Enhanced Water Permeability Research Articles

Electroregulation of graphene–nanofluid interactions to coenhance water permeation and ion rejection in vertical graphene membranes

Graphene oxide (GO) membranes with nanoconfined interlayer channels theoretically enable anomalous nanofluid transport for ultrahigh filtration performance. However, it is still a significant challenge for current GO laminar membranes to achieve ultrafast water permeation and high ion rejection simultaneously, because of the contradictory effect that exists between the water-membrane hydrogen-bond interaction and the ion-membrane electrostatic interaction. Here, we report a vertically aligned reduced GO (VARGO) membrane and propose an electropolarization strategy for regulating the interfacial hydrogen-bond and electrostatic interactions to concurrently enhance water permeation and ion rejection. The membrane with an electro-assistance of 2.5V exhibited an ultrahigh water permeance of 684.9 L m-2h-1bar-1, which is 1-2 orders of magnitude higher than those of reported GO-based laminar membranes. Meanwhile, the rejection rate of the membrane for NaCl was as high as 88.7%, outperforming most reported graphene-based membranes (typically 10 to 50%). Molecular dynamics simulations and density-function theory calculations revealed that the electropolarized VARGO nanochannels induced the well-ordered arrangement of nanoconfined water molecules, increasing the water transport efficiency, and thereby resulting in improved water permeation. Moreover, the electropolarization effect enhanced the surface electron density of the VARGO nanochannels and reinforced the interfacial attractive interactions between the cations in water and the oxygen groups and π-electrons on the VARGO surface, strengthening the ion-partitioning and Donnan effect for the electrostatic exclusion of ions. This finding offers an electroregulation strategy for membranes to achieve both high water permeability and high ion rejection performance.

Merging Proline:Xylitol Eutectic Solvent in Crosslinked Chitosan Pervaporation Membranes for Enhanced Water Permeation in Dehydrating Ethanol.

The scope of this research aims at merging a new deep eutectic mixture (DES) into a biopolymer-based membrane for a pervaporation application in dehydrating ethanol. Herein, an L-proline:xylitol (at 5:1) eutectic mixture was successfully synthesized and blended with chitosan (CS). A complete characterization of the hybrid membranes, in terms of morphology, solvent uptake, and hydrophilicity, has been conducted. As part of their applicability, the blended membranes were assayed for their ability to separate water from ethanolic solutions by means of pervaporation. At the highest temperature (50 °C), a water permeation of ca. 0.46 kg m-2 h-1 was acquired, representing a higher permeation than the pristine CS membranes (ca. 0.37 kg m-2 h-1). Therefore, CS membranes demonstrated an enhanced water permeation thanks to their blending with the hydrophilic L-proline:xylitol agent, making these membranes a good candidate for other separations containing polar solvents.

Hydrophilic-hydrophobic heterogeneous interface enables the formation of a high-performance polyamide membrane for water purification

Polyamide reverse osmosis (RO) membranes possessing high water permeance and high salt rejection are highly beneficial for efficient desalination and wastewater treatment. However, achieving desired membrane properties toward both fast water transport and outstanding salt rejection remains a great challenge. Herein, we report the fabrication of high-performance polyamide RO membrane via interfacial polymerization (IP) on a heterogeneous substrate featuring a hydrophobic surface and polyaniline modified hydrophilic pores. The heterogeneous substrate, combining the advantages of conventional hydrophilic and hydrophobic substrates for IP process, leads to the formation of an ultra-thin polyamide film with rough morphology. The obtained RO membranes thereby not only have simultaneously enhanced water permeance (3.28 L m−2h−1 bar−1) and salt rejection (NaCl rejection 99.5 %), but also exhibit outstanding pH stability, anti-fouling performance, and long-term stability. In addition, the regulation mechanism of the heterogeneous substrate on IP was comprehensively investigated by combing molecular simulation and experiments. Our work provides a novel design direction of substrate used for fabricating RO membrane with outstanding performance.

Unveiling the role of post-treatment in thin-film composite nanofiltration membranes: Performance and mechanism

The deep role and mechanism of post-treatment in the morphology and performance of thin-film composite (TFC) nanofiltration (NF) membranes have rarely been revealed. In this work, four solutions of pure water, hexane, Na2CO3, and glycerol were selected for the post-treatment of TFC-NF membranes, and the performances of the resultant NF membranes were systematically investigated. The results showed that the hexane could effectively remove the residual acyl chloride groups and prevent the subsequent second growth of polyamide (PA) layers, thus leading to the formation of smoother and thinner PA membranes with higher water permeance and excellent salt rejections. Hydrolysis and swelling of unstable PA fragments in solutions (water, Na2CO3, and glycerin) contributed to greater negative charge, higher hydrophilicity, and enlarged pore size. The resultant NF membranes exhibited significantly enhanced water permeance and comparable separation behaviors to the control NF membrane. In addition, the well-constructed NF membranes possessed superior monovalent/multivalent ion selectivity, excellent antifouling, and stability. The mechanisms of the post-treatment on the performance enhancement of NF membranes were proposed from the perspective of interfacial interactions. The facile post-treatment strategy provides new insights into tailoring high-performance NF membranes for water treatment applications.

Fabrication of novel thin-film composite membrane based on ultrathin metal-organic framework interlayer for enhancing forward osmosis performance

To improve operation efficiency, an interlayered thin-film composite forward osmosis (iTFC-FO) membrane was designed by introducing an ultrathin and porous interlayer based on aluminum tetra-(4-carboxyphenyl)porphyrin (a stable metal−organic framework nanosheet, Al-MOF). Surface characterization results revealed that Al-MOF spread evenly in the macro-porous substrate, and provided a flat and smooth reaction interface with moderate hydrophilicity and uniform small aperture. The resultant polyamide (PA) layer had a thin base (without intrusion into substrate) and crumpled surface (with abundant leaves). The leaves size and cross-linking degree of PA layer firstly increased and then decreased with the Al-MOF loading. Compared to the original membrane, the iTFC-FO showed an enhanced water permeability and a reduced reverse sodium flux in both modes of active layer facing feed solution (AL-FS) and active layer facing draw solution (AL-DS). To be specific, the specific reverse sodium flux (reverse sodium flux/pure water flux) decreased from 0.27 g/L to 0.04 g/L in the AL-FS mode, while from 1.36 g/L to 0.23 g/L in the AL-DS mode with 2 mol/L NaCl as DS. Moreover, the iTFC-FO maintained high stability and high permeability under high-salinity and contaminated environment. This study offers a new possibility for the rational fabrication of high-performance TFC-FO membranes.

Low-pressure thin-film composite nanofiltration membranes with enhanced selectivity and antifouling property for effective dye/salt separation

For better sustainable resource recovery and elevating the separation efficiency of dye/salt mixture, it is essential to develop an appropriate nanofiltration membrane for the treatment of textile dyeing wastewater containing relatively smaller molecule dyes. In this work, a novel composite polyamide-polyester nanofiltration membrane was fabricated by tailoring amino functionalized quantum dots (NGQDs) and β-cyclodextrin (CD). An in-situ interfacial polymerization occurred between the synthesized NGQDs-CD and trimesoyl chloride (TMC) on the modified multi-carbon nanotubes (MWCNTs) substrate. The incorporation of NGQDs significantly elevated the rejection (increased by ∼ 45.08%) of the resultant membrane for small molecular dye (Methyl orange, MO) compared to the pristine CD membrane at low pressure (1.5 bar). The newly developed NGQDs-CD-MWCNTs membrane exhibited enhanced water permeability without compromising the dye rejection compared to the pure NGQDs membrane. The improved performance of the membrane was primarily attributed to the synergistic effect of functionalized NGQDs and the special hollow-bowl structure of CD. The optimal NGQDs-CD-MWCNTs-5 membrane expressed pure water permeability of 12.35 L m-2h−1 bar−1 at the pressure of 1.5 bar. Noteworthily, the NGQDs-CD-MWCNTs-5 membrane not only showed high rejection for the larger molecular dye of Congo Red (CR, 99.50%) but also for the smaller molecular dye of MO (96.01%) and Brilliant Green (BG, 95.60%) with the permeability of 8.81, 11.40, and 6.37 L m-2h−1 bar−1, respectively at low pressure (1.5 bar). The rejection of inorganic salts by the NGQDs-CD-MWCNTs-5 membrane was 17.20% for sodium chloride (NaCl), 14.30% for magnesium chloride (MgCl2), 24.63% for magnesium sulfate (MgSO4), and 54.58% for sodium sulfate (Na2SO4), respectively. The great rejection of dyes remained in the dye/salt binary mixed system (higher than 99% for BG and CR, <21% for NaCl). Importantly, the NGQDs-CD-MWCNTs-5 membrane exhibited favorable antifouling performance and potential good operation stability performance. Consequently, the fabricated NGQDs-CD-MWCNTs-5 membrane suggested a prospective application for the reuse of salts and water in textile wastewater treatment owing to the effective selective separation performance.

Modeling nanovoid-enhanced water permeance of thin film composite membranes

Nanovoids in polyamide layers shape the roughness structures of thin film composite (TFC) reverse osmosis (RO) and nanofiltration (NF) membranes and have a critical influence on their water permeance. Although there have been numerous experimental works reporting enhanced water permeance by incorporating nanovoids, a systematic modeling for assessing the underlying mechanisms is still lacking. In this work, we perform numerical simulations to investigate water transport behaviors in a polyamide layer with or without a nanovoid. An analytical model, which quantifies the competition among substrate-induced unfavorable funnel effect and nanovoid-induced favorable multi-effects (i.e., surface area effect and gutter effect), is also developed and agrees well with simulation results. The model results suggest that even a tiny nanovoid of a few nanometers in size could provide an excellent self-gutter effect to minimize water transport distance. The available water permeance can be further improved by the increased effective surface area. Our modeling results reveal that the nanovoid-containing membrane can potentially offer 1–2 orders of magnitude enhancement in membrane permeance. The enhancement is greater for larger nanovoids with higher aspect ratios and for less porous substrates. Furthermore, the presence of nanovoids greatly improves the flux distribution uniformity over the membrane surface, which could potentially alleviate membrane fouling. The theoretical framework established in this work provides essential guidance for the future development of TFC membranes.

Construction of tunable “silica molecular brush” on the polyamide membrane surface for enhancing water permeability and antifouling performance

Surface modification has been widely applied for improvement permeability and antifouling performance of polyamide (PA) reverse osmosis (RO) membrane. A low-cost and easily obtained organoalkoxysilane, γ-Aminopropyl triethoxysilane (APTES), was grafted on PA RO membrane surface via a second interfacial polymerization (SIP) process combined with the activation effect of n-decane solvent, thus to form an antifouling PA surface with different silica brush-like structures, which can effectively weaken the attractive forces between the membrane surface and organic foulants. Meanwhile, n-decane solvent during the SIP process plays a dual function, which can not only minimize hydrolysis of both APTES monomers and unreacted acyl chloride groups on PA surface but also enhance microporosity of the nascent PA (solvent activation of PA), thereby grafting APTES on PA surface via amidation reaction can achieve maximization, and the water permeability of APTES modified PA (APTES-PA) membranes is improved. These APTES-PA membranes showed high water permeability (above 3.47 LMH/bar) with competitive NaCl rejection (above 98.75%), as well as excellent stability during 70 h of cross-flow test. Moreover, the existence of silica brush-like structures via grafting APTES molecules on PA layer can significantly elevate the antifouling performance of membranes against both negatively and positively charged foulants.

High-Performance Polyamide Reverse Osmosis Membrane Containing Flexible Aliphatic Ring for Water Purification

A reverse osmosis (RO) membrane with a high water permeance and salt rejection is needed to reduce the energy requirement for desalination and water treatment. However, improving water permeance while maintaining a high rejection of the polyamide RO membrane remains a great challenge. Herein, we report a rigid-flexible coupling strategy to prepare a high-performance RO membrane through introducing monoamine with a flexible aliphatic ring (i.e., piperidine (PPR)) into the interfacial polymerization (IP) system of trimesoyl chloride (TMC) and m-phenylenediamine (MPD). The resulted polyamide film consists of a robust aromatic skeleton and soft aliphatic-ring side chain, where the aliphatic ring optimizes the microstructure of polyamide network at a molecular level. The obtained membranes thereby showed an enhanced water permeance of up to 2.96 L·m-2 h-1 bar-1, nearly a 3-fold enhancement compared to the control group, meanwhile exhibiting an ultrahigh rejection toward NaCl (99.4%), thus successfully overcoming the permeability-selectivity trade-off limit. Furthermore, the mechanism of the enhanced performance was investigated by molecular simulation. Our work provides a simple way to fabricate advanced RO membranes with outstanding performance.

Silicification-interlayered nanofiber substrates regulated crumpled ultrathin polyamide nanofilms for highly enhanced nanofiltration

Thin-film nanofiber composite (TFNC) membranes have shown great potentials for highly efficient nanofiltration. However, it remains a challenge to construct defect-free ultrathin polyamide nanofilms with designed crumpled structures on polymeric nanofiber substrates via traditional interfacial polymerization (IP) to realize high permeability and selectivity synchronously. Herein, a novel strategy is reported to regulate the polyamide nanofilm by a silicification-interlayered nanofiber substrate with hydrophilic and rugged surface. The silica interlayer could enrich piperazine (PIP) monomers in aqueous solutions and control the releasing towards the interfacial reaction zone, enabling the homogeneous IP reaction and the reduced thickness of PA nanofilms. The silicified nanofiber substrate can also serve as a templating support to crumple the PA nanofilms and thus increase their effective infiltrating area. Furthermore, deep insight has been taken into the intermolecular interactions in the IP system and the fundamental mechanism of the silicification-interlayered nanofiber substrate regulating the IP process via density function theory (DFT) and dissipative particle dynamics (DPD) simulations. The membrane morphologies were observed by SEM and AFM, and chemical structures of membrane surfaces were characterized by FTIR/ATR, XPS and XRD in detail. The hydrophilicity and charged properties of different membrane surfaces were analyzed by water contact angle and Zeta potential tests, respectively. As a result, an ultrathin crumpled PA nanofilm is generated on top of the nanofiber substrate as selective layer, enabling the composite membrane with enhanced water permeability of 19.6 L m−2 h−1 bar−1 (approximately two folds higher than that of the pristine PA membranes) and high Na2SO4 rejection of 96.5%. Meanwhile, the prepared membranes reveal good structural stability not only under different operation pressures but also during long-term filtration processes. This work is believed to provide a facile approach to engineer advanced TFNC membranes with high-efficiency nanofiltration performance.

Correlating the role of nanofillers with active layer properties and performance of thin-film nanocomposite membranes

Thin-film nanocomposite (TFN) membranes are emerging water-purification membranes that could provide enhanced water permeance with similar solute removal over traditional thin-film composite (TFC) membranes. However, the effects of nanofiller incorporation on active layer physico-chemical properties have not been comprehensively studied. Accordingly, we aimed to understand the correlation between nanofillers, active layer physico-chemical properties, and membrane performance by investigating whether observed performance differences between TFN and control TFC membranes correlated with observed differences in physico-chemical properties. The effects of nanofiller loading, surface area, and size on membrane performance, along with active layer physico-chemical properties, were characterized in TFN membranes incorporated with Linde Type A (LTA) zeolite and zeolitic imidazole framework-8 (ZIF-8). Results show that nanofiller incorporation up to ~0.15 wt% resulted in higher water permeance and unchanged salt rejection, above which salt rejection decreased 0.9–25.6 % and 26.1–48.3 % for LTA-TFN and ZIF-8-TFN membranes, respectively. Observed changes in active layer physico-chemical properties were generally unsubstantial and did not explain observed changes in TFN membrane performance. Therefore, increased water permeance in TFN membranes could be due to preferential water transport through porous structures of nanofillers or along polymer-nanofiller interfaces. These findings offer new insights into the development of high-performance TFN membranes for water/ion separations.

Metal-organic frameworks for high performance desalination through thickness control and structural fine-tuning

Two-dimensional nanoporous membranes hold great promise for the design of state-of-the-art desalination architectures to alleviate the increasing global water scarcity. Herein, by employing molecular dynamics simulations, we demonstrate the great potential of two recently reported metal-organic frameworks (MOF) membranes, namely NiIT and NiAT, as efficient desalination membranes that reach super high water flux and high salt rejection. The desalination performance of the MOF membrane is highly tunable through controlling the membrane thickness from one layer to five layers. Double layer NiIT membrane exhibits excellent salt rejection of 100% for NaCl, and meanwhile achieving high water permeability of ∼45 L/cm2/MPa/day. While for the convertible double-layer NiAT, it effectively rejects ∼96% ions with an improved water permeation of over 70 L/cm2/MPa/day. Quantitative analysis of water distribution reveals a denser water solvation shell around NiAT membrane than NiIT and a higher water velocity through the nanopore of NiAT than that of NiIT, contributing to the enhanced water permeability. Through calculating free energy for water/ions translocating through two membranes, a clear energy barrier is observed for ions to penetrate through the sub-nanosized pores in both membranes, leading to the high salt rejection. The present study suggests that these two MOF membranes can serve as a promising semipermeable membrane for energy-efficient desalination which is highly prospective in industrial applications.

Tailoring the crumpled structures of a polyamide membrane with a heterostructural MXene-TiO2 interlayer for high water permeability

Thin-film composite (TFC) nanofiltration (NF) membrane having excellent permeability and desired rejection is needed for water reuse and desalination. However, it remains a tremendous challenge to boost permeability while sustaining the rejection of the membrane. Herein, a novel TFC NF membrane possessing a thin and crumpled polyamide (PA) selective layer was fabricated using heterostructural MXene-TiO2 as interlayer through a conventional interfacial polymerization (IP) reaction. The heterostructural MXene-TiO2 was obtained by the in situ MXene oxidation with peroxymonosulfate (PMS), which effectively regulated the nanostructure of the interlayer and avoided the over-stacking of the nanosheets, promoting the rapid transport of water molecules. Moreover, the large specific area and numerous edges of MXene-TiO2 boosted the adsorption and release of amine monomers on the substrates, facilitating the crumpled structure formation. In this way, the obtained membrane with 30.25 nm in thickness achieved a 98.29 % rejection for MgSO4 and an enhanced water permeance of 11.10 L m−2 h−1 bar−1, about 2.5 times that of TFC0 NF membrane. Our work presents a novel approach of feasibility to engineer a TFC NF membrane with outstanding performance for water treatment.

Unveiling the impact of imidazole derivative with mechanistic insights into neutralize interfacial polymerized membranes for improved solute-solute selectivity

Domestic wastewater (DWW) contains a reservoir of nutrients, such as nitrogen, potassium, and phosphorus; however, emerging micropollutants (EMPs) hinder its applications in resource recovery. In this study, a novel class of nanofiltration (NF) membranes was developed; it enabled the efficient removal of harmful EMP constituents while preserving valuable nutrients in the permeate. Neutral (IM-N) and positively charged (IM-P) imidazole derivative compounds have been used to chemically functionalize pristine polyamide (PA) membranes to synchronously inhibit the hydrolysis of residual acyl chloride and promote their amination. Owing to their distinct properties, these IM modifiers can custom-build the membrane physicochemical properties and structures to benefit the NF process in DWW treatment. The electroneutral NF membrane exhibited ultrahigh solute-solute selectivity by minimizing the Donnan effects on ion penetration (K, N, and P ions rejection < 25%) while imposing remarkable size-sieving obstruction against EMPs (rejection ratio > 91%). Moreover, the hydrophilic IM-modifier synergistically led to enhanced water permeance of 9.2 L m−2 h−1 bar−1, reaching a 2-fold higher magnitude than that of the pristine PA membrane, along with excellent antifouling/antibacterial fouling properties. This study may provide a paradigm shift in membrane technology to convert wastewater streams into valuable water and nutrient resources.

Hemin-Modified Multi-Walled Carbon Nanotube-Incorporated PVDF Membranes: Computational and Experimental Studies on Oil-Water Emulsion Separations.

The separation of oil/water emulsions has attracted considerable attention for decades due to the negative environmental impacts brought by wastewater. Among the various membranes investigated for separation, polyvinylidene fluoride (PVDF) membranes have shown significant advantages of ease of fabrication, high selectivity, and fair pore distribution. However, PVDF membranes are hydrophobic and suffer from severe fouling resulting in substantial flux decline. Meanwhile, the incorporation of wettable substrates during fabrication has significantly impacted the membrane performance by lowering the fouling propensity. Herein, we report the fabrication of an iron-containing porphyrin (hemin)-modified multi-walled carbon nanotube incorporated PVDF membrane (HA-MWCNT) to enhance fouling resistance and the effective separation of oil-in-water emulsions. The fabricated membrane was thoroughly investigated using the FTIR, SEM, EDX, AFM, and contact angle (CA) analysis. The HA-MWCNT membrane exhibited a water CA of 62° ± 0.5 and excellent pure water permeance of 300.5 L/m2h at 3.0 bar (400% increment), in contrast to the pristine PVDF, which recorded a CA of 82° ± 0.8 and water permeance of 59.9 L/m2h. The hydrophilic HA-MWCNT membrane further showed an excellent oil rejection of >99% in the transmembrane pressure range of 0.5−2.5 bar and a superb flux recovery ratio (FRR) of 82%. Meanwhile, the classical molecular dynamics (MD) simulations revealed that the HA-MWCNT membrane had greater solvent-accessible pores, which enhanced water permeance while blocking the hydrocarbons. The incorporation of the hemin-modified MWCNT is thus an excellent strategy and could be adopted in the design of advanced membranes for oil/water separation.

Enhancement of struvite generation and anti-fouling in an electro-AnMBR with Mg anode-MF membrane module

Severe membrane fouling and the inability to remove/recover nitrogen and phosphorus are bottlenecks of anaerobic membrane bioreactors (AnMBRs) for large-scale application in wastewater treatment. Herein, an electrochemical AnMBR with a Mg anode-membrane module (electro-AnMBR) was built and showed good performance in terms of membrane fouling mitigation and nutrient recovery during sewage treatment. Compared with the traditional AnMBR, membrane fouling in the electro-AnMBR was reduced by up to 30%. The application of an electric field decreased the zeta potential, viscosity, and EPS concentration of the sludge-water liquor in the electro-AnMBR, which could improve the cake layer structure and thus enhance water permeability. Meanwhile, 26% of NH4+ and 48% of PO43- co-precipitated with Mg2+ generating from the sacrificial Mg anode and were recovered as struvite deposited onto cathode in the electro-AnMBR. Hydrogen evolution provided a relatively alkaline pH environment, resulting in struvite electrodeposition on the graphic cathode, which partly separated the formed struvite from the sludge with a purity of 77%. In the electro-AnMBR, the electrochemical reactions provided alkalinity and effectively inhibited anaerobic acidification. The applied voltage of 0.6 V reduced the relative abundance of methanosaeta, but increased that of methanosarcina, which is also beneficial for the membrane anti-fouling.

Cannabis detection with solid sensors and paper-based immunoassays by conjugating antibodies to nanocellulose

Highly sensitive and specific diagnostics for cannabis usage are essential for rapid on-site screening for illicit drug usage. To improve the sensitivity of THC immunoassays, a proper immobilization of the sensing elements on the sensor substrate is critical. In this work, we demonstrated the utilization of EDC/NHS coupling chemistry with nanocellulose to obtain efficient anchor layers for the immobilization of anti-immune complex antibodies on surfaces. In our approach, the high surface-to-volume ratio, OH-group-rich surface, and high hygroscopicity of TOCNF enable efficient surface functionalization and enhance water permeation inside the nanocellulose network structure, offering a hydrophilic spacer for the sensing antibodies. THC detection was shown in both SPR (surface plasmon resonance technique) and paper-based sensing systems. In SPR, antibody immobilization and the related interactions with the target molecule complex with 1–10 μg/mL THC were followed in-situ in aqueous environment, revealing robust attachment of the antibody to the nanocellulose layer and preserved bioactivity. Additionally, quantitative THC detection was enabled on paper substrate by colorimetric means by employing labeled anti-THC Fab antibody fragments as detection antibodies. THC detection efficiency of covalently linked biointerface was superior compared to the performance of physically linked biointerface. The chemical conjugation of anti-IC to nanocellulose allowed efficient binding, whereas supramolecular conjugation led to insufficient binding, highlighting the relevance of the developed nanocellulose-based anchor layer.

Constructing reduced porous graphene oxide for tailoring mass-transfer channels in ultrathin MXene (Ti3C2Tx) membranes for efficient dye/salt separation

Two-dimensional (2D) membranes such as graphene oxide (GO) and MXene have attracted increasing interest in water purification. Critical challenges that impede their performance in separation applications include poor stability (swelling), low mass-transfer rate (high tortuosity), and an unavoidable trade-off between permeability and selectivity. Herein, we propose an effective multidimensional channel design strategy for preparing high-performance 2D composite membranes, featuring robust and abundant mass transfer channels. Specifically, reduced porous GO (rPGO) with high-density nanopores (size: ca. 14.7 nm, density: ca. 2.2 × 1014 m−2) and a few oxygen-containing functional groups were rationally designed and then deployed as multifunctional intercalators in MXene interlayers (rPGO-MXene, rPGM) to construct highly permeable, in-plane nanochannels and stable and tunable interlayer sieve channels. The intercalation of tailorable rPGO provides additional transport channels and weakens the interlayer repulsive hydration force, yielding composite membranes with remarkably enhanced water permeability and anti-swelling properties. As a result, the optimized membrane (10 % rPGM) exhibited an outstanding water permeability of 198.8 L m−2h−1 bar−1, 100 % rejection of Congo red, 5.3 % rejection of NaCl, and satisfactory stability (30 h) under cross-flow separation conditions. This study provides an innovative and facile approach for designing robust 2D membranes with abundant permeable nanochannels for highly efficient and precise molecular separation.

Polyamide thin film nanocomposite membranes with in-situ integration of multiple functional nanoparticles for high performance reverse osmosis

Polyamide (PA) thin film nanocomposite (TFN) reverse osmosis (RO) membranes have been vigorously developed, which could be used in saline water desalination, wastewater treatment and chemicals separation and purification. Aiming at further improving the TFN RO membrane comprehensive performances, such as the perm-selectivity, stability and anti-fouling/-microbial properties remains a great challenge. Herein, we proposed a biomimetic nanoparticle redox strategy to in-situ integration of multiple functional nanoparticles, i.e., biomimetic nanoparticles (BNPs) and silver (Ag) nanoparticles into the PA matrix for simultaneously regulating the membrane microstructure and optimizing the surface property. A much hydrophilic selective layer with interior transporting channel structure renders the resultant RO membrane PA-BNP-Ag with an enhanced water permeance of ∼4.2 L m−2·h−1bar−1 without sacrificing NaCl rejection (∼98.1%). The BNPs induce Ag nanoparticles uniformly distributed within the PA matrix, which significantly improves the membrane anti-fouling/-bacterial property. The water flux recovery ratio of PAM-BNP-Ag was improved to be higher than 96% during several cycles filtration of saline solution containing bovine serum albumin foulants. More importantly, the membrane sterilization rate against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) achieves nearly 100%. This work provides a new strategy for the construction of advanced PA TFN membranes with both high perm-selectivity and anti-fouling/-microbial property in RO desalination.

Construction the hierarchical architecture of molybdenum disulfide/MOF composite membrane via electrostatic self-assembly strategy for efficient molecular separation

• Electrostatic LBL self-assembly strategy is firstly employed to integrate MoS 2 with CMOF. • Superior rejection rates are increased above 27–55% more than that of monomer membranes for FQs. • Synergy of size exclusion, electrostatic repulsion, and hydrophilic interaction is explained. • High stability in harsh environments for 72 h and over 90% rejection against FQs in the real sample. Developing a novel nanofiltration membrane for effectively purifying antibiotic wastewater has been a daunting challenge in recent years. However, a convenient and controllable strategy for constructing membranes with two-dimensional nanomaterials (2DNMs) and metal–organic frameworks (MOFs) needs to be further studied. Herein, a loosely hierarchical architecture composite membrane has been fabricated, utilizing an electrostatic layer-by-layer (LBL) self-assembly method to intercalate chitosan crosslinked UiO-66-NH 2 MOFs (CMOF) into MoS 2 laminates. Through regulating the CMOF content, lower hydraulic-resisted channels and precise separation regions have been formed in the hierarchical architecture. The well-designed MoS 2 /CMOF composite membrane exhibited enhanced water permeance (78.98 ± 1.45 L·m -2 h −1 bar −1 ) and superior antibiotic rejection capability (98.01 ± 1.12% for ciprofloxacin and 94.31 ± 0.68% for ofloxacin), which are increased by 27–55% more than monomer membranes. Detailed analysis results indicate the nanofiltration performance of the MoS 2 /CMOF composite membrane depends heavily on the synergistic mechanism, including the molecular sieving effect (size exclusion), electrostatic repulsion, and hydrophilic-hydrophobic interaction. Besides, the MoS 2 /CMOF composite membrane has emerged with excellent antifouling ability and long-term stability, which could maintain favorable rejection efficiency in continuous nanofiltration for 72 h under an alkaline and acidic environment. Furthermore, it presents over 90% antibiotic rejection rates for real water samples obtained from the municipal domestic sewage and livestock wastewater along the Xiangjiang River in China, indicating its good availability. In general, this work provides a new vision and a reasonable design strategy to construct 2DNMs/MOFs-based nanofiltration membranes with hierarchical architecture, further expanding their application in wastewater treatment and reclamation, in harmony with the global trend of green and low-carbon development.