Synthesizing Hypercrosslinked Polymers with Deep Eutectic Solvents to Enhance CO2/N2 Selectivity.

Hypercrosslinked polymers (HCPs) are widely used in ion exchange, water purification, and gas separation. However, HCP synthesis typically requires hazardous halogenated solvents e. g., dichloroethane, dichloromethane and chloroform which are toxic to human health and environment. Herein we hypothesize that the use of halogenated solvents in HCP synthesis can be overcome with deep eutectic solvents (DES) comprising metal halides-FeCl3, ZnCl2 that can act as both the solvent hydrogen bond donor and catalyst for polymer crosslinking via Friedel Crafts alkylation. We validated our hypothesis by synthesizing HCPs in DESs via internal and external crosslinking strategies. [ChCl][ZnCl2]2 and [ChCl][FeCl3]2 was more suitable for internal and external hypercrosslinking, respectively. The specific surface areas of HCPs synthesized in DES were 20-60 % lower than those from halogenated solvents, but their CO2/N2 selectivities were up to 453 % higher (CO2/N2 selectivity of poly-α,α'-dichloro-p-xylene synthesized in [ChCl][ZnCl2]2 via internal crosslinking reached a value of 105). This was attributed to the narrower pore size distributions of HCPs synthesized in DESs.

Ice-confined synthesis of highly ionized 3D-quasilayered polyamide nanofiltration membranes.

Existing polyamide (PA) membrane synthesis protocols are underpinned by controlling diffusion-dominant liquid-phase reactions that yield subpar spatial architectures and ionization behavior. We report an ice-confined interfacial polymerization strategy to enable the effective kinetic control of the interfacial reaction and thermodynamic manipulation of the hexagonal polytype (Ih) ice phase containing monomers to rationally synthesize a three-dimensional quasilayered PA membrane for nanofiltration. Experiments and molecular simulations confirmed the underlying membrane formation mechanism. Our ice-confined PA nanofiltration membrane features high-density ionized structure and exceptional transport channels, realizing superior water permeance and excellent ion selectivity.

Surface manipulation for prevention of migratory viscous crude oil fouling in superhydrophilic membranes.

Here, we present a proactive fouling prevention mechanism that endows superhydrophilic membranes with antifouling capability against migratory viscous crude oil fouling. By simulating the hierarchical architecture/chemical composition of a dahlia leaf, a membrane surface is decorated with wrinkled-pattern microparticles, exhibiting a unique proactive fouling prevention mechanism based on a synergistic hydration layer/steric hindrance. The density functional theory and physicochemical characterizations demonstrate that the main chains of the microparticles are bent towards Fe3+ through coordination interactions to create nanoscale wrinkled patterns on smooth microparticle surfaces. Nanoscale wrinkled patterns reduce the surface roughness and increase the contact area between the membrane surface and water molecules, expanding the steric hindrance between the oil molecules and membrane surface. Molecular dynamic simulations reveal that the water-molecule densities and strengths of the hydrogen bonds are higher near the resultant membrane surface. With this concept, we can successfully inhibit the initial adhesion, migration, and deposition of oil, regardless of the viscosity, on the membrane surface and achieve migratory viscous crude oil antifouling. This research on the PFP mechanism opens pathways to realize superwettable materials for diverse applications in fields related to the environment, energy, health, and beyond.

Boosting membrane carbon capture via multifaceted polyphenol-mediated soldering.

Advances in membrane technologies are significant for mitigating global climate change because of their low cost and easy operation. Although mixed-matrix membranes (MMMs) obtained via the combination of metal-organic frameworks (MOFs) and a polymer matrix are promising for energy-efficient gas separation, the achievement of a desirable match between polymers and MOFs for the development of advanced MMMs is challenging, especially when emerging highly permeable materials such as polymers of intrinsic microporosity (PIMs) are deployed. Here, we report a molecular soldering strategy featuring multifunctional polyphenols in tailored polymer chains, well-designed hollow MOF structures, and defect-free interfaces. The exceptional adhesion nature of polyphenols results in dense packing and visible stiffness of PIM-1 chains with strengthened selectivity. The architecture of the hollow MOFs leads to free mass transfer and substantially improves permeability. These structural advantages act synergistically to break the permeability-selectivity trade-off limit in MMMs and surpass the conventional upper bound. This polyphenol molecular soldering method has been validated for various polymers, providing a universal pathway to prepare advanced MMMs with desirable performance for diverse applications beyond carbon capture.

Photo-Modulating CO2 Uptake of Hypercross-linked Polymers Upcycled from Polystyrene Waste.

Incorporating photo-switches into skeletal structures of microporous materials or as guest molecules yield photo-responsive materials for low-energy CO2 capture but at the expense of lower CO2 uptake. Here, we overcome this limitation by exploiting trans-cis photoisomerization of azobenzene loaded into the micropores of hypercross-linked polymers (HCPs) derived from waste polystyrene. Azobenzene in HCP pores reduced CO2 uptake by 19 %, reaching 37.7 cm3 g-1 , but this loss in CO2 uptake was not only recovered by trans-cis photoisomerization of azobenzene, but also increased by 22 %, reaching 56.9 cm3 g-1 , when compared to as-prepared HCPs. Computational simulations show that this increase in CO2 uptake is due to photo-controlled increments in 10-20 Šmicropore volume, i. e., adsorption sites and a photo-reversible positive dipole moment. Irradiating these HCPs with visual-range light reverted CO2 uptake to 33 cm3 g-1 . This shows that it is feasible to recycle waste polystyrene into advanced materials for low-energy carbon capture.

Symbiosis-inspired de novo synthesis of ultrahigh MOF growth mixed matrix membranes for sustainable carbon capture.

Mixed matrix membranes (MMMs) are one of the most promising solutions for energy-efficient gas separation. However, conventional MMM synthesis methods inevitably lead to poor filler-polymer interfacial compatibility, filler agglomeration, and limited loading. Herein, inspired by symbiotic relationships in nature, we designed a universal bottom-up method for in situ nanosized metal organic framework (MOF) assembly within polymer matrices. Consequently, our method eliminating the traditional postsynthetic step significantly enhanced MOF dispersion, interfacial compatibility, and loading to an unprecedented 67.2 wt % in synthesized MMMs. Utilizing experimental techniques and complementary density functional theory (DFT) simulation, we validated that these enhancements synergistically ameliorated CO2 solubility, which was significantly different from other works where MOF typically promoted gas diffusion. Our approach simultaneously improves CO2 permeability and selectivity, and superior carbon capture performance is maintained even during long-term tests; the mechanical strength is retained even with ultrahigh MOF loadings. This symbiosis-inspired de novo strategy can potentially pave the way for next-generation MMMs that can fully exploit the unique characteristics of both MOFs and matrices.

Polymer Chemistry Applications of Cyrene and its Derivative Cygnet 0.0 as Safer Replacements for Polar Aprotic Solvents.

This study explores a binary solvent system composed of biobased Cyrene and its derivative Cygnet 0.0 for application in membrane technology and in biocatalytic synthesis of polyesters. Cygnet-Cyrene blends could represent viable replacements for toxic polar aprotic solvents. The use of a 50 wt % Cygnet-Cyrene mixture makes a practical difference in the production of flat sheet membranes by nonsolvent-induced phase separation. New polymeric membranes from cellulose acetate, polysulfone, and polyimide are manufactured by using Cyrene, Cygnet 0.0, and their blend. The resultant membranes have different morphology when the solvent/mixture and temperature of the casting solution change. Moreover, Cyrene, Cygnet 0.0, and Cygnet-Cyrene are also explored for substituting diphenyl ether for the biocatalytic synthesis of polyesters. The results indicate that Cygnet 0.0 is a very promising candidate for the enzymatic synthesis of high molecular weight polyesters.

State-of-the-Art and Opportunities for Forward Osmosis in Sewage Concentration and Wastewater Treatment.

The application of membrane technologies for wastewater treatment to recover water and nutrients from different types of wastewater can be an effective strategy to mitigate the water shortage and provide resource recovery for sustainable development of industrialisation and urbanisation. Forward osmosis (FO), driven by the osmotic pressure difference between solutions divided by a semi-permeable membrane, has been recognised as a potential energy-efficient filtration process with a low tendency for fouling and a strong ability to filtrate highly polluted wastewater. The application of FO for wastewater treatment has received significant attention in research and attracted technological effort in recent years. In this review, we review the state-of-the-art application of FO technology for sewage concentration and wastewater treatment both as an independent treatment process and in combination with other treatment processes. We also provide an outlook of the future prospects and recommendations for the improvement of membrane performance, fouling control and system optimisation from the perspectives of membrane materials, operating condition optimisation, draw solution selection, and multiple technologies combination.

Molecularly soldered covalent organic frameworks for ultrafast precision sieving.

The weak interlamellar interaction of covalent organic framework (COF) nanocrystals inhibit the construction of highly efficient ion/molecular sieving membranes owing to the inferior contaminant selectivity induced by defects in stacked COF membranes and stability issues. Here, a facile in situ molecularly soldered strategy was developed to fabricate defect-free ultrathin COF membranes with precise sieving abilities using the typical chemical environment for COF condensation polymerization and dopamine self-polymerization. The experimental data and density functional theory simulations proved that the reactive oxygen species generated during dopamine polymerization catalyze the nucleophilic reactions of the COF, thus facilitating the counter-diffusion growth of thin COF layers. Notably, dopamine can eliminate the defects in the stacked COF by soldering the COF crystals, fortifying the mechanical properties of the ultrathin COF membranes. The COF membranes exhibited ultrafast precision sieving for molecular separation and ion removal in both aqueous and organic solvents, which surpasses that of state-of-the-art membranes.

Aqueous One-Step Modulation for Synthesizing Monodispersed ZIF-8 Nanocrystals for Mixed-Matrix Membrane.

Enhancing the monodispersity and surface properties of nanoporous zeolitic imidazolate frameworks (ZIFs) are crucial for maximizing their performance in advanced nanocomposites for separations. Herein, we developed an in situ method to synthesize monodispersed ZIF-8 nanocrystals with unique dopamine (DA) surface decoration layer (ZIF-8-DA) in an aqueous solution at room temperature. Interestingly, the in situ formation of the monodispersed ZIF-8-DA nanocrystals experiences a triple-stage crystallization process, resulting in a rhombic dodecahedron architecture, which is greatly different from the synthesis of conventional ZIF-8. The crystallinity and abundant microporosity of ZIF-8-DA nanocrystals is well maintained even with the DA surface decoration. Owing to the advanced surface compatibility and pore properties of ZIF-8-DA, ZIF-8-DA/Matrimid mixed-matrix membranes exhibit both higher gas permeability and selectivity than the pristine Matrimid polyimide membrane, which breaks out the traditional "trade-off" phenomena between permeability and selectivity.

Membrane Surface Functionalization with Imidazole Derivatives to Benefit Dye Removal and Fouling Resistance in Forward Osmosis.

Water contaminated with low concentrations of pollutants is more difficult to clean up than that with high pollutant content levels. Membrane separation provides a solution for removing low pollutant content from water. However, membranes are prone to fouling, losing separation performances over time. Here we synthesized neutral (IM-NH2) and positively charged (IL-NH2) imidazole derivatives to chemically functionalize membranes. With distinct properties, these imidazole grafts could tailor membrane physicochemical properties and structures to benefit forward osmosis (FO) processes for the removal of 20-100 ppm of Safranin O dye-a common dye employed in the textile industry. The water fluxes produced by IM-NH2- and IL-NH2-modified membranes increased by 67% and 122%, respectively, with DI water as the feed compared to that with the nascent membrane. A 39% flux increment with complete dye retention (∼100%) was achieved for the IL-NH2-modified membrane against 100 ppm of Safranin O dye. Regardless of the dye concentration, the IL-NH2-modified membrane exhibited steadily higher permeation performance than the original membrane in long-term experiments. Reproducible experimental results were obtained with the IL-NH2-modified membrane after cleaning with DI water, demonstrating the good antifouling properties and renewability of the newly developed membrane.

Tailoring molecular interactions between microporous polymers in high performance mixed matrix membranes for gas separations.

Membranes are crucial to lowering the huge energy costs of chemical separations. Whilst some promising polymers demonstrate excellent transport properties, problems of plasticisation and physical aging due to mobile polymer chains, amongst others, prevent their exploitation in membranes for industrial separations. Here we reveal that molecular interactions between a polymer of intrinsic microporosity (PIM) matrix and a porous aromatic framework additive (PAF-1) can simultaneously address plasticisation and physical aging whilst also increasing gas transport selectivity. Extensive spectroscopic characterisation and control experiments involving two near-identical PIMs, one with methyl groups (PIM-EA(Me2)-TB) and one without (PIM-EA(H2)-TB), directly confirm the key molecular interaction as the adsoprtion of methyl groups from the PIM matrix into the nanopores of the PAF. This interaction reduced physical aging by 50%, suppressed polymer chain mobilities at high pressure and increased H2 selectivity over larger gases such as CH4 and N2.

Control of Physical Aging in Super-Glassy Polymer Mixed Matrix Membranes.

ConspectusSince the discovery of polymers of intrinsic microporosity (PIMs) in 2004, the fast size-selective interconnected pore cavities of the polymers have caused the upper bound of membrane performance to be revised, twice. Simultaneously, porous materials have meant that mixed matrix membranes (MMMs) are now a relatively simple method of enhancing transport properties. While there are now reliable routes with mixed matrices to improve the fundamental transport properties of membrane materials, many of the other properties crucial for separation applications remain largely unaddressed. Physical aging severely affects membrane performance over time, especially for those prepared from high fractional free volume polymers. Gradual densification of the glassy polymer chains causes the connected pore channels present in these materials to constrict. Studies now suggest that aging of superglassy polymer materials is a two-step process; a rapid densification occurs within the first few days, followed by a gradual rearrangement of packed chains over longer time frames toward a theoretical equilibrium state. Although advantageous in terms of size selectivity, the considerable drop in permeation over the days and weeks after manufacture greatly impacts material applicability. While often still permeating faster than traditional membrane materials, the continuous gradual collapse of cavities in these polymers are a significant challenge in the application of high free volume polymer membranes. In 2014, we discovered that the porous aromatic framework PAF-1 not only greatly improved the membrane's void space and speed of gas transport but also seemingly froze several glassy polymers in a low-density state, holding the polymer's pore channels open, a process termed as Porosity Induced Side chain Adsorption (PISA).This discovery of PISA fundamentally challenged the conventional wisdom at the time that the aging rate could only be addressed by densification of the polymer. Unlike other high-performance glassy polymers, membranes containing PAF-1 can retain their high permeability for more than a year. Several other examples of antiaging behavior have been subsequently reported by the team, where control of aging rate as a function of gas penetrant, selectivity increases, and stability at higher pressures was reported. These works also demonstrate that these mixed matrix systems had applicability for several other separations, including pervaporation, solvent nanofiltration, and as separators for energy applications. In our subsequent studies, the antiaging mechanism has been elucidated as an effect of the interaction between the polymer's accessible pendant methyl group and the aromatic pore surface of PAF-1 or other antiaging additives. In otherwise identical MMMs, where this hypothesized methyl-π interaction is either absent or interrupted, we find that the antiaging behavior expected by the fixation of the polymer chains to the pore surface and PAF-1 does not occur. As a design approach for mixed matrix membranes, targeted interfacial interactions are a promising pathway for developing other stable membranes, enabling the exciting class of PIM materials to improve industrial separation efficiency.

Tailoring the molecular structure of crosslinked polymers for pervaporation desalination.

Polymer crosslinking imbues chemical stability to thin films at the expense of lower molecular transportation rates. Here in this work we deployed molecular dynamics simulations to optimise the selection of crosslinking compounds that overcome this trade-off relationship. We validated these simulations using a series of experiments and exploited this finding to underpin the development of a pervaporation (PV) desalination thin-film composite membrane with water fluxes reaching 234.9 ± 8.1 kg m-2 h-1 and salt rejection of 99.7 ± 0.2 %, outperforming existing membranes for pervaporation and membrane distillation. Key to achieving this state-of-the-art desalination performance is the spray coating of 0.73 µm thick crosslinked dense, hydrophilic polymers on to electrospun nanofiber mats. The desalination performances of our polymer nanocomposites are harnessed here in this work to produce freshwater from brackish water, seawater and brine solutions, addressing the key environmental issue of freshwater scarcity.

Continuous flow knitting of a triptycene hypercrosslinked polymer.

By replacing Lewis acids with Brønsted acids as catalysts, continuous flow synthesis of hypercrosslinked polymers is achieved within 10% of the time required for a typical batch reaction. Compared with batch-synthesised polymers, the flow-produced materials take up 24% more CO2, precluding the need for lengthy reaction protocols to yield high-performance hypercrosslinked polymers for carbon capture.

Zwitterion-Ag Complexes That Simultaneously Enhance Biofouling Resistance and Silver Binding Capability of Thin Film Composite Membranes.

Biofouling can be overcome with zwitterion grafts and antimicrobial, metallic nanoparticles. However, the mechanism underpinning this effective approach remains unclear. To elucidate the role of each component in this system while maximizing membrane antifouling and antimicrobial properties, here we performed a comparative study to investigate the impact of zwitterion type and their interactions with Ag of various states. Two different zwitterions (SO3--based and COO--based) were employed to modify polyamide (PA) thin film composite (TFC) membranes, and the metallized and mineralized membranes were developed via in situ formation of silver (Ag) nanoparticles and deposition of silver chloride (AgCl) particles on the zwitterion-modified TFC membranes. The presence of zwitterions was key to enhance Ag content, resulting in significantly improved antimicrobial and antifouling properties without compromising the nanofiltration separation performance. COO--based zwitterions were found more favorable toward Ag metallization and mineralization compared to SO3--based zwitterions. The underlying mechanisms underpinning this discovery were further revealed using density functional theory (DFT) to reveal Gibbs free energy of the binding between zwitterions and Ag+ ions. This fundamental knowledge is crucial for designing next-generation antibiofouling strategies.

Novel Ionic Grafts That Enhance Arsenic Removal via Forward Osmosis.

Current forward osmosis (FO) membranes are unsuitable for arsenic removal from water because of their poor arsenic selectivity. In this study, we designed and synthesized a series of novel imidazolium-based ionic liquids via one-step quaternization reactions and grafted these novel compounds on to conventional thin-film composite FO membranes for treatment of arsenic-containing water. The newly developed ionic membranes contained a functionalized selective polyamide layer grafted with either carboxylic acid/carboxylate or sulfonate groups that drastically enhanced membrane hydrophilicity and thus FO water permeation. Ionic membranes modified with sodium 1-ethanesulfonate-3-(3-aminopropyl) imidazolium bromide (NH2-IM-(CH2)2-SO3Na) outperformed pristine membranes with higher water recovery efficiency. Exceptional performance was achieved with this ionic membrane in FO arsenic removal with a water flux of 11.0 LMH and a rejection higher than 99.5% when 1000 ppm arsenic (HAsO42-) as the feed with a dilute NaCl solution (0.5 M) as the draw solution under the FO mode. Ionic membranes developed in this work facilitated FO for the treatment of arsenic-containing water while demonstrating its superiority over incumbent technologies with more efficient arsenic removal.

Tailoring the Porosity in Iron Phosphosulfide Nanosheets to Improve the Performance of Photocatalytic Hydrogen Evolution.

Metal sulfide photocatalysts are typically required during water splitting to produce hydrogen. However, the rapid recombination of photogenerated electron-hole pairs in these highly unstable photocatalysts has restricted hydrogen production to small-scale batch reactions. In this work, porous transition-metal thiophosphites were used to enable continuous long-term hydrogen production through photocatalysis. A wide bandgap (2.04 eV) was essential for generating hydrogen at a rate of 305.6 µmol h-1 g-1 , 180 % faster than nonporous FePS3 nanosheets. More importantly, the high in-plane stiffness of these approximately 7 nm thick porous FePS3 nanosheets ensured structural stability during 56 h of continuous photocatalysis reactions. The reaction results with D2 O instead of H2 O indicated that hydrogen mainly came from H2 O. Furthermore, a sacrificial reagent (triethylamine) was photodegraded into diethylamine and acetaldehyde through a monoelectronic oxidation process, as indicated by HPLC and LC-MS. This synthesis strategy reported for FePS3 porous nanosheets paves a new pathway for designing other dianion-based inorganic nanocrystals for hydrogen energy applications.

Solvation Effects on the Permeation and Aging Performance of PIM-1-Based MMMs for Gas Separation.

Membranes are particularly attractive for lowering the energy intensity of separations as they eliminate phase changes. While many tantalizing polymers are known, limitations in selectivity and stability slightly preclude further development. Mixed-matrix membranes may address these shortcomings. Key to their realization is the intimate mixing between the polymer and the additive to eliminate nonselective transport, improve selectivity, and resist physical aging. Polymers of intrinsic microporosity (PIMs) have inherently promising gas transport properties. Here, we show that porous additives can improve transport and resist aging in PIM-1. We develop a simple, low-cost, and scalable hyper-cross-linked polymer (poly-dichloroxylene, pDCX), which was hydroxylated to form an intimate mixture with the polar PIM-1. Solvent variation allowed control of physical aging rates and improved selectivity for smaller gases. This detailed study has allowed many interactions within mixed matrix membranes to be directly elucidated and presents a practical means to stabilize porous polymers for separation applications.

A Novel Multi-Charged Draw Solute That Removes Organic Arsenicals from Water in a Hybrid Membrane Process.

The potential of forward osmosis for water treatment can only be maximized with suitable draw solutes. Here a three-dimensional, multicharge draw solute of decasodium phytate (Na10-phytate) is designed and synthesized for removing organic arsenicals from water using a hybrid forward osmosis (FO) - membrane distillation (MD) process. Efficient water recovery is achieved using Na10-phytate as a draw solute with a water flux of 20.0 LMH and negligible reverse solute diffusion when 1000 ppm organic arsenicals as the feed and operated under ambient conditions with FO mode. At 50 °C, the novel draw solute increases water flux by more than 30% with water fluxes higher than 26.0 LMH on the FO side, drastically enhancing water recovery efficiency. By combining the FO and MD processes into a single hybrid process, a 100% recovery of Na10-phytate draw solute was achieved. Crucially, organic arsenicals or Na10-phytate draw solutes are both rejected 100% and not detected in the permeate of the hybrid process. The complete rejection of both organic arsenicals and draw solutes using hybrid membrane processes is unprecedented; creating a new application for membrane separations.