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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]

Nanoscale characteristics of the polyamide layer are key towards the high desalination performance of thin-film composite reverse osmosis (TFC-RO) membranes. Further advancements in the performance of TFC membranes necessitate a comprehensive understanding of the desired polyamide characteristics and its formation mechanisms. Empirical evidence has shown that the properties of the support layer is as equally important as the interfacial polymerization (IP) conditions in the fabrication of high permselectivity TFC membranes for desalination. Herein, we discuss the properties of polyamide layers formed using identical IP conditions over support membranes of different polymers and chemistries (polyethersulfone, polyetherimide and polysulfone) under fairly similar surface pore properties. The characteristics of the polyamide layers formed thereon displayed different physicochemical properties. It is postulated that the support membrane chemistry actually affects the IP reaction and polyamide formation by controlling the amine diffusion speed as well as the breadth of the IP reaction zone (i.e., the region between the interface and the furthest point in which the reaction occurs). Transmission electron microscopy analyses further revealed the nanoscale differences in the polyamide layer (heights ranging from 50 to 200 nm), including intrinsic thickness of basal layer (~10–35 nm) and leaf-like top layer (~20–85 nm), as well as the presence of nanovoids. Finally, we propose a conceptual model to underline the role of support membrane chemistry in the IP reaction, and consequently the formation mechanism of the nanoscale polyamide features. The mechanistic insights from this study are expected to provide more understanding towards a better control over the fabrication of polyamide layers for TFC membranes. The findings in this work are also expected to facilitate tailoring polyamide layers for specific osmotically driven processes. [Display omitted] • Support membrane chemistry affects MPD diffusion and partitioning extent in IP. • TEM and SEM analyses revealed changes in the polyamide (PA) nanoscale morphology. • PA layer of TFC-PES membrane was thin and smooth without any nanovoids. • PA layer of TFC-PSf membrane had thick base, thin leaves and multi-layer nanovoids. • PA layer of TFC-PEI membrane had thin basal layer with clumpy roof-like top layer. [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]

Conventional mixed-matrix membranes (MMMs) possess a dense structure with a filler material uniformly dispersed within the polymer matrix to engineer the transport properties and achieve enhanced gas separation performances with respect to pure polymeric membranes. However, a dense membrane structure increases the transport resistance and undesirably requires a high filler loading to see a substantial enhancement in separation performances. To address this problem, we fabricated asymmetric MMMs that have a thin-selective layer of around 0.5 μm and a low loading (0.03–0.10 wt%) of nitrogen-doped graphene (N-G) nanosheets. The presence of the nitrogen- and oxygen-containing functional groups on the N-G nanosheets ensured good compatibility between filler and polymer matrix, which resulted in strong polymer/filler interfacial adhesions. The N-G nanosheets were also found to be capable of migrating to the top of the membranes during phase inversion. Hence, despite the low filler loadings used in this work, the capacity of the dense selective layers was greatly enhanced. Based on our experimental results, 0.07 wt% and 0.10 wt% loading of N-G nanosheets can improve both O 2 /N 2 (126.9%) and CO 2 /N 2 (45.8%) selectivities with respect to pure polymeric membranes, resulting in O 2 /N 2 separation performance surpassing the Robeson upper bound. Image 1 • Asymmetric mixed matrix membranes (MMMs) comprising nitrogen-doped graphene (N-G) were fabricated. • Asymmetric MMMs have a thin-selective layer and a very low lading of N-G (0.03–0.10 wt%). • Most N-G fillers were migrated to the dense (top) layer to reduce interface energy during the phase inversion. • The O 2 /N 2 and CO 2 /N 2 selectivities of MMMs increased by 126.9% and 45.8%, respectively. • The selectivity improvement is due to the formation of more selective tortuous pathway by N-G fillers. [ABSTRACT FROM AUTHOR]