Bio-inspired Preparation Of Heterogeneous Hydrogel Membrane And Enhancement Of Oil-water Separation Performance

As a kind of main pollutants in water,oil droplet has attracted more and more attention from researchers.Membrane technology is widely used in oil-water separation due to its high efficiency and greenness.However,the widespread application of membranes for oil-in-water emulsion separation faces two common key scientific problems caused by non-specific interaction between oil droplets and membrane surface:low permeation flux and severe membrane fouling.In this study,with reaction enhanced surface segregation as platform technique,chemically heterogeneous and chemically-geometrically heterogeneous hydrogel layers were introduced in situ onto the membrane surface to integrate and strengthen“fouling resistance”and“fouling release”mechanisms.It was expected that the penetration,the antifouling performance and the long-term operational stability of the membranes for oil-in-water emulsions treatment could be improved remarkably during this process.The main content and conclusion were summarized as follows:Firstly,chemically heterogeneous hydrogel layers were constructed on the membrane surface based on hydrogen bonding assembly.A kind of fluorinated copolymer was synthesized as the modifier and tannic acid（TA）aqueous solution was used as the coagulation bath.During the non-solvent induced phase separation,TA could crosslink the modifier in situ at the water-polymer interface through hydrogen bonding,thereby forming a chemically heterogeneous hydrogel layer on the membrane surface.At the same time,the hydrophilicity of TA enabled the hydrogel super-oleophobic properties underwater.The thickness and chemical composition of the hydrogel layer were controlled facilely by changing the concentration of TA to coordinate the permeability and long-term antifouling performance of the membrane surface.In the process of cross-flow filtration of oil-in-water emulsions,the pure water permeation of the optimized membrane was 330 L m^-2 h^-1 and the membrane possessed zero-flux-decline feature.Secondly,chemically-geometrically heterogeneous hydrogel layers were constructed on the membrane surface based on the hydrogen-coordination bonding assembly.A kind of fluorinated copolymer and butyl titanate were used as modifiers and TA aqueous solution was used as the coagulation bath.During the non-solvent induced phase separation,butyl titanate was hydrolyzed and condensed in situ at the water-polymer interface,coordinated and cross-linked with TA to form a chemically-geometrically heterogeneous hydrogel layer on the membrane surface.Ti O₂ nanoparticles constructed a unique geometrically heterogeneous structure on the membrane surface,while increased the hydrophilicity of the membrane surface.The thickness and chemical composition of the hydrogel layer were controlled facilely by changing the amount of introduced Ti O₂ to coordinate the permeability and long-term antifouling performance of the membrane surface.During the cross-flow filtration process of oil-in-water emulsions,the pure water permeation of the optimized membrane was 621 L m^-2 h^-1 and the flux decline rate was 4.83%.Finally,a thin layer with a certain physical and chemical structure could be formed at the solvent/non-solvent interface with the application of reaction enhanced surface segregation.The chemical composition and function of the thin layer can be adjusted by changing the type of cross-linked substance and reaction time to achieve the preparation of thin layers with different filter pore sizes;in addition to phenolic hydroxyl-rich TA,hydroxyl-rich phytic acid（PA）and polyacrylic acid（PAA）,etc.can also realize the cross-linking of the modifier;The type of modifier can also be rationally designed according to different needs to achieve the preparation of thin layers of different functions.The application of the reaction enhanced surface segregation platform technology is not limited to rapid separation membranes such as oil-water separation membranes,but also expected to be further developed in the field of fine separation membranes such as dye separation membranes and even desalination membranes.