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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]

In this work, we demonstrated the effectiveness of using spray-assisted interfacial polymerization (IP) technique in fabricating liposome-integrated thin film nanocomposite (TFN) membranes for seawater reverse osmosis (SWRO). The liposome loading within the selective polyamide (PA) layer of the TFN membrane can be precisely controlled by manipulating spraying conditions to eliminate the wastage of precious additives compared to the conventional blending method. Spraying the liposomes after applying the aqueous phase of M -phenylenediamine (MPD) could prevent the loss and disruption of liposome distribution over the substrate layer. Upon incorporating 4 mg/m2 of liposomes, the best-performing S4-a membrane is able to achieve 27% higher water permeability than the liposome-free membrane, demonstrating a permeability of 3.24 L/m2·h·bar along with 99.3% NaCl rejection for seawater desalination. Characterization showed that dynamic liposomes had affected the IP process by creating a larger miscible reaction zone for IP, which led to the formation of a rougher PA surface with more nanovoids in the ultra-thin selective layer, thus, contributing to higher effective surface area and less hydraulic resistance for improving water permeability. An additional PVA layer was coated atop the liposome-integrated membrane to effectively improve the membrane stability and fouling resistance, leading to a comparable level of salt rejection with the state-of-the-art commercial membranes in treating real seawater, while water permeability was enhanced by 26–185%. This work presents a readily scalable spray-assisted IP technique to fabricate liposome-integrated SWRO membrane for seawater desalination. [Display omitted] • DOPC liposomes were integrated into PA layer via spray-assisted IP approach. • Spraying DOPC liposomes after aqueous phase of IP ensured precise control of liposome amount. • DOPC liposomes resulted in forming a rougher PA surface with larger nanovoids. • The best membrane exhibited 3.24 L/m2·h·bar permeability with 99.3% NaCl rejection. • PVA coated liposome-integrated membrane demonstrated excellent stability and fouling resistance. [ABSTRACT FROM AUTHOR]

How the membrane support affects the performance of thin-film composite (TFC) membranes has long been under debate. Our present study experimentally establishes that the support pore number density (number per unit area) as well as its surface porosity play pivotal roles in affecting the characteristics and permselectivity of TFC membranes. The structure of hollow fiber supports was finely tuned and characterized via a series of techniques, which provided a link to the physicochemical properties of the interfacially polymerized polyamide films. During the spinning process, decreasing the content of N -methyl-2-pyrrolidone in the bore fluid drastically reduced the pore size and surface porosity of the support. The resultant TFC membranes showed a lower water permeability (tested under 1 bar using 500 ppm NaCl). Adding lithium chloride to the polymer dope also led to a support with smaller pores and lower porosity, but increased surface pore number density. The resulting TFC membranes had a substantially higher water permeability and slightly higher salt rejection. In both arrays of membranes, all membranes shared similar thickness of polyamide leaf but a more crumpled film was found on a less porous support, suggesting that the surface porosity of the support affected the effective surface area of films. However, the TFC membrane with a higher effective surface area did not necessarily possess a higher permeability. Rather, a TFC membrane having a support with a higher surface porosity or a higher pore number density exhibited a higher water permeability, demonstrating that the lateral transport path of water through films had a significant impact on the water permeability of TFC membranes. Interestingly, in both cases, the selectivity of the TFC membranes was maintained when the water permeability increased. This study clarifies longstanding misunderstandings concerning the effects of the support on TFC membrane performance and provides insight into fabricating highly permeable and selective TFC membranes. • A base film embedded in the polyamide layer determines performance of TFC membranes. • Enlarging surface porosity of supports could enhance permeability of TFC membranes. • Increasing pore density of supports could enhance permeability of TFC membranes. • Supports affect lateral diffusion of water through films and thereby permeability. • Rejection was maintained while the permeability of TFC was drastically enhanced. [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]

Developing a reverse osmosis membrane with desirable water/salt selectivity and boron removal has been recognized as crucial for high-efficient seawater desalination. Herein, fluorinated seawater reverse osmosis (SWRO) membranes were fabricated via fluorine-containing monomers-mediated interfacial polymerization or surface modification by grafting fluorine-containing monomers atop nascent polyamide (PA) layer via a second interfacial reaction. The fluorinated molecules, 5-(trifluoromethyl)-1.3-phenylenediamine (TFPD), 3,5-bis(trifluoromethyl) benzoyl chloride (TFBC) or 2,2,2-trifluoroethylamine (TFEA), were confirmedly integrated into the PA matrix presumably via strong chemical covalent bonds, which manipulated the physicochemical properties of the PA layer, including surface hydrophilicity, pore size distribution, cross-linking degree and interactions between membrane and solutes, thereby producing a high-selectivity thin-film composite (TFC) membrane. The optimized membranes, i.e. , TFC-TFPD, TFC-TFBC and TFC-TFEA, presented significantly excellent separation performance than the control and commercial membrane, both in water/salt selectivity and boron removal capability, accompanied by a comparable water permeance. Among the three proposed incorporation method of fluorinated monomers, direct grafting of TFEA upon the nascent PA layer demonstrates the best efficiency in introducing fluorine elements in the TFC PA membranes, compared to the addition of TFPD and TFBC into aqueous and organic phases during IP process, respectively. The fluorine-incorporated strategy employed in this present work offered a new design of the PA layer containing fluorinated molecules to obtain the desired permselectivity of TFC SWRO membranes towards efficient removal of salt and boron acid in seawater desalination. [Display omitted] • The fluorinated PA-based TFC SWRO membranes were successfully developed. • The fluorine-containing monomers were covalently bonded with PA matrix without sacrificing its integrity. • The incorporation of fluorine elements effectively regulated physicochemical properties of the PA layer. • The in-situ integrated fluorine components enabled high-efficient water/salt selectivity and boron removal. [ABSTRACT FROM AUTHOR]

In this work, we explored the practicability of a nanochannel-based biomimetic membrane (NBM) incorporating pillar[5]arene water channels for seawater reverse osmosis (SWRO) desalination. Two classes of peptide-attached biomimetic channels, (pR)-pillar[5]arenes (pRPH) and (pS)-pillar[5]arenes (pSPH) were integrated into the selective layer of SWRO membranes via interfacial polymerization on the top side of a polysulfone (PSf) support membrane. Here, pSPH is a non-identical stereoisomer of pRPH and was used as a negative control to pRPH to elucidate the flux enhancement effect contributed by pRPH. The optimized NBM presented a water permeability of 2.52 L m-2 h-1 bar-1 and 99.5% rejection under SWRO testing conditions of 50 bar applied pressure and 32,000 mg/L NaCl as feed solution. The 62% permeability increment with reference to the control membrane is hypothesized to originate from hybrid polyamide layers that were rougher with more voids (higher effective surface area and lower hydraulic resistance for water transport) as well as the conceivable water transport pathways provided by the pRPH channels. The simulation results from module-scale modelling suggest that the optimized NBM could lead to 7.2% savings in specific energy consumption of the membrane unit stage (or reduce the required membrane area by 25%) with respect to the commercial SWC4-LD membrane. The performance of the optimized NBM was further assessed in a one-week desalination test using an actual seawater feed gathered from an SWRO plant in Singapore. The robust NBM exhibited stable performance and ∼28% higher water flux (42 L m-2 h-1) than SWC4-LD with a comparable rejection of 99.3%, suggesting the feasibility of pillar[5]arene-based biomimetic membranes for seawater desalination. [Display omitted] • pRPH nanochannel-based biomimetic membrane (NBM) was used for SWRO application. • pRPH channels were incorporated into the PA layer via interfacial polymerization. • High permeability of 2.52 Lm-2h-1bar-1 (99.5% NaCl rejection) was reported in SWRO. • The energy and footprint savings achievable was quantified by module-scale modelling. • The NBM exhibited stable flux in a 7-day desalination test using real seawater. [ABSTRACT FROM AUTHOR]

Thin film composite (TFC) polyamide (PA) membranes experience compaction at high pressure applications, resulting in the reduction in water permeability. However, the compaction mechanism is still unclear especially for different PA morphologies and substrate structures. In this work, we systematically studied the compaction of TFC PA membranes with different structures and morphologies. We first examined 2 main types of commercial reverse osmosis (RO) membranes: brackish water RO and seawater RO membranes. After that, we synthesised four types of TFC membranes with tailored PA and substrate structures to further understand the compaction behaviors. TFC membrane with a PA layer of low protuberances or nodules and dense substrate showed excellent resistance against high pressure (50 bar), with only a slight irreversible decrease of 2.1–3.5% in water permeability when retested at 5 bar. However, the PA layer of high protuberances experienced significant compaction even when it was supported by a similar dense substrate. The permeability of the TFC membrane decreased ∼10% as a result of the decrease in the effective area of the active layer. On the other hand, the TFC membrane with a PA layer of low protuberances formed atop a loose substrate showed a greater decrease (∼18.5%) in water permeability. The densified skin layer and collapsed macro-voids within the loose substrate resulted in a ∼40% decrease in the overall height of the PA layer and a 65% decline in substrate surface porosity, respectively, which are identified as the reasons for the reducing water permeability. Notably, the water-salt selectivity of this particular membrane was seriously deteriorated after compaction due to the presence of subtle defects in the PA layer caused by the drastic deformation of the loose substrate. This work deepens the understanding of the compaction behaviors of TFC PA membranes, providing a clear fundamental guidance on designing membranes applied at high operating pressures. [Display omitted] • The compaction of TFC PA membranes with different PA and substrate structures at 50-bar hydraulic pressure was investigated. • The high protuberances on the PA layer were compressed at 50 bar, resulting in an apparent decline in water permeability. • A porous substrate resulted in the decreases of water permeability and selectivity simultaneously after membrane compaction. • A TFC membrane with a low-protuberance PA layer and dense substrate is suitable for use in high-pressure processes. [ABSTRACT FROM AUTHOR]

Chlorine exposure is one of the most commonly encountered challenges that cause polyamide (PA) membrane failure in use. The synergistic effect of iron, which is ubiquitous in water environment, with chlorination is however often overlooked. This study systematically investigated the performance of thin film composite (TFC) nanofiltration (NF) membranes under dynamic exposure of free chlorine and Fe2+ in filtration process. It was found that the 36%–70% reduction of water flux after chlorine-only exposure was mainly attributed to the competing effects of reduced hydrophilicity by N-chlorination over decreased crosslinking by chlorination-promoted hydrolysis, while the opposite trends of salt rejection for mild and severe chlorination were believed to be caused by the competing effects of decreased crosslinking and increased charged density. The presence of Fe2+ in the feed generally resulted in a higher (or equivalent) water flux and a lower salt rejection compared to chlorine-only conditions, owing to catalytic oxidation and iron deposition. Fe2+-induced catalytic oxidation by hydroxyl radicals (·OH) formed by the reaction between free chlorine and Fe2+ promoted C–N breakage and led to a much looser separation layer, which contributes more remarkably to performance variation (i.e., 2.5–6.5 time increase of water flux and near-zero salt rejection for 1000 mg/L Cl 2) than chlorination. In addition, the much lower normalized salt rejection for 10 mg/L Fe2+ than 0.1–1 mg/L Fe2+ (10%–30% vs. 100%–120%) under 10–100 mg/L Cl 2 at 24 h was attributed mainly to a much denser iron deposition layer, which neutralized the membrane surface charge and decreased the electrostatic repulsion between salts and membranes. Hence, the combination of chlorination, catalytic oxidation and iron deposition was proposed to be the mechanisms synergistically affecting the membrane behavior. [Display omitted] • The synergistic effect of iron with chlorination on polyamide membranes was evaluated. • Fe2+ increased water flux and reduced salt rejection compared to chlorine-only conditions. • Fe2+-induced catalytic oxidation by ·OH led to a much looser separation layer. • Iron deposition neutralized surface charge and decreased electrostatic repulsion. • Chlorination, catalytic oxidation, and iron deposition are the proposed mechanisms. [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]

This study examined the feasibility and performance of a nanochannel-based biomimetic membrane (NBM) for brackish reverse osmosis (RO) desalination. Two types of peptide-attached synthetic nanochannels, (pR)-pillar[5]arenes (pRPH) and (pS)-pillar[5]arenes (pSPH), were incorporated into liposomes. pSPH is a diastereomer of pRPH and was used as a negative control (i.e. mutant) to pRPH in this work. The nanochannel-containing liposomes (e.g. pRPH-liposomes) were then immobilized into the active layer of the RO membranes via in situ interfacial polymerization on the top of a polysulfone support membrane to form NBM-pRPH membranes. To maximize the potential and benefits of the NBM-pRPH membrane, the physical characteristics of the polyamide layer was further tuned using some additives and the eventual membrane was named as NBM-pRPH-A. The NBM-pRPH-A membrane exhibited a water permeability of 6.09 L m−2 h−1 bar−1 and 98.2% NaCl rejection under a 15.5 bar applied pressure using 2000 mg L−1 as feed solution. The 62% flux increment with respect to the pristine control is postulated to arise from a thinner, less cross-linked (more free volume) and more hydrophilic active layer as well as the possible supplementary transport pathways of the pRPH-liposomes. The performance of the NBMs under differential feed pressures and temperatures further exemplifies the water permeation property of the pRPH nanochannels. Accordingly, the NBM-pRPH-A gave a water permeability higher than commercial RO membranes tested in this work (DuPont BW30 and Hydranautics ESPA2) as well as other RO membranes reported in the literature. This study provides a tangible foundation for the development of NBMs for brackish RO desalination. [Display omitted] • Synthetic pRPH nanochannel-based biomimetic membrane was used for BWRO application. • pRPH-liposomes were incorporated onto the PA layer via interfacial polymerization. • STEM-EDX analysis revealed the existence of liposomes in the PA layer. • High permeability of 6.09 Lm−2h−1bar−1 (98.2% NaCl rejection) was reported in BWRO. • RO tests under increasing ΔP and temperature suggested water transport across pRPH. [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]