Microstructure optimization of bioderived polyester nanofilms for antibiotic desalination via nanofiltration

Fabrication of hydrophilic defective MOF-801 thin-film nanocomposite membranes via interfacial polymerization for efficient chromium removal from water

Addressing the challenge of utilizing defect-rich MOFs as materials for thin-film nanocomposite membranes functional layers, particularly to expose more pores and functional sites to enhance pollutant selectivity, is a critical scientific issue in the current field of nanofiltration. In this study, we have innovatively employed modulators and ultrasonic techniques to synthesize a highly defective, hydrophilic MOF-801. This was then incorporated into a polyamide (PA) functional layer on a PVDF substrate through interfacial polymerization, creating a membrane specifically designed for chromium separation. Advanced characterization techniques confirmed that the PA@DMOF-801 membrane exhibits a distinct interlayer water channel structure, which facilitates the complete exposure of functional sites due to the open nature of the pores. The findings reveal that the resulting membrane exhibits pronounced hydrophilic pore characteristics, achieving a permeability coefficient of 14.5 L m-2 h-1 bar-1 and a Cr3+ retention rate of 98 % for ions with larger hydrated radii, along with high separation efficiency. The hydrophilic sites and porous features exposed by defects ensure the membrane excels in both permeability and selectivity. The primary contribution of this work lies in demonstrating that increasing MOF defect sites enhances the membrane's functional layer more significantly than any potential drawbacks, providing valuable insights for future research on exploiting MOF defects in membrane development.

A molecularly engineered large-area nanoporous atomically thin graphene membrane for ion separation

Atomically thin graphene membranes with sub-1-nm pores show promise for ion/molecular separation, osmotic energy generation, and energy storage. Narrowing the pore size distribution and controlling the surface charge are essential to achieve these applications. However, nanoporous graphene membranes fabricated via conventional methods possess a broad pore size distribution and inadequately regulated surface charge, limiting their applications. Herein, we present a molecular anchoring approach for scalable synthesis of nanoporous graphene membranes via a bottom-up technique, aiming to narrow the pore size distribution without reducing the pore density while simultaneously adjusting the charge properties of nanopores. By selecting suitable anchoring molecules, the custom-tailored pore size distribution and chemical functionality of nanoporous graphene membranes can be achieved. Leveraging the steric restriction effect, anchoring monomers selectively traverse larger nanopores to form ion-selective plugs, effectively repairing these nanopores. The centimeter-scale nanoporous graphene membrane with an ion-selective plug achieves high separation selectivity (K+/Na+=20, K+/Mg2+=330). Theoretical simulations indicate that a smaller pore size, narrow pore size distribution, and positive charge result in a larger energy barrier difference, leading to ultrahigh metal ion selectivity. Furthermore, in treating lithium battery leaching solutions, Li+/divalent ions selectivity exceeds 900. These findings provide a way for designing graphene-based membranes.

Dynamic Short Hydrogen-Bonding Network Enhancing Hydrophilicity in Biomimetic Membranes with Artificial Water Channels for Efficient Removal of Dyes and Salts

The development of an integrated biomimetic membrane capable of rejecting both dyes and salts in a single step, while sustaining stable water permeation, presents a promising solution for textile wastewater treatment. Herein, we report a novel integrated biomimetic membrane integrating an I-quartet artificial water channel (AWC) with sulfonic acid-modified polyamide (PA-SO3H), which can stably reject both dyes and inorganic salts. The I-quartet channels (2.68 Å), formed via self-assembly of alkyl-ureido-ethyl-imidazole (HC8) molecules, facilitate selective water transport and rejection of both dyes and inorganic salts. Concurrently, the sulfonic acid groups (-SO3H) could grab water molecules, forming dynamic short hydrogen-bonding network (O-H⋅⋅⋅O). These hydrogen bonds not only serve as jumping force, lowering the energy barrier for water transport through the alternating hydrophilic-hydrophobic matrix, but also act as an effective antifouling barrier, significantly reducing membrane fouling. The optimal HC83.0-PA-SO3H membrane exhibits a water permeance of 13.4 L m-2 h-1 MPa-1, approximately 2.7-fold higher than that of the pristine PA membrane, and both high dyes and salts rejection efficiency. Moreover, the membrane sustains stable antifouling characteristics throughout a 19-day endurance test. This innovative membrane design provides a promising solution for the efficient separation of both dyes and inorganic salts in textile wastewater treatment.

Advanced Adaptive Protein Membrane with Super-High Flux and Precise Molecular Sieving of Dyes from Salts

Precise separation of small organic molecules and electrolyte salts is critical for various industrial processes, necessitating advanced membranes with uniform pores. Proteins, as one typical nature polymer having the exactly same structure and molecular weight, offer a promising material for making such membranes. Here, hemoglobin (BHb) and lysozyme (Lyz) are utilized to fabricate precise nanofiltration membranes through amyloid-like co-assembly, triggered by Tris(2-carboxyethyl) phosphine. Molecular dynamics simulations reveal that BHb intercalates between Lyz molecules, enhancing tight assembly and reducing defects. The Lyz/BHb membrane exhibits a high void volume of 27.2% and achieves an exceptional permeance of 335 L m-2 h-1 bar-1. Amazingly, the Lyz/BHb membrane achieves ultra-selective molecular sieving of dyes and salts with an unparalleled high separation factor of 1.25 × 103 for the NaCl/Brilliant blue. The unique adaptive separation layer is formed by anchoring dye molecules into the larger pores and thus narrowing down the pore size distribution and enhancing electrostatic repulsion, endowing the membrane with a distinctive molecular sieving of dyes and salts. This study offers valuable insights to finely tailor the pore structure of the membrane by co-assembly of proteins and to significantly enhance the membrane perm-selectivity by creating an adaptive protein separation layer with a unique molecular sieving property.

Bioderived Polyarylester Nanofilms from Innovative Plant Materials for High-Efficient Organic Solvent Nanofiltration

The successful realization of thin film composite (TFC) organic solvent nanofiltration (OSN) membranes with high permeability and small solute selectivity for solute-solute separation to purify drugs in complex solution environments remains challenging in the pharmaceutical industry. Here, we present the preparation of high cross-linked TFC OSN membranes via interfacial polymerization (IP) utilizing phlorotannin, a plant-derived biomass phenolic compound, as a promising aqueous phase monomer. Benefiting from the presence of multiple cross-linking sites and twisted rigid structure in phlorotannin, nanofiltration membranes with excellent molecular selectivity and solvent permeability were successfully fabricated. This allowed for straightforward separation and purification of active pharmaceutical ingredients from intermediates. The membranes demonstrated remarkable stability over extended periods of operation and adaptability to a diverse array of solvent environments, making them a highly promising option for use in fine chemicals, biopharmaceuticals, and other fields.

Loose Polyester Nanofiltration Membrane Designed with Hydroxyl-Ammonium for Efficient Dye/Salt Separation

Efficient dye/salt separation poses a great challenge to nanofiltration (NF) membrane technology in the desalting sector of the dye synthesis industry. In this study, we fabricated a novel loose polyester NF membrane via an interfacial polymerization method using "hydroxyl-ammonium" biquaternary diethanolamine (MDET) and trimesoyl chloride. The molecular design of MDET provides a loose crosslinking network, showing high rejection of dyes and the passage of monovalent salt/divalent salt ions in the dye solution, exhibiting exceptional filtration efficiency with high selectivity. Furthermore, the membrane exhibits excellent operational stability for over 100 h, demonstrating superior antifouling properties and high resistance to chlorine. This study provides new insights into the role of dyes and mono- and divalent ions in desalination processes related to the dye synthesis industry.

Lignin alkali regulated interfacial polymerization towards ultra-selective and highly permeable nanofiltration membrane

Thin-film composite polyamide (TFC PA) membranes hold promise for energy-efficient liquid separation, but achieving high permeance and precise separation membrane via a facile approach that is compatible with present manufacturing line remains a great challenge. Herein, we demonstrate the use of lignin alkali (LA) derived from waste of paper pulp as an aqueous phase additive to regulate interfacial polymerization (IP) process for achieving high performance nanofiltration (NF) membrane. Various characterizations and molecular dynamics simulations revealed that LA can promote the diffusion and partition of aqueous phase monomer piperazine (PIP) molecules into organic phase and their uniform dispersion on substrate, accelerating the IP reaction and promoting greater interfacial instabilities, thus endowing formation of TFC NF membrane with an ultrathin, highly cross-linked, and crumpled PA layer. The optimal membrane exhibited a remarkable water permeance of 26.0 L m-2 h-1 bar-1 and Cl-/SO42- selectivity of 191.0, which is superior to the state-of-the-art PA NF membranes. This study provides a cost-effective scalable strategy for fabricating ultra-selective and highly permeable NF membrane for precise ion-ion separation and small organic compounds removal.

Physical and Chemical Dual Confinement Promotes Controllable Synthesis of Loose-Structured Azine-Linked Nanofilms for Fast Molecular Separation

Thin-film composite (TFC) membranes, featuring nanoscale film thickness and customizable pore structures, hold promise for solute-solute separations. However, achieving on-demand molecular sieving requires fine control over the membrane microstructure. Here, the concept of physical and chemical dual confinement (PCDC) is introduced to fabricate loose-structured TFC membranes via confined interfacial polymerization (IP). This concept leverages the synergistic effects of physically restricted monomer diffusion and a chemically inhibited reaction to achieve controlled nanofilm growth. Dorsal addition of the aqueous phase to the hydrogel reduces the diamine diffusion via electrostatic and H-bonding interactions within its nanopores. The prepassivation of hydrazine using acid protonation effectively weakens its ability for nucleophilic reactivity. This confined IP between twisted TFPA and short-chain hydrazine yielded loosely structured azine-linked nanofilms, which displayed a high permeability of 53.4 LMH bar-1 and effective differentiation of binary mixtures. This PCDC concept offers a useful guideline to finely tailor polymeric nanofilms for precise separations.

Tempospatially Confined Catalytic Membranes for Advanced Water Remediation

The application of homogeneous catalysts in water remediation is limited by their excessive chemical and energy input, weak regenerability, and potential leaching. Heterogeneous catalytic membranes (CMs) offer a new approach to facilitate efficient, selective, and continuous pollutant degradation. Thus, integrating membranes and continuous filtration with heterogeneous advanced oxidation processes (AOPs) can promote thermodynamic and kinetic mass transfers in spatially confined intrapores and facilitate diffusion-reaction processes. Despite the remarkable advantages of heterogeneous CMs, their engineering application is practically restricted due to the fuzzy design criteria for specific applications. Herein, the recent advances in CMs for advanced water remediation are critically reviewed and the design flow for tempospatially confined CMs is proposed. Further, state-of-the-art CM materials and their catalytic mechanisms are reviewed, after which the tempospatial confinement mechanisms comprising the nanoconfinement effect, interface effect, and kinetic mass transfer are emphasized, thus clarifying their roles in the construction and performance optimization of CMs. Additionally, the fabrication methods for CMs based on their catalysts and pore sizes are summarized and an overview of their application and performance evaluations is presented. Finally, future directions for CMs in materials research and water treatment, are presented.

Sustainable and ultrafast antibiotics removal, self-cleaning and disinfection with electroactive metal-organic frameworks/carbon nanotubes membrane

Although conventional nanofiltration (NF) membrane is widely applied in water treatment, it faces the challenges of insufficient selectivity toward emerging contaminants, low permeability and non-sustainable fouling control. Herein, a novel electroactive metal-organic frameworks/carbon nanotubes membrane was constructed by facile and green nanobubbles-mediated non-solvent-induced phase separation (NIPS) strategy for ultrafast antibiotics removal. It presented 3-fold to 100-fold higher permeability (101.3-105.7 L·h-1·m-2·bar-1) without compromising rejection (71.8 %-99.3 %) of common antibiotics (tetracycline, norfloxacin, sulfamethoxazole, sulfamethazine) than most commercial and state-of-the-art NF membranes. The separation mechanism was due to the synergy of loose selective layer with three-dimensional interconnected networks and UiO-66/CNTs with unique pore sieving and charge property. It also presented excellent antibiotics selectivity with high NaCl/tetracycline separation factor of 194 and CuCl2/tetracycline separation factor of 316 for remediation of antibiotics and heavy metal combined pollution. Meanwhile, it possessed efficient anti-fouling, antibacterial and electro-driven self-cleaning ability, which enabled sustainable fouling control and disinfection with short process, low energy and chemical consumption. Furthermore, potential application of UiO-66/CNTs membrane in wastewater reclamation was demonstrated by stable antibiotics rejection, efficient flux recovery and long-term stability over 260 h. This study would provide useful insights into removal of emerging contaminants from water by advanced NF membrane.

Microporous polyarylate membranes based on 3D phenolphthalein for molecular sieving

Thin-film composite (TFC) membranes have gradually replaced some traditional technologies in the extraction, separation, and concentration of high value-added pharmaceutical ingredients due to their controllable microstructure. Nevertheless, devising solvent-stable, scalable TFC membranes with high permeance and efficient molecule selectivity is urgently needed to improve the separation efficiency in the separation process. Here, we propose phenolphthalein, a commercial acid-base indicator, as an economical monomer for optimizing the micropore structure of selective layers with thickness down to 30 nanometers formed by in situ interfacial reactions. Molecular dynamics simulations indicate that the polyarylate membranes prepared using three-dimensional phenolphthalein monomers exhibit tunable microporosity and higher pore interconnectivity. Moreover, the TFC membranes show a high methanol permeance (9.9 ± 0.1 liters per square meter per hour per bar) and small molecular weight cutoff (≈289 daltons) for organic micropollutants in organic solvent systems. The polyarylate membranes exhibit higher mechanical strength (2.4 versus 0.8 gigapascals) compared to the traditional polyamide membrane.

Ultrafast Interfacial Self-Assembly toward Bioderived Polyester COF Membranes with Microstructure Optimization

The precise manipulation of the microstructure (pore size, free volume distribution, and connectivity of the free-volume elements), thickness, and mechanical characteristics of membranes holds paramount significance in facilitating the effective utilization of self-standing membranes. In this contribution, the synthesis of two innovative ester-linked covalent-organic framework (COF) membranes is first reported, which are generated through the selection of plant-derived ellagic acid and quercetin phenolic monomers in conjunction with terephthaloyl chloride as a building block. The optimization of the microstructure of these two COF membranes is systematically achieved through the application of three different interfacial electric field systems: electric neutrality, positive electricity, and negative electricity. It is observed that the positively charged system facilitates a record increase in the rate of membrane formation, resulting in a denser membrane with a uniform pore size and enhanced flexibility. In addition, a correlation is identified wherein an increase in the alkyl chain length of the surfactants leads to a more uniform pore size and a decrease in the molecular weight cutoff of the COF membrane. The resulting COF membrane exhibits an unprecedented combination of high water permeance, superior sieving capability, robust mechanical strength, chemical robustness for promising membrane-based separation science and technology.

Sequential high-recovery nanofiltration and electrochemical degradation for the treatment of pharmaceutical wastewater

The presence of antibiotics in aquatic ecosystems poses a significant concern for public health and aquatic life, owing to their contribution to the proliferation of antibiotic-resistant bacteria. Effective wastewater treatment strategies are needed to ensure that discharges from pharmaceutical manufacturing facilities are adequately controlled. Here we propose the sequential use of nanofiltration (NF) for concentrating a real pharmaceutical effluent derived from azithromycin production, followed by electrochemical oxidation for thorough removal of pharmaceutical compounds. The NF membrane demonstrated its capability to concentrate wastewater at a high recovery value of 95 % and 99.7 ± 0.2 % rejection to azithromycin. The subsequent electrochemical oxidation process completely degraded azithromycin in the concentrate within 30 min and reduced total organic carbon by 95 % in 180 min. Such integrated treatment approach minimized the electrochemically-treated volume through a low-energy membrane approach and enhanced mass transfer towards the electrodes, therefore driving the process toward zero-liquid-discharge objectives. Overall, our integrated approach holds promises for cost-effective and sustainable removal of trace pharmaceutical compounds and other organics in pharmaceutical wastewater.

Recycling and 3D-Printing Biodegradable Membranes for Gas Separation-toward a Membrane Circular Economy

Polymer membranes employed in gas separation play a pivotal role in advancing environmental sustainability, energy production, and gas purification technologies. Despite their significance, the current design and manufacturing of these membranes lack cradle-to-cradle approaches, contributing to plastic waste pollution. This study explores emerging solutions, including the use of biodegradable biopolymers such as polyhydroxybutyrate (PHB) and membrane recycling, with a focus on the specific impact of mechanical recycling on the performance of biodegradable gas separation membranes. This research represents the first systematic exploration of recycling biodegradable membranes for gas separation. Demonstrating that PHB membranes can be recycled and remanufactured without solvents using hot-melt extrusion and 3D printing, the research highlights PHB's promising performance in developing more sustainable CO2 separations, despite an increase in gas permeability with successive recycling steps due to reduced polymer molecular weight. The study emphasizes the excellent thermal, chemical, and mechanical stability of PHB membranes, albeit with a marginal reduction in gas selectivity upon recycling. However, limitations in PHB's molecular weight affecting extrudability and processability restrict the recycling to three cycles. Anticipating that this study will serve as a foundational exploration, we foresee more sophisticated recycling studies for gas separation membranes, paving the way for a circular economy in future membrane technologies.

Scalable Preparation of Ultraselective and Highly Permeable Fully Aromatic Polyamide Nanofiltration Membranes for Antibiotic Desalination

Membranes are important in the pharmaceutical industry for the separation of antibiotics and salts. However, its widespread adoption has been hindered by limited control of the membrane microstructure (pore architecture and free-volume elements), separation threshold, scalability, and operational stability. In this study, 4,4',4'',4'''-methanetetrayltetrakis(benzene-1,2-diamine) (MTLB) as prepared as a molecular building block for fabricating thin-film composite membranes (TFCMs) via interfacial polymerization. The relatively large molecular size and rigid molecular structure of MTLB, along with its non-coplanar and distorted conformation, produced thin and defect-free selective layers (~27 nm) with ideal microporosities for antibiotic desalination. These structural advantages yielded an unprecedented high performance with a water permeance of 45.2 L m-2 h-1 bar-1 and efficient antibiotic desalination (NaCl/adriamycin selectivity of 422). We demonstrated the feasibility of the industrial scaling of the membrane into a spiral-wound module (with an effective area of 2.0 m2). This module exhibited long-term stability and performance that surpassed those of state-of-the-art membranes used for antibiotic desalination. This study provides a scientific reference for the development of high-performance TFCMs for water purification and desalination in the pharmaceutical industry.

Energy-efficient trehalose-based polyester nanofiltration membranes for zero-discharge textile wastewater treatment

Recovery of water, salts, and hazardous dye from complex saline textile wastewater faces obstacles in separating dissolved ionic substances and recovering organic components during desalination. This study realized the simultaneous fractionation, desalination, and dye removal/recovery treatment of textile wastewater by using trehalose (Tre) as an aqueous monomer to prepare polyester loose nanofiltration (LNF) membrane with fine control microstructure via interfacial polymerization. Outperforming the NF270 commercial membrane, the Tre-1.05/TMC optimized membrane achieves zero-discharge textile wastewater treatment, cutting energy consumption by 295% and reducing water consumption by 42.8%. This efficiency surge results from remarkable water permeability (130.83 L m-2 h-1 bar-1) and impressive dye desalination (NaCl/ Direct Red 23 separation factor of 275) of the Tre-1.05/TMC membrane. For a deeper comprehension of filtration performance, the sieving mechanism of polyester LNF membranes was systematically elucidated. This strategic approach offers significant prospects for energy conservation, carbon emission mitigation, and enhanced feasibility of membrane-based wastewater treatment systems.

New directions on membranes for removal and degradation of emerging pollutants in aqueous systems

Emerging pollutants (EPs) refer to a group of non-regulated chemical or biological substances that have been recently introduced or detected in the environment. These pollutants tend to exhibit resistance to conventional treatment methods and can persist in the environment for prolonged periods, posing potential adverse effects on ecosystems and human health. As we enter a new era of managing these pollutants, membrane-based technologies hold significant promise in mitigating impact of EPs on the environment and safeguarding human health due to their high selectivity, efficiency, cost-effectiveness and capability for simultaneous separation and degradation. Moreover, these technologies continue to evolve rapidly with the development of new membrane materials and functionalities, advanced treatment strategies, and analyses for effectively treating EPs of more recent concerns. The objective of this review is to present the latest directions and advancements in membrane-based technologies for addressing EPs. By highlighting the progress in this field, we aim to share valuable perspectives with researchers and contribute to the development of future directions in sustainable treatments for EPs.

Polyester Nanofiltration Membranes for Efficient Cations Separation

Polyester nanofiltration membranes highlight beneficial chlorine resistance, but their loose structures and negative charge result in poor cations retention precluding advanced use in cations separation. This work designs a new monomer (TET) containing "hydroxyl-ammonium" entities that confer dense structures and positive charge to polyester nanofiltration membranes. The TET monomer undergoes efficient interfacial polymerization with the trimesoyl chloride (TMC) monomer, and the resultant TET-TMC membranes feature one of the lowest molecular weight cut-offs (389 Da) and the highest zeta potential (4 mv, pH: 7) among all polyester nanofiltration membranes. The MgCl2 rejection of the TET-TMC membrane is 95.5%, significantly higher than state-of-the-art polyester nanofiltration membranes (<50%). The Li+ /Mg2+ separation performance of TET-TMC membrane is on par with cutting-edge polyamide membranes, while additionally, the membrane is stable against NaClO though polyamide membranes readily degrade. Thus the TET-TMC is the first polyester nanofiltration membrane for efficient cations separation.

Membranes based on Covalent Organic Frameworks through Green and Scalable Interfacial Polymerization using Ionic Liquids for Antibiotic Desalination

Covalent organic framework (COF) membranes featuring uniform topological structures and devisable functions, show huge potential in water purification and molecular separation. Nevertheless, the inability of uniform COF membranes to be produced on an industrial scale and their nonenvironmentally friendly fabrication method are the bottleneck preventing their industrial applications. Herein, we report a new green and industrially adaptable scraping-assisted interfacial polymerization (SAIP) technique to fabricate scalable and uniform TpPa COF membranes. The process used non-toxic and low-volatility ionic liquids (ILs) as organic phase instead of conventional organic solvents for interfacial synthesis of TpPa COF layer on a support membrane, which can simultaneously achieve the purposes of (i) improving the greenness of membrane-forming process and (ii) fabricating a robust membrane that can function beyond the conventional membranes. This approach yields a large-area, continuous COF membrane (19×25 cm2 ) with a thickness of 78 nm within a brief period of 2 minutes. The resulting membrane exhibited an unprecedented combination of high permeance (48.09 L m-2 h-1 bar-1 ) and antibiotic desalination efficiency (e.g., NaCl/adriamycin separation factor of 41.8), which is superior to the commercial benchmarking membranes.

Ultrafiltration and Nanofiltration for the Removal of Pharmaceutically Active Compounds from Water: The Effect of Operating Pressure on Electrostatic Solute-Membrane Interactions

The present work investigates nanofiltration (NF) and ultrafiltration (UF) for the removal of three widely used pharmaceutically active compounds (PhACs), namely atenolol, sulfamethoxazole, and rosuvastatin. Four membranes, two polyamide NF membranes (NF90 and NF270) and two polyethersulfone UF membranes (XT and ST), were evaluated in terms of productivity (permeate flux) and selectivity (rejection of PhACs) at pressures from 2 to 8 bar. Although the UF membranes have a much higher molecular weight cut-off (1000 and 10,000 Da), when compared to the molecular weight of the PhACs (253-482 Da), moderate rejections were observed. For UF, rejections were dependent on the molecular weight and charge of the PhACs, membrane molecular weight cut-off (MWCO), and operating pressure, demonstrating that electrostatic interactions play an important role in the removal of PhACs, especially at low operating pressures. On the other hand, both NF membranes displayed high rejections for all PhACs studied (75-98%). Hence, considering the optimal operating conditions, the NF270 membrane (MWCO = 400 Da) presented the best performance, achieving permeate fluxes of about 100 kg h-1 m-2 and rejections above 80% at a pressure of 8 bar, that is, a productivity of about twice that of the NF90 membrane (MWCO = 200 Da). Therefore, NF270 was the most suitable membrane for this application, although the tight UF membranes under low operating pressures displayed satisfactory results.