Novel Composite Nanofiltration Membranes Via Dopamine-assisted Co-deposition

Nanofiltration has created attractive application prospects in the fields of drinkable water production,seawater desalination and wastewater treatment due to its superiorities of high water flux,high rejection to multivalent ions or organic molecules,and low operation pressure.This membrane technology can help alleviate the global water crisis by producing sustainable and high-quality water.In general,nano filtration membranes(NFMs)have a thin film composite substructure.The most recent mussel-inspired polydopamine(PDA)deposition technology provides a new method for composite NFMs fabrication with advantages of universality,versatility and simplicity.Herein,we developed a dopamine assisted co-deposition technology to further improve the separation and service performance of the prepared NFMs.This strategy shows great potential in controllable construction of NFM selective layers,fabrication of organic-inorganic composite NFMs,and photocatalytic functionalization of composite NFMs.Firstly,we developed a novel composite NFM fabrication strategy via dopamine(DA)/polyethylenimine(PEI)co-deposition followed by glutaraldehyde(GA)crosslinking.A PDA/PEI selective layer is generated on the ultrafiltration membrane substrate with a uniform,robust and defect-free structure,which can be facially tailored by DA/PEI ration and deposition time.The optimized membrane surface is positively charged with good wettability,endowing the composite NFMs with high rejection performance for bivalent cations and good permeate flux.Moreover,the composite NFMs show a good structural stability for immersing in ethanol or for long-term nanofiltration process with good antifouling properties for proteins.Secondly,we developed a facial strategy to fabricate thin film nanocomposite(TFN)nanofltration membranes based on the co-deposition of PDA,PEI with silica and gold nanoparticles followed by crosslinking.As compared with those NFMs without nanoparticles,tripled and doubled water flux can be obtained from the TFN NFMs containing SiO2 NPs and GNPs,respectively,ascribing to the enlarged pore sizes of the selective layer and the improved wettability of the membrane surfaces.The optimized NFMs are defect-free and positively charged,showing good rejection ratio for both bivalent cations and neutral solutes.The rigid inorganic nanoparticles also improve the surface mechanical strength of the TFN NFMs effectively,resulting in good structural stability and thus compaction resistance during the pressure-driven filtration process.Moreover,the GNPs with quaternary amine cations on surfaces endows the NFM with biocidal capability,benefiting for their service performance.Thirdly,we proposed and developed a novel organic-inorganic composite NFM via the mussel-inspired PDA/PEI modification of ultrafiltration substrate followed by a surface-induced mineralization process.The composite NFM surface is finely covered by a defect-free,uniform,and ultrathin(10?20 nm)ZrO2 layer with slight positive charges and good wettability.As a result,the composite NFMs show high rejection ration(>90%)for bivalent cations and good permeate flux,which is 4 times higher than the former PDA/PEI composite NFMs.Furthermore,the organic-inorganic composite NFMs show good structure stability during the long-term(120 hours)nanofiltration operation with excellent antifouling property for proteins.-Lastly,we developed a photocatalytic NFM with self-cleaning property via a facile biomimetic mineralization process.The PDA/PEI is co-deposited on an ultrafiltration substrate followed by crosslinking as selective layer,which then induce the surface mineralization of?-FeOOH nanorods as a photocatalytic layer.The optimized NFMs show high rejection(>99.6%)for target dye molecules with satisfactory permeability.In visible light,the ?-FeOOH layer can degrade dyes through the photo-Fenton reaction in the presence of H2O2 efficiently,endowing the NFM with excellent anti-organic fouling and self-cleaning capability.Moreover,the NFMs exhibit stable separation and photocatalysis performance during cyclically testing processes,indicating good stability of the as-prepared NFMs and great potential in advanced textile wastewater treatment.