Enhanced Water Permeability Research Articles

A water-stable two-dimensional Zn(BDC) lamellar membranes for efficient molecular separation with enhanced water permeability

Although 2D Zn(BDC) MOFs exhibit exceptional water stability, the synthesis of ultrathin 2D Zn(BDC) nanosheets has proven to be a formidable challenge. Conventional bottom-up methods suffer from limitations such as low yield and difficulties in eliminating surfactant molecules or end ligands, which are introduced to control the directional growth of 2D Zn(BDC). In this work, 2D Zn(BDC) nanosheets featuring a two-nuclear paddlewheel zinc structure were successfully synthesized through a three-phase synthesis method, exhibiting a thickness of about 2 nm. The 2D Zn(BDC) lamellar membranes were prepared through simple vacuum filtration. By adjusting the colloidal concentration of the 2D Zn(BDC) nanosheets, fine control over the resulting membrane thickness was achieved. Moreover, the incorporation of polyvinyl alcohol (PVA) as a cross-linking agent significantly enhanced the stability of the 2D Zn(BDC) lamellar membranes. The addition of PVA demonstrated effective regulation of pore size in the membrane, facilitating well-ordered stacking of nanosheets for superior screening efficiency in dye/ion separation applications. The permeability of 2D Zn(BDC) lamellar membranes was observed to be 372.9 L m−2 h−1 bar−1, while exhibiting a rejection rate exceeding 99.7 % for dye molecules, such as direct red (DR23), reactive black (RB5), chromium black T (CBT), Congo red (CR). The remarkable performance is ascribed to a synergistic effect between molecular sieving and electrostatic repulsion. 2D Zn(BDC) lamellar membranes exhibit exceptional long-term stability, and resistance to fouling and chlorine, thereby showcasing their immense potential for diverse applications in the realm of dye wastewater treatment.

Preparation of porous chitosan aerogels for efficient adsorption and sustained release of chlorogenic acid via enhanced water permeability

This study aimed to prepare novel chitosan (CS)-based aerogels for efficient loading of hydrophilic chlorogenic acid (CGA) and to facilitate its sustained release in vivo. The mechanical properties and water permeability of the CS-based aerogels were enhanced by incorporating sodium alginate. Melonal sodium alginate CS (MSCS) was synthesised by crosslinking melonal with CS aerogel via a Schiff base reaction. MSCS possesses a three-dimensional porous structure, featuring abundant micropores and mesoporous distributions. Due to the addition of melonal, MSCS demonstrates environmental stability and moisture resistance, with a surface contact angle of 121°. Adsorption capacity tests revealed that MSCS exhibits high adsorption capacity for CGA, reaching 769.4 mg/g, with an adsorption efficiency of 76.94 %. Molecular dynamics simulation results indicate that the adsorption process is exothermic, with increased adsorption capacity at lower temperatures, and is a combination of physical and chemical adsorption. Through quantum chemistry calculations, we identified the adsorption sites of CGA on MSCS and the tendency of MSCS to donate electrons. The in vitro sustained-release experiments demonstrated continuous release of CGA for 48 h in both artificial gastric juice and intestinal fluid, with release rates of 34.26 % and 34.96 %, respectively.

Designing bioinspired nanofiltration membrane for enhanced water permeance and efficient ion sieving

The precise separation of molecules or ions using nanofiltration (NF) membranes at a sub-Angstrom scale is a crucial aspect of water purification. Drawing inspiration from the rapid water transfer phenomenon observed in aquaporins found in nature, in this study, the incorporation of bola-amphiphile-imidazole-ureido (IU) into the polyamide (PA) layer was carried out via interfacial polymerization (IP). IU groups provided hydrogen bonds, which facilitated the rapid water transfer, and enabled the appropriate physical confinement transport channels that mimic the confined cavity structures of the biological selectivity filter for ions sieving. When the loading of IU reached 1.0 mg mL−1 (8.5 wt% IU/PA), the water permeance reached its highest value of 7.65 L m−2h−1 MPa−1 at 25 ℃, which was 1.5 times that of the pristine PA membrane. The rejection rates of 1.0 mg mL−1 IU-containing PA membrane for Na2SO4, MgSO4, and NaCl were 99.67 %, 99.3 %, and 98.46 %, respectively. At varying NaCl concentrations of up to 4000 ppm and throughout 210-hour continuous test, the 1.0 mg mL−1 IU-containing PA membrane maintained close to 100 % NaCl rejection, highlighting its great applicability in industry. This work offered an effective and promising synthesis strategy to obtain bioinspired nanofiltration membrane with excellent water performance and efficient ion sieving performance.

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.

Enhanced water permeation through the terahertz-induced phase and diffusion transition in metal-organic framework membranes.

Freshwater scarcity is a pressing global concern, and water desalination has emerged as a promising solution. Metal-organic framework (MOF) membranes have demonstrated exceptional potential in this regard. However, previous efforts to improve the permeability of MOFs have primarily focused on chemical modifications and synthesis rather than exploring physical methods. Using molecular dynamics simulations, we propose that the use of terahertz waves at a specific frequency of 7.5 ± 1.0 THz significantly enhances water permeability across MOF membranes, up to 27-fold, while maintaining effective ion rejection capabilities throughout the process. The mechanism behind this enhancement involves the resonance between the terahertz wave and the hydrogen bond vibrations of water within the MOF. This resonance amplifies the rotational kinetic energy of water molecules, disrupting the hydrogen bonds and causing a phase transition from quasi 1D square ice to a gas-like phase. Additionally, the diffusion behavior shifts from Fickian diffusion to sub-diffusion, resulting in improved water permeation across the MOF membrane. This study highlights the potential of terahertz waves as a physical tool to enhance the permeability of MOFs in water desalination, providing new avenues for efficient water treatment and resource sustainability.

Uniqueness of Nanoscale Confinement for Fast Water Transport: Effect of Nanotube Diameter and Hydrophobicity.

Inspired by the enhanced water permeability of carbon nanotubes (CNTs), molecular dynamics simulations were performed to investigate the transport behavior through nanotubes made of boron nitride (BNNT), silicon carbide (SiC), and silicon nitride (SiN) alongside carbon nanotubes (which have different hydrophobic attributes) considering their implication for reverse osmosis (RO) membranes under different practical environments. According to our findings, not only do CNTs but also other kinds of nanotubes exhibit transition anomalies with increasing diameter. Utilizing the robust two-phase thermodynamic (2PT) methods, the current examinations shed light on thermodynamic origin of favorable water filling of these nanotubes. The results show that regardless of the nanotube material, the filling of water inside small nanopores (d < 10 Å) as well as within pores of diameter larger than 15 Å will always be favored by the entropy of filling. However, the entropic preference for filling nanotubes with a diameter of 10-15 Å depends on the constituent material. In particular, the enhancement in total entropy of confined water was mainly due to the increased rotational freedom of confined water molecules. The thermodynamic origin of water transport was correlated with the structural and fluidic behavior of water inside these nanotubes. The observed data for density, flow, structure correlation functions, water-water coordination, tetrahedral order parameter, hydrogen bonds, and density of states functions quantitatively support the observed entropy behavior. Of critical importance is that the present study demonstrates the effectiveness of RO filtration using nanotubes of boron nitride rather than carbon. Furthermore, it was found that one should avoid the use of silicon nanotubes unless filtration needs to be performed under harsh environments where nanotube of other materials cannot survive. Specifically, the results show that both the structural and dynamic properties of water confined in BNNTs are similar to those of CNT's, and for SiNT it is similar as SiC. Our results show that besides the nanotube material, the chirality index of the nanotube also plays a significant role in determining the structure, dynamics and thermodynamics of confined water molecules.

Amino acid-bonded Ti3C2Tx MXene nanofiltration membranes with superior antifouling property for enhanced water purification

MXene nanosheets have been identified as promising building blocks for high-performance nanofiltration (NF) membranes in water purification. Herein, we report a series of amino acid-bonded Ti3C2Tx MXene membranes with enhanced NF performance and antifouling properties via glycine (Gly), l-glutamic acid (L-Glu), l-lysine (L-Lys) or l-cysteine (L-Cys) modification. The physicochemical properties, separation performances and anti-fouling behaviors of the pure Ti3C2Tx MXene membrane, Gly-, L-Glu-, L-Lys- and L-Cys-bonded Ti3C2Tx MXene membranes were comparatively investigated. The stable Ti–N bonds were found between the amino acids and the MXene nanosheets and different amino acids lead to different properties of the corresponding membranes. While maintaining ultra-high rejections to various organic dyes, all the amino acid functionalized membranes exhibited enhanced water permeability (7.17–13.11 L·m−2·h−1·bar−1) compared with that of the pure MXene membrane. Importantly, the Gly-bonded membrane showed the optimal separation performance with high salt rejections of 86.28%, 81.36%, 72.88% and 66.82% to MgSO4, MgCl2, Na2SO4 and NaCl, respectively, and the membrane also exhibited superior anti-fouling property with a flux recovery rate of 80.59% to bovine serum albumin (BSA). The separation mechanism was further revealed which may offer a simple yet efficient way for enhancing 2D MXene-based NF membranes.

Synergistic design of polylactic acid/functionalized multi-walled carbon nanotubes composite membrane for enhanced oil-water separation

The increasing concerns over environmental pollution and the discharge of oily wastewater have prompted the development of advanced technologies for efficient water treatment. In this study, mixed matrix polymeric polylactic acid (PLA)/Amino-SiO2 functionalized multi-walled carbon nanotubes (f-MWCNTs) membrane was fabricated by phase inversion at different nanoparticle loadings for the treatment of oily wastewater. The membranes were evaluated for their oil-water separation efficiency, flux, and flux recovery using synthetic oily wastewater as a model system. The experimental results revealed that the addition of a 0.5 wt% of f-MWCNTs in the mixed matrix solution significantly enhanced water permeability, resulting in a 75% improvement, while achieving about 100% oil rejection. The flux recovery of membranes loaded with 0.5 wt% f-MWCNTs exhibited a flux recovery of 60% compared to the initial value. After two cyclic flux study, pristine membranes showed a flux recovery of 11%, while the modified membranes achieve a flux recovery of approximately 42%. Taking advantage of the recyclable and biocompatible properties of PLA, this study presents a promising development and application of environmentally friendly, sustainable membranes for the effective separation of oil-water emulsions.

MOFs and surface modification synergistically modulated cellulose membranes for enhanced water permeability and efficient tellurium separation in wastewater

With the widespread use of tellurium-containing products such as cadmium telluride solar cells in daily life, tellurium-containing wastewater inevitably enters the environmental water system. Removal of the ionic contaminant tellurite is essential in wastewater reclamation due to its potential threat to human health and difficulty of elimination. Herein, a rational design of separation membranes with synergistic physical and chemical effects to enhance separation efficiency with almost complete compensation for the loss of water flux was proposed. Membranes for tellurium separation with high efficiency and enhanced water flux were prepared by surface modification on the MOF-based support layer forming a dense separation layer (TSNTCM). The membrane separation efficiency was enhanced by the introduction of NH2-MIL-125 in the support layer, while the water flux was improved by its nano water channels. The abundant hydroxyl and anionic groups in the structure of the polymer monomer sodium lignosulfonate not only endowed the separation layer with chemical interaction (hydroxyl substitution), but also made the membrane surface highly negatively charged and improved the physical interaction. TSNTCM showed excellent tellurium separation efficiency (>95%) over a wide concentration range and achieved the highest rejection (99.16%) at pH = 6. Besides, the rejection of tellurium by TSNTCM was above 90% in the presence of common coexisting ions, but decreased in the presence of selenite, which may be due to the similar structure and properties of selenite and tellurite. Moreover, TSNTCM demonstrated satisfactory reusability and anti-fouling properties. Overall, MOFs and surface modification enhanced the comprehensive performance of TSNTCM, providing great potential for its application in wastewater reclamation.

Synchronously improved permeability, selectivity and fouling resistance of Fe-N-C functionalized ceramic catalytic membrane for effective water treatment: The critical role of Fe

Constructing catalytic membrane simultaneously displaying high permeability, selectivity and antifouling performance in water treatment remains challenging. Herein, the surface and pore channels of the ceramic membrane were co-functionalized with nitrogen doped carbon supported Fe catalyst (CN-F), and the Fe content was varied to investigate its effect on performance of CN-F coupled with peroxymonosulfate (PMS) activation (CN-F/PMS) for water treatment. Results confirmed the introduced Fe (in Fe-N coordination form) greatly enhanced the permeability, selectivity and fouling resistance of CN-F. Optimal CN-F3/PMS achieved 96.5% removal and 52.1% mineralization of sulfamethoxazole in short retention duration (2.7 min), whose performance was 5.4 and 6.7 times higher than that of nitrogen doped carbon functionalized ceramic catalytic membrane (CN/PMS) and CN-F3 filtration alone, respectively. CN-F3/PMS also efficiently inhibited fouling on both surface and pores with 2.8 and 2.4 times lower flux loss than that of CN/PMS and CN-F3 filtration alone, respectively. Moreover, CN-F3/PMS displayed superior performance in long-term treatment of real coking wastewater. The outstanding performance of CN-F was mainly attributed to the dual role of supported Fe, which served as hydrophilic site for enhanced water permeation and major active site for PMS adsorption and reduction into reactive species (mainly high-valent Fe(IV)=O species) towards pollutant elimination.

Artificial water channels-embedded PVDF membranes for direct contact membrane distillation and ultrafiltration

Innovative self-supported flat-sheet polyvinylidene fluoride (PVDF) membranes were developed incorporating amphiphilic I-quartet Artificial Water Channels (AWCs) and applied for membrane distillation (MD) and Dyes Ultrafiltration (UF). The presence of AWCs was aimed to increase the amount of water within hydrophobic PVDF pores increasing water permeability and preserving high selectivity and consequently to improve the MD and dyes UF performances. We explored novel strategies in which water channels structures contribute to water cluster stabilization and the increase of water (vapors or liquid) within hydrophobic pore structures. With this novel strategy in mind, three PVDF polymer grades with different molecular weights as well as the variation of their mass concentration as well as of AWCs were studied to shed in light their influence on the water permeability using a dead-end filtration setting. An enhanced water permeability of 75.3 L.m−2.h−1.bar−1 was attained for the PVDF-AWC hybrid membrane prepared using 16 wt% PVDF (530,000 g/mol) and 0.05 wt% AWCs when compared with a reference membrane with a water permeability of 30.6 L.m−2.h−1.bar−1. The MD performances of both membranes were assessed using a 35 g/L NaCl aqueous solution to yield a salt rejection of 95.3% and 85.2%, respectively. Furthermore, both the reference and the PVDF-AWC membranes showed improved separation performance in terms of rejection efficiency and dye permeability for binary dyes mixture as compared to single dyes. Among all the tested membranes, while methylene blue was completely removed in both cases, the 14 wt% PVDF membrane incorporating 0.075 wt% AWC showed a methyl orange rejection efficiency of up to 99.8% compared to 98.4% for its reference membrane. This hybrid membrane also displayed an almost doubled filtered dye feed permeability of 84 L.m−2.h−1.bar−1, compared to 40 L.m-2.h−1.bar−1 for its 14 wt% PVDF reference membrane.

Thin-Film Composite Membrane with Porous Interlayer Composed of Dendritic Mesoporous Silica Nanoparticles for Enhanced Nanofiltration.

Positively charged nanofiltration (NF) membranes show great potential in the fields of water treatment and resource recovery. However, this kind of NF membrane usually suffers from relatively low water permeance. Herein, a positively charged NF membrane with a porous interlayer is developed, where the interlayer is formed by assembling dendritic mesoporous silica nanoparticles (DMSNs) after the formation of a polyamide layer. This post-assembly strategy avoids the adverse effect of the interlayer on the formation of positively charged NF membranes. The porous DMSN interlayer provides abundant connected channels for water transport, thus endowing the NF membrane with enhanced water permeance. A series of DMSNs with different sizes was synthesized, and their influence on membrane formation and membrane performance was systematically investigated. The optimized membrane exhibits a CaCl2 rejection rate of 95.2% and a water flux of 133.6 L·h-1·m-2, which is 1.6 times that of the control group without an interlayer. This work represents an approach to the fabrication of a positively charged NF membrane with porous interlayers for high-efficiency cation rejection.

Thin film composite membrane with self-cleaning properties via a catalytic interlayer for dye wastewater treatment

Fouling control is the most critical concern in the implementation of nanofiltration (NF) for dye wastewater treatment. In this study, integration of NF and Fenton-like advanced oxidation was realized by tailoring a thin film composite NF membrane (TFNi) with in situ synthesized PDA/MnO2 interlayer. TFNi was optimized by controlling the amount of MnO2 nanoparticles incorporated within the interlayer which endowed the membrane with self-cleaning property. Besides it improved the membrane surface hydrophilicity and optimized the water transport path, resulting in alleviated fouling risks and an enhanced water permeance of 24 ± 2 L m−2 h−1 bar−1 compared to the control membrane. Fouling and subsequent chemical cleaning experiments were carried out on TFNi under various water chemistry conditions to elucidate the underlying mechanisms governing the self-cleaning properties. Accordingly, a high flux recovery ratio (FRR) (above 95%) was maintained thanks to the generation of free radicals by MnO2–H2O2 system which was validated by determining the free radical scavenging activities. Moreover, the interlayer confined radicals can facilitate the decomposition of foulants on TFNi. Conclusively, H2O2-initiated self-cleaning of TFNi can be of great prospect for the efficient treatment of dye wastewater via in-situ generated free radicals.

Thin film composite membrane with improved permeance for reverse osmosis and organic solvent reverse osmosis

Reverse osmosis (RO) is a widely used pressure-driven membrane process for desalination. Advancements in membrane materials have driven RO technologies' development and widespread application. Thin-film composite (TFC) membranes of a thin polyamide (PA) layer, porous substrate, and nonwoven fabric support are considered the gold standard in desalination technology. These membranes exhibited excellent separation performance and mechanical strength. Recently, TFC membranes with PA layers have been successfully employed in organic solvent reverse osmosis (OSRO) to differentiate organic liquids molecularly. Developing TFC membranes with improved solvent resistance and permeance is required to expand the applications of TFC membranes beyond solvent-solute systems. This study explored polyketone (PK) membranes as porous substrates in TFC membranes for general reverse osmosis processes. PK membranes offer excellent solvent resistance and are easier to prepare than other membranes. Furthermore, a surface modification approach was proposed to enhance the interfacial polymerization (IP) of the polyamide layer on both PK and polysulfone (PSf) substrates, resulting in improved TFC membranes with enhanced water permeance for RO and increased organic liquid permeance for OSRO while maintaining permselectivity. These findings highlight surface chemistry's significance in controlling crumpled PA layers' formation, ultimately improving the filtration efficiency for general RO applications. This study provides an example of the design of composite structures of TFC membranes for broader RO applications.

Design of a novel TA-MoS2 nanosheets interlayer-based loose nanofiltration membrane for enhanced dye/salt separation

From the view of sustainable development, the loose nanofiltration (LNF) membrane with high permeability and excellent separation of dye/salt mixture becomes more attractive for dye-containing wastewater. However, the previous LNF membranes inevitably suffered from the permeability-selectivity trade-off due to the inherent nature of polymer-based selective layer. This study reported a tannic acid (TA)-MoS2 nanosheets (NSs) interlayered nanocomposite polyester (PE) LNF membrane (iLNF-3) that exhibited a remarkably enhanced water permeance of 55.8 LMH·bar−1 compared to the control LNF membrane of 27.3 LMH·bar−1, and a higher separation selectivity of dye/salt (rejection rate: 99.6 % for congo red, 98.0 % for methyl blue, 5.6 % for Na2SO4, respectively). Furthermore, the iLNF-3 showed high ionic interference resistance, long-term stability, and superior antifouling performance. The enhanced permeance and dye/salt separation were mainly attributed to the introduction of a high-permeability TA-MoS2 NSs interlayer. In particular, the permeability was improved due to the “gutter” effect and nanochannels and the formed thinner PE selective layer caused by TA-MoS2 NSs interlayer. Notably, the selectivity was enhanced owing to the looser porous structure of PE layer resulting from the slow diffusion rate of aqueous monomer. This study can provide a foundational framework for the development of iLNF membranes for treating dye containing wastewater.

Thin film composite reverse osmosis membranes with metal-organic coordination complexes stabilized CNTs interlayer for enhanced removal of trace organic contaminants

Reverse osmosis (RO) has been recognized as a reliable technique for wastewater reclamation. To enhance its rejection of trace organic contaminants (TrOCs), a novel strategy was proposed to improve reverse osmosis (RO) membranes by fabricating thin-film nanocomposite membrane (TFNi) with a TA-Fe3+/CNTs interlayer. The TFNi-30 membrane was obtained by optimizing the loading capacity. This optimized membrane gave rise to an enhanced water permeance of 3.2 ± 0.2 L m-2 h-1 bar-1, which was two times higher than that of the control membrane (1.1 ± 0.2 L m-2 h-1 bar-1), while achieving a considerably higher rejection of inorganic salts and trace organic contaminants (TrOCs) thanks to the formation of a denser polyamide rejection layer. In addition, the specific roles of the interlayer structure in determining the separation performance of RO membranes were investigated by tailoring the support-free RO membranes and comparing them with the conventional membranes. This study would provide a peer reference for designing high performance RO membranes for wastewater reclamation via the TFNi strategy.

In Situ Formation of Silver Nanoparticles Induced by Cl-Doped Carbon Quantum Dots for Enhanced Separation and Antibacterial Performance of Nanofiltration Membrane.

Polyamide (PA) nanofiltration (NF) membranes suffer from biofouling, which will deteriorate their separation performance. In this study, we proposed a strategy to incorporate silver nanoparticles (Ag NPs) into PA NF membranes in situ, in order to simultaneously enhance water permeability and antibacterial performance. The chloride-doped carbon quantum dots (Cl-CQDs) with photocatalytic performance were pre-embedded in the PA selective layer. Under visible light irradiation, the photogenerated charge carriers generated by Cl-CQDs rapidly transported to silver ions (Ag+ ions), resulting in the in situ formation of Ag NPs. The proposed strategy avoided the problem of aggregating Ag NPs, and the amount of Ag NPs on the membrane surfaces could be easily tuned by changing silver nitrate (AgNO3) concentrations and immersion times. These uniformly dispersed Ag NPs increased membrane hydrophilicity. Thus, the obtained thin film nanocomposite Ag NPs (TFN-Ag) membrane exhibited an improved water flux (31.74 L m-2 h-1), which was ~2.98 times that of the pristine PA membrane; meanwhile, the sodium sulfate (Na2SO4) rejection rate was 96.11%. The sterilization rates of the TFN-Ag membrane against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were 99.55% and 99.52%, respectively. Thus, this facile strategy simultaneously improved the permeability and antibacterial property of PA NF membranes.

Polyamide–based membranes with nanoscale homogeneity and asymmetric structure for ultrafast ion separation

Polymeric membranes are the most practical separation technology for extracting target ionic species necessary for water purification and clean energy, but are limited by the multi-scale heterogeneity, and transient and dynamic free volume pores. Modulated interfacial polymerization techniques are emergent concepts for preparing polyamide composite membranes with reduced thickness and homogeneous pore structures to satisfy the requirements for efficient ion separation applications. Herein, N–Cyclic cation-assisted kinetically regulated interfacial polymerization strategy to generate polyamide nanofilm composite membranes with tuned pore network and asymmetric structures for water purification is reported. Experimental characterization techniques and molecular dynamic simulations revealed that the N-Cyclic cations control the kinetic diffusion behaviour of the amine monomers to the aqueous/organic interface conducing to the formation of nanofilm membranes with fine-tuned polyamide network structures. Meanwhile, the N–Cyclic cation–regulated IP process not only affords to decrease the thickness of the formed polyamide nanofilm selective layers but also effectively narrows the effective pore size of the membranes. These membranes with thinner, homogeneous and asymmetric polyamide network structures exhibit enhanced water permeance of 55.7–60.42 L m−2 h−1 bar−1, and showed Na2SO4 rejection of 99.59–99.66% and MgCl2 rejection of 98.94–98.96% in nanofiltration separations, thereby outperforming the permeance–selectivity performance of the state-of-the-art polyamide-based membranes. The membranes also exhibit improved forward osmosis performances. We envision that this research will provide insightful foundations for the molecular tuning and construction of the next-generation structurally modulated polyamide nanofilms for various applications in molecular separation and water purification.

Constructing low-friction mass transfer channel in laminar graphene oxide membrane for efficient molecular separation with enhanced permeability

In recent years, graphene oxide (GO) has attracted increasing interest in fabricating next-generation separation membranes. The perm-selectivity of laminar GO membrane is generally determined by their interlayer nanochannel structure. Herein, we used a new molecule called 5, 5′-diamine-2, 2′-biphenol (BIPOL-NH2) as the intercalator of laminar GO-based membrane to construct low-friction interlayer mass transfer channels. The aromatic BIPOL-NH2 molecules act as hydrophobic side walls of the mass transfer channels between adjacent GO nanosheets, reducing the interaction between water molecules and channel structure, thereby enhancing water permeability of GO membranes. This was confirmed by the further molecular dynamics simulation. Compared with pristine GO membrane, the BIPOL-GO membrane showed a water permeability increase by a factor of about 3 (up to 72.4 L m-2h−1 bar−1), which was consistent with our simulation results. Also, it represented excellent dye/salt separation performance (the selectivity of NaCl/CR is more than 117.2) and good structural stability. Overall, our work provides a novel and efficient approach to modify GO-based membranes for enhanced permeability.

Engineering Ultra-Permeable and Antifouling Water Channel-based Biomimetic Membranes toward Sustainable Water Purification

Water channel-based biomimetic membranes (WBMs) are gaining increasing attention due to the effectiveness of water channels in enhancing water permeability and breaking the permselectivity trade-off. However, the ultra-permeable WBMs may suffer from severe membrane fouling issue because a high-water flux tends to result in an accelerated fouling and thus compromises the benefits gained from the usage of water channels. Herein, a novel in-situ modification protocol was proposed to enhance the antifouling performance of ultra-permeable WBMs. The nanovesicles incorporated with aquaporin (AQP) water channels were functionalized with polyethylene glycol brushes (i.e., PEGylation) via a facile self-assembly approach and subsequently encapsulated in the selective layer of thin-film composite membranes through interfacial polymerization. The modification had minimal impact on the function of AQPs, resulting in WBMs with a high water permeance (∼8.2 LMH/bar) and good NaCl rejection (96.4%) comparable to the unmodified WBMs. Moreover, the in-situ modification drastically enhanced the surface hydrophilicity, which endowed the membrane with a superior fouling resistance to organic foulants. The improved fouling resistance ensured a more sustainable operation of ultra-permeable WBMs, particularly in scenarios that favor high water fluxes. This facile modification strategy provides an efficient way to fabricate ultra-permeable and antifouling WBMs for sustainable water purification.