When self-assembly meets interfacial polymerization

Carboxyl-free polyamide reverse osmosis membrane with sustainable anti-fouling performance in treating industrial coke wastewater

Carboxyl groups in polyamide (PA) reverse osmosis (RO) membrane contribute significantly to fouling and scaling, hindering the sustainable operation of RO in practical applications. Herein, we developed a novel interfacial polymerization (IP) strategy to finely engineer the molecular structure of PA with no carboxyl groups, and to significantly enhance RO membrane fouling/scaling-resistance. During IP, trimesoyl chloride (TMC) at the interface was consumed completely by the diffused m-phenylenediamine (MPD) and glycerol (GLY) under the assistance of benzalkonium chloride (BAC) surfactant. The fabricated RO membrane with no carboxyl groups exhibits sustainable anti-fouling performance with low flux decline ratios and high flux recovery ratios during the five cycles of fouling and cleaning when treating real coke wastewater, surpassing the reported anti-fouling membranes and the renowned commercial fouling-resistant RO membrane (DuPont FilmTec™ CR100). This work provides some insights to precisely tailor the molecular structure of PA RO membrane with sustainable anti-fouling performance.

Seamless incorporation of artificial water channels in defect-free polyamide membrane for desalination of brackish water

Artificial water channels (AWCs) show the potential for overcoming the permeability-selectivity tradeoff of polyamide (PA) membranes. However, the availability of biomimetic materials and limitations posed by fabrication-induced defects make the development of AWC-PA membranes a daunting task. Herein, we synthesize imidazolylethyl-ureidoethyl-phenyl (IUP) compounds to form AWC by self-assembling and provide a strategy to seamlessly incorporate AWC in defect-free PA membranes. IUP compounds are molecularly designed with enhanced nature to form AWC due to π-π stacking interactions. In addition, nanosized colloid AWC aggregates can be obtained in water directly with the aid of sodium dodecyl sulfate (SDS) and conveniently incorporated into PA layers. The AWC not only promotes the preferential selective passage of water but also exhibits good compatibility with the surrounding PA matrix. The biomimetic membranes demonstrate a water permeance of 4.3 L·m-2·h-1·bar-1 and NaCl rejection of 99.3%, much higher than that observed with marketed state-of-the-art membranes. Mechanism understanding reveals that the compatible interaction between AWC, SDS and PA matrix is a necessary requisite to fabricate defect-free AWC-PA layers. This strategy can be easily extended to industrial scale and the biomimetic membranes may represent the development direction of the next generation of high-performance reverse osmosis membranes.

Nodular networks in hydrated polyamide desalination membranes enhance water transport

For nearly half a century, thin-film composite reverse osmosis membranes have served as key separation materials for desalination. However, the precise structure of their polyamide selective layer under hydrated conditions and its relationship to membrane transport remain poorly understood. Using cryo-electron tomography, we successfully reconstructed the three-dimensional structure of six commercial polyamide membranes under hydrated conditions, revealing a fully swollen nodular network. The highly heterogeneous nodules, measuring 17.2 ± 2.8 nanometer in thickness, were directly connected to the pores of the underlying polysulfone substrate. The nodules occupied most of the surface area compared to the 75.9 ± 26.8-nanometer-thick dense layer of the polyamide film. Key structural parameters of the nodules, including surface area index and wall thickness, were correlated with the water permeance of an additional 16 polyamide membranes, validating the major role of these nodules in water transport. This study enhances our understanding of the heterogeneous structure of desalination membranes and its role in membrane transport.

Advanced fabrication and characterization of thin-film composite polyamide membranes for superior performance in reverse osmosis desalination

Thin film composite (TFC) polyamide membranes are crucial for efficient reverse osmosis (RO) desalination, offering high selectivity and permeability. This study investigates the fabrication and optimization of TFC membranes on polysulfone supports, focusing on their structural, morphological, and performance properties for enhanced desalination efficiency using the phase inversion technique, a method that enables precise control over membrane structure. Key fabrication parameters including the concentrations of m-phenylene diamine (MPD) and trimesoyl chloride (TMC), and the immersion times for both monomers were systematically varied to investigate their impact on membrane hydrophilicity, morphology, and structure. Hydrophilicity was assessed via contact angle measurements, Scanning electron microscopy was used to characterize the morphology (SEM), and structural properties were analyzed by Fourier-transform infrared spectroscopy (FTIR). The RO membranes' desalination performance was evaluated by measuring water flux and salt rejection in a cross-flow setup with saline water (10,000 ppm) under controlled processing conditions. Results indicated that variations in MPD and TMC concentrations, as well as immersion times, significantly influenced membrane hydrophilicity and pore structure, affecting water flux and salt rejection. The maximum salt rejection and water flux for the prepared thin film composite reverse osmosis membrane were 98.6% and 19.1 L/m2 h, respectively obtained at m-phenylenediamine concentration of 2 wt% and tri mesoyl chloride concentration of 0.1 wt/v reacted for 1 min. The study provides insights into optimizing TFC-RO membrane fabrication parameters to enhance desalination efficiency, highlighting the potential of these membranes for high-performance RO desalination applications.

Nanomorphogenesis of interlayered polyamide membranes for precise ion sieving in lithium extraction

Nanofiltration (NF) offers a scalable and energy-efficient method for lithium extraction from salt lakes. However, the selective separation of lithium from magnesium, particularly in brines with high magnesium concentrations, remains a significant challenge due to the close similarity in their hydrated ionic radii. The limited Li+/Mg2+selectivity of current NF membranes is primarily attributed to insufficient control over pore size and surface charge. In this study, we report the development of an interlayered thin-film composite (iTFC) membrane incorporating functionalized sulfonated carrageenan to regulate the interfacial polymerization process. This integrated interlayer plays a crucial role in controlling the diffusion and spatial distribution of amine monomers, leading to the formation of dense, nano-striped polyamide networks. These structural improvements including refined pore size and reduced negative charge significantly enhanced Li+/Mg2+selectivity (133.5) and increased permeance by 2.5 times compared to conventional TFC membranes. Additionally, the nano-striped structure optimized the membrane filtration area while minimizing ion transport resistance, effectively overcoming the traditional trade-off between ion selectivity and permeability. This study highlights the potential of iTFC membranes for achieving both high lithium purity and recovery, offering a promising avenue for large-scale lithium extraction from brines.

Nanofiltration membranes with fast water transport induced by controlled interfacial diffusion to enhance desalination and micropollutant removal

Nanofiltration (NF) membranes offer tremendous potential in wastewater reuse, desalination, and resource recovery to alleviate water scarcity and environmental contamination. However, separating micropollutants and charged ions from wastewater while maintaining high water permeation remains challenging for conventional NF membranes. Customizing diffusion and interaction behavior of monomers at membrane-forming interfaces is promising for regulating interior pore structures and surface morphology properties for polyamide NF membranes, reaching efficient screening and retaining of solutes from water. In this work, photopolymerization occurred on two-phase interfaces of interfacial polymerization to modulate monomer diffusion toward reaction interfaces, accelerating reaction process and narrowing reaction area thus improving interior pore uniformity and free-volume regularity. Density distributions and interactive energies of monomers at the interface were explored to illustrate the effect of monomer diffusive behavior regulated by photopolymerization on membrane physicochemical properties and separation performance through molecular dynamics simulations. Pore size distributions were simulated to verify experimental results. Layers of nodules and rod-like structures appeared on the membrane surfaces. Membranes with interface photopolymerization exhibited a water permeability of 46.0 L·m-2·h-1·bar-1 more than five-fold that of the control, with improved monovalent and multivalent ions separation. Surface photopolymerized membranes with water permeation of 26.6 L·m-2·h-1·bar-1 (more than three times as high as the control) achieved excellent micropollutant and salt removal. This work provides a foundation for constructing NF membranes with specific separation functions for environmental applications.

Fabrication of Self-Standing Inorganic-Organic Composite Films at a Miscible Interface by "Soft Spray" Technique

Membranes have extensive applications in catalysis, separation, antimicrobial activities, and sensing. However, developing a simple and environmentally friendly method for preparing membranes remains challenging. Here, we report a novel strategy for fabricating self-standing inorganic-organic composite films at the miscible liquid/liquid interface using a soft spray technique. Specifically, metal salt solutions are sprayed onto the interface between an alkaline poly(vinyl alcohol) (PVA) solution to form heterogeneous metal hydroxide/PVA composite films with PVA as the supporting substrate. The preparation method is simple, easy to manipulate, environmentally friendly, and resource-efficient. It has been extended to prepare metal phosphate/PVA, metal carbonate/PVA, and metal sulfide/PVA composite films. Notably, the copper hydroxide/PVA (Cu(OH)2/PVA) composite films exhibit exceptional tensile strength (19.0 MPa) and remarkable antimicrobial properties (99.9%). This simple soft spray-assisted technique provides a novel approach for fabricating miscible interface composite films.

Reverse Osmosis Membrane Engineering: Multidirectional Analysis Using Bibliometric, Machine Learning, Data, and Text Mining Approaches

Membrane engineering is a complex field involving the development of the most suitable membrane process for specific purposes and dealing with the design and operation of membrane technologies. This study analyzed 1424 articles on reverse osmosis (RO) membrane engineering from the Scopus database to provide guidance for future studies. The results show that since the first article was published in 1964, the domain has gained popularity, especially since 2009. Thin-film composite (TFC) polymeric material has been the primary focus of RO membrane experts, with 550 articles published on this topic. The use of nanomaterials and polymers in membrane engineering is also high, with 821 articles. Common problems such as fouling, biofouling, and scaling have been the center of work dedication, with 324 articles published on these issues. Wang J. is the leader in the number of published articles (73), while Gao C. is the leader in other metrics. Journal of Membrane Science is the most preferred source for the publication of RO membrane engineering and related technologies. Author social networks analysis shows that there are five core clusters, and the dominant cluster have 4 researchers. The analysis of sentiment, subjectivity, and emotion indicates that abstracts are positively perceived, objectively written, and emotionally neutral.

Bubble Drainage Assisted Fabrication of Polyamide Membranes with Crater-like Structures for Efficient Desalination

Bubble drainage (BD) occurs in various natural phenomena and industrial activities, in which bubbles rise toward the water surface and create a progressively thinned two-sided liquid film, called a lamella. Surfactant, as an important regulator in the BD process, not only assembles on both sides of the lamellae, generating a configuration of lamellae sandwiched by monolayers of surfactants (lamellae/MS), but also induces interfacial deformation by lowering interfacial tension. Herein, we developed a strategy of BD assisted interfacial polymerization for the fabrication of polyamide (PA) membranes. The regulated interfacial deformation at the water-oil interface produced a membrane with crater-like structures, which greatly increased the surface area of the PA membrane. Moreover, the lamellae/MS configuration served as a reservoir to spontaneously enrich amine monomers and thus modulate the diffusion-reaction kinetics. The resulting PA membranes exhibited superior separation performance with a water permeance of 44.7 L m-2 h-1 bar-1 and a Na2SO4 rejection of 99.2%.

Supramolecular Electronics: Monolayer Assembly of Nonamphiphilic Molecules via Water Surface-Assisted Molecular Deposition

Utilizing softly confined self-assembly at the water surface represents a promising approach for the fabrication of two-dimensional molecular monolayers (2D MMs), which have predominantly been concentrated on amphiphilic organic compounds before. Herein, we introduce a straightforward method termed "water surface-assisted molecular deposition (WSAMD)" to organize nonamphiphilic molecules into dense monolayers with high reproducibility. To underscore the versatility and merit of this methodology in the field of supramolecular electronics, we have successfully fabricated a range of defect-free, uniform semiconducting polymer monolayers, featuring a thickness reflective of molecular architectures. The charge carrier mobility could reach 0.05 cm2 V-1 s-1 for holes and 3.5 × 10-4 cm2 V-1 s-1 for electrons, respectively, in p-type and n-type polymeric monolayers when tested as the active layer in field-effect transistors. Furthermore, in situ polymerization reactions can be exploited to generate conductive monolayers of macromolecules such as polybenzylaniline (PBnANI) and polypyrrole (PPy), where PBnANI monolayers exhibit channel length-dependent conductivity, up to 0.37 S cm-1. The advent of the WSAMD method heralds a significant leap forward in the advancement of molecular 2D materials, catalyzing new avenues of exploration within material chemistry.

Chaperone solvent-assisted assembly of polymers at the interface of two immiscible liquids

The assembly of polymers at liquid-liquid interfaces offers a promising strategy for fabricating two-dimensional polymer films. However, a significant challenge arises when the polymers lack inherent interfacial traction. In response, we introduce an approach termed chaperone solvent-assisted assembly. This approach utilizes a target polymer, X, along with three solvents: α, β, and γ. α and β are poor solvents for X and immiscible with each other, while γ is a good solvent for X and miscible with both α and β, thus serving as the chaperone solvent. The cross-interface diffusion of γ induces the assembly of interfacially nonactive X at the α-β interface, and this mechanism is verified through systematic in situ and ex situ studies. We show that chaperone solvent-assisted assembly is versatile and reliable for the interfacial assembly of polymers, including those that are interfacially nonactive. Several practical applications based on chaperone solvent-assisted assembly are also demonstrated.

An investigation of a strengthening polysaccharide interfacial membrane strategy utilizing an anionic polysaccharide-alkaline ligand interfacial assembly for all-liquid printing

The applications of polysaccharides as emulsifiers are limited due to the lack of hydrophobicity. However, traditional hydrophobic modification methods used for polysaccharides are complicated and involve significant mechanical and thermal losses. In this study, soy hull polysaccharide (SHP) and terminally aminopropylated polydimethylsiloxane (NPN) were selected to investigate the feasibility of a simple and green interfacial membrane strengthening strategy based on the interfacial polymerization of anionic polysaccharides and fat-soluble alkaline ligands. Our results show that deprotonated SHP and protonated NPN can be complexed at the water/oil (W/O) interface, reduce interfacial tension, and form a strong membrane structure. Moreover, they can quickly form a membrane at the W/O interface upon the moment of contact to produce stable all-liquid printing products with complex patterns. However, the molecular weight of NPN affects the complexation reaction. Consequently, this study has long-term implications to expanding the areas of application for anionic polysaccharides.

Empowering ultrathin polyamide membranes at the water-energy nexus: strategies, limitations, and future perspectives

Membrane-based separation is one of the most energy-efficient methods to meet the growing need for a significant amount of fresh water. It is also well-known for its applications in water treatment, desalination, solvent recycling, and environmental remediation. Most typical membranes used for separation-based applications are thin-film composite membranes created using polymers, featuring a top selective layer generated by employing the interfacial polymerization technique at an aqueous-organic interface. In the last decade, various manufacturing techniques have been developed in order to create high-specification membranes. Among them, the creation of ultrathin polyamide membranes has shown enormous potential for achieving a significant increase in the water permeation rate, translating into major energy savings in various applications. However, this great potential of ultrathin membranes is greatly hindered by undesired transport phenomena such as the geometry-induced "funnel effect" arising from the substrate membrane, severely limiting the actual permeation rate. As a result, the separation capability of ultrathin membranes is still not fully unleashed or understood, and a critical assessment of their limitations and potential solutions for future studies is still lacking. Here, we provide a summary of the latest developments in the design of ultrathin polyamide membranes, which have been achieved by controlling the interfacial polymerization process and utilizing a number of novel manufacturing processes for ionic and molecular separations. Next, an overview of the in-depth assessment of their limitations resulting from the substrate membrane, along with potential solutions and future perspectives will be covered in this review.

Self-assembly morphology transition mechanism of similar amphiphilic molecules

Molecular self-assembly is a powerful synthesis method for nanomaterials. Promoting the development of self-assembly is not only conducive to the efficient preparation of nanomaterials but also promotes progress in other research fields. Therefore, it is necessary to enhance the advancement of molecular self-assembly, and the key is to deepen the understanding of the correlation between molecular characteristics and self-assembly morphologies. However, some similar amphipihlic molecules self-assemble into assemblies with significant morphology difference, which is challenging to clear the mechanism for experimenters. In this work, we explore the microscopic mechanism of six similar molecules by MD simulations, and the influences of molecular conformation, atomic groups, and polycyclic aromatic hydrocarbons on morphologies are discussed in detail. Our findings enrich the design principles of amphiphilic molecules for self-assembly, which promotes the modular design of molecular self-assembly.

Water-Assisted Programmable Assembly of Flexible and Self-Standing Janus Membranes

Janus membranes with asymmetric wettability have been considered cutting-edge for energy/environmental-sustainable applications like water/fog harvester, breathable skin, and smart sensor; however, technical challenges in fabrication and accurate regulation of asymmetric wettability limit their development. Herein, by using water-assisted hydrogen-bonded (H-bonded) assembly of small molecules at water/oil interface, a facile strategy is proposed for one-step fabrication of membranes with well-regulable asymmetric wettability. Asymmetric orderly patterns, beneficial for mass transport based on abundant high-permeability sites and large surface area, are constructed on opposite membrane surfaces. Upon tuning water-assisted H-bonding via H-sites/configuration design and temperature/pH modulation, double-hydrophobic, double-hydrophilic, and hydrophobic-hydrophilic membranes are facilely fabricated. The Janus membranes show smart vapor-responsive curling and unidirectional water transport with promising flux of 1158±25 L m-2  h-1 under natural gravity and 31500±670 L·(m-2  h-1  bar-1 ) at negative pressure. This bottom-up approach offers a feasible-to-scalable avenue to precise-manipulation of Janus membranes for advanced applications, providing an effective pathway for developing tailor-made self-assembled nanomaterials.

Effect of Polydopamine/Sodium Dodecyl Sulfate Modified Halloysite on the Microstructure and Permeability of a Polyamide Forward Osmosis Membrane

Mine water cannot be directly consumed by trapped people when a mine collapses, so it is difficult for people to carry out emergency rescues to ensure their safety. Therefore, a water bag made of a forward osmosis (FO) membrane has been designed that can efficiently filter coal mine water to meet the urgent needs of emergency rescue. Before interfacial polymerization (IP), sodium-dodecyl-sulfate-modified halloysite (SDS-HNT) was added to an MPD aqueous solution to prepare an SDS-HNT polyamide active layer, and then the prepared membrane was placed into a polydopamine (PDA) solution formed by the self-polymerization of dopamine and a PDA/SDS-HNT composite film was prepared. The results showed that the original ridge-valley structure of the polyamide membrane was transformed to a rod-, circular-, and blade-like structure by the addition of SDS-HNTs. Subsequently, a dense PDA nanoparticle layer was formed on the modified membrane. The polyamide/polysulfone forward osmosis membrane modified by co-doping of PDA and SDS-HNTs displayed both the best water flux and rejection rate, confirming the synergistic effect of compound modification. Therefore, the high-performance permeability of the polyamide membrane modified by SDS-HNTs and PDA provides great convenience for the emergency filtration of coal mine water, and also has potential applications in wastewater treatment and seawater desalination.