Highly water-permeable and stable hybrid membrane with asymmetric covalent organic framework distribution

Organic Solvent Nanofiltration Membrane with In Situ Constructed Covalent Organic Frameworks as Separation Layer

Organic solvent nanofiltration (OSN) technology is advantageous for separating mixtures of organic solutions owing to its low energy consumption and environmental friendliness. Covalent organic frameworks (COFs) are good candidates for enhancing the efficiency of solvent transport and ensuring precise molecular sieving of OSN membranes. In this study, p-phenylenediamine (Pa) and 1,3,5-trimethoxybenzene (Tp) are used to construct, in situ, a TpPa COF skin layer via interfacial polymerization (IP) on a polyimide substrate surface. After subsequent crosslinking and activation steps, a kind of TpPa/polyimide (PI) OSN membrane is obtained. Under optimized fabrications, this OSN membrane exhibits an ethanol permeance of 58.0 LMH/MPa, a fast green FCF (FGF) rejection of 96.2%, as well as a pure n-hexane permeance of 102.0 LMH/MPa. Furthermore, the TpPa/PI OSN membrane exhibits good solvent resistance, which makes it suitable for the separation, purification, and concentration of organic solvents.

COF-based membranes for liquid phase separation: Preparation, mechanism and perspective

Covalent organic frameworks (COFs) are a new kind of crystalline porous materials composed of organic molecules connected by covalent bonds, processes the characteristics of low density, large specific surface area, adjustable pore size and structure, and easy to functionalize, which have been widely used in the field of membrane separation technology. Recently, there are more and more researches focusing on the preparation methods, separation application, and mechanism of COF membranes, which need to be further summarized and compared. In this review, we primarily summarized several conventional preparation methods, such as two-phase interfacial polymerization, in-situ growth on substrate, unidirectional diffusion method, layer-by-layer assembly method, mixed matrix membranes, and so on. The advantages and disadvantages of each method are briefly summarized. The application potential of COF membrane in liquid separation are introduced from four aspects: dyeing wastewater treatment, heavy metal removal, seawater desalination and oil-water separation. Then, the mechanisms including pore structure, hydrophilic/hydrophobic, electrostatic repulsion/attraction and Donnan effect are introduced. For the efficient removal of different kind of pollutions, researchers can select different ligands to construct membranes with specific pore size, hydrophily, salt or organic rejection ability and functional group. The ideas for the design and preparation of COF membranes are introduced. Finally, the future direction and challenges of the next generation of COF membranes in the field of separation are prospected.

Pervaporation Membranes Based on Polyelectrolyte Complex of Sodium Alginate/Polyethyleneimine Modified with Graphene Oxide for Ethanol Dehydration

Pervaporation is considered the most promising technology for dehydration of bioalcohols, attracting increasing attention as a renewable energy source. In this regard, the development of stable and effective membranes is required. In this study, highly efficient membranes for the enhanced pervaporation dehydration of ethanol were developed by modification of sodium alginate (SA) with a polyethylenimine (PEI) forming polyelectrolyte complex (PEC) and graphene oxide (GO). The effect of modifications with GO or/and PEI on the structure, physicochemical, and transport characteristics of dense membranes was studied. The formation of a PEC by ionic cross-linking and its interaction with GO led to changes in membrane structure, confirmed by spectroscopic and microscopic methods. The physicochemical properties of membranes were investigated by a thermogravimetric analysis, a differential scanning calorimetry, and measurements of contact angles. The theoretical consideration using computational methods showed favorable hydrogen bonding interactions between GO, PEI, and water, which caused improved membrane performance. To increase permeability, supported membranes without treatment and cross-linked were developed by the deposition of a thin dense layer from the optimal PEC/GO (2.5%) composite onto a developed porous substrate from polyacrylonitrile. The cross-linked supported membrane demonstrated more than two times increased permeation flux, higher selectivity (above 99.7 wt.% water in the permeate) and stability for separating diluted mixtures compared to the dense pristine SA membrane.

Efficient adsorption of chloroquine phosphate by a novel sodium alginate/tannic acid double-network hydrogel in a wide pH range

In this work, a novel double-network composite hydrogel (SA/TA), composed of sodium alginate (SA) and tannic acid (TA), was designed and fabricated by a successive cross-linking method using Ti(IV) and Ca(II) as crosslinkers. SA/TA exhibited reinforced mechanical strength and anti-swelling properties because of the double-network structure. SA/TA was used as an adsorbent for removal of a popular antiviral drug, chloroquine phosphate (CQ), in water. The adsorption performance of SA/TA was systematically investigated, to study various effects including those of TA mass content, solution pH, adsorption time, and initial CQ concentration. Adsorption was also examined in presence of inorganic and organic coexisting substances commonly found in wastewater, and under different actual water samples. Batch experimental results indicated that SA/TA could maintain higher and more stable CQ uptakes within a wide solution pH range from 3.0 to 10.0, compared to its precursor, SA hydrogel, owing to the addition of TA-Ti(IV) coordination network. The maximum experimental CQ uptake exhibited by the 1:1 (by wt) SA/TA (SA/TA2) was as high as 0.699 mmol/g at the initial pH of 9.0. A high concentration of coexisting NaCl evidently reduced the CQ uptakes of SA/TA2 due to the electrostatic shielding effect, moreover, divalent cations including Ca(II) and Mg(II) also inhibited the adsorption of CQ due to competitive adsorption. However, humic acid had little effect on this adsorption. Considering the apparent adsorption performance, the aforementioned effects of various factors and the spectroscopic characterizations, multi-interactions are suggested for adsorption including chelation, electrostatic interactions, π-π electron donor-acceptor interaction and hydrogen bonding. SA/TA showed a slight loss in adsorption capacity toward CQ and sustained physicochemical structural stability, even after six adsorption-desorption cycles. In addition to CQ, SA/TA could be efficiently used for adsorption of two other antivirus drugs, namely, hydroxychloroquine sulfate and oseltamivir phosphate. This work provides an effective strategy for the design and fabrication of novel adsorbents that can effectively adsorb antiviral drugs over a wide pH range.

Covalent Organic Framework Membranes and Water Treatment

Covalent organic frameworks (COFs) are an emerging class of highly porous crystalline organic polymers comprised entirely of organic linkers connected by strong covalent bonds. Due to their excellent physicochemical properties (e.g., ordered structure, porosity, and stability), COFs are considered ideal materials for developing state-of-the-art separation membranes. In fact, significant advances have been made in the last six years regarding the fabrication and functionalization of COF membranes. In particular, COFs have been utilized to obtain thin-film, composite, and mixed matrix membranes that could achieve effective rejection (mostly above 80%) of organic dyes and model organic foulants (e.g., humic acid). COF-based membranes, especially those prepared by embedding into polyamide thin-films, obtained adequate rejection of salts in desalination applications. However, the claims of ordered structure and separation mechanisms remain unclear and debatable. In this perspective, we analyze critically the design and exploitation of COFs for membrane fabrication and their performance in water treatment applications. In addition, technological challenges associated with COF properties, fabrication methods, and treatment efficacy are highlighted to redirect future research efforts in realizing highly selective separation membranes for scale-up and industrial applications.

Ongoing Progress on Pervaporation Membranes for Ethanol Separation

Ethanol, a versatile chemical extensively employed in several fields, including fuel production, food and beverage, pharmaceutical and healthcare industries, and chemical manufacturing, continues to witness expanding applications. Consequently, there is an ongoing need for cost-effective and environmentally friendly purification technologies for this organic compound in both diluted (ethanol-water-) and concentrated solutions (water-ethanol-). Pervaporation (PV), as a membrane technology, has emerged as a promising solution offering significant reductions in energy and resource consumption during the production of high-purity components. This review aims to provide a panorama of the recent advancements in materials adapted into PV membranes, encompassing polymeric membranes (and possible blending), inorganic membranes, mixed-matrix membranes, and emerging two-dimensional-material membranes. Among these membrane materials, we discuss the ones providing the most relevant performance in separating ethanol from the liquid systems of water-ethanol and ethanol-water, among others. Furthermore, this review identifies the challenges and future opportunities in material design and fabrication techniques, and the establishment of structure-performance relationships. These endeavors aim to propel the development of next-generation pervaporation membranes with an enhanced separation efficiency.

Recent Advances in the Support Layer, Interlayer and Active Layer of TFC and TFN Organic Solvent Nanofiltration (OSN) Membranes: A Review

Although separation of solutes from organic solutions is considered a challenging process, it is inevitable in various chemical, petrochemical and pharmaceutical industries. OSN membranes are the heart of OSN technology that are widely utilized to separate various solutes and contaminants from organic solvents, which is now considered an emerging field. Hence, numerous studies have been attracted to this field to manufacture novel membranes with outstanding properties. Thin-film composite (TFC) and nanocomposite (TFN) membranes are two different classes of membranes that have been recently utilized for this purpose. TFC and TFN membranes are made up of similar layers, and the difference is the use of various nanoparticles in TFN membranes, which are classified into two types of porous and nonporous ones, for enhancing the permeate flux. This study aims to review recent advances in TFC and TFN membranes fabricated for organic solvent nanofiltration (OSN) applications. Here, we will first study the materials used to fabricate the support layer, not only the membranes which are not stable in organic solvents and require to be cross-linked, but also those which are inherently stable in harsh media and do not need any cross-linking step, and all of their advantages and disadvantages. Then, we will study the effects of fabricating different interlayers on the performance of the membranes, and the mechanisms of introducing an interlayer in the regulation of the PA structure. At the final step, we will study the type of monomers utilized for the fabrication of the active layer, the effect of surfactants in reducing the tension between the monomers and the membrane surface, and the type of nanoparticles used in the active layer of TFN membranes and their effects in enhancing the membrane separation performance.

Salt-Assisted Fabrication of a Water-Based Covalent Organic Framework Ink and Its Hybrid Films for Photothermal Actuators

The exceptional properties of two-dimensional covalent organic framework materials (2D-COFs), including their large π-conjugated structure at the molecular level and π-π multilayer stacking, have attracted interest for soft photothermal actuator applications. However, the conventional synthesis of COFs as microcrystalline powders limits their processing in water due to their limited dispersibility. Herein, we present a simple and environmentally friendly method to fabricate water-suspended COF inks by adjusting the surface potential of COF powders through adsorption of ionic species such as Na⁺ and Cl^-. This technique effectively prevents the accumulation and aggregation of COF powder, resulting in an aqueous COF ink that can be easily cast into homogeneous hybrid COF films by Mayer-rod coating. In addition, the resulting photothermal actuator exhibited a fast response time within 3 s at a curvature of 2.35 cm^-1 in the near-infrared light. This facile and practical approach to fabricating water-based COFs ink represents a promising strategy for the development of practical applications of COFs in photothermal actuators.

The recent advance of precisely designed membranes for sieving

Developing new membranes with both high selectivity and permeability is critical in membrane science since conventional membranes are often limited by the trade-off between selectivity and permeability. In recent years, the emergence of advanced materials with accurate structures at atomic or molecular scale, such as metal organic framework, covalent organic framework, graphene, has accelerated the development of membranes, which benefits the precision of membrane structures. In this review, current state-of-the-art membranes are first reviewed and classified into three different types according to the structures of their building blocks, including laminar structured membranes, framework structured membranes and channel structured membranes, followed by the performance and applications for representative separations (liquid separation and gas separation) of these precisely designed membranes. Last, the challenges and opportunities of these advanced membranes are also discussed.

Multi-function hollow nanorod as an efficient sulfur host accelerates sulfur redox reactions for high-performance Li-S batteries

The "shuttle effect" of lithium polysulfides (LiPSs) leads to loss of active materials and the deterioration of cycle stability, which seriously restricts the practical progress of lithium-sulfur (Li-S) batteries. The diffusion of soluble discharge intermediate is the root cause of the above problems. Herein, we synthesized a porous organic framework material (HUT-8) based on triazine network, the polar groups above the hollow structure can not only adsorb LiPSs through electron donating effect, but also anchored cobalt (II) ions provide a large number of binding sites for the in-situ growth of CoS2. This ensured maximized exposure of catalytic centre and improve their interactions with sulfur redox species under the confinement of mesopores, which can catalytically accelerate capture/diffusion of LiPSs and precipitation/decomposition of Li2S. Based on the synergistic effect of the composite materials, the CoS2-HUT-8/S cathode maintained a capacity of 583 mAh g-1 after 500 cycles at 1 C, and a minimum capacity fading rate of 0.046% per cycle. A freestanding CoS2-HUT-8/S cathode with sulfur loading of 5.2 mg cm-2 delivered a high areal capacity of 4.01 mAh cm-2 under a lean electrolyte, which would provide great potential for the practical progress of Li-S batteries.

Pervaporation as a Successful Tool in the Treatment of Industrial Liquid Mixtures

Pervaporation is one of the most active topics in membrane research, and it has time and again proven to be an essential component for chemical separation. It has been employed in the removal of impurities from raw materials, separation of products and by-products after reaction, and separation of pollutants from water. Given the global problem of water pollution, this approach is efficient in removing hazardous substances from water bodies. Conventional processes are based on thermodynamic equilibria involving a phase transition such as distillation and liquid-liquid extraction. These techniques have a relatively low efficacy and nowadays they are not recommended because it is not sustainable in terms of energy consumption and/or waste generation. Pervaporation emerged in the 1980s and is now becoming a popular membrane separation technology because of its intrinsic features such as low energy requirements, cheap separation costs, and good quality product output. The focus of this review is on current developments in pervaporation, mass transport in membranes, material selection, fabrication and characterization techniques, and applications of various membranes in the separation of chemicals from water.

Two-Dimensional Polymers and Polymerizations

Synthetic chemists have developed robust methods to synthesize discrete molecules, linear and branched polymers, and disordered cross-linked networks. However, two-dimensional polymers (2DPs) prepared from designed monomers have been long missing from these capabilities, both as objects of chemical synthesis and in nature. Recently, new polymerization strategies and characterization methods have enabled the unambiguous realization of covalently linked macromolecular sheets. Here we review 2DPs and 2D polymerization methods. Three predominant 2D polymerization strategies have emerged to date, which produce 2DPs either as monolayers or multilayer assemblies. We discuss the fundamental understanding and scope of each of these approaches, including: the bond-forming reactions used, the synthetic diversity of 2DPs prepared, their multilayer stacking behaviors, nanoscale and mesoscale structures, and macroscale morphologies. Additionally, we describe the analytical tools currently available to characterize 2DPs in their various isolated forms. Finally, we review emergent 2DP properties and the potential applications of planar macromolecules. Throughout, we highlight achievements in 2D polymerization and identify opportunities for continued study.

High-Temperature Proton Conduction in Covalent Organic Frameworks Interconnected with Nanochannels for Reverse Electrodialysis

The crystalline porous organic framework offers a highly ordered and stable structure under hydrated conditions at high temperatures. Here, we demonstrated a method for preparing high-performance membrane buildup using "heterogeneous networks" and "polymer phase-separated nanochannels". A well-interconnected "nanochannel" with a "crystalline organic framework" forms a highly stable hybrid membrane above 80 °C under 100% hydration under acidic and basic conditions. The prepared structure provides a self-standing membrane that easily overcomes the problem faced by conventional high ion-exchange capacity (IEC)-based membranes such as swelling, gelling, fragility, and dissolving at elevated temperatures. Apart from structural stability, it also shows better chemical stability with enhanced proton conduction at elevated temperatures. This proton conduction with better structural stability in the high IEC sample confirms from thermal analysis, whereas it also offers relatively low in-plane membrane swelling as compared to the conventional membranes. These hybrid membranes were further combined with the FAA-3 membrane to manufacture a reverse electrodialysis system for generating a power output. We also evaluated the maximum power density (P_max) of the stack theoretically and experimentally. The determined net power density (P_net) is reported to be 0.45 W m^-2 at a flow rate of 40 mL min^-1. These results confirm that the developed membrane can withstand robustly under realistic ambient conditions maintaining stable cell performance.

Novel Pervaporation Membranes Based on Biopolymer Sodium Alginate Modified by FeBTC for Isopropanol Dehydration

Modern society strives for the development of sustainable processes that are aimed at meeting human needs while preserving the environment. Membrane technologies satisfy all the principles of sustainability due to their advantages, such as cost-effectiveness, environmental friendliness, absence of additional reagents and ease of use compared to traditional separation methods. In the present work, novel green membranes based on sodium alginate (SA) modified by a FeBTC metal–organic framework were developed for isopropanol dehydration using a membrane process, pervaporation. Two kinds of SA-FeBTC membranes were developed: (1) untreated membranes and (2) cross-linked membranes with citric acid or phosphoric acid. The structural and physicochemical properties of the developed SA-FeBTC membranes were studied by spectroscopic techniques (FTIR and NMR), microscopic methods (SEM and AFM), thermogravimetric analysis and swelling experiments. The transport properties of developed SA-FeBTC membranes were studied in the pervaporation of water–isopropanol mixtures. Based on membrane transport properties, 15 wt % FeBTC was demonstrated to be the optimal content of the modifier in the SA matrix for the membrane performance. A membrane based on SA modified by 15 wt % FeBTC and cross-linked with citric acid possessed optimal transport properties for the pervaporation of the water–isopropanol mixture (12–100 wt % water): 174–1584 g/(m2 h) permeation flux and 99.99 wt % water content in the permeate.

Novel Membranes Based on Hydroxyethyl Cellulose/Sodium Alginate for Pervaporation Dehydration of Isopropanol

Membrane methods, especially pervaporation, are quickly growing up. In line with that, effective membrane materials based on biopolymers are required for the industrially significant mixtures separation. To essentially improve membrane transport characteristics, the application of the surface or/and bulk modifications can be carried out. In the present study, novel dense and supported membranes based on hydroxyethyl cellulose (HEC)/sodium alginate (SA) were developed for pervaporation dehydration of isopropanol using several approaches: (1) the selection of the optimal ratio of polymers, (2) the introduction of fullerenol in blend polymer matrix, (3) the selection of the optimal cross-linking agent for the membranes, (4) the application of layer-by-layer deposition of polyelectrolytes on supported membrane surface (poly(sodium 4-styrenesulfonate) (PSS)/poly(allylamine hydrochloride) (PAH) and PSS/SA). Structural and physicochemical characteristics of the membranes were analyzed by different methods. A cross-linked supported membrane based on HEC/SA/fullerenol (5%) composite possessed the following transport characteristics in pervaporation dehydration of isopropanol (12–50 wt.% water): 0.42–1.72 kg/(m²h) permeation flux, and 77.8–99.99 wt.% water content in the permeate. The surface modification of this membrane with 5 bilayers of PSS/PAH and PSS/SA resulted in the increase of permeation flux up to 0.47–3.0 and 0.46–1.9 kg/(m²h), respectively, with lower selectivity.

In situ controllable synthesis of Schiff base networks porous polymer coatings for open-tubular capillary electrochromatography

A uniform Schiff base network (SNW) film was synthesized in situ in a controllable way through continuous flow of reactants inside the capillary. The properties and application of the as-prepared capillary was investigated in capillary electrochromatography. The effects of reaction monomer concentration and reaction time on coating thickness were studied by SEM. The results show that the reaction condition has a significant influence on the morphology and thickness of the SNW films. The thickness of the film can be controlled by changing the concentration of reaction solution and reaction time. Capillaries coated under different conditions were employed to separate four nucleotides by capillary electrochromatography, which demonstrated significant variation of migration time, peak order, and separation efficiency. Analytes containing nitrogen heterocycle structures, such as nucleotides, methylimidazole isomers, and β-lactam antibiotics, were successfully separated with the prepared open-tubular columns. Under the selected separation conditions, theoretical plate number of four nucleotides is in a range 45,237-104,505 plates·m^-1, and the resolutions are 1.98-8.07. A resolution of 1.75 is obtained for methylimidazole isomers. The nucleotides in a real sample, chicken essence seasoning, were determined using the prepared capillary column with satisfactory recoveries in the range 95 to 105%.

Self-supporting covalent organic framework membranes synthesized through two different processes: solvothermal annealing and solvent vapor annealing

Rigid, freestanding covalent organic framework (COF-1) membranes have been synthesized from 1,4-benzenediboronic acid (BDBA) precursors using two different approaches: room temperature solvent-vapour annealing (SVA) and solvothermal annealing (SA). Characterization of films using Fourier-transform infrared (FTIR) spectroscopy, x-ray diffraction (XRD), and various microscopies shows that the films obtained through the two different routes vary in their retained BDBA proportion, crystal size and macroscale morphology. Gas adsorption measurements give specific surface areas of 579 ± 7 m² g^-1 and 739 ± 11 m² g^-1 respectively, suggesting that the average porosity of these films is competitive with bulk-synthesized COF-1 particles. The films have a stratified structure, with a dense, thin top layer and a thicker, sponge-like base layer. Using nanoindentation, we measured the Young's modulus at the top surface of the SVA and SA films to be 3.64 ± 1.20 GPa and 3.33 ± 0.12 GPa respectively, with the smaller uncertainty for the SA film attributed to a more uniform morphology. These measurements provide useful experimental data pertaining to COF-1 mechanical properties, furnishing information relevant to the use of these free-standing membranes in applications such as gas filtration or storage.

Emerging new-generation hybrids based on covalent organic frameworks for industrial applications

This review highlights the advancement of COF hybrid-based materials for diverse industrial applications.

Novel covalent organic framework/PVDF ultrafiltration membranes with antifouling and lead removal performance

Membrane separation technology is recognized as a competitive approach to remove Pb²⁺ from water system due to its high efficiency and low operating cost. In present study, a simple and facile approach was developed to fabricate covalent organic framework (COF) modified PVDF ultrafiltration membranes with comprehensive antifouling property and superior Pb²⁺ removal ability. Herein, COF was synthesised in a homogenous PVDF/DMAc solution to fabricate hydrophilic COF modified PVDF ultrafiltration membranes with the Pb²⁺ removal property. The filtration test demonstrated that the COF modified PVDF ultrafiltration membranes exhibited excellent antifouling property and high water flux. Moreover, the membranes showed remarkable potential for treating Pb²⁺-containing water. The removal efficiency was determined at 92.4%, and its removal efficiency was 87.5% at the fourth treatment cycle with Pb²⁺-containing water. The present work provides a valuable platform for further development of efficient composite membranes for the treatment of Pb²⁺-containing water.

Covalent Organic Frameworks in Separation

In the wake of sustainable development, materials research is going through a green revolution that is putting energy-efficient and environmentally friendly materials and methods in the limelight. In this quest for greener alternatives, covalent organic frameworks (COFs) have emerged as a new generation of designable crystalline porous polymers for a wide array of clean-energy and environmental applications. In this contribution, we categorically review the merits and shortcomings of COF bulk powders, nanosheets, freestanding thin films/membranes, and membranes on porous supports in various separation processes, including separation of gases, pervaporation, organic solvent nanofiltration, water purification, radionuclide sequestration, and chiral separations, with particular reference to COF material pore size, host–guest interactions, stability, selectivity, and permeability. This review covers the fabrication strategies of nanosheets, films, and membranes, as well as performance parameters, and provides an overview of the separation landscape with COFs in relation to other porous polymers, while seeking to interpret the future research opportunities in this field.

Metal and Covalent Organic Frameworks for Membrane Applications

Better and more efficient membranes are needed to face imminent and future scientific, technological and societal challenges. New materials endowed with enhanced properties are required for the preparation of such membranes. Metal and Covalent Organic Frameworks (MOFs and COFs) are a new class of crystalline porous materials with large surface area, tuneable pore size, structure, and functionality, making them a perfect candidate for membrane applications. In recent years an enormous number of articles have been published on the use of MOFs and COFs in preparation of membranes for various applications. This review gathers the work reported on the synthesis and preparation of membranes containing MOFs and COFs in the last 10 years. Here we give an overview on membranes and their use in separation technology, discussing the essential factors in their synthesis as well as their limitations. A full detailed summary of the preparation and characterization methods used for MOF and COF membranes is given. Finally, applications of these membranes in gas and liquid separation as well as fuel cells are discussed. This review is aimed at both experts in the field and newcomers, including students at both undergraduate and postgraduate levels, who would like to learn about preparation of membranes from crystalline porous materials.

Novel Mixed Matrix Sodium Alginate-Fullerenol Membranes: Development, Characterization, and Study in Pervaporation Dehydration of Isopropanol

Novel mixed matrix dense and supported membranes based on biopolymer sodium alginate (SA) modified by fullerenol were developed. Two kinds of SA–fullerenol membranes were investigated: untreated and cross-linked by immersing the dry membranes in 1.25 wt % calcium chloride (CaCl₂) in water for 10 min. The structural and physicochemical characteristics features of the SA–fullerenol composite were investigated by Fourier-transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopic methods, scanning electron (SEM) and atomic force (AFM) microscopies, thermogravimetric analysis (TGA), and swelling experiments. Transport properties were evaluated in pervaporation dehydration of isopropanol in a wide concentration range. It was found that the developed supported cross-linked SA-5/PAN^CaCl2 membrane (modified by 5 wt % fullerenol) possessed the best transport properties (the highest permeation fluxes 0.64–2.9 kg/(m² h) and separation factors 26–73,326) for the pervaporation separation of the water–isopropanol mixture in the wide concentration range (12–90 wt % water) at 22 °C and is suitable for the promising application in industry.

Covalent organic frameworks for separation applications

Covalent organic frameworks (COFs) are an emerging class of crystalline porous polymers with highly tuneable structures and functionalities. COFs have been proposed as ideal materials for applications in the energy-intensive field of molecular separation due to their notable intrinsic features such as low density, exceptional stability, high surface area, and readily adjustable pore size and chemical environment. This review attempts to highlight the key advancements made in the synthesis of COFs for diverse separation applications such as water treatment or the separation of gas mixtures and organic molecules, including chiral and isomeric compounds. Methods proposed for the fabrication of COF-based columns and continuous membranes for practical applications are also discussed in detail. Finally, a perspective regarding the remaining challenges and future directions for COF research in the field of separation has also been presented.