Rapid engineering of bio-inspired membranes with superhydrophilicity for versatile applications

Oil pollution has caused severe environmental problems and is deteriorating with frequent oil spilling events and growing oily wastewater discharge from industry. Various methods, such as in-situ burning, physical adsorption and membrane technologies have been employed to eliminate the oil species from these polluted oily wastewaters. Specially, membrane technologies, such as ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO), are playing a critical role in treating oilwater mixtures, because of excellent selectivity, high flexibility and smaller pore size. However, these typical polymer membranes have to be limited to a smaller scale of application due to some evident disadvantages, including inferior mechanical stability, fouling and bacteria affinity of hydrophobic polymer membranes and extra driven pressure. Therefore, developing an excellent mechanically-stable, antifouling, antibacterial, cost-effective and environmentally friendly oil-water separation method is urgently needed for realizing the continuously sufficient recovery of oil and water from the oily wastewaters. Inspired by the phenomena of super-wetting in nature, a various of materials with superwetting properties (classified to two main types, e.g., the superhydrophobic and superhydrophilic) have been developed by researchers. Among them, the type of superhydrophilic and underwater superoleophobic membranes, which have a higher water permeation and a stronger antifouling to organic compounds, is considered as a more promising direction. Recently, scientists made a great effort in engineering superhydrophilic surface through the approaches, such as surface grafting, layer-bylayer self-assembly and surface coating. Among these modifications, surface coating is the simplest and lowest-cost used technique to transform membrane hydrophobicity into high hydrophilicity via depositing a thin superhydrophilic layer onto the surface of materials. Therefore, based on this concept, designing a superhydrophilic coating on the porous membrane surface can be a feasible method to realize the efficient oil-water separation with high flux under only driven by gravity condition. Mussel-inspired dopamine chemical method has set a wave of upsurge in surface biomimetic modification, since firstly reported in 2007. Dopamine is a typical catecholamine with 3, 4-dihydroxy-L-phenylalanine and lysine, which can selfpolymerize in a slightly alkaline environment to form a thin polydopamine (PDA) coating. Due to the strong covalent/non-covalent interaction between catechins and substrates, the dopamine can firmly deposit onto various surfaces, showing a great superiority in versatility, flexibility and economic practicality. However, this PDA coating is not impeccable with some problems. Generally, it requires at least 4-5 hours to form an intact PDA coating. Moreover, the obtained PDA layer still suffers from some limitations such as the instability, poor homogeneity, and insufficient hydrophilicity. Recently, oxidation strategies, which were proposed as triggers to accelerate the deposition of bio-inspired coating, were considered as a feasible approach for the time-costing problem. Therefore, in our work, we will compare the performances of several common oxidants in accelerating dopamine polymerization processes and determine the optimal reaction conditions. Additionally, on the basis of the reaction between catechol (CT) and polyamines, seeking a set of applicable materials with excellent hydrophilicity, antibacterial and multifunctional properties combined with dopamine was a handy way to tackle out the currently problems of pure PDA layer. Therefore, based on this dopamine modification strategy, we will rapidly construct a series of multifunctional bio-inspired separation membranes with extremely high flux, long-term stability and strong antifouling for gravitational oil-water separation and other applications. The PhD study aims at fabricating multifunctional bio-inspired polydopaminebased membranes with high water permeability, long-term stability, and excellent antifouling and antimicrobial properties for versatile application. And it will focus on exploring the polymerization behavior of polydopamine-based coating on the porous substrate at different fabrication conditions and filtration performance in different applications.