Search

The photocatalytic membranes have been reported to treat textile dye effluents; however, it is challenging to maintain their long-term functionality due to the poor binding stability of nanoparticles on the membrane surface and the low stability of the membrane to UV radiation. To address this, PVDF photocatalytic hollow fiber membranes were prepared by coating with polydopamine (PDA) for 1–4 h, then with titanium dioxide nanoparticles (TiO 2) in the current study. SEM and EDX results showed that TiO 2 adhered firmly to the PDA-pretreated membrane after ultrasonic treatment. The PDA layer protected the membranes from UV irradiation. The PVDF-TiO 2 membrane without PDA pretreatment was destroyed after 24 h of UV irradiation, while after 9 days of continuous irradiation, the membranes treated with PDA for 2 h remained unchanged. Compared with the original membrane, applying PVDF membranes coated with PDA for 2 h and TiO 2 for 1 h increased the Reactive Red 239 rejection and flux recovery rates by 13% and 40%, respectively, achieving 60% COD removal. The permeate flux and dye rejection rate were stable after 5 cycles (20 h of operation). This study demonstrates that the obtained membranes can perform prolonged membrane filtration with high-performance durability for dye wastewater treatment. [Display omitted] • TiO 2 was strongly bonded to the PVDF membrane pretreated with PDA. • Introducing PDA-TiO 2 enhanced the stability of dye permeate flux and dye rejection. • The PVDF-PDA-TiO 2 membranes significantly improved the COD removal efficiency. • PVDF-PDA-2h-TiO 2 -1 h membrane showed excellent resistance to UV and reusability. • Self-protecting/cleaning, hydrophilicity, and durability of membrane all improved. [ABSTRACT FROM AUTHOR]

In view of the proliferating applications involving membrane-based separation, the inevitable membrane fouling phenomenon is well-studied. However, the influence of foulant shape on membrane fouling remained incompletely understood. Therefore, the goal of this study was to investigate the fouling behaviors by three different shapes of latex particles (namely, peanut, pear and sphere) with similar mean diameters in the range of 3.5–3.8 μm. External and internal fouling were studied using polycarbonate track-etched (PCTE) membranes with nominal pore sizes of 2 and 8 μm, respectively. Flux data were taken, and fouling models, optical coherence tomography (OCT) and field-emission scanning electron microscope were employed. Regarding external membrane fouling, the sphere-shaped particles displayed the worst flux decline, which is tied to the greatest tendency to deposit on the membrane pores, as revealed by the network fouling model. As for internal fouling, the flux decline curves were more similar among the particle types. The fouling model shows the sphere-shaped particles gave the densest internal cake, which caused slightly steeper flux decline in the latter part of the filtration. Furthermore, OCT indicates that the highest fouling fractions at 7.5 μm below the membrane were exhibited for the peanut-shaped particles, which is due to the preferential vertical orientation resulting in deeper penetration. Results here highlight the non-negligible influence of foulant particle shape, which warrants further understanding and accounting for membrane fouling studies. [Display omitted] • Used OCT to reveal influence of foulant particle shape on membrane fouling. • Spheres were more prone to pore-blockage and thus gave worst flux decline. • Non-spherical particles gave less dense internal cakes due to rotational effects. • Peanut-shaped particles penetrated deeper due to preferential vertical orientation. • Particle shape affected flux decline more when external fouling was dominant. [ABSTRACT FROM AUTHOR]

The Derjaguin-Landau-Verwey-Overbeek (DLVO) model, as well as the extended model (XDLVO), is popularly employed to quantify the interfacial interactions underlying membrane fouling. However, disagreements between membrane fouling extent and the interaction energies derived from DLVO or XDLVO models have been reported, which suggests gaps in the understanding. This study demonstrates that the DLVO approximation methods for predicting the interfacial foulant-membrane interaction are sensitive to the boundary condition assumptions (e.g., constant charge versus constant potential). In particular, while both the Poisson-Boltzmann (P–B) and linear superposition approximation (LSA) equations can quantify the electrostatics (EL) interaction energy component, the former assumes constant potential, while the latter additionally considers constant charge scenarios. The relative accuracy of these two equations were evaluated here. For dead-end filtration tests, flux decline trends, OCT analysis results and fouling model parameters were obtained. Regarding fouling of pristine PCTE membrane by latex particles of opposite charge signs, both the P–B and LSA equations contribute to predict relative fouling extents correctly. However, for the case of the BPEI-coated membrane, the P–B equation failed whereas the LSA equation gave good agreements. For cross-flow filtration tests in organic solvents, LSA also out-performed the P–B equation in providing more accurate predictions of membrane fouling. The results here highlight the shortcomings in the commonly used P–B equation and are expected to be potentially valuable in the development of better approximations for quantifying interfacial interaction energies. [Display omitted] • Both P–B and LSA equations predict fouling of pristine membrane by latex correctly. • Only LSA predict affinity between coated membrane layer and latex correctly. • Superiority of LSA also applies to fouling in organic solvents. • P–B equation is more limited due to underlying constant-potential assumption. • Boundary condition assumptions need to be considered in use of DLVO model. [ABSTRACT FROM AUTHOR]

With recent focus on achieving carbon neutrality to tackle global warming, there is an increasing need for advanced carbon capture technology to reduce carbon emission to the atmosphere. Membrane separation is one of such technologies that can remove carbon dioxide (CO 2) in an energy-efficient and cost-effective way. In particular, the well-studied thin-film composite (TFC) membranes based on commercial polyethylene oxide (PEO)-containing materials have demonstrated strong promise for large-scale industrial post-combustion CO 2 capture. However, to realize high-performance PEO-based TFC membranes, a key challenge lies in maximizing the reduction in the thickness of the selective layer without compromising membrane integrity, which to date has achieved little progress probably due to the failure in addressing the poor selective/gutter layer interfacial compatibility issue. Here, we adopted a facile spray coating method to design a TFC membrane comprising an ultrathin Pebax-1657 selective layer, a polydimethylsiloxane (PDMS) gutter layer, and a porous polysulfone (PSF) substrate. To increase surface hydrophilicity and wettability for enhancing interfacial compatibility between the selective and gutter layers, the surface of the PDMS gutter layer was activated for a few seconds by air plasma prior to Pebax-1657 spray coating. Coupled with well-controlled spray coating manipulation, a defect-free Pebax-1657 selective layer with an ultrathin thickness as low as 30 nm could be formed. Correspondingly, the optimized TFC membrane exhibited a highest CO 2 permeance at 2022 GPU with a CO 2 /N 2 selectivity of close to 30.0, far surpassing the threshold for commercially viable post-combustion CO 2 capture (CO 2 permeance ≥1000 GPU and CO 2 /N 2 selectivity ≥20). More importantly, the use of spray coating endows the TFC design with great scalability potential, rendering our membranes, which are made solely from commercially available materials, highly relevant for industrial CO 2 separation. [Display omitted] • Pebax/PDMS/PSF TFC membranes with ultrathin selective layers were fabricated. • Air plasma was utilized to process the PDMS gutter layer to facilitate the formation of Pebax selective layer. • The best performed membrane exhibited an CO 2 permeance at 2022 GPU and a CO 2 /N 2 selectivity of 29.3. • Spray coating fabrication endows the TFC membranes with great scale-up potential. [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]

Efforts have been made in thermally induced phase separation (TIPS) process to modify the morphology of polyvinylidene fluoride (PVDF) membranes in order to improve their permeation performance and mechanical properties. Nevertheless, many methods not only altered the outer surface but also impacted the overall membrane structure, resulting in a trade-off between permeability and mechanical properties. In this study, we utilized a modified TIPS process to refine the outer surface morphology without altering the bulk structure. This was achieved by introducing NaCl in the coagulation bath. The PVDF membranes were fabricated using a dope with water insoluble diluent dimethyl phthalate (DMP) as main solvent and water-soluble additives polyethylene glycol 400 (PEG400)/triethylene glycol (TEG) as pore formers. The inclusion of NaCl in the coagulation bath serves to decrease the solubility of PEG within this medium, owing to the salting-out effect. Consequently, the NaCl concentration in the coagulation bath emerges as a crucial factor in regulating the migration of PEG400 toward the membrane surface. This control mechanism facilitates the precise adjustment of the outer surface morphology in the fabrication of membranes. As the NaCl concentration increases in the coagulation bath, the outer surface of the fabricated membrane transited from a mesh-like structure to a spherulite structure. As 0.5 mol L−1 NaCl was added to the coagulation bath, the membranes displayed a pure water permeability of 1073.9 L m−2 h−1 bar−1 while maintaining a narrow pore size distribution. Compared to the membranes fabricated without NaCl addition, the increment of the PWP contributed to the slight increase in mean pore size from 65 nm to 84 nm. Meanwhile, the water-insoluble diluent DMP was not affected by the addition of NaCl, which means that the bulk structure of the membrane could be maintained. Consequently, the increase in permeability did not compromise the mechanical properties of the membranes. All the membranes fabricated in this study maintained a reasonable tensile strength of approximately 3 MPa. This study introduces a simple and environmental method to increase the permeability effectively and fine-tune the pore size of the TIPS membranes while having little effect on the bulk structure. Furthermore, the study provides valuable insights into how changes in outer surface morphology can impact the pore size and permeability of TIPS PVDF membranes. [Display omitted] • Ultrafiltration PVDF membranes was fabricated by a modified TIPS method. • NaCl coagulation bath could control the outflow of PEG toward membrane surface. • The surface of the membranes could be fine-tuned without altering the bulk structure. • The ultrafiltration membranes present a narrow pore size distribution and high permeability. [ABSTRACT FROM AUTHOR]

Membrane fouling in organic solvent environments remains poorly explored despite its significance in chemical and pharmaceutical industries. This study uses molecular dynamics (MD) simulations and experiments to explore lysozyme fouling in water, as well as four organic solvent environments, namely, 30 % v/v and 50 % v/v isopropyl alcohol (IPA), and 30 % v/v and 50 % v/v dimethyl sulfoxide (DMSO). Experimentally, flux declines were least with IPA and worst with DMSO. Biased simulations indicate the worst fouling in DMSO is tied to the most attractive lysozyme-membrane energy in the presence of DMSO. However, the relative attractive energies for IPA and water do not agree with the relative flux declines, indicating other factors are more influential when the interaction energies are similar. To understand the gentler flux decline for IPA despite the more attractive lysozyme-membrane energy, radial distribution functions (RDFs) were obtained from unbiased simulations. Analyss of the water and solvent films around both the membrane and the lysozyme molecule reveal that the denser water film around both entities induced by the presence of IPA serves as a barrier for fouling and thus leads to less flux decline. The results underscore the complexity of fouling in organic solvent systems, cautioning against direct use of the understanding based on aqueous systems. [Display omitted] • Membrane fouling by lysozyme in water, IPA and DMSO studied. • Flux decline worst in DMSO and least in IPA. • Worst fouling in DMSO tied to most significant lysozyme-membrane attraction. • Least fouling in IPA tied to denser water film around membrane and lysozyme. • Both biased and unbiased molecular dynamics simulations needed for full explanation. [ABSTRACT FROM AUTHOR]

The use of amphiphilic pore formers and hydrophilic non-solvents has demonstrated its effectiveness in improving the surface porosity and permeability of polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes through the nonsolvent induced phase separation (NIPS) process in literatures. However, in the thermally induced phase separation (TIPS) process, few reports illustrated how the amphiphilic pore-former and water-soluble non-solvent interact with water-insoluble diluents. In this study, water-insoluble dimethyl phthalate (DMP) was used as the main diluent to rule out the effect of diluent outflow. The amphiphilic pore former polyethylene glycol 400 (PEG400) failed to open pores on the outer surface of the membranes because of its amphiphilic nature. On the contrary, UF membranes with a mean pore size of 55 nm could be obtained by adding hydrophilic triethylene glycol (TEG) to the dope with a satisfactory pure water permeability (PWP) of 262.6 L m−2 h−1 bar−1. Moreover, PEG400 can serve as a stabilizer for the TEG droplets during the phase separation if both were added to the polymer dope solution. The addition of both PEG400 and TEG could significantly increase the membrane's PWP to 645.4 L m−2 h−1 bar−1 with moderate enlargement of the mean pore size of the membrane to 84 nm. Additionally, the well-connected membrane structure resulted in the tensile strength of the membranes ranging from 3.07 to 6.65 MPa. This study expands the range of additives used in the TIPS process and demonstrates the different roles of amphiphilic and hydrophilic non-solvents in the TIPS process. [Display omitted] • The effects of hydrophilic and amphiphilic non-solvent in the TIPS process are analyzed. • Hydrophilic non-solvent TEG could tailor the surface morphologies of the PVDF membranes. • Amphiphilic PEG failed to open pores on the outer surface of the PVDF membrane. • Amphiphilic PEG served as the stabilizer of TEG in the PVDF dope, increasing the porosity and pore size of the membranes. • The resulting PVDF membranes sit within the UF range, presenting narrow pore distribution and high pure water permeability. [ABSTRACT FROM AUTHOR]

In this work, a tight polyethersulfone (PES) -based ultrafiltration (UF) membrane was fabricated to separate dye and salt of textile wastewater via a novel polyion complex assisted phase inversion method in one step. Thereinto, sulfonated polysulfone (SPSF) and poly-(diallyl dimethylammonium chloride) (PDADMAC) were added into the PES dope and coagulation bath, respectively. During the phase inversion process of the precast PES/SPSF film, polycation PDADMAC could assemble with anionic SPSF and facilitate SPSF enrichment on membrane surface, forming a dense barrier layer via the electrostatic interaction between quaternary ammonium and sulfonate groups. Morphology, chemical composition, surface charges and pore size analysis characterized via SEM, FTIR, XPS, Zeta potential and Dextran filtration experiment, respectively, testified that a nonporous skin layer comprising of polyion complex and enriched SPSF was successfully constructed on the top of the PES matrix with an effective pore radius of 1.44 nm, which is smaller than that of the reference membrane prepared without using polyion complex assisted phase inversion (2.74 nm). This resultant membrane exhibited a high pure water permeance of 94 LMH/bar. When it was utilized to separate a dye/salt mixture of 100 ppm Congo red (CR) and 2 g/L Na 2 SO 4 at 1 bar, the rejection of CR could reach 99.7%, alongside a very low Na 2 SO 4 rejection of 8.4%, while the water permeance of dye solution maintained 61 LMH/bar. In addition, the membrane also possessed excellent stability in the pH range of 1–13 due to the strong electrostatic interaction between SPSF and PDADMAC and long-term operation stability, demonstrating its application potential in textile wastewater treatment. [Display omitted] • Tight UF membranes were prepared via polyion complex assisted phase inversion. • The assembly between SPSF and PDADMAC made a thin and nonporous skin layer. • The membrane exhibited 99.7% and 8.4% of Congo red and Na 2 SO 4 rejections, respectively, alongside 61 LMH/bar water permeance. • The separation performance can maintain in the pH range of 1–13 and 12-h stability testing. [ABSTRACT FROM AUTHOR]

In this work, a positively charged hollow fiber nanofiltration (NF) membrane based on twice interfacial polymerization (IP) reactions was developed for water soften and heavy metal ions removal. The first IP reaction was conducted on the polyethersulfone (PES) hollow fiber substrate using a mixture of branched polyethyleneimine (PEI) and piperazine (PIP) as the aqueous phase monomers in the aqueous phase reacting with trimesoyl chloride (TMC) in the cyclohexane solution. Then, a secondary IP reaction was performed between tris(2-aminoethyl) amine (TAEA) solution and the residual acyl chloride groups on the membrane to increase the positive charge density on the membrane surface. Consequently, a NF membrane with intensified positive surface charge density was successfully fabricated. The optimized membranes achieved a high rejection of MgCl 2 of 97.6% while maintaining a pure water permeability (PWP) of 16.0 L m−2 h−1 bar−1. Meanwhile, the membranes exhibit high rejection values of 99.8% to Cu2+ and 99.7% to Zn2+, respectively. In conclusion, this work provides a facile way to prepare a positively charged membrane for efficient water softening and metal ions removal. [Display omitted] • A novel polyamide NF hollow fiber membrane via a secondary IP reaction had been successfully fabricated. • The secondary IP reaction between TAEA and the residual acyl chloride groups effectively enhances the positive change density on membrane surface. • This modification method has no influence on membrane structure. • The optimum membrane shows more than 90% rejection of Mg2+ and Ca2+ and 99% rejection of heavy metals. [ABSTRACT FROM AUTHOR]

Facilitated transport mixed matrix membranes (FTMMMs) separation technology has shown advantages in improving CO 2 recycling efficiency and reducing the environmental impacts associated with carbon emission. The design of FTMMMs is highly dependent on the selection of a compatible combination of polymer and filler. Herein, a novel grafted nanoparticles (GNPs) filler UiO-66-NM@PEG with multiple groups prone to hydrogen bond was designed to alleviate the phase separation and performance degradation caused by filler/polymer poor compatibility. In the GNPs configuration, by employing the coexistence strategy of coupling reaction and covalent bonds, maleic anhydride (MAH) was coupled with the amino group on UiO-66-NH 2 without clogging or cracking, and the generated carboxyl groups can be cross-linked with the hydroxyl groups on the poly (ethylene glycol) (PEG) by covalent bonds. The UiO-66-NM@PEG demonstrated excellent interface compatibility between the filler and matrix phase of UiO-66-NM@PEG/PVDF, which was further convinced by molecular modelling. The resultant UiO-66-NM@PEG/PVDF achieved a simultaneous enhancement of gas permeability (537.6 Barrer) and ideal CO 2 /N 2 selectivity (47.8), which surpassed Robenson upper bound. Moreover, the UiO-66-NM@PEG/PVDF has a lasting sustainability over 960 h (40 days), and a valid anti-acid/alkali corrosion resistance in harsh environments. More importantly, UiO-66-NM@PEG can also be well mixed with other mixture matrices such as hydroxy-terminated polydimethylsiloxane (PDMS) and polyether-block-polyamide copolymer (PEBAX) to promote permeability/ideal selectivity up to (724.1 Barrer/21.1) and (307.4 Barrer/31.4). We thus concluded that this rational-design GNPs approach provides a general toolbox for controllable engineering in GNPs whereby enhanced favorable filler/matrix compatibility in FTMMMs with optimized CO 2 /N 2 separation properties. By the means of covalent "bridge-crosslinking", the UiO-66-NM@PEG/PVDF FTMMM with favorable phase compatibility between filler/matrix displayed excellent gas separation performance. [Display omitted] • A novel grafted filler UiO-66-NM@PEG was synthesized via Covalent "Bridge-crosslinking" strategy. • The membrane showed excellent sustainability over 40 days and corrosion resistance. • UiO-66-NM@PEG exhibited favorable filler/matrix compatibility in other two matrices. • The performance of UiO-66-NM@PEG/PVDF surpassed Robenson upper bound. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) is a promising desalination technology as it is less sensitive to feed's salinity and can handle high-salinity water. However, the industrial application of MD is restricted by the limited availability of cost-effective hydrophobic membranes. This study developed a simple method to fabricate hydrophobic MD membranes through the coating of a fluoroethylene vinyl ether polymer called LUMIFLON™ LF-200. The fluoropolymer was effectively coated on porous nitrocellulose (NC) and nylon membrane through dip-coating followed by a thermal crosslinking. The coating layer was thin and uniform, covering the surface of the whole membrane matrix, while the high porosity and the microstructure of the membranes were still mostly preserved. After modification, the originally hydrophilic NC and nylon membranes were transformed into hydrophobic, with water contact angles of ∼130°. The 12LF-NC membrane showed a high flux of 10.1 kg m−2 h−1 with salt rejection >99.99% over 120 h in the direct contact MD fed with 10 wt% NaCl solution, which outperformed the commercial PVDF membrane. This coating method has the potential to modify various substrates to produce MD membranes with good performance, which broadens the availability of appropriate membranes for MD application. [Display omitted] • Fluorinated copolymer, LUMIFLON LF-200 is used to prepare hydrophobic MD membranes. • LF-200 was simply dip-coated on hydrophilic substrates and crosslinked under mild heating. • The WCAs of modified nitrocellulose and nylon membranes increased to ∼130° from 0°. • The 12LF-NC membrane had excellent flux >10 kg m−2 h−1 treating 10 wt% salt water. • This method has high efficiency, wide versatility and the potential to scale up. [ABSTRACT FROM AUTHOR]

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]

Carbon molecular sieve (CMS) membranes have great promise in CO 2 capture. However, tortuous transport passageways restrict the enhancement in the permeability due to the presence of disordered porous structure and dead-end pore. Herein, the growth of ZIF-8 layer on the surface of Fe 3 O 4 formed magnetic core-shell Fe 3 O 4 @ZIF-8 particles, which were fixed into 6FDA/ODA:DABA polyimides under magnetic field-induction to fabricate a precursor membrane with vertically oriented chain-like particles. It was then pyrolyzed to form hybrid carbon molecular sieve (HCMS) membranes with ordered microporous structure under high temperature conditions. The cross-section scanning electron microscopy images and N 2 adsorption for resultant HCMS membranes indicate that Fe 3 O 4 @ZIF-8-derived carbons frameworks were vertically oriented to form the ordered microporous structure, which also had good compatibility with carbon matrix stemmed from 6FDA/ODA:DABA polyimides. The as-prepared HCMS membranes embedded with 5 wt% Fe 3 O 4 @ZIF-8 manifested a highest gas separation performance (permeability of 5130 Barrer; CO 2 /N 2 selectivity of 29; CO 2 /CH 4 selectivity of 48), outperforming the pristine CMS membranes, which were near and beyond 2019 CO 2 /N 2 and CO 2 /CH 4 upper bounds, separately. These good separation performances resulted from vertical chain-like microporous particles, which provided fast transport channels to accelerate CO 2 diffusion rate. In addition, we supposed that Fe 3 O 4 prevent ZIF-8 frameworks from destruction during the pyrolysis and promote the size screening capability. More importantly, this membrane exhibited excellent aging resistance over 30 days aging testing compared to pristine CMS membranes. Therefore, it affords a feasible way for carbon capture from flue gas and natural gas. [Display omitted] • HCMS membranes with ordered microporous structure were engineered by magnetic-induced orientation. • Fe 3 O 4 inhibited the collapse of ZIF-8 frameworks during the pyrolysis. • The oriented chain-like channels for facilitating CO 2 transport were constructed. • HCMS membranes had a CO 2 permeability of 5130 Barrer with the CO 2 /N 2 (CH 4) selectivity of 29 (48). [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]

Solvent resistant membrane distillation (SR-MD) is a novel technology to effectively separate water from waste streams containing solvents with high boiling points, avoiding the high chemical costs and release of harmful gas in conventional treatments. Ceramic membranes are promising for this process as they are highly stable chemically but they require modification to tune the hydrophilicity to hydrophobicity. However, the widely used silanization for hydrophobic modification often involves expensive chemicals and may produce toxic substances. Here, we present a new hydrophobic modification method with the use of fatty acid chloride (FAC), as a greener and cheaper alternative to silanes. In the grafting reaction, the acyl chloride groups react with the –OH groups on the ceramic membranes to form strong ester bonds. We successfully grafted stearoyl chloride (SC) and palmitoyl chloride (PC) on the ceramic tubular membranes. With long carbon chains grafted, the modified membranes exhibited high hydrophobicity with a water contact angle >141° and a liquid entry pressure >3 bar. When tested in SR-MD with a feed solution containing 50 wt% dimethyl sulfoxide, the PC-modified membrane demonstrated a flux of 3.2 kg m−2 h−1, with rejection >98% and separation factor >110 at 60 °C, and a high flux of 4.5 kg m−2 h−1 with rejection >96% at 70 °C. The FAC-modified membranes allow a cost-effective treatment of challenging wastewater containing organic solvents through SR-MD. [Display omitted] • Hydrophobic ceramic membranes for solvent resistant MD were synthesized through fatty acid chloride grafting. • The acyl chloride groups formed strong ester bonds on ceramic surface and the modified membranes had high hydrophobicity. • Flux of 3.2 kg m−2 h−1, rejection >98% and separation factor >110 can be achieved when treating 50 wt% DMSO in SR-MD. • The hydrophobicity and separation performance are comparable to ceramic membrane grafted with silanes. • This study presents a greener and cheaper surface modification chemistry to synthesize hydrophobic ceramic membranes. [ABSTRACT FROM AUTHOR]

Aquaporins are water channel proteins with high permeability and solute rejection, making them ideal components for the preparation of desalination biomimetic membranes. In one strategy, E. coli aquaporin Z (AqpZ) proteoliposomes are immobilized in a polyamide layer formed by interfacial polymerization at the inner surface of hollow fibers. However, once polymerization occurs, the system is almost a black box where it is difficult to disentangle the relative contribution to performance of (i) water permeation through AqpZ channels and (ii) the possible modification of the properties or structure of the polymer layer by the mere presence of protein and lipid. Indeed, the fate of protein and lipid once the polymer is formed, and how much of it is actually used, is under debate. Also, the performance of these modules has been reported to be stable over several months. This is intriguing because of the expected degradation of functional AqpZ and lipid with time. Herein, we used lipid and AqpZ, both fluorescently labeled, to unequivocally localize both components only at the inner surface of the hollow fibers. To characterize module performance, we tested about 30 half-inch modules containing five hollow fibers each. Those reconstituted with wild type AqpZ produced higher permeability (∼8.5 ± 0.9 LMH/bar) than those reconstituted with AqpZ mutant (R189A) (∼5.6 ± 1.7 LMH/bar) or lipid-only liposomes (3.7 ± 1.1 LMH/bar). However, while these differences are significant, they are smaller than expected from the comparison of relative permeabilities of membranes incorporating wild-type AqpZ, R189A mutant and only-lipid. In addition, we show that in a five-month long experiment, performance of two of these modules showed only minor deterioration, if any, which is not consistent with the observed rapid degradation of proteoliposomes at room temperature. Overall, these data obtained in this set-up suggests that although both AqpZ and lipid are localized at the inner of the hollow fibers, they mainly behave as additives that modify the properties of the robust polyamide layer. A small contribution of AqpZ channel activity to module performance is possible, but to be significant it would require full coverage and a higher protein density in the proteoliposomes, which at present cannot be achieved in the current protocol. [Display omitted] • Thirty half-inch modules (5 hollow fibers each) were tested. • Fluorescent lipid and AqpZ are only found co-localized with the IP layer. • Modules perform better with wild type AqpZ than with R189A inactive mutant. • Module performance does not directly correlate with proteoliposome permeability. • Long-term module performance is inconsistent with degradation of proteoliposomes. [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]

Synthetic interlayers with multiple functions and structural stability have a high potential to construct novel thin film composite (TFC) membranes with demanding permselective property for precise separations. Herein, a functional interlayer derived from the polyelectrolyte-based layer-by-layer (LBL) self-assembly is reported to prepare interlayer engineered organic solvent nanofiltration (OSN) membranes using β-cyclodextrin (β-CD) as a monomer via interfacial polymerization (IP) process. Compared to the interlayer-free OSN membrane, a smoother selective layer with higher crosslinking degree is obtained for our developed membranes, enabling an improved organic dye rejection (e.g. , 91.9% for methyl orange and 98.8% for brilliant blue R). Importantly, the LBL-aided β-CD nanofilm exhibits competitive permeances towards both polar (e.g. , methanol, 5.8 LMH/bar) and nonpolar solvents (e.g. , hexane, 7.0 LMH/bar). These performances can be attributed to the multiple roles of LBL-based interlayer as preventing the intrusion of selective layer and creating dual linkages (i.e. , amide and ester), along with tailoring the physicochemical properties of caped β-CD nanofilm. Besides, the newly developed OSN membrane can discriminate between dye molecules with similar molecular weights and same charge but different molecular configurations. Meanwhile, its good structural integrity and long-term stability are also demonstrated by the 7-day filtration test using tetracycline in methanol and β-carotene in hexane, respectively, as evidence of constant solute rejections (≥90%) during the entire filtration process. This work unravels the functions of LBL-based interlayer in enhancing the OSN performance, offering new insights into shaping the development of interlayer engineered OSN membranes for real-life applications. [Display omitted] • An interlayer derived from polyelectrolyte-based LBL is constructed for OSN application. • The multiple roles of LBL-based interlayer in tailoring β-CD nanofilm are investigated. • Interlayered membranes possess high permeances for both polar and nonpolar solvents. • Structural integrity and long-term stability are confirmed by a 7-day filtration test. [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]

The layer-by-layer (LbL) self-assembly is a common method for fabricating nanofiltration (NF) membranes. However, most multilayers are usually too thick and lack the necessary attributes to endow NF membranes with good permselectivity. In this study, we present a polyelectrolyte multilayered method by integrating dopamine as a "bio-glue". A three-step deposition was applied to the negatively charged PES substrate surface, following an alternate sequence of poly(allylamine hydrochloride) (PAH), dopamine (DA) and poly(sodium 4-styrenesulfonate) (PSS). The dopamine molecules were intercalated between the PAH and PSS layers to achieve a thinner thickness, higher hydrophilicity, smaller surface roughness and narrower pore size distribution. The resultant flat sheet (PAH/DA/PSS)4 polyelectrolyte multilayered (PEM) membranes exhibited enhanced water permeability (more than 60% increment from 13.5 to 21.9 LMH/bar) and higher rejection toward divalent ions (increasing MgCl 2 rejection from 91.0% to 94.8%) as compared with the control (PAH/PSS)4 NF membrane. Furthermore, the developed LbL method was applied on hollow fiber membrane modules and was able to achieve a higher Li+/Mg2+ selectivity from 15.6 to 37.8 and Na+/Mg2+selectivity from 11.0 to 19.1 using different simulated brines as feed solutions. On the whole, this polyelectrolyte multilayered method shows great potential for practical applications, including groundwater softening, seawater pretreatment and lithium extraction. [Display omitted] • A novel three-step LbL self-assembly method was proposed by integrating dopamine. • Dopamine intercalated selective layer exhibited a thinner and smoother surface. • The NF (PAH/DA/PSS)4 membrane showed better water permeability and higher divalent ion rejection. • Higher Na+/Mg2+ and Li+/Mg2+ selectivity was achieved due to the smaller pore size distribution. [ABSTRACT FROM AUTHOR]

The addition of co-solvents in aqueous or organic phases of interfacial polymerization is a feasible strategy to tune the performance of aromatic polyamide (PA) thin-film composite (TFC) membrane for brackish water desalination, however, limited progress has been made in developing co-solvent-tailored seawater reverse osmosis (SWRO) membrane. Herein, SWRO membranes were prepared by adding various types of aqueous and organic co-solvents to reveal their impacts on the formation of the PA crumples. It was found that the aqueous/organic co-solvents affected the solubility parameter distance and interfacial tension between two immiscible phases, facilitating the diamine diffusion rate and resulting in a significant change in PA structure. The PA layer with modulated microstructure and varied surface features such as widened void structure, rougher surface, better wettability, and controlled cross-linking degree can be derived from the high interfacial instability that existed between the co-solvent and initial PA film due to the close mutual affinity. Besides, the additional polyvinyl alcohol coating layer atop the PA membrane successfully further enhanced the membrane selectivity. Overall, the mechanistic insights attained in this study revealed the relationship of diamine diffusion, physicochemical properties of PA layer and membrane separation performance for co-solvent-assisted membrane fabrication to render resultant SWRO membrane with more comparable permselectivity. The optimized TFC-SWRO membranes exhibited pure water permeability of 2.2 and 3.2 L m−2 h−1 bar−1 upon the assistance of aqueous and organic co-solvents, respectively, while maintaining excellent NaCl rejection of approximately 99% under seawater desalination tests. [Display omitted] ✓ Aqueous or organic co-solvents were used aiming to flexibly design high-performance SWRO membrane. ✓ The synergistic impacts of solubility parameter and interfacial tension were established to elucidate diamine diffusion behavior. ✓ The relationship of "monomer diffusion - structure property - separation performance" was elaborated. ✓ The formation of a PVA coating layer enhanced the selectivity of co-solvent-assisted SWRO membrane. [ABSTRACT FROM AUTHOR]

A scaled-up hollow fibre thin-film composite (TFC) module was successfully developed for organic solvent forward osmosis (OSFO) application in the pharmaceutical industry. The membrane consists of cross-linked P84 polyimide substrate with a polyamide selective layer, formed via interfacial polymerisation. The performance of the lab-scale module was compared to the scaled-up module in reverse osmosis and forward osmosis modes. The results from both tests revealed that the solvent permeability of the scaled-up module decreased while its selectivity increased slightly. This might be caused by the uneven distribution of liquids during interfacial polymerisation, leading to varied membrane performance. The scaled-up module was further tested for OSFO performance using a range of PEG-400 concentrations (0.5–2 M) in acetone and isopropanol as draw solutions. At 2 M PEG-400 concentration, the module demonstrated high isopropanol and acetone permeability of 0.63 LMH and 13.9 LMH, respectively. Moreover, the reverse solute flux of PEG-400 in acetone and isopropanol were relatively low at 0.188 g/l and 0.153 g/l, respectively. The module was further tested for OSFO application in the pharmaceutical industry by concentrating levofloxacin in acetone, using 2 M PEG-400 as draw solution. The process was able to concentrate levofloxacin from 1000 ppm to 16,000 ppm with very low reverse solute flux of 0.178 g/l. Therefore, this work presents a scalable TFC membrane for OSFO application in the pharmaceutical industry. [Display omitted] • Scaled-up module (0.4 m2) of TFC hollow fibre membrane for organic solvent forward osmosis process was successfully fabricated. • High porosity (79%) and low structural parameter (217 μm) for membrane substrate was achieved. • Membrane exhibited excellent acetone and IPA solvent flux of 13.9 LMH and 0.63 LMH, respectively, using a 2 M PEG-400 draw solution. • A pharmaceutical stream was concentrated to a factor of 16 with low specific reverse solute flux [ABSTRACT FROM AUTHOR]

A scaled-up hollow fibre thin-film composite (TFC) module was successfully developed for organic solvent forward osmosis (OSFO) application in the pharmaceutical industry. The membrane consists of cross-linked P84 polyimide substrate with a polyamide selective layer, formed via interfacial polymerisation. The performance of the lab-scale module was compared to the scaled-up module in reverse osmosis and forward osmosis modes. The results from both tests revealed that the solvent permeability of the scaled-up module decreased while its selectivity increased slightly. This might be caused by the uneven distribution of liquids during interfacial polymerisation, leading to varied membrane performance. The scaled-up module was further tested for OSFO performance using a range of PEG-400 concentrations (0.5–2 M) in acetone and isopropanol as draw solutions. At 2 M PEG-400 concentration, the module demonstrated high isopropanol and acetone permeability of 0.63 LMH and 13.9 LMH, respectively. Moreover, the reverse solute flux of PEG-400 in acetone and isopropanol were relatively low at 0.188 g/l and 0.153 g/l, respectively. The module was further tested for OSFO application in the pharmaceutical industry by concentrating levofloxacin in acetone, using 2 M PEG-400 as draw solution. The process was able to concentrate levofloxacin from 1000 ppm to 16,000 ppm with very low reverse solute flux of 0.178 g/l. Therefore, this work presents a scalable TFC membrane for OSFO application in the pharmaceutical industry. [Display omitted] • Scaled-up module (0.4 m2) of TFC hollow fibre membrane for organic solvent forward osmosis process was successfully fabricated. • High porosity (79%) and low structural parameter (217 μm) for membrane substrate was achieved. • Membrane exhibited excellent acetone and IPA solvent flux of 13.9 LMH and 0.63 LMH, respectively, using a 2 M PEG-400 draw solution. • A pharmaceutical stream was concentrated to a factor of 16 with low specific reverse solute flux [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]

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]

Municipal solid waste (MSW) gasification is an attractive waste-to-energy (WTE) technology with promise for future solid waste management, owing to the production of syngas which can be used as an alternative energy resource. However, quality of produced syngas is not meeting expectation. One promising solution is to use oxygen-enriched gas (OEG) to elevate produced syngas quality but producing OEG is costly. Herein, we demonstrated an asymmetric defect-free hollow fiber membrane made up of Matrimid® 5218 polyimide for scaling-up to 2-inch membrane modules. Our modules have an effective surface area up to 2.6 m2 with a packing density of up to 44% to produce OEG of 45% O 2 purity. The 2-inch membrane module was integrated into a lab-scale gasification process to produce syngas using refuse derived fuel (RDF) generated from MSWs collected from the university campus. Prior to this, the lab-scale gasification was first optimized by tuning the gasification temperature, O 2 purity and equivalence ratio (ER). Then, MSW gasification using membrane-based OEG was carried out, and compared against air gasification and synthetic OEG of the same O 2 purity. Our results showed that, at O 2 purity of 45%, gasification temperature of 900 °C and ER of 0.15, the quality of produced syngas was elevated with a lower heating value (LHV) of 9.15 MJ/m3 and H 2 /CO ratio of 1.43, which was substantially higher than air gasification with LHV and H 2 /CO ratio reported at 5.38 MJ/m3 and 0.81, respectively. Gasification results for membrane-based OEG and synthetic OEG were also comparable, while process simulation evidence suggested that membrane-based separation was at least 2-fold less energy-intensive than cryogenic distillation and pressure swing adsorption. Overall, this proof-of-concept successfully demonstrates the viability and competitiveness of membrane process for producing OEG at medium O 2 purity (i.e. , 40–50%) to support MSW gasification for WTE conversion. [Display omitted] • Hollow fiber membrane modules with up to 2.6 m2 surface area were developed. • OEG with O 2 purity of c.a. 45% can be produced at close to 2 L/min flow rate. • Membrane-based OEG gasification produces syngas with 70% higher LHV as that of air gasification. • Membrane-based OEG produces syngas with comparable LHV as that of synthetic OEG. • Simulation shows that membrane separation is less energy-intensive for producing OEG of medium purity. [ABSTRACT FROM AUTHOR]

High-efficient CO 2 capture using membrane separation technology is a promising approach towards environmental redemption in recent years. Thin-film composite (TFC) membrane with selective layer made of CO 2 -philic materials is the preferred membrane type for industrial-scale application, owing to its high permselectivity and good processability. Herein, we propose a facile direct spray-coating method to fabricate Pebax® 1657 thin-film on a porous polysulfone (PSF) substrate. Unlike most conventional multilayer TFC membranes, the unnecessary need for gutter layer in this work greatly simplifies the membrane fabrication process. Pebax® 1657 thin films were deposited through direct spraying of the polymer solution containing Pebax® 1657 on PSF substrate under ambient temperature. The as-prepared Pebax®1657 TFC membranes showed decent separation performances with CO 2 permeance of >200 GPU and CO 2 /N 2 selectivity of >50 for mixed gas (vol. (CO 2)/vol. (N 2) = 20/80) tests. The facile TFC membrane fabrication and good CO 2 separation performances make the direct spray coated Pebax®1657 membranes a promising strategy for large-scale CO 2 capture applications. [Display omitted] • TFC membranes are fabricated through direct spray of Pebax® 1657 solution on PSF ultrafiltration substrate. • The unnecessary need for gutter layer greatly improved the simplicity of TFC membrane preparation process. • The obtained Pebax® 1657 TFC membranes exhibit competitive CO 2 permeance (>200 GPU) and CO 2 /N 2 selectivity (>50). • The successful fabrication of A4-sized TFC membrane demonstrates the scale-up potential of the direct spray coating method. [ABSTRACT FROM AUTHOR]

The current study aimed to understand both external and internal membrane fouling by three proteins with different net charges, namely, negatively charged pepsin and bovine serum albumin (BSA), as well as positively charged lysozyme. Polycarbonate track-etched (PCTE) membranes were used. Per electrostatic attraction, the flux decline was the worst for lysozyme, which is attributed by the fouling model to the greatest pore blockage (α) and pore constriction (β), and by field-emission scanning electron microscope (FESEM) and optical coherence tomography (OCT) to the most extensive external fouling. Between pepsin and BSA, BSA gave worse flux decline despite its more negative net charge. The fouling model indicates that BSA gave greater pore blockage (α) and denser internal cake (R c / R m), while the quartz crystal microbalance with dissipation (QCM-D) indicates a rigid cake structure. Notably, despite monotonic flux decline with filtration, the OCT fouling voxel trends show significant fluctuations, which has not been reported before and thus signify the unique behavior of protein foulants in straight-through pores. Specifically, the trends below and above the −4.5 μm layer (i.e., 4.5 μm below the feed-membrane interface) are perfectly opposite, indicating the non-uniform protein deposits slipping downwards in the membrane pores as filtration progressed. The dynamic movements of the protein cakes unveiled here warrant more understanding in future studies. • Surprising fluctuations of OCT fouled voxels despite monotonically decreasing flux. • Dynamic downward motion of fouled protein deposit in the straight-through pores. • Delayed fluctuations by BSA tied to densest and most rigid cake. • Worst flux decline by lysozyme due to high pore blockage and pore constriction. [ABSTRACT FROM AUTHOR]

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]

Membrane fouling, which is a key obstacle in implementing membrane technology, has been studied extensively for aqueous feeds. With increasing interests in organic solvent applications, a corresponding effort on understanding membrane fouling is warranted. This study employs molecular dynamics simulations to unveil the mechanisms underlying the different adsorption behaviors of dextran onto a polyacrylonitrile (PAN) membrane in three polar and protic solvents, namely, water, formamide and ethanol. The dextran-membrane separation distance is the lowest for water, followed by ethanol then formamide, which agrees with the worse flux decline for water relative to formamide observed experimentally. The greatest adsorption tendency in water is tied to the most attractive dextran-membrane interaction. On the other hand, the lower adsorption tendency in formamide and ethanol is linked to enhanced solvation of the dextran molecule and membrane, which deters dextran adsorption onto the membrane. Specifically, formamide, which leads to the least adsorption, exhibits the most attractive solvent-dextran and solvent-membrane interaction energies, the highest solvent-accessible surface area (SASA) for dextran, and also the highest density of solvent molecules in the solvation shell closest to the membrane. As for ethanol, it gives the highest density of solvent molecules in the solvation shell closest to a part of the dextran. The solvation of foulant and membrane by water deviates from that by other similarly polar and protic solvents, which has important implications in membrane fouling and highlights the need for enhancing the understanding of membrane fouling behaviors in organic solvents. [Display omitted] • Adsorption tendency of dextran on membrane is greatest in water and least in formamide. • Dextran-membrane interaction is most attractive in water. • Solvent-dextran and solvent-membrane interactions are most attractive in formamide. • Competitive solvent and dextran adsorption onto membrane governs fouling. • Greater solvation of foulant and membrane in ethanol and formamide reduces fouling. [ABSTRACT FROM AUTHOR]

Seawater reverse osmosis (SWRO) is the key technology driving an energy-efficient and cost-effective desalination process. At the center of this technology are the thin film composite (TFC) membranes, which not only promise a stable operation but also high separation performances. The objective of this review is to consolidate recent advances in SWRO membranes from the standpoint of membrane materials, fabrication methodologies and applications. First, the thermodynamic limit and energy consumption of SWRO desalination are reviewed, before we discuss the current status of SWRO membranes, highlighting the four main challenges to date – permselective tradeoff, relatively low single-pass boron rejection, membrane fouling and poor chlorine resistance. Thereafter, a comprehensive review of the membrane development is presented. We examine findings reported in research papers and patents, and various methods to achieve SWRO membranes of higher permselectivity, boron rejection, and chlorine resistance as well as lower fouling propensity. Key insights from the membrane industry are also furnished. Then, we put together an outlook, featuring our perspectives on SWRO membrane development. Empirical data in this review are collated into an upper-bound relationship, which is tailored specifically for SWRO membranes and expected to provide benchmarking for future SWRO membrane development. Since the traits of SWRO membranes are unique from those of brackish water RO (BWRO) membranes, we also distinguish the methods used for SWRO membrane fabrication to help zero in on the correct strategies, and provide insights for advancing new membrane designs. Overall, this review sums up the current state-of-the-art SWRO membranes, looking at the array of fabrication methods used thus far, and putting into perspective critical strategies to realize the next-generation TFC membranes that can address the future demands of SWRO and deliver a more competitive desalination process. [Display omitted] • Recent advances in SWRO membrane are collated from papers and industrial patents. • Current status and future outlook of SWRO membrane industry are discussed. • A permselectivity upper bound is established specifically for SWRO membranes. • The upper bound is given by A/B = 46.75 A −1.72 (A/B in bar−1 and A in Lm−2h−1 bar−1). • A roadmap for SWRO membrane fabrication is proposed (short/long-term strategies). [ABSTRACT FROM AUTHOR]