Augmenting the Efficacy of a Polyvinyl Alcohol Selective Layer Coated on Polyvinylidene Fluoride Support Membranes with Kaolinite Introduction for Improved Pervaporation Dehydration of Epichlorohydrin/Isopropanol/Water Ternary Systems.

Composite membranes with a polyvinyl alcohol (PVA) selective layer composed of well-dispersed hydrophilic kaolinite particles coated on a polyvinylidene fluoride (PVDF) support were developed. They were applied to the pervaporation dehydration of the industrially important epichlorohydrin (ECH)/isopropanol (IPA)/water ternary mixture. In comparison with raw kaolinite (RK), hydrophilic kaolinite (HK) enhanced the mechanical properties, hydrophilicity, and thermal stability of the PVA selective layer, as confirmed by universal testing, the contact angle, and TGA analyses, respectively. The pervaporation results revealed that the addition of HK particles significantly enhanced the separation factor (3-fold). Only a marginal reduction in flux was observed with ECH/IPA/water, 50/30/20 (w/w %) at 40 °C. An HK particle concentration of 4 wt.% with respect to PVA delivered the highest flux performance of 0.86 kg/m2h and achieved a separation factor of 116. The PVA-kaolinite composite membrane exhibited pronounced resistance to the ECH-containing feed, demonstrating a sustained flux and separation factor throughout an extended pervaporation stability test lasting 250 h.

Synergistic pervaporation dehydration of ethanol/water mixture: Exploring the potential of a covalently designed hybrid membrane structure of polyacrylic acid grafted carbon nitride and polyvinyl alcohol.

Polyacrylic acid (PAA) grafted CN sheet (P-g-CN) was synthesized to enhance the dispersive properties of carbon nitride (CN) in the membrane. A successful PAA grafting to the CN was confirmed from FTIR, TGA, and Zeta potential and XRD analyses. The A PVA membrane embedded P-g-CN, including a covalently constructed polymer-filler network, was developed to separate ethanol-water mixtures using pervaporation (PV). XPS study has confirmed a covalent attachment of P-g-CN sheets to the PVA matrix. Thereby, a defect-free membrane matrix was observed in the FESEM analysis. A 10 wt% loaded PVA-P-g-CN10 composite membrane was compared to the pristine PVA membrane, demonstrating improved PV dehydration performance. The flux decreased from 0.21 kg/m2h of pristine PVA membrane to 0.17 kg/m2h of PVA-P-g-CN10 membrane, while the separation factor improved from 49 to 176 in a 90/10 wt % ethanol/water feed at 40 °C. This improvement can be attributed to the selective diffusion of water through the P-g-CN interlayer spacing and tiny triangular nanopores in the s-triazine network, along with their dispersibility in the PVA matrix, resulting in well-ordered membrane morphology. Furthermore, PVA-P-g-CN10 exhibited higher water permeance (43.31-86.07 GPU) than ethanol (1.18-10.47 GPU) as the feed temperature increased from 30 to 70 °C, suggesting P-g-CN successfully inhibits swelling in the feed solution through proper interaction with PVA. In a long-term PV test lasting 250 h, the PVA-P-g-CN10 membrane displayed excellent structural stability and maintained its performance.

Thin Film Composite Membranes as a New Category of Alkaline Water Electrolysis Membranes.

Alkaline water electrolysis (AWE) is considered a promising technology for green hydrogen (H2 ) production. Conventional diaphragm-type porous membranes have a high risk of explosion owing to their high gas crossover, while nonporous anion exchange membranes lack mechanical and thermochemical stability, limiting their practical application. Herein, a thin film composite (TFC) membrane is proposed as a new category of AWE membranes. The TFC membrane consists of an ultrathin quaternary ammonium (QA) selective layer formed via Menshutkin reaction-based interfacial polymerization on a porous polyethylene (PE) support. The dense, alkaline-stable, and highly anion-conductive QA layer prevents gas crossover while promoting anion transport. The PE support reinforces the mechanical and thermochemical properties, while its highly porous and thin structure reduces mass transport resistance across the TFC membrane. Consequently, the TFC membrane exhibits unprecedentedly high AWE performance (1.16 A cm-2 at 1.8 V) using nonprecious group metal electrodes with a potassium hydroxide (25 wt%) aqueous solution at 80 °C, significantly outperforming commercial and other lab-made AWE membranes. Moreover, the TFC membrane demonstrates remarkably low gas crossover, long-term stability, and stack cell operability, thereby ensuring its commercial viability for green H2 production. This strategy provides an advanced material platform for energy and environmental applications.

Improving the Separation Properties of Polybenzimidazole Membranes by Adding Acetonitrile for Organic Solvent Nanofiltration.

In research on membranes, the addition of co-solvents to the polymer dope solution is a common method for tuning the morphology and separation performance. For organic solvent nanofiltration (OSN) applications, we synthesized polybenzimidazole (PBI) membranes with high separation properties and stability by adding acetonitrile (MeCN) to the dope solution, followed by crosslinking with dibromo-p-xylene. Accordingly, changes in the membrane structure and separation properties were investigated when MeCN was added. PBI/MeCN membranes with a dense and thick active layer and narrow finger-like macrovoids exhibited superior rejection properties in the ethanol solution compared with the pristine PBI membrane. After crosslinking, they displayed superior rejection properties (96.56% rejection of 366-g/mol polypropylene glycol). In addition, the membranes demonstrated stable permeances for various organic solvents, including acetone, methanol, ethanol, toluene, and isopropyl alcohol. Furthermore, to evaluate the feasibility of the modified PBI OSN membranes, ecamsule, a chemical product in the fine chemical industry, was recovered. Correspondingly, the efficient recovery of ecamsule from a toluene/methanol solution using the OSN process with PBI/MeCN membranes demonstrated their applicability in many fine chemical industries.

Improvement in Acid Resistance of Polyimide Membranes: A Sustainable Cross-Linking Approach via Green-Solvent-Based Fenton Reaction.

In this study, we present a facile surface modification method using green solvents for a commercial polyimide (PI) nanofiltration membrane to exhibit good acid stability. To enhance acid stability, the PI organic solvent nanofiltration membrane was modified using Fenton's reaction, an oxidative cross-linking process, using environmentally friendly solvents: water and ethanol. The surface properties of the pristine and modified PI membranes were investigated and compared using various analytical tools. We studied the surface morphology using scanning electron microscopy, performed elemental analysis using X-ray photoelectron spectroscopy, investigated chemical bonds using attenuated total reflectance-Fourier transform infrared spectroscopy, and studied thermal stability using thermogravimetric analysis. The acid resistances of the pristine and modified membranes were confirmed through performance tests. The pristine PI nanofiltration membrane exposed to a 50 w/v% sulfuric acid for 4 h showed an increase in the normalized water flux to 205% and a decrease in the MgSO4 normalized rejection to 44%, revealing damage to the membrane. The membrane modified by the Fenton reaction exhibited a decline in flux and improved rejection, which are typical performance changes after surface modification. However, the Fenton-modified membrane exposed to 50 w/v% sulfuric acid for 4 h showed a flux increase of 7% and a rejection increase of 4%, indicating improved acid resistance. Furthermore, the Fenton post-treatment enhanced the thermal stability and organic solvent resistance of the PI membrane. This study shows that the acid resistance of PI membranes can be successfully improved by a novel and facile Fenton reaction using green solvents.

Tannic acid-assisted in-situ interfacial formation of Prussian blue-assembled adsorptive membranes for radioactive cesium removal.

There is a growing interest in advanced materials that can effectively treat wastewater contaminated with radioactive cesium (137Cs), which is an extremely hazardous material. Here, we report a new class of Cs-adsorptive membranes compactly assembled with Cs-adsorptive Prussian blue (PB) particles. The PB particle assembly was formed via an in-situ interfacial reaction between two PB precursors in the presence of tannic acid (TA) as a binder on a porous support. While the interfacial reaction enabled the formation of a defect-less PB network, TA enhanced the PB-PB and PB-support compatibilities, consequently producing a uniform, densely packed PB assembly near the support surface. The fabricated TA-assisted PB membrane (PB/TA-M) synergistically rejected Cs via a combination of adsorption and membrane filtration, although adsorption predominantly determined Cs rejection initially. Hence, the PB/TA-M membrane showed considerably higher Cs removal performance than commercial nanofiltration (NF) and reverse osmosis (RO) polyamide (PA) membranes for a sufficiently long operation time. Furthermore, the PB/TA-M membrane displayed excellent radioactive 137Cs removal performance, significantly exceeding those of commercial NF and RO PA membranes due to its higher radiation stability, indicating its viability for application in treating actual radioactive wastewater.

Poly(ethylene-co-vinyl alcohol) Electrospun Nanofiber Membranes for Gravity-Driven Oil/Water Separation.

Fabrication of highly efficient oil/water separation membranes is attractive and challenging work for the actual application of the membranes in the treatment of oily wastewater and cleaning up oil spills/oil leakage accidents. In this study, hydrophilic poly(ethylene-co-polyvinyl alcohol) (EVOH) nanofiber membranes were made using an electrospinning technique for oil/water separation. The as-prepared EVOH electrospun nanofiber membranes (ENMs) exhibited a super-hydrophilic property (water contact angle 33.74°) without further treatment. As prepared, ENMs can provide continuous separation of surfactant-free and surfactant-stabilized water-in-oil emulsions with high efficiency (i.e., flux 8200 L m−2 h−1 (LMH), separation efficiency: >99.9%). In addition, their high stability (i.e., reusable, mechanically robust) would broaden the conditions under which they can be employed in the real field oil/water separation applications. Various characterization techniques (including morphology investigation, pore size, porosity, mechanical properties, and performance test) for gravity-driven oil/water separation were employed to evaluate the newly prepared EVOH ENMs.

Isoporous Polyvinylidene Fluoride Membranes with Selective Skin Layers via a Thermal-Vapor Assisted Phase Separation Method for Industrial Purification Applications.

The membrane filtration process is the most widely used purification process in various industries due to its high separation efficiency, process simplicity, and low cost. Although there is a wide range of membrane products with diverse materials and pore sizes on the market, there is a technological gap between microfiltration and ultrafiltration membranes. Here we developed highly porous polyvinylidene fluoride (PVDF) membranes with a selective skin layer with a pore size range of 20 to 80 nm by using a thermal-vapor assisted phase separation method. Porous and bi-continuous sublayers were generated from spinodal decomposition induced by cooling. The overall membrane structure and pore size changed with the dope composition, while the pore size and thickness of the selective skin layer were effectively controlled by water vapor exposure. The excellent nanoparticle removal efficiencies of the prepared PVDF membranes were confirmed, indicating their potential application in high-level purification processes to remove small trace organic or inorganic impurities from various industrial fluids.

Tailoring the Stabilization and Pyrolysis Processes of Carbon Molecular Sieve Membrane Derived from Polyacrylonitrile for Ethylene/Ethane Separation.

For ethylene/ethane separation, a CMS (carbon molecular sieve) membrane was developed with a PAN (polyacrylonitrile) polymer precursor on an alumina support. To provide an excellent thermal property to PAN precursor prior to the pyrolysis, the stabilization as a pre-treatment process was carried out. Tuning the stabilization condition was very important to successfully preparing the CMS membrane derived from the PAN precursor. The stabilization and pyrolysis processes for the PAN precursor were finely tuned, and optimized in terms of stabilization temperature and time, as well as pyrolysis temperature, heating rate, and soaking time. The PAN stabilized at >250 °C showed improved thermal stability and carbon yield. The CMS membrane derived from stabilized PAN showed reasonable separation performance for ethylene permeance (0.71 GPU) and ethylene/ethane selectivity (7.62), respectively. Increasing the pyrolysis temperature and soaking time gave rise to an increase in the gas permeance, and a reduction in the membrane selectivity. This trend was opposite to that for the CMS membranes derived from other polymer precursors. The optimized separation performance (ethylene permeance of 2.97 GPU and ethylene/ethane selectivity of 7.25) could be achieved at the pyrolysis temperature of 650 °C with a soaking time of 1 h. The separation performance of the CMS membrane derived from the PAN precursor was comparable to that of other polymer precursors, and surpassed them regarding the upper bound trade off.

Controlled Synthesis of Metal-Organic Frameworks in Scalable Open-Porous Contactor for Maximizing Carbon Capture Efficiency.

Metal-organic frameworks (MOFs) are a class of microporous materials that have been highlighted with fast and selective sorption of gas molecules; however, they are at least partially unstable in the scale-up process. Here, we report a rational shaping of MOFs in a scalable architecture of fiber sorbent. The long-standing stability challenge of MOFs was resolved by using stable metal oxide precursors that are subject to controlled surface oxide dissolution-growth chemistry during the Mg-based MOF synthesis. Highly uniform MOF crystals are synthesized along with the open-porous fiber sorbents networks, showing unprecedented cyclic CO2 capacities in both flue gas and direct air capture (DAC) conditions. The same chemistry enables an in situ flow synthesis of Mg-MOF fiber sorbents, providing a scalable pathway for MOF synthesis in an inert condition with minimal handling steps. This modular approach can serve both as a reaction stage for enhanced MOF fiber sorbent synthesis and as a "process-ready" separation device.

A Review on Polymer Precursors of Carbon Molecular Sieve Membranes for Olefin/Paraffin Separation.

Carbon molecular sieve (CMS) membranes have been developed to replace or support energy-intensive cryogenic distillation for olefin/paraffin separation. Olefin and paraffin have similar molecular properties, but can be separated effectively by a CMS membrane with a rigid, slit-like pore structure. A variety of polymer precursors can give rise to different outcomes in terms of the structure and performance of CMS membranes. Herein, for olefin/paraffin separation, the CMS membranes derived from a number of polymer precursors (such as polyimides, phenolic resin, and polymers of intrinsic microporosity, PIM) are introduced, and olefin/paraffin separation properties of those membranes are summarized. The effects from incorporation of inorganic materials into polymer precursors and from a pyrolysis process on the properties of CMS membranes are also reviewed. Finally, the prospects and future directions of CMS membranes for olefin/paraffin separation and aging issues are discussed.

Hydrophilic and organophilic pervaporation of industrially important α,ß and α,ω-diols.

The distillation-based purification of α,ß and α,ω-diols is energy and resource intensive, as well as time consuming. Pervaporation separation is considered to be a remarkable energy efficient membrane technology for purification of diols. Thus, as a core pervaporation process, hydrophilic polyvinyl alcohol (PVA) membranes for the removal of water from 1,2-hexanediol (1,2-HDO) and organophilic polydimethylsiloxane-polysulfone (PDMS-PSF) membranes for the removal of isopropanol from 1,5 pentanediol (1,5-PDO) were employed. For 1,2-HDO/water separation using a feed having a 1 : 4 weight ratio of 1,2-HDO/water, the membrane prepared using 4 vol% glutaraldehyde (GA4) showed the best performance, yielding a flux of 0.59 kg m-2 h-1 and a separation factor of 175 at 40 °C. In the organophilic pervaporation separation of the 1,5-PDO/IPA feed having a 9 : 1 weight ratio of components, the PDMS membrane prepared with a molar ratio of TEOS alkoxy groups to PDMS hydroxyl groups of 70 yielded a flux of 0.12 kg m-2 h-1 and separation factor of 17 638 at 40 °C. Long term stability analysis found that both hydrophilic (PVA) and organophilic (PDMS) membranes retained excellent pervaporation output over 18 days' continuous exposure to the feed. Both the hydrophilic and organophilic membranes exhibited promising separation performance at elevated operating conditions, showing their great potential for purification of α,ß and α,ω-diols.

Surface innovation to enhance anti-droplet and hydrophobic behavior of breathable compressed-polyurethane masks.

With the emergence of the coronavirus disease (COVID-19), it is essential that face masks demonstrating significant anti-droplet and hydrophobic characteristics are developed and distributed. In this study, a commercial compressed-polyurethane (C-PU) mask was modified by applying a hydrophobic and anti-droplet coating using a silica sol, which was formed by the hydrolysis of tetraethoxysilane (TEOS) under alkaline conditions and hydrolyzed hexadecyltrimethoxysilane (HDTMS) to achieve hydrophobization. The modified mask (C-PU/Si/HDTMS) demonstrated good water repellency resulting in high water contact angle (132°) and low sliding angle (17°). Unmodified and modified masks were characterized using attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). A drainage test confirmed the strong interaction between the mask surface and coating. Moreover, the coating had negligible effect on the average pore size of the C-PU mask, which retained its high breathability after modification. The application of this coating is a facile approach to impart anti-droplet, hydrophobic, and self-cleaning characteristics to C-PU masks.

Blood Oxygenation Using Fluoropolymer-Based Artificial Lung Membranes.

Artificial lung (AL) membranes are used for blood oxygenation for patients undergoing open-heart surgery or acute lung failures. Current AL technology employs polypropylene and polymethylpentene membranes. Although effective, these membranes suffer from low biocompatibility, leading to undesired blood coagulation and hemolysis over a long term. In this work, we propose a new generation of AL membranes based on amphiphobic fluoropolymers. We employed poly(vinylidene-co-hexafluoropropylene), or PVDF-co-HFP, to fabricate macrovoid-free membranes with an optimal pore size range of 30-50 nm. The phase inversion behavior of PVDF-co-HFP was investigated in detail for structural optimization. To improve the wetting stability of the membranes, the fabricated membranes were coated using Hyflon AD60X, a type of fluoropolymer with an extremely low surface energy. Hyflon-coated materials displayed very low protein adsorption and a high contact angle for both water and blood. In the hydrophobic spectrum, the data showed an inverse relationship between the surface free energy and protein adsorption, suggesting an appropriate direction with respect to biocompatibility for AL research. The blood oxygenation performance was assessed using animal sheep blood, and the fabricated fluoropolymer membranes showed competitive performance to that of commercial polyolefin membranes without any detectable hemolysis. The data also confirmed that the bottleneck in the blood oxygenation performance was not the membrane permeance but rather the rate of mass transfer in the blood phase, highlighting the importance of efficient module design.

Stability and pervaporation characteristics of PVA and its blend with PVAm membranes in a ternary feed mixture containing highly reactive epichlorohydrin.

In order to find an alternative for classical distillation in the recovery of ECH/IPA from azeotropic ECH/IPA/water (50/30/20 w/w, %) mixtures, a pervaporation process has been applied. Membranes from the crosslinking of poly(vinyl alcohol)/poly(vinyl amine) (PVA/PVAm) were prepared, and then the membrane stability and pervaporation efficiency of the crosslinked PVA/PVAm membranes were studied for highly reactive ECH systems containing a ternary feed mixture. From the Fourier-transform infrared (FT-IR) spectroscopy analysis, it was observed that all of the membranes were chemically stable for 15 days of immersion in a 50 : 30 : 20 ECH/IPA/water (w/w, %) feed mixture at 60 °C. The degree of membrane swelling increased with increasing PVAm content in the membrane composition, water content in the feed composition, and feed temperature, which was attributed to the increase in the number of hydrophilic sites in the membrane. The field-emission scanning electron microscopy (FE-SEM) study revealed that higher PVAm content membranes (PVAm1.0 and PVAm1.5) show polymer phase extraction in ECH/IPA/water (50 : 30 : 20) (w/w, %) at 60 °C in long-term stability tests. The pervaporation dehydration characteristics for all of the membranes with the feed comprising an ECH/IPA/water (50 : 30 : 20 by weight) azeotropic mixture at 30 °C were examined and excellent pervaporation dehydration efficiency was found. Quantitatively, the flux increased from 0.025 to 0.32 kg (m2 h)-1 and the separation factor decreased from 1908 to 60 with increasing PVAm content in the blended membrane.

Ag-exchanged NaY zeolite introduced polyvinyl alcohol/polyacrylic acid mixed matrix membrane for pervaporation separation of water/isopropanol mixture.

Ag-exchanged NaY zeolite (Ag-NaZ) particles were prepared by ion exchange and introduced to a polyvinyl alcohol (PVA) membrane cross-linked with polyacrylic acid (PAA) for the pervaporation dehydration of an isopropanol (IPA) aqueous mixture. The Ag-exchanged NaY zeolite particles were characterized by FE-SEM, EDS, BET, and XRD studies. The prepared Ag-NaZ-loaded PVA/PAA composite membrane was characterized by FE-SEM, XRD, a swelling study, and contact angle measurements. Pervaporation characteristics were investigated in terms of Ag-NaZ concentrations within PVA/PAA membranes using diverse feed solution conditions. The preferential sorption of IPA/water mixtures for Ag-NaZ-introduced membranes were also determined by calculating the apparent activation energies of IPA and water permeation, respectively. As a result, flux and selectivity increased with the Ag-NaZ concentration to 5 wt% in the membrane. Optimum pervaporation performance was observed in a 5 wt% Ag-NaZ-incorporated membrane with a flux equal to 0.084 kg m-2 h-1 and a separation factor of 2717.9 at 40 °C from an 80 wt% IPA aqueous feed solution.