PA Layer Research Articles

Construction of PTFE/PI-PI/PANI-PA composite nanofibrous membrane for efficient photothermal membrane distillation and VOCs interception

Water-soluble volatile organic compounds (VOCs) are one of the difficult substances in seawater and industrial wastewater treatment. Photothermal membrane distillation (PMD) technology has great advantages in solving the problems of low energy conversion efficiency and serious pollution of traditional membrane distillation (MD) technology, but it still faces the challenge that VOCs cannot be effectively removed.To solve this problem, we prepared photothermal Polytetrafluoroethylene/Polyimide-Polyimide/Polyaniline-Polyamide (PTFE/PI-PI/PANI-PA) composite membranes with VOCs interception. The composite membrane was fabricated by applying the previously studied PTFE/PI-PI/PANI/PANI membrane by interfacially polymerising an ultrathin PA layer with controllable pore sizes. Among them, the PTFE/PI-PI/PANI base membrane in the composite membrane not only provides strong support and durability as a backbone structure, but the PANI photothermal layer also provides photothermal conversion for effective PMD operation. In addition, the ultra-thin PA layer acts as a molecular sieve separator to effectively intercept VOCs in the feed solution. When the feed solution was 35 g⋅L−1 NaCl, the average permeate flux of the #M-PA-0.1 membrane was 1.44 ± 0.02 L⋅m−2⋅h−1 with a salt interception rate of 99.99 % or more after 80 h of PMD testing. Meanwhile, when 50 mg⋅L−1 of VOCs was added to the feed solution, the VOCs retention rate >99.35 %, and the concentration of VOCs on the permeate side was much lower than the corresponding concentration in the drinking water standards recommended by the World Health Organisation (WHO) and the US Environmental Protection Agency (EPA). This study effectively combines the molecular sieve effect with the solar-powered evaporation process, which provides a research basis for the preparation of high-performance PMD membranes that can effectively remove volatile organic compounds.

Chloride-Salt Separation Type Nanofiltration Membranes for Efficient Crude Salt Refinement

Application of unrefined crude salt not only leads to a serious equipment scaling and a low product quality, but also increases operational risks and poses health hazards. Therefore, it is essential to refine crude salt prior to its use. However, traditional methods of crude salt refinement are energy-intensive and probably produce additional chemical by-products. In this work, membrane technology was used to accomplish the refinement of crude salt due to its unique characteristics, such as environmentally friendly and lower energy consumption. To improve the separation performance, the membranes were fabricated by simply adjusting the aqueous monomer concentration. For single-salt feed, the membrane (M10) prepared with a high ratio of 10 exhibited excellent salt rejection due to the formation of a thicker and denser PA layer. And it owned a superior MgCl2/NaCl selectivity of ∼22.0, demonstrating that the membrane can achieve outstanding selectivity for mono-/divalent ions. The selectivity of Mg2+/Na+ increased to ∼23.5 for bi-salt feed and further improved to 66.2 for multi-salt feed due to the stronger charge shielding effect. Most importantly, the membrane was also successfully applied in the refinement of crude salt. When using crude salt (NaCl 30 g/L, purity 0.90) as feed, the M10 exhibited both excellent retention of bivalent ions and permeation of univalent ions, resulting in the corresponding Mg2+/Na+ selectivity up to ∼251.6 and the tremendous enhancement in the Na+ purity of ∼0.997. This work offers a feasible strategy for crude salt refinement, and could expand to some other potential applications such as resource utilization in the salinization industry and zero-liquid discharge of industrial wastewater.

Antibacterial of PSf substrate and PA active layer of TFN membrane made by POM/3-API hybrid in situ FO separation performance and photo-degradation of organic pollutant

Membrane bacterial studies are stable in modified FO membrane that shows superior antibacterial activity against Tetrasphaeria (minimal inhibitory concentration (MIC) = 0.00350, 0.11 μg/mL). Due to augmented interventions of the containments in the water resources, essential novel hybrids construct of polyoxometalate with imidazole for the separation process and photo catalytic degradation of organic pollutants have been recognized and scouted in this paper. This work demonstrated the separation and photocatalytic extraction of the organic pollutants from the potable and waste water using organo-polyoxometalate ionic salts as hybrids designated as polyoxometalate with 3-(aminopropyl) imidazole (POM/3-API). Hybrid materials are strategically prepared in one-pot via counter acidic proton exchange between POM (O- ions) which tends to move towards N- containing organic molecules, which are doped with manganese (IV) ions. Scanning Electron Microscope (SEM) studies show physico-chemical adsorption of the hybrids, PSf substrate and on PA layer of membranes, proving the multifunctional surface characteristics morphological formation. In addition, POM/3-API hybrids were synthesized via shock acoustic that reveals higher permeate flux through separation process and almost disappears (PAPI-1: 81.4 %) with MO during degradation process. Remarkably, the morphological changes of observed shapes before and after MO clearly show an effective performance, as was definite by the successful interfacial polymerization between membrane and POM/3-API. These help towards elimination of MO dyes at waste water sources, making the process environment-friendly.

Modulating interfacial polymerization dynamics in nanostructured thin-film composite membranes: The role of polyvinylpyrrolidone and NaCl

Optimizing the performance of thin-film composite polyamide (TFC-PA) membranes is crucial for enhancing filtration efficiency across diverse applications. This study investigated the role of polyvinylpyrrolidone (PVP) in modulating the diffusion kinetics of piperazine (PIP) during the interfacial polymerization (IP) process, essential for membrane fabrication. By incorporating PVP into the aqueous phase, and combining it with selected inorganic salts such as sodium chloride (NaCl), the formation of a more controlled Turing-like nanostructure within the PA layer was achieved, significantly improving membrane permeability and structural uniformity. Employing molecular simulations alongside diverse characterization techniques, the mechanisms by which PVP and NaCl additives influence the diffusion of PIP monomers at the water-oil interface were elucidated. The optimized membranes demonstrated a substantial increase in water permeability, achieving 16.2 ± 0.9 L m−2 h−1 bar−1, and an impressive sodium sulfate (Na2SO4) rejection rate of 97.5 ± 0.6 %, outperforming untreated nanofiltration (NF) membranes. The findings provide a deeper understanding of the molecular interactions during IP and open avenues for the development of advanced filtration membranes with tailored properties.

Enhancing rejection of endocrine disrupting compounds by nanofiltration membrane: Dominant role of hydrophilic coordination barrier layer

The removal of endocrine disrupting compounds (EDCs) from water/wastewater is of significant importance. However, current nanofiltration (NF) membranes exhibit limited water permeance and hydrophobic EDCs rejection rates. Herein, we fabricated a novel NF membrane intercalated with the 3,4-dihydroxyphenylalanine-vanadium (DOPA-V) complex barrier layer. The DOPA-V intercalated NF membrane possessed a notable water permeance of ~38 L·m−2·h−1·bar−1, thanks to the formation of a thin and loosely structured PA layer in comparison to the control, as well as the gutter effect optimizing the pathway of water molecule transport induced by the DOPA-V layer. The rejections of methylparaben, nonylphenol, bisphenol AF, propiconazole, dioctyl phthalate, and heptachlorobiphenyl by the DOPA-V intercalated NF membrane were both enhanced compared with those of the control. The enhanced rejection of hydrophobic EDCs by the DOPA-V intercalated NF membrane was primarily dominated by the barrier role of DOPA-V layer. According to the resistance-in-series model, DOPA-V predominated the membrane resistance to hydrophobic EDCs, resulting in a reduction of 68.8 %, 76.5 %, 58.0 %, 58.1 %, 63.0 %, and 72.0 %, respectively, in the diffusion rates of those hydrophobic EDCs compared to the control. This research offers a novel strategy on customizing NF membranes to effectively remove specific trace organic contaminants from water/wastewater.

Dehydration-modulated pomelo peel cellulose nanofiber interlayer customized polyamide membrane with highly uniform pores for efficient nanofiltration

The development of high-performance polyamide nanofiltration (PA NF) membranes by introducing interlayers holds promise for efficient desalination. In this study, a novel PA NF membrane was prepared by incorporating the special biomass interlayer, which consisted of dehydration-modulated pomelo peel cellulose nanofiber (PCNF). Due to the removal of water, the proportion of exposed oxygen-containing functional groups within the PCNF interlayer increased significantly, and thus the diffusion of piperazine (PIP) could be slowed down effectively. Consequently, the diffusion-restricted PIP was enriched and anchored by PCNF and formed a PA layer with a unique layered structure in the interfacial polymerization (IP) reaction. The surface PA layer with lower a cross-linking degree could optimize water transport pathways and improve membrane permeability (28.67 LMH/bar). Meanwhile, the bottom PA layer, which was closely interspersed with PCNF, reduced pore size of the membrane and enhanced the rejection of Na2SO4 (98.63%). This study reveals a low-cost and eco-friendly strategy for preparing effective biomass interlayers, which provides a feasible approach for designing high-performance NF membranes.

PA/APVC nanofiltration membrane from reactive positively charged substrate membrane

Efficient Li+ and Mg2+ from natural seawater and salt lakes using nanofiltration is essential for efficient extraction of lithium resources and to address the global energy shortage. The combination of size sieving and the Donnan effect is crucial for optimal selectivity. We proposed a positively charged reactive support layer to design dual positively charged layer to enhance the magnesium-lithium separation. The positively charged support layer was prepared by ammoniating the PVC membrane with PEI, and then reacted with TMC to successfully prepare a dual positively charged layer PA/APVC nanofiltration membrane with high Li+/Mg2+ selectivity. The reactive support layer not only established a covalent bond connection with the PA layer, which increased the stability of the active layer, but also showed a positive charge (23.59 mV at pH=7) after ammonization, which further enhanced the Mg2+ repulsion from 82.57 % to 98.56 %. Furthermore, the highest separation factor achieved was 23.34 when a mixed solution containing Mg2+ and Li+ in a mass ratio of 50:1 was utilized, which was 13.48 times that of commercial nanofiltration membranes. The utilization of a reactive substrate membrane in the fabrication process of the PA/APVC membrane offers innovative prospects for future investigations on magnesium-lithium separation, contributing to the advancement of nanofiltration membranes.

Influence of polar solvent in formation and organic solvent separation performance of novel fluorine-containing polyamide membranes

Polyamide thin film composite (PA-TFC) membranes have shown great potential in organic solvent separations. However, the intrinsic polar feature of the amide group limits their permeability to specific solvents, such as nonpolar solvents. In this study, we used a fluorine-containing monomer [4,4′-oxybis(3-(trifluoromethyl)aniline), OTFA] to conduct interfacial polymerization (IP) with trimesoyl chloride, resulting in the fabrication of novel PA-TFC membranes with permeability to both polar and nonpolar solvents. Interestingly, by simply adjusting the composition of OTFA solvents [DMF and DMF/water (1:1, v: v)], we obtained two PA-TFC membranes (OTFA-D and OTFA-DH, respectively) featuring completely different structures and surface properties, including PA layer thickness, water contact angle, surface element composition, surface charge, and polarity. Due to their distinct structures and surface features, the two membranes exhibited different performances in organic solvent nanofiltration (OSN). The OTFA-DH membrane showed higher permeability to polar solvents (e.g., methanol), while the OTFA-D membrane was more permeable to nonpolar solvents (e.g., toluene). The mechanism on the formation of the two PA layers was clarified by combining the experimental results with the molecular dynamics simulations. The significantly different interfacial properties and monomer diffusion during IP led to the substantial differences in the formation of the PA network. This work provides a strategy to fabricate tailored PA-TFC membranes for various OSN scenarios by simply adjusting the solvent compositions.

GO and surfactant assisted regulation of polyamide nanofiltration membranes for improved separation performance

Fabricating nanofiltration membranes with high water permeance and selectivity by tailoring the structure and morphology is crucial to efficient water purification. In this work, the fabrication of thin film nanocomposite (TFN) nanofiltration membranes by combining two methods, the surfactant-assembly interfacial polymerization (SARIP) and the addition of graphene oxide (GO) or ionic liquid functionalized graphene oxide (GO-IL) for the preparation of the selective PA layer on a novel porous substrate is reported. For the preparation of the porous substrate, mechanically robust, aromatic polyethers containing polar pyridine units (PDSPP) were chosen targeting to improved hydrophilicity and thus enhanced water permeability. The anionic sodium dodecyl sulfate (SDS) surfactant was used to regulate the interfacial polymerization thereby enabling the formation of dense PA layers with high cross-linking degree and consequently high salt rejections. On the other hand, the addition of GO/GO-IL nanosheets could impart hydrophilicity and antifouling properties. The novel porous PDSPP substrate was selected for the fabrication of TFN membranes due to its improved water permeability and superior salt rejection and increased hydrophilicity compared to commercial PSf substrate. The detailed study of the fabricated TFN membranes by ATR-FT-IR, SEM, AFM, XPS, contact angle measurements revealed the formation of polyamide selective layers with rougher surfaces, increased hydrophilicity and high cross-linking degrees (from 44 % to 94 %), resulted from the synergistic effect of SDS and GO incorporation. Moreover, the prepared TFN membranes exhibited high salt rejections while maintaining a moderate water permeability. In particular, the membrane containing the neat GO (TFNGO50) displayed excellent Na2SO4 and MgSO4 rejections (98.8 % and 99.5 %, respectively) while the NaCl rejection was 47.0 % and a water permeability value of 4.2 L m-2h−1 bar−1. The divalent salt rejections were among the highest values reported in the literature in comparison with commercial NF membranes and TFN membranes containing GO/functionalized GO. When GO-IL nanosheets were embedded in the PA layer, the water permeability was slightly improved while the salt rejections were significantly reduced compared to TFNGO50. Lastly, the incorporation of GO enhanced the anti-fouling properties of the prepared membranes due to increased hydrophilicity of the PA surface.

Exploiting sulfonated covalent organic frameworks to fabricate long-lasting stability and chlorine-resistant thin-film nanocomposite nanofiltration membrane

Incorporating hydrophilic and charged porous nanofillers to prepare high-performance thin film nanocomposite (TFN) nanofiltration (NF) membranes is an effective method to achieve efficient water treatment. In this study, we synthesize the sulfonated covalent organic framework nanosheets (S-CONs) with higher hydrophilicity and electronegativity by immobilizing sulfonic acid groups (–SO3H) on TpPa-1 nanosheets. The S-CONs are incorporated in the PA layer by interfacial polymerization (IP) reaction. The results indicated that the S-CONs could modulate the hydrophilicity, thickness, and electronegativity of TFN-NF membranes. At the optimal addition of S-CONs (0.006 g), the pure water permeance increases to 8.84 L⋅m−2⋅h−1⋅bar−1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\rm{L}}\\cdot{\\rm{m}}^{-2}\\cdot{\\rm{h}}^{-1}\\cdot{\\rm{bar}}^{-1}$$\\end{document}, which is about 1.75 times than the TFC membrane, with a high Na2SO4 rejection reaching 98.97%. The improvement of the separation performance mainly results from the reduction of PA layer thickness (from ~178.00–198.00 to ~100.00–128.00 nm) and the increase of surface electronegativity (from −20.37 to −44.41 mV at pH = 7.00). More interestingly, the amide bond formed between the S-CONs and TMC improved the chlorine resistance of the membranes. This study reveals the potential of using functionalized 2D CONs as nanofillers to modify TFC membranes for efficient nanofiltration.

Effect of poly(2-(dimethylamino)ethyl methacrylate) brush-grafted graphene oxide on polyamide layer formation and nanofiltration performance

Thin film composite (TFC) membrane performance is often restricted by permeability and selectivity trade-off effect, even with the modification of nanoparticles. Graphene oxide-poly(2-(dimethylamino)ethyl methacrylate) (GO-PDMAEMA) with brush structure has abundant hydrophilic oxygen-containing functional groups and amine groups. It was synthesized via the atom transfer radical polymerization method and incorporated into TFC polyamide layer using interfacial polymerization. The GO-PDMAEMA-modified thin film nanocomposite membranes (TFNG-P) with Turing structure and higher surface hydrophilicity enhanced water permeability by 40.7–55%, with relatively low nanoparticle loading (0.005–0.02 wt%). Besides, TFNG-P2 (0.01 wt% GO-PDMAEMA) has the highest Na2SO4 rejection (97.8%), 4.4% higher than TFC. The PDMAEMA brushes on GO with additional amine groups promoted the amide linkage and increased the PA layer cross-linking by 16.2%. The higher cross-linking did not negatively affect the membrane flux, as the better hydrophilicity offset this effect. The utilization of the modified membranes in the treatment of palm oil mill effluent demonstrated enhanced resistance to fouling with TFNG-P2, which exhibited the highest flux recovery rate, reaching 89.4%. Thus, this study showed GO modification by grafting PDMAEMA brushes had enhanced the membrane properties, resulting in TFNG-P with higher permeability, promising separation and antifouling performance.

A novel in-situ hydrolysis approach to prepare ultra-selective and ultrasmooth nanofiltration membrane for efficient and sustainable ion separation

Nanofiltration (NF) membranes are increasingly recognized for their proficiency in monovalent/divalent ion separation, making them highly suitable for application such as water softening and resource recovery. This study introduces an innovative in-situ hydrolysis method to enhance the ion selectivity of thin-film composite nanofiltration (TFC-PA NF) membranes. In this method, the reactive monomer in the oil phase was pre-hydrolyzed by contacting with water, producing a partially hydrolyzed monomer that remained soluble in the oil phase. This in-situ hydrolysis process introduced more carboxylic groups to the membrane. That could lead to a proper enlargement of the pore size, subsequently facilitating the separation of Cl−/SO42−. Additionally, the hydrolysis altered the polarity of the acyl chloride molecule, prompting its accumulation at the oil/water interface and accelerating the polymerization reaction rate. This resulted in a thin and exceptionally smooth PA layer. The resulting membrane exhibited a remarkable Cl−/SO42−separation factor of ∼316 under moderate feed concentration and ∼478 under high feed concentration, while maintaining decent water permeance (14.4 L m−2 h−1 bar−1). Moreover, its maintained surface carboxylic group density, combined with ultra-low surface roughness, offered drastically enhanced fouling resistance. Our study illuminates the pathway for a straightforward and scalable method to fabricate highly selective membranes with superior fouling resistance.

Comprehensive analysis of permeation resistance changes of the TFC RO/NF membranes during heat curing

The TFC RO/NF membranes are the predominant membranes applied in desalination, and heat curing is an essential step in its industrial production, which increases the polyamide cross-linking degree and facilitate packing but leads permeability decrease. Nevertheless, the mechanism of heat curing on TFC membranes permeation resistance changes is still ambiguous. Figuring it out will aid in crafting a more effective optimization strategy in high flux membrane preparation. Herein, we prepared a range of TFC RO/NF membranes with various monomer concentrations on different substrates and quantified the permeation resistance changes by a resistance-in-series model. For nascent TFC RO/NF membranes, the PA layer provided almost all permeation resistance. After heat curing, the substrate exhibited a marked increase in permeation resistance. The change in the permeation resistance composition was further exacerbated by the decrease in monomer concentration. For TFC NF membranes with heat curing, the proportion of substrate permeation resistance increased significantly, rising from 31.62 % to 75.05 %. This study made a comprehensive analysis of the impact of the permeation resistance in TFC RO/NF membranes caused by heat curing, enriched the insight into the impact of heat curing on TFC membranes, and helped to prepare TFC membranes with better desalination performance.

Enhancing the perm-selectivity of thin-film nanocomposite membranes intercalated with cyclodextrin-chelated Metal-Organic Framework via modulated interfacial polymerization

Nanofiltration (NF), an exceedingly promising technology, has been extensively implemented within the domain of desalination. The pursuit of optimizing water permeance, while upholding outstanding rejection rates to ameliorate the vexing permeability-selectivity trade-off effect, has raised tremendous concerns. Herein, a novel approach has been proposed, involving the construction of a cyclodextrin-chelated Metal-Organic Framework (MOF) interlayer through vacuum-assisted filtration, aimed at orchestrating the interfacial polymerization (IP) process and sculpting the membrane morphologies of polyamide membranes. The results demonstrated that cyclodextrin-chelated MOF interlayer produced a “gutter” effect for faster water transport and enhanced the interaction of the substrate and PA layer. Simultaneously, the interlayer helped to alleviate the diffusion rate of piperazine (PIP) via the interactions (e.g., hydrogen bonds, electrostatic attraction and steric hindrance) between interlayer and PIP, leading to a lower cross-linking degree and a defect-free thinner active layer. Meanwhile, cyclodextrin with intrinsic nano-cavity created more free volume for water transport inside the polymer. Furthermore, the crumpled interlayer established a hydrophilic undulated interface, followed by the generation of micro-wrinkled polyamide layer with larger filtration areas. The optimal membrane exhibited a high permeability of 39.59 L/m2 h bar, nearly 6.5 times than that of the original membrane, while maintaining a remarkable Na2SO4 rejection of 95.71 %. The strategic deployment of cyclodextrin-chelated MOF interlayers in membrane modification held the potential to efficaciously mitigate the trade-off effect, thereby presenting a promising avenue for the realization of highly-efficient desalination processes.

Hydrophilic-hydrophobic bilayer interlayer for high performance thin-film composite reverse osmosis membranes

The strategy of modifying substrates with hydrophilic interlayers has been widely used to improve the performance of thin-film composite (TFC) nanofiltration (NF) membranes. However, the preparation of TFC reverse osmosis (RO) membranes with excellent performance on hydrophilic substrates through conventional interfacial polymerization (IP) method has proven to be very challenging. In this work, a hydrophilic polycarboxylic acid – hydrophobic ZIF-8 nanoparticles bilayer interlayer was developed to enhance the performance of TFC RO membranes. Based on this, the interlayer was designed to improve the performance of TFC RO membranes by creating a synergistic effect between the hydrophilic polycarboxylic acid and the hydrophobic ZIF-8 nanoparticles. The hydrophilic polycarboxylic acid interlayer was used to heal defects in the PSF substrate and provide growth sites for the in-situ growth of ZIF-8 nanoparticles. Hydrophobic ZIF-8 nanoparticles weakened the inhibition of the hydrophilic polycarboxylic acid interlayer on the diffusion of MPD, thus promoting the IP reaction and forming a dense PA separation layer (NaCl rejection 98.8%). The modulation of MPD erupted from the pores of the modified substrate by the bilayer interlayer results in the formation of an asymmetric PA layer, which has a dense PA in the upper region and loose PA encapsulating ZIF-8 nanoparticles in the lower region. ZIF-8 nanoparticles encapsulated by PA not only provided a low-resistance channel for water to pass through the separation layer but also enhanced the compaction resistance of the RO membrane, thus improving the permeance of the TFC RO membrane (4.2 L m−2 h−1·bar−1). In addition, thanks to the good compatibility between ZIF-8 nanoparticles and the PA matrix, as well as the smoother PA layer, TFC RO membranes with the bilayer interlayer presented excellent long-term stability and antifouling ability. This work presents a new idea to improve the performance of TFC RO membranes using interlayer strategies.

Fabrication of CuO/UiO-66-NO2/TFC-PA catalytic film for the removal of organic contaminant

CuO/UiO-66-NO2/TFC-PA catalytic film was successfully fabricated by embedding CuO/UiO-66-NO2 catalyst nanoparticles onto the PA layer of TFC-PA film through the interfacial polymerization technique. The as-prepared catalytic films were characterized by various techniques such as XRD, FTIR, ATR-IR, EDX, UV-Vis DRS, and N2 adsorption-desorption isotherm. The photocatalytic activity was evaluated by the decomposition of Methylene blue (MB) dye in the aqueous phase under visible light irradiation. The results indicated that the highest removal efficiency achieved was 98.5%, which was consistent with the pseudo-first-order kinetics. Additionally, the proposed mechanism for the charge transfer process was based on the results of radical scavenging experiments, which showed that superoxide and hydroxyl radicals were the predominant reactive species. Finally, the catalyst was stable and could be reused at least four times without loss of photocatalytic activity.

Robust thin film composite membrane with Cu2+ integrally-crosslinking for organic solvent nanofiltration

Thin film composite (TFC) membranes are commonly used for organic solvent nanofiltration (OSN) application. However, these membranes normally suffer from the layer delamination under harsh conditions. Chemically integral crosslinking is a common method to address this problem, but the resultant tightened polymeric chains and denser microstructure will inevitably bring the reduced solvent permeance. In this work, a facile metal integral crosslinking strategy, which has minimal adverse effect on the solvent permeance, was developed to improve the tolerance to the majority of organic solvents as well as enhance the adhesions of upper selective layers and underlying substrates simultaneously for the first time. The as-developed Cu2+ integrally-crosslinked membranes demonstrated a high permeance for organic solvents and a high rejection towards rose bengal. In comparison to the Cu2+ partially-crosslinked membranes (with substrate crosslinked only), the integrally-crosslinked ones exhibited superior solvent resistance and OSN performance. This improvement was attributed to the enhanced interactions and a defect-free PA layer. Additionally, the effects of solvent activation, crosslinking solution concentration as well as crosslinking time were also studied. It is believed that metal integral crosslinking strategy will offer a novel approach to develop promising TFC membranes with satisfactory OSN performance for practical applications.

In-situ growth of poly(m-phenylenediamine) in polyethylene (PE) matrix for nanofiltration membranes enabling outstanding selectivity of both mono-/di-valent ions and dyes/salt mixtures with enhanced water flux

Membrane-based nanofiltration is a crucial technique for treating dyestuff-salts wastewater, owing to its excellent selectivity towards mono/multivalent ions and organic matter. In this study, a facile and highly practical method was employed to enhance the hydrophilicity of the PE matrix through in-situ growth of poly(m-phenylenediamine) on the PE fibrils via the chemical oxidative polymerization of MPD. The inclusion of the poly(m-phenylenediamine) on PE enables the formation of homogenous and defect-free PA layer showing a unique honeycomb-like Turing morphology with characteristic crater-belt structure. Furthermore, the pendant amine groups from the poly(m-phenylenediamine) chain promotes the formation of a PA layer with a smaller effective mean pore size and a sharper pore size distribution, resulting from the formation of an extra polyamide network (reaction of PMPD with TMC) within the PA layer. The as-prepared PE-based NF membrane exhibits a high pure water permeance of 17.7 LMH bar−1, exceptional Na2SO4 rejection of 99.3%, and a long-term stability for cross-flow filtration for over 10 days. The PE-based NF membrane exhibits the water flux 2.2 times higher than that of the commercially available DK and DL membranes while maintaining a high salt rejection. Additionally, the PE-based NF membrane demonstrates exceptional selectivity, with a value of 115 for the separation of NaCl/Na2SO4 and 339.8 for Cl-/SO42- in a binary salt mixture. Furthermore, the PE-based NF membrane shows ultra-high selectivity values of 990 for CR/NaCl and 1039 for MB/NaCl in the treatment of dye/salt mixtures, respectively, which are significantly higher than those of the DK and DL membranes. The findings of this study highlight the potential of the in-situ growth of poly(m-phenylenediamine) on PE fibrils as a simple and cost-effective method for the modulation of hydrophilicity to enhance the NF membrane performance.

Impact of Polymer Chain Rearrangements in the PA Structure of RO Membranes on Water Permeability and N-Nitrosamine Rejection.

The use of solvents is overall recognized as an efficient method to improve the water permeability of polyamide thin film composite membranes (PA-TFC). The objective of this work was to test the performance of the membranes after exposing them to n-propanol (n-PrOH) to improve the permeability of the membranes while maintaining the rejection factor for small uncharged organic molecules, namely N-nitrosamines (NTRs). After the membranes were exposed to n-PrOH, the water permeability of the UTC73AC membrane increased by 98%, with minimal change in rejection. N-nitrosodiethylamine (NDEA) rejection decreased (3.4%), while N-nitrosodi-n-propylamine (NDPA) and N-nitrosodi-n-butylamine (NDBA) rejection increased by 0.9% and 2.8%, respectively. In contrast, for the BW30LE membrane, water permeability decreased (by 38.7%), while rejection factors increased by 14.5% for NDEA, 6.2% for NDPA, and 15.0% for NDBA. In addition, the morphology of the membrane surface before and after exposure to n-PrOH was analyzed. This result and the pore size distribution (PSD) curves obtained indicate that the rearrangement of polymer chains affects the network or aggregate pores in the PA layer, implying that a change in pore size or a change in pore size distribution could improve the permeability of water molecules, while the rejection factor for NTRs is not significantly affected.

Ionic liquid‐induced deep grafting of polyelectrolyte to reform polyamide layer for antifouling nanofiltration membrane

AbstractSurface grafting has been widely used to tune hydrophilicity and chargeability of nanofiltration membranes for reducing membrane fouling potential. However, surface grafting typically leads to a significant pore narrowing and resultant permeability loss, and monocharged surface still struggles to resist mixed foulants with different charges. Herein, ionic liquid (IL)‐ethanol (EtOH) solution containing polyethyleneimine (PEI) is used to rearrange the nascent polyamide layer. The high affinity of IL to the PA layer and the low diffusion steric hindrance of EtOH contribute to the polyamide swelling and PEI deep grafting, during which the “self‐regulation” effect (larger pores would be filled with more PEI molecules) narrows the pore size distribution and enhances hydrophilicity. The nearly charge‐neutral and smooth separation layer shows impressive antifouling capacity to hydrophobic macromolecules and mixed charged molecules, along with long‐term operating stability for real wastewater treatment. This study emphasizes the importance of solvent properties on the membrane grafting behavior.