A Low-pollution Separation Membrane Is Constructed Based On The Bionic Surface Modification Technology

In recent years,membrane separation technology is regarded as one of the most crucial methods for wastewater treatment,and membrane fouling is a severe and inevitable problem hampering separation efficiency and service life.However,surface functionalization modification method can render superior antifouling performance of the membrane,and it offers a new method to mitigate membrane fouling.In this work,based on the characteristics of secondary functionalization and rapid co-deposition of mussel-inspired surface modification technology,dopamine(DA)deposition technology was utilized as a surface modification method by introducing different functional coating layer.The antifouling coating layer of passive defense mechanism or active antibacterial mechanism was selected to establish onto membrane surface.The interaction between hydrophilic polymer and water molecular promote the formation of hydration layer with passive defense function which could prevent oil droplet from contacting.Nanoparticle or poly(quaternary ammonium compound)with active antibacterial activity inhibited bacterial growth for mitigating biofouling.It would design PVDF membrane with antifouling performance for oil droplet and microorganism.Thiolated hyperbranched zwitterionic polymer(HPS)was categorized as sulfonate betaine polymer which was synthesized by controlled/living RAFT polymerization and sulfonation reaction.PVDF membrane was hydrophilized via Micheal addition reaction between end thiol moiety and PDA.The stable hydration layer with passive defense performance was analyzed in terms of antifouling for oil droplet.The superior hydration ability for water molecules could promote the formation of hydration layer onto membrane surface,the hydrophilicity of the modified membrane surface was significantly improved and water pure water contact angle of the modified membrane was 52.7°which was low that pristine membrane.The existence of hydration layer could effectively prevent the oil droplets from adhering onto membrane surface so that the underwater oil contact angle was above150°.During the dynamic hexane/water emulsion separation process,the passive defense effect of the hydration layer could limit oil droplets to contact membrane surface,oil concentration in filtrate was 4.5 ppm,the rejection ratio was 99.9%for different types of oil/water emulsions.Meanwhile,the recovery performance within a certain time for emulsified oil separation was stable.The modified membranes exhibited excellent separation performance for oil/water emulsion and antifouling property for oil droplet.To improve the zwitterionization degree,optimize the synthesis and preparation process as well as enhance antifouling property of the membrane.Acryloylmorpholine with good affinity for water molecules was utilized as functional monomer to synthesized hyperbranched poly(N-acryoyl morpholine)(HPA)by RAFT polymerization.Basis on PDA coating as a secondary functional platform,the reduction process of end thiol moiety and surface functionalization modification process were achieved by one-step method.The effect of polymer layer for oil droplet fouling was investigated.The results showed that water contact angle in air of the modified membrane pure water was 42.6°,which decreased to 0° within 13 s,and the underwater oil contact angle was greater than 150°.HPA had a good affinity for water molecules that promoted the formation of hydration layer onto membrane surface which declined the resistance of water molecules to go through the membrane,improved the permeation flux and reduced oil droplet adhesion.Besides,protein adsorption mass of the modified membrane was 28.78μg/cm~2,the bacteria could hardly attach and the rejection ratio for oil/water emulsion was 99.57%.Relative flux ratio was 36.76%and flux recovery ratio was 82.63%for dynamic separation of the composite emulsion containing the above three pollutants that was better than pristine membrane.The hydration layer with passive defense effect could reduce the pollution of oil droplet during the separation process.In order to mtigate microbial contamination of the membrane during the separation process,according to chemical bond between thiol group and PDA or metal nanoparticle,benefiting on the reduction PDA and and thiolated HPA immobilize Ag nanoparticle,it could fabricate PVDF membrane with active antifouling and antibacterial.The presence of Ag nanoparticle could increase the surface roughness.Polymers improved the hydration capacity of the membrane and offered the active sites for immobilizing nanoparticle.The results showed that water contact angle of the modified membrane was 52.2°,and it reduced to 0° within 12 s.The permeation was no significant decline due to the synergistic effect of roughness and hydrophilicity,the protein rejection ratio was 92.28%and static protein adsorption was only 20.56μg/cm~2,which was low than the pristine membrane that of Gram-negative bacterial and Gram-positive bacteria.The release quantity for Ag~+ was21 ppb that could render membrane with antibacterial performance in a long-term.Poly(quaternary ammonium compound)(PQAC)with active antibacterial capability were synthesized by RAFT polymerization to avoid Ag~+release,which used small molecular quaternary ammonium as functional monomer.The benzene ring in PDA and quaternary amine nitrogen in quaternary ammonium compound reacted by cation-πinteraction to prepare PVDF membrane with active antibacterial behaviour by dopamine assisted co-deposition strategy.The results showed that the introduction of hydrophilic poly(quaternary ammonium compound)could prevent the existence of aggregation,the zeta potential was-1.23 m V,water contact angle declined to 0° within 4.3 s.The increased hydrophilicity rendered the modified membrane with low bacterial adhesion behavior,the microorganism was difficult to cause membrane fouling during dynamic bacterial solution separation,relative flux reduction ratio was less than 13%,flux recover ratio reached 90%.Meanwhile,the active antibacterial effect of PQAC could inhibit the growth of Gram-negative bacterial and Gram-positive bacteria,and the inhibition bacterial ratios were 99.2%and 100%,resulting in excellent antifouling property of the modified membranes for microorganism.