Preparation Of High Flux And Antifouling Fluorinated Nanofiltration Membranes

Nanofitration membrane technology has been widely used in advanced water treatment and utilization for its high separation efficiency,low energy consumption and environmental friendliness.Nevertheless,membrane fouling caused by various organic foulants in membrane separation process has become a common challenge for academics and industry.Fluorine-containing materials have been pioneered as effective candidates for constructing low-surface-energy surfaces(20-30 mJ m^-2)and displayed superior antifouling performance to both the spreading and non-spreading foulants.However,rare success has been reported for high-flux fluorine-based membranes because the amphiphobic nature of fluorine materials would inevitably increase hydrophobicity and decrease water flux therefrom.Furthermore,sufficient and uniform enrichment of fluorine components on the surface is tough because their weak interaction with substrate or other membrane-forming components.Inspired by bioadhesion phenomenon,this study is devoted to prepare ultrathin fluorine-based membranes based on the assembly strategy of strong metal coordination interaction and electrostatic complex interaction.A series of membranes with high dye separation performance are prepared by regulating the membrane structure and surface chemistry to achieve high flux and antifouling.The details are summarized as follows:Inspired by the strong mussel adhesion system strengthened by coordination,the ultrathin self-cleaning membrane was prepared by coordination-driven metal-bridging assembly method.Phytic acid（PA）,a natural multidentate phosphate ligand with high density of coordination sites,was first assembled with iron chloride on porous substrates to form a dense iron phytate layer that could offer plentiful exterior Fe³⁺ions.Subsequently,Nafion^?bearing abundant perfluorinated groups and sulfonate ligands,was employed as building unit and assembled via the bridging of Fe³⁺ions to obtain the metal-bridging fluorine-based membranes（MBFMs）.By manipulating the metal ion content and assembly time,a defect-free 58-nm-thick MBFM with low surface energy(23.5 mJ m^-2)and underwater superoleophobicity（～160°）was achieved,which displayed superior water permeance of 125.2 L m^-2 h^-1 bar^-1 along with dye rejections above 90%and versatile resistance towards both the spreading and non-spreading foulants（flux decline ratios below 8%,flux recovery ratios above 95%）.Inspired by the sandcastle worms adhesion system based by strong electrostatic complex coacervation,the fluorine-based separation membrane was prepared by electrostatic assembly method.The natural coordination compound（PA）,quaternary ammonium salt polymer（JR-400）,and commercial perfluorosulfonate polymer(Nafion^?)were provided as building units to assembly on the porous substrate via the strong electrostatic complex coacervation between the quaternary ammonium salt polymers and organic molecules to obtain the electrostatic-driven-assembled fluorinated membranes（EDAFMs）.By manipulating the reaction and assembly time of the phytic acid and quaternary ammonium polymer,respectively,the structure and surface chemistry of the fluorine-based separation membrane were optimized,realizing the constructing of ultrathin membrane（～75 nm）and low-surface-energy surface(24.1mJ m^-2).The resultant membrane exhibited high water flux of 93.3 L m^-2 h^-1 bar^-1 along with dye rejections above 90%and excellent antifouling performance to both the spreading and non-spreading（flux decline ratios below 7%,flux recovery ratios above 96%）.