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High‐precision separation with increased water permeability is critical for efficient membrane‐based water treatment processes. To achieve high selectivity toward different targeted species while allowing rapid water transportation, the structure of the membrane polyamide selective layer requires delicate regulation. Herein, an effective approach to systematically expand the pore size of polyamide layers by incorporating ammonium ion‐modified carbon dots (CDs) into the polyamide network is developed. The ammonium ions with different alkyl chain lengths attached to the CDs create nanochannels of different sizes in the network to lower the energy barrier for water transportation while maintaining high selectivity to targeted species. When the alkyl chain length of the ammonium ions reaches eight carbon atoms (i.e., C8 ions), the amphiphilic C8‐CDs induce the formation of the ridged nanostructure on the membrane surface and hence the increased membrane filtration area. The resultant thin‐film nanocomposite (TFN) membrane, denoted as the TFN‐C8‐CDs membrane, demonstrates a higher Na2SO4 rejection of 98.9% and NaCl/Na2SO4 selectivity of 83.1 than the pristine polyamide membrane, together with a tripled pure water permeability of 29.0 L m−2 h−1 bar−1. Herein, a viable approach for ingeniously designing the nanochannels and surface nanostructure of polyamide membranes for more efficient filtration processes is provided. [ABSTRACT FROM AUTHOR]

Interfacial polymerization is an effective technique to synthesize high performance polyamide thin film membranes. However, it is still very challenging to apply this technique on ceramic hollow fibres or tubular membranes, especially when the substrate pore size is in the microfiltration range. In this study, we demonstrated that thin polyamide layer can be synthesized directly on microfiltration ceramic tubular membranes with a surface pore size of 0.1–0.2 μm via interfacial polymerization without an intermediate layer. A thin polyamide layer with a thickness 30–40 nm was coated on the inner surface of the ceramic substrate by circulating the monomers of branched polyethyleneimine (PEI), piperazine (PIP), and trimesoyl chloride (TMC) through the membrane lumen. The thin film layer showed good integration with the ceramic substrate and could withstand high pressure of at least 10 bar. The mechanical property of the polyamide layer was examined using AFM and the modulus was measured. The thin film composite membranes demonstrated excellent nanofiltration performance with a pure water permeability of 16–18 LMH bar−1 and a molecular weight cut-off of ∼250 Da. The membranes also showed good salt rejections (>90%) to CaCl 2 , MgCl 2 and MgSO 4 , and still maintained high rejections of MgCl 2 and sucrose at elevated temperature of 80 °C. The use of highly inert ceramic substrates has enabled the application of polyamide membranes under more challenging conditions. Image 1 • PEI-based polyamide thin film was synthesized on microfiltration ceramic tubular membranes without an intermediate layer. • The membranes demonstrated excellent nanofiltration performance with a PWP of 16–18 LMH bar−1 and a MWCO of ∼250 Da. • The membranes also showed good divalent salt rejections for CaCl 2 , MgCl 2 and MgSO 4. • The rejections of MgCl 2 and sucrose remained high at elevated temperature of 80 °C. • The mechanical property of the polyamide film was studied using the AFM pinpoint mode and the modulus was measured. [ABSTRACT FROM AUTHOR]

A facile metal–organic framework (MOF)‐mediated interfacial polymerization (IP) method is developed to prepare a polyamide (PA) layer directly on the ceramic substrate for nanofiltration. MOF is introduced to connect ceramic substrate and PA layer via chemical bonding, resulting in a robust separation layer. The optimization of IP can be controlled by MOF growth process via tuning the surface roughness as well as hydrophilicity. This method will provide a new way for the preparation of next generation of organic–inorganic composite membranes. [ABSTRACT FROM AUTHOR]

Ion-selective permeable membranes show enormous potential in salt separation and resource recovery, but the permselectivity of current membranes restricts their broad application. Here, we presented a novel strategy for constructing a polyamide (PA) nanofiltration (NF) membrane with high water permeability, excellent divalent ion rejection, and outstanding Cl−/SO 4 2− selectivity via a facile substrate-tailored method. A nano-nodular substrate with some polyvinylpyrrolidone (PVP) on the surface was fabricated via vapor-induced phase inversion. This novel substrate with a unique pattern could duplicate the nano-nodule pattern on the PA layer and decrease the diffusion rate of piperazine (PIP) due to the open-nanodular structure with appropriate PVP on the surface. Consequently, a PA membrane with nano-nodular pattern, thin skin layer, narrow pore size distribution and negative charge was formed. The nano-nodular surface and thinner thickness exhibited a remarkable contribution to water permeability, which reached 38.3 L m−2h−1bar−1. The narrow pore size distribution made an outstanding Na 2 SO 4 rejection of 99.1 % and Cl−/SO 4 2− selectivity of 83 at 1000 mg/L of mixed salt solution. The Cl−/SO 4 2− selectivity increased to 110 with 5000 mg/L of mixed salt solution. The permselectivity of this novel membrane was superior to the state-of-the-art NF membranes. This work pioneers a new approach to tuning the PA layer structure, which can be readily achieved, and offers a fresh perspective on constructing high-performance NF membranes. [Display omitted] • Nano-nodular PES substrate was fabricated via VIPS with PVP and TEG as additives. • Nano-nodular patterned PA skin layer was constructed on this novel substrate. • The acquired PA layer was rougher and thinner and had a narrow pore size distribution. • Pure water permeability was 38.3 LMH/bar with Na 2 SO 4 rejections of 99.1 %. • The Cl−/SO 4 2− selectivity reached 83 testing with a binary salt solution. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microfiltration PTFE hollow fibres were transformed into durable, high value OSN membranes. • A PEI/PIP based polyamide thin film was successfully synthesized on PTFE hollow fibre substrates. • A two-time interfacial polymerization was conducted to obtain a defect-free polyamide layer. • The resultant membranes could withstand strong aprotic solvents like DMF and DMSO. • The membranes had high solute rejections, of up to 95 % methyl orange (327 Da) rejection in DMF. Polymeric membranes have been extensively studied for organic solvent nanofiltration (OSN) but many fail to show sufficient chemical resistance in strong solvents like dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). This study focuses on harnessing the outstanding chemical resistance of polytetrafluoroethylene (PTFE), to develop polyamide-PTFE thin film composite (TFC) membranes that are resistant to such aprotic solvents. A defect-free polyamide thin film layer was successfully synthesized on the microfiltration PTFE hollow fibre substrates, overcoming challenges such as large and uneven pore size, and hydrophobicity of the PTFE substrates. A simple polydopamine (PDA) coating was carried out to improve the substrate's hydrophilicity prior to the polyamide synthesis via interfacial polymerization (IP). Polyethyleneimine (PEI) and trimesoyl chloride (TMC) were used as the monomers and a two-time IP method was employed to obtain a defect-free polyamide coating. The synthesized membranes showed high acetonitrile (ACN) and DMF permeabilities of 7.94 and 3.70 lm−2h−1bar−1, respectively, with acid fuchsin (585 Da) rejections of > 90 %. The molecular weight cut-off (MWCO) of the membranes could be further reduced to ∼300 Da by the addition of piperazine (PIP) monomers. The membranes also showed excellent stability and performance in a 72-hour OSN test performed in DMF indicating their great potential in effective molecular separation in harsh solvents. This study demonstrates how a simple modification and coating technique can transform commercially available microfiltration PTFE hollow fibres into durable and high value OSN membranes. [ABSTRACT FROM AUTHOR]

Polyamide thin film membranes have shown outstanding performance in organic solvent nanofiltration (OSN). However, it is still challenging to produce polyamide hollow fibres for OSN, mainly due to limited solvent resistance of hollow fibre substrates and the difficulty to synthesize polyamide thin film on the surface of hollow fibre substrates. In this study, polyamide-based hollow fibre composite members for low pressure OSN were successfully developed. Solvent resistant polyimide hollow fibre substrates were first prepared through a non-solvent induced phase separation process, followed by chemical cross-linking with hexamethylene diamine. A polyamide thin film layer was then synthesized via interfacial polymerization, by circulating the reactant monomers including polyethyleneimine (PEI), piperazine (PIP) and trimesoyl chloride (TMC) through the hollow fibre lumen. The polyamide thin film with a thickness of ~60 nm was formed on the inner surface of the hollow fibre substrates. The membranes exhibited excellent nanofiltration (NF) performance under 2 bar operating pressure. The permeability of water, acetone and isopropanol was 6.8, 11.6 and 4.5 l m−2 h−1 bar−1, respectively. The membranes also achieved 99.9% and 91.8% rejection to rose bengal (1017 Da) and acid fuchsin (585 Da), respectively, in acetone. Furthermore, a 72-h filtration test was conducted and the membrane showed steady performance throughout the testing period. This study demonstrates the possibility of fabricating polyamide hollow fibre membranes for organic solvent nanofiltration at low pressure, which is desirable for practical applications. • Solvent resistant polyimide hollow fibre membranes were fabricated through chemical cross-linking. • Polyamide-based (PEI/PIP) layer was formed onto polyimide substrate to obtain a relatively loose selective layer. • Membranes achieved 11.6 and 4.5 l m−2 h−1 bar−1 permeability in acetone and isopropanol at 2 bar respectively. • Membranes maintained more than 90% rejection for acid fuchsin in 72-h filtration test, showing stable OSN performance. [ABSTRACT FROM AUTHOR]