Bioinspired Preparation And Properties Of Antifouling, Highly Stable Nanofiltration Membranes

The target of the thesis is to prepare antifouling composite nanofiltration(NF) membranes with good structural stability. Based on the understanding of the hydrophilic antifouling surface in cell membrane, low surface energy self-cleaning surface in lotus and the adhesive proteins found in mussels, we design the amine monomer or modifiers, and combine the existing method(e.g., interfacial polymerization, biomimetic adhesion, grafting, etc.) to invent new fabrication approach of NF membrane. The preparation and performance enhancement of the antifouling membranes with good structural stability are achieved.The details of this study were summarized as follows:Firstly, a novel fluorinated amine monomer(C7F15CONH(CH2CH2NH)2CH2CH2NH2, fluorinated polyamine, FPA) was synthesized and utilized to perform interfacial polymerization with trimesoyl chloride(TMC), producing thin-film composite NF membranes. Herein, FPA played two roles:(1) the amine groups of FPA could react with acid chloride groups of TMC, forming cross-linked active layer to reject dyes and inorganic salts;(2) the perfluoroalkyl groups of FPA could engineer a low free energy membrane surface, rendering membrane with prominent fouling-release property. In filtration of BSA solution, FPA-TMC/PES membrane exhibited 9.1% total flux decline and the flux recovery ratio reached 99.8%.Secondly, inspired by the hydrophilic antifouling surface in cell membrane and low surface energy self-cleaning surface in lotus, FPA and hexa?uorobutyl methacrylate(HFBM) were separately grafted onto the hydrophilic NF membrane prepared by interfacial polymerization to engineer amphiphilic membrane surfaces comprising hydrophilic fouling resistant domains and hydrophobic(low surface free energy) fouling release microdomains. The synergistic effect of the two types domains endowed the amphiphilic NF membrane excellent antifouling performance. In filtration of BSA solution, F3-PA/PES membrane exhibited 8.8% total flux decline and the flux recovery ratio reached 99.4%.Thirdly, thin-film composite NF membranes with good structural stability were prepared by interfacial polymerization under the mediation of polydopamine(PDA). Polyethersulfone(PES) support layer was firstly modified by PDA prior to the interfacial polymerization of piperazine(PIP) and TMC to form polyamide active layer. PDA could firmly adhere to support layer through strong intermolecular interactions and render the support layer with the reactive groups to generate amide bonds between the active layer and the support layer. Robust and multiple interfacial binding forces between the support layer and the active layer would enhance the interfacial compatibility and raise the structural stability of the NF membrane. Water flux of PA/PDA-PES membrane had a little variation after alcohol treatment for 15 days and the Na2SO4 rejection declined less than 5%.Lastly, a facile method for fabricating antifouling NF membranes with good structural stability was developed based on bioinspired PDA. PES support layer was first deposited a thin PDA layer and then grafted FPA via Michael addition reaction between FPA and quinone groups of PDA. After alcohol treatment for 144 hours, F3-PDA/PES membrane exhibited good structural stability due to the strong and multiple interactions between the PDA layer and PES support layer. In filtration of BSA solution, F3-PDA/PES membrane exhibited good antifouling performance(12.7% total flux decline, 94.5% flux recovery), which was close related to the low surface free energy microdomains and hydrophilic domains.