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Depth profiles of thin, latex films using gas cluster ion beam (GCIB) secondary ion mass spectrometry (SIMS) show an oscillation of surfactants and polymer signal that is related to the organization of the particles in the film as layers. These results demonstrate the application of GCIB-SIMS to the distribution of water soluble species with molecular sensitivity, which has implications to film performance in areas of adhesion, appearance, and cohesion. Specifically, surfactant species were found at the highest concentrations at the air interface, decreasing through the top few particle layers to a steady state, whereas salt-rich species (sulfates, oligomers) were found at every particle boundary with a high concentration at the substrate interface. [ABSTRACT FROM AUTHOR]

The fabrication of new membrane that is able to produce stable high power density is essential for the development of pressure retarded osmosis (PRO) technology. In this work, thin film composite (TFC) polyetherimide membranes with three different substrate structures were fabricated and characterized. The PRO performance of the resultant membrane was evaluated through two pressure cycle experiments and stability tests. The primary objective of this work is to systematically study PRO membrane’s mechanical stability and mass transfer properties under high operating pressures, which determine the power density of the membrane in the PRO process. Experiments revealed that water permeability ( A p ) and salt permeability ( B p ) under different pressures varied. The A p and B p are better indicators for examining the variation of PRO membrane structure under pressure. Within the operating pressure range of 17.2 bar, the top polyamide layer of TFC PEI-2# membrane mainly experienced a reversible deformation. In the two pressure cycle tests, the water flux, specific salt flux and power density obtained in the upward and downward measurements in each cycle are close to each other. The first cycle and the second cycle also show excellent reproducibility. The membrane was able to maintain almost unchanged water flux and power density of 12.8 W/m 2 at 17.2 bar over the 10 h testing time, suggesting the membrane’s great potential to be used in practical application in the future. [ABSTRACT FROM AUTHOR]

The pressure retarded osmosis (PRO) process is a novel technology which generates green electrical energy via semi-permeable membranes. However, a major challenge in the PRO system is the lack of suitable membranes with satisfactory power density (i.e., the power output per unit membrane area). In this study, we have successfully fabricated a novel thin-film composite (TFC) PRO membrane consisting of a tiered structure of polyetherimide (PEI) nanofibrous support reinforced by functionalized multi-walled carbon nanotubes (f-CNTs) and an ultrathin polyamide-based selective top skin layer. The tiered support was made by a fine and a coarse PEI nanofiber layers. The thin finer fiber reinforced with well dispersed f-CNTs has been found to increase mechanical stability of the polyamide selective layer, allowing the support to withstand high hydraulic pressure in the PRO system. Our optimized membrane can endure a trans-membrane pressure up to 24 bar and generate a peak power density as high as 17.3 W/m 2 at 16.9 bar using synthetic seawater brine (1.0 M NaCl) as the draw solution against deionized (DI) water. In addition, the long term PRO result shows that this membrane can generate a stable power density of 15.0±0.5 W/m 2 for a test period of 10 h. This demonstrates that our membrane holds great potential to be used in the PRO process. [ABSTRACT FROM AUTHOR]

Abstract: There has been a recent surge of interest to mimic the performance of natural cellular membranes by incorporating water channel proteins-aquaporins (AQPs) into various ultrathin films for water filtration applications. To make biomimetic membranes one of the most crucial steps is preparing a defect-free platform for AQPs incorporation on a suitable substrate. In this study two methods were used to prepare supported lipid membranes on NF membrane surfaces under a benign pH condition of 7.8. One method was direct vesicle fusion on a hydrophilic membrane NF-270; the other was vesicle fusion facilitated by hydraulic pressure on a modified hydrophilic NF-270 membrane whose surface has been spin-coated with positively charged lipids. Experiments revealed that the supported lipid membrane without AQPs prepared by the spin coating plus vesicle fusion had a much lower defect density than that prepared by vesicle fusion alone. It appears that the surface roughness and charge are the main factors determining the quality of the supported lipid membrane. Aquaporin Z (AqpZ) proteins were successfully incorporated into 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) liposomes and its permeability was measured by the stopped-flow experimental procedure. However, after the proteoliposomes have been fused onto the modified substrate, the AqpZ function in the resultant membrane was not observed and AFM images showed distinct aggregations of unfused proteoliposomes or AqpZ proteins on the substrate surface. It is speculated that the inhibition of AqpZ function may be caused by the low lipid mobility on the NF membrane surface. Further investigations to evaluate and optimize the structure-performance relationship are required. [Copyright &y& Elsevier]

Abstract: For the first time, a specially designed pressure retarded osmosis (PRO) hollow fiber membrane has been successfully developed and applied in the PRO process to demonstrate its potential for power generation. The membrane fabrication method is similar to that used for making thin-film composite (TFC) forward osmosis hollow fiber membranes, but further optimization and improvement have led to a new type of TFC hollow fiber membranes with much greater mechanical strength in addition to its excellent separation property and high water flux. The TFC PRO hollow fiber membranes have a water permeability (A) of 9.22×10−12 m/(sPa), salt permeability (B) of 3.86×10−8 m/s and structural parameter (S) of 4.6×10−4 m. It can withstand hydrostatic pressure as high as 9bar with its relatively large dimension of 0.98mm lumen diameter. This PRO hollow fiber membrane is superior to all other PRO membranes reported in the open literature in terms of power density. A power density as high as 10.6W/m2 can be achieved using seawater brine (1.0M NaCl) and wastewater brine (40mM NaCl), which suggests that the newly developed PRO hollow fiber membrane has great potential to be applied in PRO processes to harvest salinity gradient energy. A higher pressure is preferred as it allows generation of higher power density (pressures of 12bar may be optimal for seawater as the high salinity stream), and this can be realized by reduced fiber dimension. Further optimization of the membrane structure will be performed. [Copyright &y& Elsevier]

Abstract: Forward osmosis (FO) has received intensive studies recently for a range of potential applications such as wastewater treatment, water purification and seawater desalination. One of the major challenges to be overcome is the lack of an optimized FO membrane that can produce a high water flux comparable to commercial RO membranes. Two types of thin-film composite FO hollow fibers with an ultra-thin polyamide-based RO-like skin layer (300–600nm) on either the outer surface (#A-FO) or inner surface (#B-FO) of a porous hollow fiber substrate have been successfully fabricated. These novel composite FO hollow fibers have been characterized by a series of standard protocols and benchmarked against commercially available FO flat sheet membranes and reported NF hollow fibers used for the FO process. The characterization reveals that the FO hollow fiber membranes possess a large lumen. The substrates are highly porous with a narrow pore size distribution. The active layers present excellent intrinsic separation properties with a hydrophilic rejection layer and good mechanical strength. The #B-FO hollow fiber membrane can achieve a high FO water flux of 32.2L/m2 h using a 0.5M NaCl draw solution in the active rejection layer facing draw solution (AL-facing-DS) configuration at 23°C. The corresponding salt flux is only 3.7g/m2 h. To the best of our knowledge, the performance of the #B-FO hollow fiber is superior to all FO membranes reported in the open literature. The current study suggests that the optimal FO membrane structure would possess a very small portion of sponge-like layer in a thin and highly porous substrate, which suggests a way for further improvement. [Copyright &y& Elsevier]

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]

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]

For the first time, the permeation experiments of CO2 are carried out on ultra-thin dense polyimide films (0.5–1.8 μm). The observation of accelerated CO2 plasticization indicates that the conventionally defined “plasticization pressure” as an inherent material properties measured from thick dense films is strongly thickness dependent. This accelerated plasticization phenomenon observed in ultra-thin dense films is probably attributed to two factors: (1) the swelling and softening effects of the sorbing CO2 molecules on the polymer chains; and (2) weak micro-mechanical properties and less sorption capacity of ultra-thin films to accommodate the sorbed CO2 molecules. Experimental results suggest that chemically modified ultra-thin films show characteristics of retarded aging process and significantly suppressed plasticization. [Copyright &y& Elsevier]

In recent years, novel superwetting membranes have gained popularity for oily wastewater treatments via synergy between surface chemistry and topography. However, the water fluxes of the superwetting membranes normally decrease rapidly due to pore clogging and surface fouling, especially when treating surfactant-stabilized oil-in-water emulsions. Herein, a facile strategy is proposed to develop a superwetting thin film nanofibrous composite (TFNC) membrane with remarkable antifouling and self-cleaning properties to effectively separate surfactant-stabilized oil-in-water emulsions. The membrane is composed of an ultrathin carbon nanotubes (CNTs)-polyvinyl alcohol (PVA) composite skin layer, and a highly porous electrospun nanofibrous substrate as well as a non-woven mechanical support. The robust three-dimensional (3D) CNTs composite skin layer were immobilized on the nanofibrous substrate surface by crosslinking the CNTs with PVA. This skin layer serves as a functional barrier to reject oil droplets, which exhibited excellent performance in treating surfactant-stabilized oil-in-water emulsions with a rejection of 95% and a competitive flux of ~60 Lm−2h−1 under an ultra-low pressure (20 kPa) in a cross-flow filtration process. Moreover, the CNTs composite layer also protects the membrane surface from fouling. The TFNC membrane possesses outstanding reusability, as the water flux could be recovered by 100% in a continuous cyclic operation without cleaning, which should be attributed to the underwater oil repellence of its superhydrophilic surface and self-cleaning property based on the capillary pumping effect occurred in the micron/nano-channels of the membrane surface. Image 1 • Spray coating was used to fabricate separation layer on nanofibrous substrate. • An ultrathin carbon nanotubes-polyvinyl alcohol composite layer was crosslinked. • The membrane exhibited excellent performance in treating surfactant-stabilized emulsions. • The membrane had a rejection of 95% and a competitive flux of ~60 Lm−2h−1 at 20 kPa. • The membrane showed a flux recovery rate of ~100% in a continuous cyclic operation. [ABSTRACT FROM AUTHOR]

A new class of thin film nanocomposite (TFN) hollow fiber (HF) membrane of polydopamine (PDA) modified HKUST-1 (mHKUST-1) incorporated in polyamide (PA) matrix supported by polyethersulfone (PES) substrate was constructed via interfacial polymerization method for brackish water desalination in low-pressure reverse osmosis (RO) process. The PDA modification facilitated the HKUST-1 even dispersion, thus resulting in better compatibility between the inorganic nanofillers and the organic matrix. The impact of HKUST-1 loadings on the overall performances of the resultant HKUST-1@PA/PES membranes was investigated. Introducing the mHKUST-1 nanofillers not only enhanced surface hydrophilicity and negative surface charges for the selective layer, which improved membrane's fouling resistance to humic acid (HA), but also led to nearly doubled water permeance when comparing with the pristine PA membrane (increasing from 3.51 to 6.94 Lm−2h-1bar−1), without obvious salt rejection deterioration (~98.2% at 2 bar and 97.4% rejections at 4 bar for 500/2000 ppm NaCl solutions, respectively). The integrity of the HKUST-1@PA/PES membrane was examined and verified after 30-days operation. Overall, the results achieved in this work demonstrate promising potential of the metal organic framework (MOF)-based TFN membranes used for desalination in low-pressure RO process. To sum up, this work has exhibited a facile method to incorporate the metal organic framework (MOF) into the PA layer, and the resultant MOF-based TFN membrane indicates its great potential for desalination in low-pressure RO process. • A thin film nanocomposite hollow fiber membrane was constructed via interfacial polymerization. • Polydopamine (PDA) modified HKUST-1 was incorporated in polyamide matrix supported by polyethersulfone substrate. • The PDA modification facilitated the HKUST-1 even dispersion in PA matrix, without the formation of defects. • A water permeability of 6.94 Lm−2h-1bar−1 and 97.4% rejections at 4 bar for 2000 ppm NaCl solution were achieved. • The long-term stability test verified the good integrity of the HKUST-1@PA/PES membranes after 30-days operation. [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]

Abstract Forward osmosis (FO) membranes have received attention as an energy-efficient and low-cost technique in stream concentrating processes. In this work, a novel double-skinned hollow fiber thin film composite (TFC) FO membrane has been successfully fabricated, which consists of a one-step prepared dual layer substrate and a thin inner selective layer formed via interfacial polymerization. The substrate consists of a relatively dense ultrafiltration (UF) outer layer and a porous UF inner layer, both of which were constructed from polyethersulfone (PES) as the substrate material by using dual-layer co-extrusion technique. Compared to the commercial and reported double-skinned FO membranes, the FO membrane developed in this work exhibited a higher permeate flux with humic acid solution as feed. Furthermore, the double-skinned FO membrane was applied in concentrating activated sludge using 0.5 M NaCl as draw solution, and a permeate flux at 5.4 L/m2h was achieved after 5 h operation, which was higher than or comparable to those of the reported FO membranes. Membrane autopsies and foulant analysis suggested that the dense UF skin layer helped to reject greater-sized organic foulants (> 300 Da). This study shed light on the important fabrication features and promising application of the double-skinned hollow fiber TFC FO membrane in sludge concentration. Graphical abstract fx1 Highlights • A dual-layer UF substrate was prepared via a single-step fabrication process. • TFC FO membrane was fabricated via interfacial polymerization in the lumen of the substrate. • FO performance in sludge thickening process was investigated. • Tight UF layer helped rejecting greater-sized organics in sludge. • A permeate flux of 5.4 L/m2h was achieved after 5 h operation using 0.5 M NaCl as draw solution. [ABSTRACT FROM AUTHOR]

Pressure retarded osmosis (PRO) demonstrates great potential in energy harvesting when combining with seawater reverse osmosis. However, the lack of suitable membrane modules and the issue caused by the membrane fouling greatly impede the practical application of PRO to a larger scale. In this study, two-inch thin film composite hollow fiber modules were fabricated by using in-house developed PRO membranes. The produced PRO modules have a maximum effective area of 0.5 m 2 . By assessing the PRO performances of the modules with different sizes, external concentration polarization (ECP) was found to have significant impact on the flux reduction during module scale-up. Different module designs, including fiber bundles, distribution baffles and distribution tubes, were thus adopted as an attempt to boost the membrane performance. A power density of 8.9 W/m 2 at 15 bar was obtained using tap water as feed and 1 M NaCl solution as draw solution. PRO performance tests were also carried out using the developed two-inch modules on a pilot-scale setup with actual wastewater retentate as feed solution. Low pressure nanofiltration was selected as the pretreatment of the wastewater retentate to mitigate fouling. A power density of larger than 8 W/m 2 was obtained when pretreated wastewater retentate was used as the feed solution, implying high potential of PRO in the pilot scale. Nevertheless, full potential of PRO can only be realized by mitigating ECP, which could be achieved by improving the module design in the further endeavor. [ABSTRACT FROM AUTHOR]

The salinity gradient is a renewable and sustainable energy source that can be utilized by a pressure-retarded osmosis (PRO) process. Development of the PRO technology was impeded by shortage of efficient membranes until recent surge on PRO research. In this work, flat-sheet thin film composite (TFC) PRO membranes with reinforced support layer were developed. The membrane properties were optimized by blending high molecular weight polyvinylpyrrolidone (PVP) into the polysulfone (PSf) casting solution. Influences of PVP addition on the kinetic and thermodynamic properties of the casting solution, resultant membrane properties as well as PRO performance were systematically investigated. It is showed that PVP can effectively improve the membrane morphology and pore structure. By adjusting the PSf/PVP composition in the substrate recipe, the reinforced TFC membrane is able to achieve a power density of 12.9 W/m 2 at 22 bar using 1 M NaCl draw solution and pure water feed. Long-term PRO test at the peak power density and multi-pressure cycle tests were performed on the membranes. Consistent power density and low salt flux/water flux ratio were observed in the whole tests. The results demonstrated that the reinforced TFC membrane in this study had excellent mechanical strength and stability. It would be promising for future engineering application. [ABSTRACT FROM AUTHOR]

Highlights: [•] Phytic acid increases compactness of self-assembled nanoparticle (SANP) film. [•] SANP-P layer in composite film indicates good barrier property against corrosion. [•] Improved adhesion of composite film obtained in a corrosive service environment. [•] SANP film with phytic acid (SANP-P) shows high thermal stability. [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]

Abstract: Exploitation of osmotically-driven membrane (OM) technologies and accompanying semi-permeable OM fabrication have become promising topics with numerous potential applications. This paper presents a systematic comparison study of nanofiltration (NF)-like and reverse osmosis (RO)-like thin film composite (TFC) OMs in terms of flux performance and fouling behavior. Major governing mechanisms of OM performance were elucidated and revealed to be related with properties of membrane, draw and feed solutions. Results showed the crucial influence of draw solute reverse diffusion (M ICP-Js ) on OM water flux. Thus the high-rejection RO-like OMs generally performed better than NF-like counterpart in sodium chloride based osmotic processes. On the other hand, the high permeability of NF-like OMs can achieve higher water flux when proper draw solutes were used to minimize M ICP-Js . Fouling tests also suggest that the NF-like TFC OMs tend to be more fouling resistant due to its smooth membrane surface. The current study led to a set of systematic criteria for the selection of osmotically-driven membranes, draw solution and other operational conditions, of which the practicability was further elucidated in potential OM applications. [Copyright &y& Elsevier]

Abstract: Forward osmosis (FO) process as an alternative to conventional desalination techniques has attracted much attention in recent years. Since mineral salt scaling is one of the major limitations for seawater desalination, the current study focused on the behaviors of thin film composite (TFC) FO hollow fibers, which were fabricated in our laboratory, under the circumstance of calcium sulfate (CaSO4) scaling with sodium chloride as draw solution. The performance of FO hollow fiber membranes was compared with commercially available FO flat sheet membranes. Several cleaning strategies were also explored. Depending on the membrane orientation, experimental results suggested that the scaling of the FO hollow fibers was dominated by cake layer formation along with pore blocking in the orientation of active layer facing draw solution (AL-DS). The pore blocking could be a result of the penetration of crystals from the feed solution into the support matrix of the membrane, or the formation of crystals inside the porous support layer. At the same driving force, the water flux of the FO hollow fibers in the orientation of active layer facing feed solution (AL-FS) was twice higher than the water flux of the flat sheet membrane in both orientations. The water flux of scaled FO hollow fibers and flat sheet membranes in the AL-DS orientation could be successfully restored by hydraulic backwash procedure. To the best of our knowledge, this is the first study to examine the inorganic scaling of FO membranes in the AL-DS orientation. [Copyright &y& Elsevier]

Abstract: Polyamide thin film composite (TFC) membranes with tailored porous substrate and rejection layer are promising for forward osmosis (FO) applications. The current study investigates the effect of rejection layer synthesis conditions on the performance of the resulting TFC polyamide FO membranes. The influence of monomer concentrations (i.e., m-phenylenediamine (MPD) and trimesoyl chloride (TMC) concentrations) on the membrane separation properties as well as FO performance was systematically studied. A strong trade-off between the water permeability and salt rejection was observed, where increasing the TMC concentration or reducing the MPD concentration resulted in higher membrane permeability but lower salt rejection. In FO tests, membranes with poor salt rejection had severe solute reverse diffusion, which enhanced the internal concentration polarization (ICP). It was found that the FO water flux was governed by both the membrane water permeability and its solute rejection. For a membrane with higher water permeability but lower solute rejection, the reduced membrane frictional resistance was compensated by the simultaneously more severe solute-reverse-diffusion-induced ICP. The net effect on the FO water flux depends on the competition of these two opposing mechanisms. Under conditions where solute reverse diffusion may cause severe ICP (e.g., high draw solution concentration and high water flux level), membranes need be optimized to achieve a high salt rejection even if this is at the expense of lower water permeability. [Copyright &y& Elsevier]

Abstract: Forward osmosis (FO) technology has become increasingly attractive in the past decades for water related applications and will likely continue to develop rapidly in the future. This calls for the development of high performance FO membranes. Thin film composite (TFC) polyamide FO membranes with tailored support structure were prepared in the current study. The porous polysulfone substrates with finger-like pore structures were prepared via phase inversion, and the polyamide rejection layers were synthesized by interfacial polymerization. The resulting TFC FO membranes had small structural parameters (s =0.67–0.71mm) due to the thin cross-section, low tortuosity, and high porosity of the membrane substrates. Meanwhile, their rejection layers exhibited superior separation properties (higher water permeability and better selectivity) over commercial FO membranes. When the rejection layer is oriented towards the draw solution, FO water flux as high as 54L/m2 h can be achieved with a 2M NaCl draw solution while maintaining relatively low solute reverse diffusion. Comparison of the synthesized TFC FO membranes with commercial FO and RO membranes reveals the critical importance of the substrate structure, with straight finger-like pore structure preferred over spongy pore structure to minimize internal concentration polarization. In addition, membranes with high water permeability and excellent selectivity are preferred to achieve both high FO water flux and low solute flux. [Copyright &y& Elsevier]

Recent research pays much attention to the correlations between structural properties of porous substrate and the separation performance of polyamide (PA) thin film composite (TFC) membrane prepared by interfacial polymerization (IP). However, there are limited studies focused on seawater reverse osmosis (SWRO) membrane preparation and optimization. This study reveals profound impacts of substrate surface properties on the separation properties of SWRO membranes, by using different substrates including commercial ultrafiltration (UF) membrane, lab-scale casted polysulfone (PSF) substrate and pilot-scale casted PSF substrates. We demonstrate that the membrane substrates casted using pilot-scale machine led to better SWRO performance than hydrophilic UF membrane or lab-scale casted substrate; and very different SWRO membranes could be made from pilot-scale substrates casted using the same polymer dope solution. These results showed that a high-performance SWRO membrane relies on appropriate substrate possessing the surface properties of relatively hydrophobic, small surface pore size (20-35 nm) and high surface porosity, which directly affect the supply and transport rate of amine for the IP reaction. Our best SWRO membrane exhibits an excellent NaCl rejection of 99.5% together with high water permeance of 1.72 L m−2 h−1 bar−1 under seawater desalination conditions. This work helps pave the way for substrate selection for SWRO membrane fabrication, narrowing the gap between lab-made and commercial SWRO membranes. [Display omitted] • Substrates with tuned surface properties were used to tailor SWRO membrane performance. • PSF substrates casted by a pilot-scale machine exhibited better SWRO performance. • The best-performing membrane demonstrated water permeance of 1.72 Lm−2h−1bar−1 and rejection of 99.5%. • Hydrophobic substrate of small surface pore size and high surface porosity was important for making excellent SWRO membrane. [ABSTRACT FROM AUTHOR]

A 100-piece hollow fibre thin-film composite membrane module was successfully developed for pharmaceutical concentration and solvent recovery. To increase its packing density, thinner P84 polyimide hollow fibre substrates were spun using a smaller spinneret. The substrates were subsequently cross-linked with hexamethylene diamine to achieve organic solvent resistance. An MPD-based thin-film composite was synthesized through interfacial polymerisation to increase selectivity for solutes of less than 300 Da. The thin-film composite was then solvent-activated using N , N -dimethylformamide to increase its solvent permeability. The resulting membrane exhibited excellent performance with 24.2 l m−2 h−1 bar−1 acetone permeability and 90.1% methyl red (269 Da) rejection. In addition, the solvent-activated membrane maintained its performance for prolonged period, demonstrating the scalability of the thin-film composite fabrication process and stability of solvent-activated membranes. The membrane was also able to concentrate levofloxacin (361 Da) from 500 ppm to 20,000 ppm in acetone using a batch process, showing promising results for pharmaceutical applications. Image 1 • 100-piece thin-film composite OSN membrane was successfully fabricated. • 7-day filtration test showed stable organic solvent nanofiltration (OSN) performance. • High acetone permeability of 24.2 l m−2 h−1 bar−1 and 90.1% methyl red rejection. • Active pharmaceutical ingredient was concentrated to 2 wt%. [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]

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]

In this study, we presented a novel nanofiltration membrane fabrication strategy through rapid co-deposition of a versatile platform – metal phenolic networks (MPNs) and piperazine (PIP) on a porous substrate followed by trimesoyl chloride (TMC) crosslinking. Inspired by the catechol chemistry, tannic acid (TA) was functionalized to tether PIP monomers, and participated in the co-deposition via coordination bonds with Fe3+ ions on a substrate to form Fe3+/TA-PIP complex. A series of analyses (SEM, XPS, FT-IR, water contact angle and zeta potential) confirmed the successful synthesis Fe3+/TA-PIP deposition and polyamide (PA) layer. The resultant membrane exhibited water permeability of 13.73 LMH/bar and 89.52 % for MgSO 4 rejection. The fabrication was further improved by embedding modified graphene oxide (GO) nanosheets into the Fe3+/TA-PIP complex. The optimized nanocomposite membrane achieved a water permeability at 21.66 LMH/bar, along with a well maintained MgSO 4 rejection at 91.25 % and NaCl/MgSO 4 selectivity (α) at 10.02 under 2 bar operation pressure. The rapid co-deposition mediated by nanomaterials incorporation provides an effective approach to design high performance thin film composite (TFC) membrane. Image 1 • A novel fabrication strategy was designed for nanofiltration membrane. • Metal phenolic networks were rapidly co-deposited with piperazine followed by interfacial polymerization. • Graphene oxide was incorporated into the deposited layer without additional fabrication step. • The optimized thin film composite membrane exhibited high separation performance. [ABSTRACT FROM AUTHOR]