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Modifications to the surface of polymeric membranes to integrate supplemental properties like surface charge or catalytic activity are the cornerstone of the membrane process advancement to effectuate improvements in functionality and selectivity. Herein, a new approach is demonstrated to construct nanofiltration membranes with a metal–organic coordinated selective layer. Polyethylenimine (PEI) was integrated with phosphite linkages to form a characteristic aminophosphonate ester polymer based on the Kabachnik–Fields reaction, and a thin polymer layer was deposited on an ultrafiltration (UF) membrane to form the aminophosphonate networks surface-modified membranes. The aminophosphonate polymer interlayer facilitated the immobilization of metal cation moieties through the strong coordinative chemical bonding with the amino groups and phosphite moieties. Typically, the incorporated Fe3+strengthened the membranes’ electropositivity leading to excellent heavy metal ion removal (>98%) and efficient organic dye separation (>99.8%). Meanwhile, the strategy also enabled the embedment of a photocatalytic layer comprising nanoneedle-like α-FeOOH that endowed the membrane with high photo-Fenton activity for organic dye mineralization. Subsequently, the α-FeOOH-embedded membrane afforded the photocatalytic self-cleaning potentiality for organic fouling mitigation. This contribution underscores the prospect of advancing the integration of metal-specific functionalities and the membrane process for advanced membrane technologies in water treatment.

Surface modulation of polyamide structures and the development of nanochanneled membranes with excellent water transport properties are crucial for the separation performance enhancement of thin-film composite membranes. Here, we demonstrate the fabrication of a modular nanochannel-integrated polyamide network on a nanoporous interlayer membrane comprising Mxene-reinforced protein–polyphenol nanoaggregates. The research indicates that the confined growth of the polyamide matrix inside this hydrophilic sub-10 nm nanochannel nanoporous intermediate layer stiffened the interfacial channels, leading to the formation of a polyamide layer with a spatial distribution of a network of unique 3D crumpled globule-like nanostructures. The high specific surface area of such a morphology bestowed the membrane with increased filtration area while facilitating the nanofluidic transport of water molecules through the nanochanneled membrane structure, leading to enhanced water flux of up to 26.6 L m–2h–1(active layer facing the feed solution) and 41.0 L m–2h–1(active layer facing the draw solution) using 1.0 M NaCl as the draw solution. The membrane equally exhibited good treatment for organic solvent forward osmosis filtration and typical seawater desalination. Moreover, the hierarchical nanostructures induced antimicrobial activity by effectively reducing the biofilm formation of Gram-negative Escherichia colibacteria. This work provides significant insights into the interfacial engineering and compatibility of the nanomaterials and the polymers in interlayer mixed-matrix membranes, which are environmentally sustainable and cost-effective for the fabrication of advanced forward osmosis membranes for water purification and osmotic energy applications.

Lithium separation is of great significance to overcome the lithium supply shortage resulting from a heightened demand in the energy sector. The low selectivity of polymer nanofiltration membranes for lithium extraction from concentrated Mg/Li mixtures caused by miniaturized pore structures and weak and unstable positive surface charges limits their practical implementation. To address the surface charge strength and stability, a novel ionic liquid monomer, N1-(6-aminohexyl)-N1,N1,N6,N6,N6-pentamethylhexane-1,6-diaminium bromide (denoted as DABIL), is first synthesized and covalently anchored on a pristine polyamide thin-film composite (TFC) membrane via a secondary amidation reaction for improved selective lithium separation from Mg/Li mixtures. DABIL modification of the polyamide network contributes to increased surface hydrophilicity, an enlarged membrane pore structure, and reinforced Donnan exclusion effects. Molecular dynamics simulation confirmed that the difference of the interaction energies between water and the multication groups dominates the surface properties. The DABIL membrane exhibits sixfold enhancement of water permeability compared to the unmodified membrane and outperforms the recently reported state-of-the-art positively charged membranes. It presents an improved Li+/Mg2+selectivity of 26.49, suggesting the membranes’ potential for lithium recovery. Moreover, the membrane shows efficient antibacterial activity for mitigating biofilm formation. We establish that functionalization of TFC membranes with ionic liquids containing multication side chains could be a promising approach to achieve improved and sustainable permselectivity for the recovery of critical metal resources.