Bioinspired Construction Of Antifouling And Self-cleaning Membrane Surfaces And Process Intensification For Oil/water Separation

Surface fouling is the common scientific challenge of various advanced technologies. Porous surface fouling, that is membrane fouling, is the main bottleneck preventing its wide application in treating the wastewater and resolving fresh water resource scarcity. So far, majority of the research followed the four principles proposed by Whitesides and focused on intensifying the antifouling ability of the membrane surfaces, but neglecting the self-cleaning ability. During the application for the wasteter reclamation, the permeation ?ux of the antifouling membranes is still reduced by 1, 2 orders of magnitude in a short time although the permeation ?ux recovery properties are often improved significantly. Learning from nature, innovating the methods and theories of the manipulation over membrane surface structure, preparing antifouling and self-cleaning membranes, improving the membrane performences, will possess great theoretical and practical significance.The present work is aimed to solving the serious memrbane fouling of the polymer membrane during the wastewater reclamation using the typical foulant oil as the model foulant. Inspired by the hydrophilic antifouling surface in cell membrane and low surface energy self-cleaning surface in lotus, the membrane bulk materials or membrane surface modification agents were rationally designed at the molecular level for achieving the architecture of antifouling and self-cleaning membrane surfaces through free surface segregation or forced surface segregation. The membrane separation performances were tentatively correlated with several surface attributes, such as the surface wettability, chemical composition and free energy and so on. The process intensification for oil/water separation application was conducted.Firstly, inspired by the hydrophilic antifouling surface in cell membrane, the free surface segregation method was developed for the antifouling membranes surfaces construction. The amphiphilic cellulose acetate-grafted-polyacrylonitrile (CA-g-PAN) copolymers were fabricated by grafting the PAN segments onto the CA backbone chains via the free radical polymerization. It was found that the thermodynamics difference between CA and PAN chains significantly accelerated the phase inversion process and enlarged the pore sizes in the skin layer, leading to a substantial increase (about 100 times) of the permeation property for the CA-g-PAN membranes compared with CA membranes. During the phase inversion process, most of the PAN segments were embedded in the membrane matrix in order to decreasemembrane surface energy, endowing the CA-g-PAN membranes with the high hydrophilicity close to CA membrane. The in situ generation of silica (SiO2) nanoparticles was coupled with polymer phase separation process for preparing CA(TEOS) membranes with enhanced permeation and surface hydrophilicity. The in situ generated nanoparticles acted as both pore-forming and surface modification agent. During the application for oil/water separation, the as-prepared CA-g-PAN and CA(TEOS) antifouling ultrafiltration membranes exhibited satisfactory flux recovery properties (FRR values higher than 90%), but still serious flux decline (total flux decline ratio higher than 50%).Secondly, inspired by the hydrophilic antifouling surface in cell membrane and low surface energy self-cleaning surface in lotus, the forced surface segregation method was explored for the antifouling and self-cleaning membranes surfaces construction, endowing the surfaces with superior antifouling and self-cleaning abilities simultaneously for further enhancing the membrane separation performaces. Amphiphilic copolymers composed of hydrophilic segments, poly(polyethylene glycol meth-acrylate) (PEGMA) or ([3-(Methacryloylamino)propyl]-dimethyl(3-sulfopropyl)ammonium hydroxide inner salt (PSPP) segments, and non-polar hydrophobic segments, polyhexa?uorobutyl methacrylate (PHFBM) segments were specifically designed as membrane-formation or membrane-modification materials. Consequently, amphiphilic porous membrane surfaces, comprising hydrophilic fouling resistant domains and hydrophobic fouling release microdomains, were explored via a"forced surface segregation"approach. The as-prepared membrane surfaces exhibited superior antifouling and self-cleaning abilities, simultaneously achieving nearly 100% permeation flux recovery and ultralow total permeation flux-decline (only 3.4%). When the hydrophilic segments were chosen as zwitterionic segments, the membrane also exhibited smart responsive properties.Lastly, inspired by the natural hydrophilic antifouling surface in cell membrane and low surface energy self-cleaning surface in lotus, the versatile antifouling and self-cleaning membranes surfaces were engineered basing on the forced surface segregation method and regulation of the phase microseparation for combating different surface foulants. The target ternary amphiphilic P(F127-g-FAM) copolymers were prepared by soap-free emulsion polymerization of low free energy fluorine-containing segments onto the commercial Pluronic F127 (PEO-PPO-PEO) triblock copolymers. Ternary amphiphilic copolymers bearing strong solvophilicity, low surface energy block, or casting solvent with high volatility favored the construction of amphiphilic PVDF/P(F127-g-HFBM) nonfouling surfaces, which exhibited superior antifouling and self-cleaning performance for oily foulants. In sharp contrast, ternary amphiphilic copolymers bearing weak solvophilicity, low surface energy block, or casting solvent with low volatility favored the construction of hydrophilic PVDF/P(F127-g-DFHM) nonfouling surfaces, which exhibited superior antifouling performance for biofoulants.