was employed to synthesize the zwitterion by quaternary amination reaction with sodium chloroacetate. A novel zwitterionic surface with neutral surface charge was constructed by grafting PEI-based zwitterion(Z-PEI) onto the hydrolyzed PAN(H-PAN) membrane surface. Covalent bonds were formed between Z-PEI and H-PAN membrane while the electrostatic attraction would promote this reaction. The zwitterionic membranes exhibited superior antifouling ability and demonstrated long term and chemical stability.Thirdly, positively polyelectrolyte quaternized chitosan was grafted onto negatively charged hydrolyzed polyacrylonitrile which aims to construct zwitterionic memebrane surface. One hand, the positively polyelectrolyte quaternized chitosan could form a hydration layer on membrane surface by electrostatic interaction to inhibit the contact between the pollutant and membrane surfaces. On the other hand, the nearly electric neutral surface after grafting the positively polyelectrolyte quaternized chitosan could alleviate the specific adhesion of foulants.