Fabrication Of High Flux,Anti-fouling Loose Nanofiltration Composite Membranes For Desalination Of Textile Wastewater

According to the existing data,around 7×10⁵ tons dyestuffs have gotten wide range of applications in textile,plastic,rubber as well as leather tanning industry annually.In the procedure of dye synthesis,inorganic salt would decrease the purity and stability of dyes.Besides,inorganic salts also have been extensively used to enhance the dye uptake of the fabric.The direct discharge of wastewater would result in serious environmental pollution and waste massive valuable resources.Therefore,dyes recycle and salts removal from the textile wastewater has caused widespread concerns.?1?Natural polyphenols?gallic acid?was used to modify polyethylene imine?PEI?and then the modified PEI deposited on negatively charged hydrolyzed PAN ultrafiltration membrane surface by electrostatic attraction.The morphologies and structures of the resulted loose NF membranes were characterized by proton nuclear magnetic resonance?¹H NMR?,scanning electron microscope?SEM?and Fourier transform infrared?FTIR?.The membrane prepared at optimized condition achieved a high flux for dyes?51 L/?m²·h?at 0.2 MPa?and the rejection of Methyl Blue and Gongo red were 97.3%and 97.1%,the rejection of salt was 5%.Meanwhile,this membrane also exhibited a good flux recovery ratio?91.7%?and the best satisfactory antifouling stability in the long-term operation for dyes and salts mixture solution.?2?The?-Poly-L-lysine??-PL?and natural material pyrogallic?PG?were co-deposited on negative charged hy-drolyzed polyacrylonitrile?HPAN?substrate by Michael addition/Schiffbase reaction.Then,the four-arm polyethylene glycol methoxy?4-arm-PEG?was firmly immobilized to form the?pine-shaped?structure on the surface of the modified HPAN substrate The membrane prepared at optimized condition?the mass ratio of?-PL to pyrogallic was 1:1 in coating solution and the concentration of 4-arm-PEG was 0.4 g/L?achieved a high permeability?76.3L/?m²·h·MPa??,high rejection for dyes?methyl blue:98.9±0.2%,Acid fuchsin:97.5±0.1%,Crystal violet:81.1±0.5%and Methylene blue:69.5±0.5%?and low NaCl rejection?17%?.Besides,excellent antibacterial activity against E.coli and S.aureus was observed for the prepared membrane.?3?The negative charged hydrolyzed polyacrylonitrile?HPAN?surface was modified with PEI though electrostatic interaction.Due to the complexation of Co²⁺and PEI molecules,the Co²⁺was immobilized on the modified membrane,then provided a Co²⁺source for the low temperature?50°C?in-situ growth of Ni/Co LDHs.This method created more 2D mass transfer channels on the membrane surface improving the permeability of membrane.The membranes were characterized by SEM,XRD and XPS.The membrane prepared at optimized condition(the concentration of Co²⁺and Ni²⁺was fixed at 4 mmol/500ml in coating solution and the growth time was 5 h)achieved a high permeability?198.6 L/?m²·h·MPa??,high rejection for dyes?methyl blue 97.9%and acid fuchsin 97.5%?and salt rejection lower than 3%.besides,the membrane also exhibit best satisfactory antifouling stability.?4?A facile and scalable method combining the inter-layer modification with external treatment was used to fabricate freestanding GO membrane with wide range of tunable interlayer spacing.The GO membrane were characterized by SEM,XRD and XPS.In addition,the transfer mechanism of graphene oxide membrane was simulated.