Nanofiltration Membranes Modified with a Clustered Multiquaternary Ammonium-Based Ionic Liquid for Improved Magnesium/Lithium Separation.

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.

Crumpled Globule-Heterotextured Polyamide Membrane Interlayered with Protein-Polyphenol Nanoaggregates for Enhanced Forward Osmosis Performance.

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-2 h-1 (active layer facing the feed solution) and 41.0 L m-2 h-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 coli bacteria. 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.

Towards improved protein anti-fouling and anti-microbial properties of poly (vinylidene fluoride) membranes by blending with lactate salts-based polyurea as surface modifiers.

It is a big challenge to develop membrane fouling-resistant materials for long-term water filtration applications in order to reduce the operating cost. Herein, for the first time, we have proposed the utilization of lactate salts-based polyurea additives as surface modifiers (SMs) to endow anti-microbial and anti-protein activities which increase the life of poly (vinylidene fluoride) (PVDF) membrane filters in terms of attaining anti-fouling properties for prolonged and stable water flux in water treatment. Membrane fouling was examined by taking into account the important influencing factors such as surface hydrophilicity and functional lactate groups present on the surface. The results showed that the surface hydrophilicity was enhanced leading to higher water flux of the PVDF membrane blended with sodium lactate-based polyurea (Na-PVDF) (174.2 L m-2 h-1), which was almost 12 times higher than that of the neat PVDF membrane. The fabricated SMs-blended PVDF membranes displayed satisfactory rejection and fouling resistant performance for the bovine serum albumin (BSA) molecules. The PVDF membrane blended with zinc lactate-based polyurea (Zn-PVDF) ensured effective anti-microbial activity against bacteria and fungi. Besides, the SMs-blended PVDF membranes displayed a higher zone of inhibition (ZOI) and higher colony reduction than the neat PVDF membranes in the anti-microbial test. The long-term water filtration test carried out after 200 days showed that PVDF membranes blended with SMs retained more than 90% of the original water flux, suggesting the long-term stability of SMs in the PVDF matrix. Therefore, the synergistic effect of SMs can be considered as an important life enhancer of polymeric membrane materials in the field of membrane technology.

Nanofiltration Membranes with Metal Cation-Immobilized Aminophosphonate Networks for Efficient Heavy Metal Ion Removal and Organic Dye Degradation.

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.

Nickel hydroxide nanosheet membranes with fast water and organics transport for molecular separation.

Two-dimensional nanosheets of late show great promise as novel materials for size-selective separation membranes of high efficiency. Herein, we demonstrate a novel laminated nanofiltration membrane for fast water purification and organic solvent nanofiltration using the 1 nm-thick and 50 nm-wide nickel hydroxide nanosheets that are facilely prepared by a green chemistry method. The resulting membranes exhibit uniform and flectional two-dimensional laminated structure. With about 1 nm high laminated channels, they allow super-fast transport of water and organic solvents. The water and organic fluxes are three orders of magnitude higher than commercially available polymeric nanofiltration membranes. In addition, the membranes have high retention for organic dyes in aqueous and organic solutions. Typically, the 3.18 µm-thick membrane with the molecular weight cut-off of 328 g mol-1 has an outstanding pure water flux of 99 L m-2 h-1 bar-1 and up to 97% rejection for direct yellow dye molecules. The newly developed nickel hydroxide nanosheets and the subsequent membranes have great potential application in water purification, organic solvent filtration and electronic devices.