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Recent advances in nanotechnology have brought great opportunities to the developing next-generation nanofiltration membranes for addressing the concern of global water scarcity and energy crisis. Carbon dots have been deemed as a promising nanomaterial for enhancing the nanofiltration performance of polymeric membranes. Herein, carbon dots with cationic amine groups (PEI-CDs) and those with anionic sulfonate groups (PS-CDs) are incorporated into the polyamide selective layer of thin-film nanocomposite (TFN) membranes to create charged nanovoids (free volume) between the carbon dots and the surrounding polyamide network for high-efficiency nanofiltration. The positively charged amine group-based and negatively charged sulfonate group-based nanovoids in the resultant TFN-PEI-CDs and TFN-PS-CDs membranes, respectively, provide alternative pathways for efficient water permeation while effectively rejecting divalent ions via the Donnan and dielectric exclusion effects, thereby overcoming the recurring trade-off between permeability and selectivity encountered by dense polymeric membranes. In particular, the creation of negatively charged nanovoids enables the TFN-PS-CDs membrane to achieve one of the best performances among the recently reported nanofiltration membranes, by showing a nearly tripled pure water permeability of 30.9 L m−2 h−1 bar−1 as well as a higher Na 2 SO 4 rejection rate of 99.4% than the membrane with a pristine polyamide selective layer. Moreover, the TFN membranes demonstrate greater resistance to foulants with charges of the same sign as the nanovoids. This work provides insights into the design of nanovoids with desired properties in other polymeric membranes for high-efficiency filtration processes. [Display omitted] • Nanofiltration performance was improved by incorporating cationic and anionic CDs in the PA layer. • The ionic CDs created charged nanochannels between them and the surrounding PA matrix. • High pure water permeability of 30.9 L m−2 h−1 bar−1 and Na 2 SO 4 rejection rate of 99.4%. • Excellent filtration stability under different operating conditions and through a 14-day test. • Improved antifouling performance was demonstrated by using four types of ionic foulants. [ABSTRACT FROM AUTHOR]

Electrospun polymeric membranes are promising substrates for thin-film composite (TFC) membranes due to their unique interconnected pores and high porosity. However, it is still challenging to fabricate desirable electrospun substrates for organic solvent nanofiltration (OSN) owing to the relatively complex processing procedures and the organic operating environment. In this work, solvent-resistant electrospun polyimide (PI) nanofiber substrates were successfully fabricated through electrospinning followed by chemical cross-linking and heat-pressing. The cross-linking step improved the solvent tolerance of the membranes, while the heat-pressing step reduced the substrate pore size and surface roughness. However, it was found that heat-pressing at high temperatures (>140 °C) could degrade the cross-linking of PI, undermining their solvent-resistant property. A polyamide thin film layer was then synthesized on the solvent-resistant electrospun nanofibrous substrates via interfacial polymerization using reactant monomers m -phenylenediamine (MPD) and trimesoyl chloride (TMC). The TFC membranes exhibited excellent acetonitrile and acetone permeabilities of 31.28 ± 1.93 and 26.58 ± 1.13 L m−2 h−1 bar−1, respectively, with acid fuchsin (585 Da) and methyl orange (327 Da) rejections of 98.55 ± 1.24% and 92.42 ± 1.66%, respectively, in acetone. This study successfully demonstrated the potential use of electrospun PI nanofibers substrates for TFC membranes in OSN. [Display omitted] • Solvent resistant nanofibrous PI substrates were prepared by electrospinning followed by chemical cross-linking and heat-pressing. • Heat-pressing influenced the PI substrates' surface properties and solvent resistance, and the optimal point was 140 °C. • Polyamide thin film was synthesized on the PI substrates via interfacial polymerization for OSN application. • Acetone permeability was 26.58 L m−2 h−1 bar−1 with high rejection to acid fuchsin and methyl orange. [ABSTRACT FROM AUTHOR]

Conventional biomimetic membranes for desalination are mostly fabricated by incorporating water channels using self-assembled lipid or polymer vesicles as key platforms for protein or water channel reconstitution. Herein, we propose a thin film composite nanofiltration membrane via an unconventional liposomes-assisted fabrication without the incorporation of protein or water channels. The polyamide skin layer containing liposomes was thinner and filled with wrinkles and nanovoids. As a result, compared with the liposome-free control membrane, our optimized liposome-assisted membrane was able to achieve an increased water permeability from 11.17 to 18.21 LMH/bar, alongside an excellent MgCl 2 rejection of 95.87% and a monovalent/divalent (NaCl/MgCl 2) ion selectivity (α) of 18.2. Extensive membrane characterization showed that the liposome-assisted skin layer indeed exhibited a smaller thickness with an increased effective membrane area and a reduced surface hydrophobicity, which contribute towards a reduction in the hydrodynamic resistance of the polyamide layer. Furthermore, our approach of liposome-assisted thin film composite membrane is simpler and more scalable to fabricate without protein or water channels incorporation, rendering our design more attractive for future nanofiltration using vesicle-embedded biomimetic membranes. Image 1 • Lipid hollow vesicle was utilized to construct a thin film composite membrane. • The pathway of liposomes involved in the interfacial polymerization was confirmed via systematic characterization results. • Thinner polyamide with nanovoids and wrinkled structures was formed to facilitate water transportation. • The LE-TFC membrane exhibited better water permeability and higher divalent ion rejection. [ABSTRACT FROM AUTHOR]