Fabrication of composite polyamide/Kevlar aramid nanofiber nanofiltration membranes with high permselectivity in water desalination

Bio-Inspired Underwater Superoleophobic Aramid Nanofiber-Based Aerogel Membranes for Highly Efficient Removal of Emulsified Oils and Organic Dyes

Effective elimination of insoluble emulsified oils and soluble organic dyes has received extensively attention in wastewater treatment. In this work, a chitosan and polydopamine @ aramid nanofibers (CS&PDA@ANFs) aerogel membrane was fabricated through an integration methodology consisting of phase inversion and successive deposition of PDA and CS. The as-prepared aerogel membrane possessed a satisfactory three-dimensional interpenetrating network architecture with high porosity and desirable mechanical property. Furthermore, due to the synergistic effect of hydrophilic CS and PDA, the resultant membrane exhibited good superhydrophilicity and underwater superoleophobicity associated with favorable oil resistance/antioil fouling properties. The combination of the interconnected porous structures and super wettability endowed the aerogel membranes with desirable oil-in-water emulsion separation performance. Particularly, an extremely high permeation flux (3729 L/m2/h) and a rejection rate (99.3%) were achieved for the CS&PDA@ANFs membrane. Moreover, diverse dyes could be also adsorbed by the resultant membrane, and the equilibrium adsorption capacity of cationic dye malachite green could reach 36 mg/g, with a high rejection rate over 97%. This study indicated that the CS&PDA@ANFs aerogel membrane held great promise for practical applications in complex wastewater remediation.

Synergistic interfacial polymerization between hydramine/diamine and trimesoyl chloride: A novel reaction for NF membrane preparation

Polyester-amide (PEA) thin film composite (TFC) NF membranes have rapidly evolved towards a competitive performance, benefiting from their remarkable antifouling capability and superior chlorine resistance. In this report, a new concept of synergistic interfacial polymerization is explored, which promptly triggers the reaction between hydramines and trimesoyl chloride (TMC) in the presence of a trace amount of diamines. This rapid-start mode enables the formation of defect-free PEA films without the requirement of catalysis. A comprehensive characterization of physicochemical properties using high-resolution mass spectrometer (HRMS) reveals that the recombination and formation of a "hydramine-diamine" coupling unit plays a decisive role in activating the synergistic interfacial polymerization reaction with TMC molecules. Taking the pair of serinol and piperazine (PIP) as an example, the PEA-NF membrane fabricated with 0.1 w/v% serinol mixed with 0.04 w/v% PIP as water-soluble monomer and 0.1 w/v% TMC as oil phase monomer was found to have a pure water permeability (PWP) of 18.5 L·m-2·h-1·bar-1 and a MgSO4 rejection of 95.5 %, which surpasses almost all the reported PEA NF membranes. Findings of the current research provide more possibilities for the low-cost and rapid synthesis of high-performance PEA membranes aiming for water purification.

Membranes for Osmotic Power Generation by Reverse Electrodialysis

In recent years, the utilization of the selective ion transport through porous membranes for osmotic power generation (blue energy) has received a lot of attention. The principal of power generation using the porous membranes is same as that of conventional reverse electrodialysis (RED), but nonporous ion exchange membranes are conventionally used for RED. The ion transport mechanisms through the porous and nonporous membranes are considerably different. Unlike the conventional nonporous membranes, the ion transport through the porous membranes is largely dictated by the principles of nanofluidics. This owes to the fact that the osmotic power generation via selective ion transport through porous membranes is often referred to as nanofluidic reverse electrodialysis (NRED) or nanopore-based power generation (NPG). While RED using nonporous membranes has already been implemented on a pilot-plant scale, the progress of NRED/NPG has so far been limited in the development of small-scale, novel, porous membrane materials. The aim of this review is to provide an overview of the membrane design concepts of nanofluidic porous membranes for NPG/NRED. A brief description of material design concepts of conventional nonporous membranes for RED is provided as well.

Ultrathin and Ultrastrong Kevlar Aramid Nanofiber Membranes for Highly Stable Osmotic Energy Conversion

An ion-selective membrane can directly convert the osmotic energy to electricity through reverse electrodialysis. However, developing an advanced membrane that simultaneously possesses high power density, excellent mechanical strength, and convenient large-scale production for practical osmotic energy conversion, remains challenging. Here, the fabrication of ultrathin and ultrastrong Kevlar aramid nanofiber (KANF) membranes with interconnected three-dimensional (3D) nanofluidic channels via a simple blade coating method is reported. The negatively charged 3D nanochannels show typical surface-charge-governed nanofluidic ion transport and exhibit excellent cation selectivity. When applied to osmotic energy conversion, the power density of the KANF membrane-based generator reaches 4.8 W m^-2 (seawater/river water) and can be further increased to 13.8 W m^-2 at 328 K, which are higher than most of the state-of-the-art membranes. Importantly, a 4-µm-thickness KANF membrane shows ultrahigh tensile strength (565 MPa) and Young's modulus (25 GPa). This generator also exhibits ultralong stability over 120 days, showing great potential in practical energy conversions.

Synthesis and Water Treatment Applications of Nanofibers by Electrospinning

In the past few decades, the role of nanotechnology has expanded into environmental remediation applications. In this regard, nanofibers have been reported for various applications in water treatment and air filtration. Nanofibers are fibers of polymeric origin with diameters in the nanometer to submicron range. Electrospinning has been the most widely used method to synthesize nanofibers with tunable properties such as high specific surface area, uniform pore size, and controlled hydrophobicity. These properties of nanofibers make them highly sought after as adsorbents, photocatalysts, electrode materials, and membranes. In this review article, a basic description of the electrospinning process is presented. Subsequently, the role of different operating parameters in the electrospinning process and precursor polymeric solution is reviewed with respect to their influence on nanofiber properties. Three key areas of nanofiber application for water treatment (desalination, heavy-metal removal, and contaminant of emerging concern (CEC) remediation) are explored. The latest research in these areas is critically reviewed. Nanofibers have shown promising results in the case of membrane distillation, reverse osmosis, and forward osmosis applications. For heavy-metal removal, nanofibers have been able to remove trace heavy metals due to the convenient incorporation of specific functional groups that show a high affinity for the target heavy metals. In the case of CECs, nanofibers have been utilized not only as adsorbents but also as materials to localize and immobilize the trace contaminants, making further degradation by photocatalytic and electrochemical processes more efficient. The key issues with nanofiber application in water treatment include the lack of studies that explore the role of the background water matrix in impacting the contaminant removal performance, regeneration, and recyclability of nanofibers. Furthermore, the end-of-life disposal of nanofibers needs to be explored. The availability of more such studies will facilitate the adoption of nanofibers for water treatment applications.

Alginate Hydrogel Assisted Controllable Interfacial Polymerization for High-Performance Nanofiltration Membranes

The deepening crisis of freshwater resources has been driving the further development of new types of membrane-based desalination technologies represented by nanofiltration membranes. Solving the existing trade-off limitation on enhancing the water permeance and the rejection of salts is currently one of the most concerned research interests. Here, a facile and scalable approach is proposed to tune the interfacial polymerization by constructing a calcium alginate hydrogel layer on the porous substrates. The evenly coated thin hydrogel layer can not only store amine monomers like the aqueous phase but also suppress the diffusion of amine monomers inside, as well as provide a flat and stable interface to implement the interfacial polymerization. The resultant polyamide nanofilms have a relatively smooth morphology, negatively charged surface, and reduced thickness which facilitate a fast water permeation while maintaining rejection efficiency. As a result, the as-prepared composite membranes show improved water permeance (~30 Lm⁻²h⁻¹bar⁻¹) and comparable rejection of Na₂SO₄ (>97%) in practical applications. It is proved to be a feasible approach to manufacturing high-performance nanofiltration membranes with the assist of alginate hydrogel regulating interfacial polymerization.

Preparation of lignosulfonate-based nanofiltration membranes with improved water desalination performance

Pulping and papermaking generate large amounts of waste in the form of lignosulfonates which have limited valorized applications so far. Herein, we report a novel lignosulfonate-based nanofiltration membrane, prepared by using polyethylenimine (PEI) and sodium lignosulfonate (SL) via a layer-by-layer (LbL) self-assembly. As a low-cost and renewable natural polyelectrolyte, SL is selected to replace the synthetic polyelectrolyte commonly used in the conventional LbL fabrication for composite membranes. The prepared LbL (PEI/SL)7 membranes were crosslinked by glutaraldehyde (GA) to obtain (PEI/SL)7-GA membranes with compact selective layer. We characterized (PEI/SL)7 and (PEI/SL)7-GA membranes to study the chemical compositions, morphologies, and surface hydrophilicity. To improve the nanofiltration performances of the (PEI/SL)7-GA membranes for water desalination, we investigated the effects of the crosslinking time, GA concentration and the NaCl supporting electrolyte on membrane structure and performance. The optimized (PEI/SL)7-GA membrane exhibited a permeating flux up to 39.6 L/(m2·h) and a rejection of 91.7% for the MgSO4 aqueous solution 2.0 g/L concentration, showing its promising potential for water desalination. This study provides a new approach to applying the underdeveloped lignin-based biomass as green membrane materials for water treatment.

Highly Permeable Polyamide Nanofiltration Membrane Mediated by an Upscalable Wet-Laid EVOH Nanofibrous Scaffold

For energy-saving purposes, the pursuit of ultrahigh permeance nanofiltration membranes without sacrificing selectivity is never-ending in desalination, wastewater treatment, and industrial product separation. Herein, we reported a novel facile route to engineer a highly porous and superhydrophilic nanofibrous substrate to mediate the interfacial polymerization between trimesoyl chloride and piperazine, generating an ultrathin PA active layer (∼13 nm) with a hierarchical crumpled surface. The wet laying process and subsequent plasma treatment endowed a rougher and more hydrophilic surface for ethylene vinyl alcohol copolymer (EVOH) nanofibers in the thin compact nanofibrous scaffold (∼9 μm) with a mean pore size of 210 nm, radically different from the nanofibrous membrane by other methods. Nanofibrous scaffold with these features provide abundant thin-thick alternative continuous water layers between nanofibers and organic phase, facilitating the formation of the abovementioned PA layer. As a result, an ultrahigh permeance of 42.25 L·m^-2 h^-1 bar^-1 and a reasonably high rejection of 95.97% to 1000 ppm Na₂SO₄ feed solution were obtained, superior to most state-of-the-art NF membranes reported so far. Our work provides an easy and scalable method to fabricate advanced PA NF membranes with outstanding performance, highlighting its great potential in liquid separation.

Fabrication of Antiswelling Loose Nanofiltration Membranes via a "Selective-Etching-Induced Reinforcing" Strategy for Bioseparation

With diverse selectivity, higher permeance, and good antifouling property, loose polyamide nanofiltration (NF) membranes can be potentially deployed in various bioseparation applications. However, the loose NF membrane with a low crosslinking degree generally suffers from the alkali-induced pore swelling during chemical cleaning, resulting in degradation of separation performance with time. In this work, we conceive a novel strategy to tailor the separating layer through alkaline post-etching following the interfacial polymerization process, where piperazine and tannic acid (TA) were used as water-phase monomers, and trimesoyl chloride (TMC) and ferric acetylacetonate were employed as organic monomers in n-hexane. Thereinto, the polyester network formed by TA and TMC was selectively etched by alkaline treatment, thus obtaining a loose NF membrane, whose structure and performance could be facilely tailored by controlling the TA ratio and the etching pH. As a result, the well-designed loose NF membrane exhibited higher flux, better selectivity, and more stable separation performance in a long-term filtration of diluted cane molasses. Interestingly, the obtained loose NF membrane showed excellent antiswelling ability during alkaline cleaning because of network locking induced by Fe³⁺ chelation, decrease in the carboxyl proportion (more hydroxyl generation due to the ester bond hydrolysis), and enhanced interface interaction between the separation layer and the sublayer attributed to catechol adhesion effect. Therefore, such a "selective-etching-induced reinforcing" strategy could endow the polyamide NF membrane with both loose and antiswelling separation layer in a reliable and scalable way, which provides a new perspective for preparing highly selective and stable NF membrane for resource recovery.

Green Approaches for Sustainable Development of Liquid Separation Membrane

Water constitutes one of the basic necessities of life. Around 71% of the Earth is covered by water, however, not all of it is readily available as fresh water for daily consumption. Fresh water scarcity is a chronic issue which poses a threat to all living things on Earth. Seawater, as a natural resource abundantly available all around the world, is a potential water source to fulfil the increasing water demand. Climate-independent seawater desalination has been touted as a crucial alternative to provide fresh water. While the membrane-based desalination process continues to dominate the global desalination market, the currently employed membrane fabrication materials and processes inevitably bring adverse impacts to the environment. This review aims to elucidate and provide a comprehensive outlook of the recent efforts based on greener approaches used for desalination membrane fabrication, which paves the way towards achieving sustainable and eco-friendly processes. Membrane fabrication using green chemistry effectively minimizes the generation of hazardous compounds during membrane preparation. The future trends and recommendations which could potentially be beneficial for researchers in this field are also highlighted.

Composite Aramid Membranes with High Strength and pH-Response

The pH-responsive membrane is a new wastewater treatment technology developed in recent years. In this paper, a novel film with intelligent pH-responsiveness was first prepared by blending functional gates comprised of hydrolyzed aramid nanofibers (HANFs) into aramid nanofiber (ANF) membranes via a vacuum filtration method. Those as-prepared membranes exhibited dual pH-responsive characteristics, which were featured with a negative pH-responsiveness in an acidic environment and a positive pH-responsiveness in basic media. These dual pH-responsive membranes also exhibited a high tensile strength which could still reach 55.74 MPa (even when the HANFs content was as high as 50 wt%), a high decomposition temperature at ~363 °C, and good solvent resistance. The membranes described herein may be promising candidates for a myriad of applications, such as the controlled release of drugs, sensors, sewage treatment, etc.

Polydopamine-Assisted Two-Dimensional Molybdenum Disulfide (MoS2)-Modified PES Tight Ultrafiltration Mixed-Matrix Membranes: Enhanced Dye Separation Performance

Tight ultrafiltration (TUF) membranes with high performance have attracted more and more attention in the separation of organic molecules. To improve membrane performance, some methods such as interface polymerization have been applied. However, these approaches have complex operation procedures. In this study, a polydopamine (PDA) modified MoS₂ (MoS₂@PDA) blending polyethersulfone (PES) membrane with smaller pore size and excellent selectivity was fabricated by a simple phase inversion method. The molecular weight cut-off (MWCO) of as-prepared MoS₂@PDA mixed matrix membranes (MMMs) changes, and the effective separation of dye molecules in MoS₂@PDA MMMs with different concentrations were obtained. The addition amount of MoS₂@PDA increased from 0 to 4.5 wt %, resulting in a series of membranes with the MWCO values of 7402.29, 7007.89, 5803.58, 5589.50, 6632.77, and 6664.55 Da. The MWCO of the membrane M3 (3.0 wt %) was the lowest, the pore size was defined as 2.62 nm, and the pure water flux was 42.0 L m⁻² h⁻¹ bar⁻¹. The rejection of Chromotrope 2B (C2B), Reactive Blue 4 (RB4), and Janus Green B (JGB) in aqueous solution with different concentrations of dyes was better than that of unmodified membrane. The separation effect of M3 and M0 on JGB at different pH values was also investigated. The rejection rate of M3 to JGB was higher than M0 at different pH ranges from 3 to 11. The rejection of M3 was 98.17–99.88%. When pH was 11, the rejection of membranes decreased with the extension of separation time. Specifically, at 180 min, the rejection of M0 and M3 dropped to 77.59% and 88.61%, respectively. In addition, the membrane had a very low retention of salt ions, Nacl 1.58%, Na₂SO₄ 10.52%, MgSO₄ 4.64%, and MgCl₂ 1.55%, reflecting the potential for separating salts and dyes of MoS₂@PDA/PES MMMs.

Removal of Different Dye Solutions: A Comparison Study Using a Polyamide NF Membrane

The removal of organic dyes in aquatic media is, nowadays, a very pressing environmental problem. These dyes usually come from industries, such as textiles, food, and pharmaceuticals, among others, and their harm is produced by preventing the penetration of solar radiation in the aquatic medium, which leads to a great reduction in the process of photosynthesis, therefore damaging the aquatic ecosystems. The feasibility of implementing a process of nanofiltration in the purification treatment of an aqueous stream with small size dyes has been studied. Six dyes were chosen: Acid Brown-83, Allura Red, Basic Fuchsin, Crystal Violet, Methyl Orange and Sunset Yellow, with similar molecular volume (from 250 to 380 Å). The nanofiltration membrane NF99 was selected. Five of these molecules with different sizes, shapes and charges were employed in order to study the behavior of the membrane for two system characteristic parameters: permeate flux and rejection coefficient. Furthermore, a microscopy study and a behavior analysis of the membrane were carried out after using the largest molecule. Finally, the Spiegler-Kedem-Katchalsky model was applied to simulate the behavior of the membrane on the elimination of this group of dyes.

Tuning the Ion-Selectivity of Thin-Film Composite Nanofiltration Membranes by Molecular Layer Deposition of Alucone

This work addresses a key challenge of tailoring the ion selectivity of a thin-film composite nanofiltration membrane to a specific application, such as water softening, without altering the water permeability. We modified the active surface of a commercial NF270 membrane by molecular layer deposition (MLD) of ethylene glycol-Al (EG-alucone). With increasing deposition cycles, we found that the MLD precursors first infiltrated and deposited in the active layer of NF270, then inflated the active layer, and finally deposited on the surface as a distinct EG-alucone layer. The deposition process changed the morphology of the membrane active layer and decreased the overall density of its fixed negative charge by embedding the positively charged EG-alucone. Filtration experiments revealed that these modifications affected the ion separation properties of the membrane without significantly hindering the water permeability. Specifically, the permeation of Na⁺ increased relative to that of Mg²⁺, as indicated by the permselectivity of Na⁺ salts over Mg²⁺ salts. The changes in permselectivities with an increasing number of MLD cycles were rationalized using the dielectric, steric, and electrostatic ion exclusion mechanisms, which are related to the membrane material, pore size, and fixed charge, respectively. These relations open a path for the rational design of nanofiltration membranes with tailored selectivity by tuning the properties of the MLD layer. Filtration results of natural brackish groundwater using the MLD modified membranes agreed with the single salt experiments. As a result, water hardness was 26% lower for the permeate obtained using the MLD-modified membranes, which were found stable even during a 24 h filtration run. These results highlight the practical potential of this approach in enhancing water softening efficiency.

High-performance nanofiltration membranes with a sandwiched layer and a surface layer for desalination and environmental pollutant removal

To overcome the permeability-selectivity limitation and improve the performance of desalination membranes, novel methods and design strategies are needed to prepare new types of thin film composite (TFC) nanofiltration (NF) membranes. In this work, a modified TFC membrane with a sandwiched layer and a surface layer was fabricated through a facile additional two-step approach. The microfiltration (MF) substrate and TFC surface were modified by a cellulose nanocrystal (CNC) sandwiched layer and a polydopamine (PDA) layer, respectively. Scanning electron microscopy (SEM) analysis indicated that the support modified by CNCs presented a more homogeneous surface than the control TFC. Cross-sectional SEM images showed that the underneath MF support, CNC interlayer, polyamide layer and PDA deposition layer were perfectly integrated. The surface charge was determined by an electrophoretic analyzer and revealed that the CNC interlayer increased the membrane electronegativity, while the PDA layer presented the opposite effect. Compared to the control TFC membrane, the solute permeability and rejection of the resultant CNC-TFC-PDA membrane were simultaneously increased, indicating a breakthrough in the trade-off limitation. The modified membranes exhibited a high removal rate for Congo red, Rose Bengal, sodium lignosulfonate and alkaline lignin, suggesting their excellent rejection performance for textile dyes and lignin derivatives. Fouling tests indicated that both the interlayer and surface layer exhibited positive effects on fouling alleviation. The effects of each functional layer were explored, and the main factors for performance improvement, including the modified hydrophilicity, surface charge, pore size and surface roughness, were discussed.

Functionalized electrospun nanofiber membranes for water treatment: A review

Electrospun nanofiber membranes (ENMs) have high porosity, high specific surface area and unique interconnected structure. It has huge advantages and potential in the treatment and recycling of wastewater. In addition, ENMs can be easily functionalized by combining multifunctional materials to achieve different water treatment effects. Based on this, this review summarizes the preparation of functionalized ENMs and its detailed application in the field of water treatment. First, the process and influence factors of electrospinning process are introduced. ENMs with high porosity, thin and small fiber diameter have better performance. Secondly, the modification methods of ENMs are analyzed. Pre-electrospinning and post-electrospinning modification technology can prepare specific functionalized ENMs. Subsequently, functionalized ENMs show water treatment capabilities such as separation, adsorption, photocatalysis, and antimicrobial. Subsequently, the application of functionalized ENMs in water treatment capabilities such as separation, adsorption, photocatalysis, and antimicrobial capabilities were listed. Finally, we also made some predictions about the future development direction of ENMs in water treatment, and hope this article can provide some clues and guidance for the research of ENMs in water treatment.

Flexible Aliphatic-Aromatic Polyamide Thin Film Composite Membrane for Highly Efficient Organic Solvent Nanofiltration

Membranes with strong solvent resistance and efficient molecular separation are desirable in industries. Especially the fractionation of organic molecules in harsh organic solvents still remains a challenge in the pharmaceutical industry. Here, we report a flexible aliphatic-aromatic polyamide thin-film composite (TFC) membrane with high stability, permeability, and precise selectivity in mild solvents as well as in polar aprotic solvents. This composite organic solvent nanofiltration (OSN) membrane integrates a cross-linked sub-100 nm nanofilm and a nanofibrous sublayer. The flexible aliphatic chains in the polyamide network render the selective layer with a tunable free volume in different organic solvents. Consistent with the solvent swelling degrees, the membrane shows a cutoff in a sequence of dimethyl sulfoxide (DMSO, MWCO: 814 g mol^-1) > N,N-dimethylformamide (DMF, MWCO: 648 g mol^-1) > methanol (MWCO: 506 g mol^-1, with DMF activation) > methanol (MWCO: 327 g mol^-1). The membrane can precisely fractionate two molecules with difference in molar mass of <166 g mol^-1 in a polar aprotic solvent, DMSO. Long-term filtration tests in DMF further demonstrate that the TFC membrane has an outstanding chemical stability and molecular selectivity in aggressive organic media. This work provides an efficient way to control OSN membrane separations by introducing flexible alkane chains into the rigid polymer structure followed by solvent activation. Additionally, the high permeance and excellent separation efficiency of the TFC membrane highlight its great potential for molecular separation in pharmaceutical and chemical industries.

Clean Water through Nanotechnology: Needs, Gaps, and Fulfillment

Sustainable nanotechnology has made substantial contributions in providing contaminant-free water to humanity. In this Review, we present the compelling need for providing access to clean water through nanotechnology-enabled solutions and the large disparities in ensuring their implementation. We also discuss the current nanotechnology frontiers in diverse areas of the clean water space with an emphasis on applications in the field and provide suggestions for future research. Extending the vision of sustainable and affordable clean water to environment in general, we note that cities can live and breathe well by adopting such technologies. By understanding the global environmental challenges and exploring remedies from emerging nanotechnologies, sustainability in clean water can be realized. We suggest specific pointers and quantify the impact of such technologies.

Development in Additive Methods in Aramid Fiber Surface Modification to Increase Fiber-Matrix Adhesion: A Review

This review article highlights and summarizes the recent developments in the field of surface modification methods for aramid fibers. Special focus is on methods that create a multifunctional fiber surface by incorporating nanostructures and enabling mechanical interlocking. To give a complete picture of adhesion promotion with aramids, the specific questions related to the challenges in aramid-matrix bonding are also shortly presented. The main discussion of the surface modification approaches is divided into sections according to how material is added to the fiber surface; (1) coating, (2) grafting and (3) growing. To provide a comprehensive view of the most recent developments in the field, other methods with similar outcomes, are also shortly reviewed. To conclude, future trends and insights are discussed.

Phosphonium Modification Leads to Ultrapermeable Antibacterial Polyamide Composite Membranes with Unreduced Thickness

Water transport rate in network membranes is inversely correlated to thickness, thus superior permeance is achievable with ultrathin membranes prepared by complicated methods circumventing nanofilm weakness and defects. Conferring ultrahigh permeance to easily prepared thicker membranes remains challenging. Here, a tetrakis(hydroxymethyl) phosphonium chloride (THPC) monomer is discovered that enables straightforward modification of polyamide composite membranes. Water permeance of the modified membrane is ≈6 times improved, give rising to permeability (permeance × thickness) one magnitude higher than state-of-the-art polymer nanofiltration membranes. Meanwhile, the membrane exhibits good rejection (R_Na2SO4 = 98%) and antibacterial properties under crossflow conditions. THPC modification not only improves membrane hydrophilicity, but also creates additional angstrom-scale channels in polyamide membranes for unimpeded transport of water. This unique mechanism provides a paradigm shift in facile preparation of ultrapermeable membranes with unreduced thickness for clean water and desalination.

Custom-Tailoring Loose Nanofiltration Membrane for Precise Biomolecule Fractionation: New Insight into Post-Treatment Mechanisms

Loose nanofiltration (NF) membranes with diverse selectivity can meet the great demands in various bioseparation applications. Thus, a facile strategy to tune the properties such as pore size, surface charge, and hydrophilicity of the NF membrane is required to produce tailor-made loose NF membranes without changing the existing production line. Herein, we systematically investigated the post-treatment of the nascent poly(piperazine amide) NF membranes using different reagents (organic acids, weak bases, organic solvents and ionic liquid (IL)). Various characterizations revealed that the skin/separation layer became looser and permeance was promoted with the decrease of salt rejection in varying degrees. It was found that the O/N ratio did not rigorously represent the cross-linking degree of the skin layer, because besides the hydrolysis of the residual acyl chloride impeding the amido bond formation, the breaking of existing amido bonds and the grafting of free trimesoyl chloride molecules on the nascent membranes could also increase the O/N ratio during post-treatments. Then three mechanisms including hydrolysis, swelling rearrangement and capping reaction effects were proposed to better understand the membrane properties variations. All these effects resulted in larger pore size of the NF membrane, and the hydrolysis/capping effect might increase negative charge and hydrophilicity on the membrane, while the swelling rearrangement could produce less defective skin structure. These three effects might be involved together during a single treatment. Finally, the NF membrane post-treated by N-hexane could efficiently separate antibiotics and NaCl with the highest permeate flux, whereas the one post-treated by ionic liquid outperformed others for the decoloration of cane molasses (much more efficient than NF270, DL, and NTR7450 membranes). The long-term operating stability of the post-treated membranes selected was also confirmed by a continuous crossflow filtration for 15 h with regular alkaline cleaning.

Organic Liquid Mixture Separation Using an Aliphatic Polyketone-Supported Polyamide Organic Solvent Reverse Osmosis (OSRO) Membrane

Energy-efficient membrane technology has received tremendous attention for the separation of organic molecules; however, the separation of molecules of less than 100 Da has remained challenging. Herein, a membrane fabricated from interfacial polymerization on a polyketone support was used as an organic solvent reverse osmosis (OSRO) membrane for the separation of organic liquid mixtures. The chemically stable and highly cross-linked selective layer exhibited outstanding separation factors toward large nonpolar molecules from small polar ones with high fluxes. For example, separation factors of 8.4, 11.1, 14.9, and 38.0 were achieved toward toluene, pentane, hexane, and heptane (10 wt % in mixtures), respectively, from methanol solution at 3 MPa, with fluxes around 5 LMH. This membrane outperformed the currently available reverse osmosis membrane and organic solvent nanofiltration membranes in terms of stability and separation factor. This work promotes the development of OSRO separation of organic liquid mixtures without phase change.