Search Results (404)

Highly permeable and selective membranes are crucial for energy-efficient gas separation. Two-dimensional (2D) graphitic carbon nitride (g-C₃N₄) has attracted significant attention due to its unique structural characteristics, including ultra-thin thickness, inherent surface porosity, and abundant amine groups. However, the interfacial defects caused by poor compatibility between g-C₃N₄ and polymers deteriorate the separation performance of membrane materials. In this study, amino-functionalized g-C₃N₄ nanosheets (CN@PEI) was prepared by a post-synthesis method, then blended with the polymer Pebax to fabricate Pebax/CN@PEI mixed matrix membranes (MMMs). Compared to g-C₃N₄, MMMs with CN@PEI loading of 20 wt% as nanofiller exhibited a CO₂ permeance of 241 Barrer as well as the CO₂/CH₄ and CO₂/N₂ selectivity of 39.7 and 61.2, respectively, at the feed gas pressure of 2 bar, which approaches the 2008 Robeson upper bound and exceeded the 1991 Robeson upper bound. The Pebax/CN@PEI (20) membrane showed robust stability performance over 70 h continuous gas permeability testing, and no significant decline was observed. SEM characterization revealed a uniform dispersion of CN@PEI throughout the Pebax matrix, demonstrating excellent interfacial compatibility between the components. The increased free volume fraction, enhanced solubility, and higher diffusion coefficient demonstrated that the incorporation of CN@PEI nanosheets introduced more CO₂-philic amino groups and disrupted the chain packing of the Pebax matrix, thereby creating additional diffusion channels and facilitating CO₂ transport. Full article

Developing highly permeable and selective membranes for energy-efficient CO₂/CH₄ separation remains challenging. Mixed-matrix membranes (MMMs) integrating polymer matrices with metal–organic frameworks (MOFs) offer significant potential. However, rational filler–matrix matching presents substantial difficulties, constraining separation performance. In this work, defects were engineered within fluorinated MOF ZU-61 through the partial replacement of 4,4′-bipyridine linkers with pyridine modulators, producing high-porosity HP-ZU-61 nanoparticles exhibiting a 267% BET surface area enhancement (992.9 m² g⁻¹) over low-porosity ZU-61 (LP-ZU-61) (372.2 m² g⁻¹). The HP-ZU-61/6FDA-DAM MMMs (30 wt.%) demonstrated homogeneous filler dispersion and pre-served crystallinity, achieving a CO₂ permeability of 1626 barrer and CO₂/CH₄ selectivity (33), surpassing the 2008 Robeson upper bound. Solution-diffusion modeling indicated ligand deficiencies generated accelerated diffusion pathways, while defect-induced unsaturated metal sites functioned as strong CO₂ adsorption centers that maintained solubility selectivity. This study establishes defect engineering in fluorinated MOF-based MMMs as a practical strategy to concurrently overcome the permeability–selectivity trade-off for efficient CO₂ capture. Full article

MOF-808 was synthesized using different (perfluoro)carboxylic acid modulators, including acetic acid (AA), butyric acid (BA), trifluoroacetic acid (TFAA) and heptafluorobutyric acid (HFBA). These samples were incorporated into co-polyimide 6FDA-DAM:DABA (6FDD), and the performance of the resulting MMMs was assessed for C₂ and C₃ olefin/paraffin separation. Enhanced permeability was observed for both C₂H₄/C₂H₆ and C₃H₆/C₃H₈ mixtures thanks to the introduced porosity upon filler incorporation in all cases. Due to the large pore size of MOF-808, diffusion-selective permeation through the polymer phase of the MMMs determined the eventual selectivity for C2 gases, leading to separation factors similar to that of the unfilled 6FDD membrane. For C₃H₆/C₃H₈ separation, the incorporation of fluorinated MOFs significantly improved separation performance, unlike their non-fluorinated counterparts. The unfilled 6FDD membrane exhibited a C₃H₆/C₃H₈ separation factor of 7.4 with a C₃H₆ permeability of 22 Barrer, while the incorporation of MOF-808-TFAA and MOF-808-HFBA led to C₃H₆/C₃H₈ separation factors of 13.1 and 13.5 with corresponding improved C₃H₆ permeabilities of 42 Barrer and 33 Barrer, respectively. Considering that these MMMs showed C₃H₆ permeabilities similar to those of MMMs containing their non-fluorinated MOF counterparts that exhibited no enhancement in membrane selectivity, the improved C₃H₆/C₃H₈ separation factor was attributed to the preferential adsorption of C₃H₈ over C3H6 on the fluorinated MOFs, acting as a trap for C₃H₈ and reducing its diffusivity. These results highlight the significance of matching the permeation characteristics of the selected polymer-filler pair on MMM performance for different gas pairs. Full article

Wider adoption of membrane technology is hindered by fouling and flux/rejection challenges. Recent practice in mitigating these is to incorporate hydrophilic and porous fillers. Herein the addition of hydrophilic graphene oxide (GO) in conjunction with porous mixed ZIFs (ZIF-67/ZIF-8) crystallites were used as inorganic fillers in the preparation of polyphenylenesulfone (PPSU) ultrafiltration (UF) membranes. The morphology of the resultant composite membranes was assessed using atomic force microscopy (AFM) and scanning electron microscopy (SEM) whilst surface hydrophilicity through water contact angle. The pure water flux (PWF) and membrane permeability were found to increase with increasing filler content. This was attributed to the combined hydrophilicity of GO and porous structure of the ZIF materials because of increasing alternative water pathways in the membrane matrix with increasing filler content. Furthermore, the increase in the ZIF component led to increasing bovine serum albumin (BSA) fouling resistance as demonstrated by increasing fouling recovery ratio (FRR). The dye rejection was due to a combination of electrostatic interaction between the fillers and the dyes as well as size exclusion. The chemical interactions between the ZIFs and the dyes resulted in slightly different rejection profiles for the smaller dyes, the cationic methylene blue being rejected less efficiently than the anionic methyl orange, potentially leading to their separation. The larger anionic dye, Congo red was rejected predominately through size exclusion. Full article

Bioelectrochemical systems (BESs) are technologies capable of converting chemical energy into electrical energy or producing value-added compounds. These systems typically employ Nafion membranes as proton exchange separators; however, Nafion is costly and prone to fouling. In this study, mixed-matrix membranes (MMMs) based on chitosan and its derivatives, incorporated with Er- and Al-doped ZnO nanoparticles, were synthesized and evaluated. Key properties assessed included antimicrobial activity, antifouling behavior, chemical stability, water retention, and proton conductivity. The results demonstrated that the chitosan-based membranes doped with Er/Al/ZnO outperformed Nafion in terms of antifouling properties, water retention, and a protective effect on the surface of the membrane against Escherichia coli and Staphylococcus aureus, while exhibiting comparable proton conductivity and chemical stability. Full article

Developing efficient bio-based membranes is key to sustainable wastewater treatment, especially when they can be applied across multiple separation processes for components of varying molecular weights. This study reports the development and characterization of bio-based mixed matrix membranes from carboxymethyl cellulose (CMC) modified with synthesized carboxylated graphene oxide (GOCOOH), aimed at improving performance in both pervaporation and nanofiltration for water treatment. Membrane design was optimized by adjusting the GOCOOH content, applying chemical cross-linking (by immersing in glutaraldehyde with H₂SO₄), and developing highly effective supported membranes (by the deposition of a thin selective CMC-based layer onto a porous substrate). Comprehensive characterization was performed using spectroscopic, microscopic, and thermogravimetric analyses and contact angle measurements. The optimized cross-linked supported CMC/GOCOOH (5%) membrane demonstrated significantly improved transport properties: a 2.5-fold increased permeation flux and over 99.9 wt.% water in permeate in pervaporation dehydration of isopropanol, and high rejection rates—above 98.5% for anionic dyes and over 99.8% for heavy metal ions in nanofiltration. These findings demonstrate that CMC/GOCOOH membranes are promising, sustainable materials suitable for multiple separation processes involving components of varying molecular weights, contributing to more efficient and eco-friendly wastewater treatment solutions. Full article

Background: Polybasic peptides are being developed as components of reagents for diagnosing and treating patients with systemic amyloidosis. In addition to fibrils, amyloid deposits ubiquitously contain heparan sulfate proteoglycans. We have hypothesized that pan amyloid-targeting peptides can specifically engage, in addition to fibrils, a subset of glycosaminoglycans (GAGs) with high negative charge density. In this study, we characterized the binding of peptides p5+14 (a PET imaging agent for amyloid [¹²⁴I-evuzamitide]) and p5R (a fusion protein used in the therapeutic AT-02) to GAGs. Methods: The peptide structure was evaluated in the presence of low molecular weight heparin using circular dichroism, and their interaction with synthetic GAGs of varying length and charge was interrogated. The binding patterns of p5+14 and p5R were compared using correlation analyses. Results: The peptides exist as mixed structural-fractions in solution but adopt an α-helical structure in the presence of heparin. Both peptides preferentially recognize heparin and heparan sulfate GAGs with a linear positive correlation between binding and the total charge and charge density. Conclusions: These peptides have previously been shown to specifically target amyloid deposits in vivo. A component of this specificity is their preferential interaction with a subset of heparan sulfate GAGs that have high charge density, potentially related to the degree of 6-O-sulfation. These data support the hypotheses that amyloid-associated GAGs have unique sulfation patterns, thereby explaining why these peptides do not bind GAGs found on the plasma membrane and extracellular matrix of healthy tissues. Full article

Under elevated loading conditions, the aggregation of fillers emerges as a pivotal factor driving the degradation of separation performance in mixed matrix membranes. The two-dimensional (2D) modification of fillers, aimed at enhancing interfacial contact with polymers, has been recognized as an effective strategy to improve interphase compatibility and increase filler loading capacity. However, it is worth noting that the BET surface area of 2D fillers is typically relatively low. In this study, a two-step approach was developed. First, a “diffusion-mediated” process was combined with a solvent optimization strategy based on first-principles (DFT) calculations, achieving a 20-fold suppression in ZIF-67 nucleation-crystallization rate. This enabled the successful synthesis of a 2D amorphous nanoflower structure. Subsequently, the processing parameters were fine-tuned to enhance the specific surface area of ZIF-67 to 403 m²/g while preserving its 2D structural integrity. Ultimately, the as-prepared 2D ZIF-67 was incorporated into a hydrogenated styrene-butadiene block copolymer (SEBS) matrix to fabricate a mixed matrix membrane. Remarkably, at a filler loading of 20 wt%, the CH₄ permeability coefficient increased significantly from 11.7 barrer to 35.3 barrer, while the CH₄/N₂ selectivity was maintained at 3.21, indicating minimal interfacial defects and demonstrating the feasibility and effectiveness of the proposed methodology. Full article

Cu-BTC (HKUST-1) metal–organic framework (MOF) is widely recognized for its carbon capture capability due to its unsaturated copper sites, high surface area, and well-defined porous structure. This study developed mixed matrix membranes (MMMs) using cellulose triacetate (CTA), incorporating bimetallic Ni-Cu-BTC MOFs for CO₂/CH₄ separation, and benchmarked them against membranes fabricated with monometallic Cu-BTC. CTA was selected for its biodegradability, membrane-forming properties, and cost-effectiveness. The optimized membrane with 10 wt.% Ni-Cu-BTC achieved a CO₂ permeability of 22.9 Barrer at 25 °C and 5 bar—more than twice that of pristine CTA—with a CO₂/CH₄ selectivity of 33.8. This improvement stems from a 51.66% increase in fractional free volume, a 49.30% rise in the solubility coefficient, and a 51.94% boost in the diffusivity coefficient. Dual-sorption model analysis further confirmed enhanced solubility and adsorption mechanisms. These findings establish CTA/Ni-Cu-BTC membranes as promising candidates for high-performance CO₂ separation in natural gas purification and related industrial processes. Full article

The growing scarcity of freshwater worldwide has increased interest in forward osmosis (FO) membranes as a promising solution for water desalination and wastewater treatment. This study investigates the enhancement of thin-film composite (TFC) FO membranes via the incorporation of carboxyl-functionalized multiwalled carbon nanotubes (COOH-MWCNTs) into the polyethersulfone (PES) support layer. The membranes were fabricated using a combination of phase inversion and interfacial polymerization techniques, with COOH-MWCNTs incorporated into the membrane support layers at different concentrations (0–0.75 wt.%). Comprehensive characterization was carried out using various analytical methods and mechanical testing to evaluate the physicochemical and structural properties of the membranes. The modified membranes demonstrated improved hydrophilicity, enhanced mechanical and thermal stability, and improved surface charge properties. Performance tests using a 1 M NaCl draw solution showed that the optimized membrane (0.5 wt.% COOH-MWCNTs) attained a 161% enhancement in water flux (7.48 LMH) compared to the unmodified membrane (2.86 LMH), while also reducing internal concentration polarization (ICP). The antifouling properties were also significantly improved, with a flux recovery rate of 91.92%, attributed to enhanced electrostatic repulsion as well as surface and microstructural modifications. Despite a moderate rise in reverse solute flux, the specific reverse solute flux (J_s/J_w) remained within acceptable limits. These findings highlight the potential of COOH-MWCNT-modified membranes in enhancing FO desalination performance, offering a promising option for next-generation water purification technologies. Full article

The demand for anion exchange membranes (AEMs) is growing due to their applications in water electrolysis, CO₂ reduction conversion and fuel cells, as well as water treatment, driven by the increasing energy demand and the need for a sustainable future. However, current AEMs still face challenges, such as insufficient permeability and stability in strongly acidic or alkaline media, which limit their durability and the sustainability of membrane fabrication. In this study, polyvinyl alcohol (PVA) and chitosan (CS) biopolymers are selected for membrane preparation. Zinc oxide (ZnO) and porous organic polymer (POP) nanoparticles are also introduced within the PVA-CS polymer blends to make mixed-matrix membranes (MMMs) with increased OH⁻ transport sites. The membranes are characterized based on typical properties for AEM applications, such as thickness, water uptake, KOH uptake, Cl⁻ and OH⁻ permeability and ion exchange capacity (IEC). The OH⁻ transport of the PVA-CS blend is increased by at least 94.2% compared with commercial membranes. The incorporation of non-porous ZnO and porous POP nanoparticles into the polymer blend does not compromise the OH⁻ transport properties. On the contrary, ZnO nanoparticles enhance the membrane’s water retention capacity, provide basic surface sites that facilitate hydroxide ion conduction and reinforce the mechanical and thermal stability. In parallel, POPs introduce a highly porous architecture that increases the internal surface area and promotes the formation of continuous hydrated pathways, essential to efficient OH⁻ mobility. Furthermore, the presence of POPs also contributes to reinforcing the mechanical integrity of the membrane. Thus, PVA-CS bio-based membranes are a promising alternative to conventional ion exchange membranes for various applications. Full article

In this paper, MXene nanosheets were used as nano additives for the preparation of MXene-modified polyvinyl chloride (PVC) mixed max membranes (MMMs) for the rejection of lead (Pb²⁺) ions from wastewater. MXene nanosheets were introduced into the PVC matrix to enhance membrane performance, hydrophilicity, contact angle, porosity, and resistance to fouling. Modeling and optimization techniques were used to examine the effects of important operational and fabrication parameters, such as pH, contaminant concentration, nanoadditive (MXene) content, and operating pressure. Predictive models were developed using experimental data to assess the membranes’ performance in terms of flux and Pb²⁺ rejection. The ideal circumstances that struck a balance between long-term operating stability and high removal efficiency were found through multi-variable optimization. The optimized conditions for the best rejection of Pb²⁺ ions and the most stable permeability over time among the membranes that were manufactured were the initial metal ions concentration (2 mg/L), pH (7.89), pressure (2.99 bar), and MXene mass (0.3 g). The possibility of combining MXene nanoparticles with methodical optimization techniques to create efficient membranes for the removal of heavy metals in wastewater treatment applications is highlighted by this work. Full article

Water scarcity poses a formidable challenge around the world, especially in arid regions where limited availability of freshwater resources threatens both human well-being and ecosystem sustainability. Membrane-based desalination technologies offer a viable solution to address this issue by providing access to clean water. This work ultimately aims to develop a novel permselective polymeric membrane material to be employed in an electrochemical desalination system. This part of the study addresses the optimization, preparation, and characterization of a polyvinylidene difluoride (PVDF) polymeric membrane using the electrospinning technique. The membranes produced in this work were fabricated under specific operational, environmental, and material parameters. Five different additives and nano-additives, i.e., graphene oxide (GO), carbon nanotubes (CNTs), zinc oxide (ZnO), activated carbon (AC), and a zeolitic imidazolate metal–organic framework (ZIF-8), were used to modify the functionality and selectivity of the prepared PVDF membranes. Each membrane was synthesized at two different levels of additive composition, i.e., 0.18 wt.% and 0.45 wt.% of the entire PVDF polymeric solution. The physiochemical properties of the prepared membranes were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), zeta potential, contact angle, conductivity, porosity, and pore size distribution. Based on findings of this study, PVDF/GO membrane exhibited superior results, with an electrical conductivity of 5.611 mS/cm, an average pore size of 2.086 µm, and a surface charge of −38.33 mV. Full article

Hybrid materials based on porous organic polymers (POPs) and metal–organic frameworks (MOFs) are increasing attention for advanced separation processes due to the possibility to combine their properties. POPs provide high surface areas, chemical stability, and tunable porosity, while MOFs contribute a high variety of defined crystalline structures and enhanced separation characteristics. The combination (or hybridization) with PIMs gives rise to mixed-matrix membranes (MMMs) with improved permeability, selectivity, and long-term stability. However, interfacial compatibility remains a key limitation, often addressed through polymer functionalization or controlled dispersion of the MOF phase. MOF/COF hybrids are more used as biochemical sensors with elevated sensitivity, catalytic applications, and wastewater remediation. They are also very well known in the gas sorption and separation field, due to their tunable porosity and high electrical conductivity, which also makes them feasible for energy storage applications. Last but not less important, hybrids with other POPs, such as hyper-crosslinked polymers (HCPs), covalent triazine frameworks (CTFs), or conjugated microporous polymers (CMPs), offer enhanced functionality. MOF/HCP hybrids combine ease of synthesis and chemical robustness with tunable porosity. MOF/CTF hybrids provide superior thermal and chemical stability under harsh conditions, while MOF/CMP hybrids introduce π-conjugation for enhanced conductivity and photocatalytic activity. These and other findings confirm the potential of MOF-POP hybrids as next-generation materials for gas separation and carbon capture applications. Full article

Polyethersulfone (PES) membranes are essential in separation processes; however, their inherent hydrophobicity can limit their effectiveness in water-intensive applications. This study aims to enhance PES membranes by modifying them with a NiFe₂O₄–nanoclay composite nanoparticle to improve both their hydrophilicity and photocatalytic potential as a photocatalytic membrane. The nanoparticles were synthesized using the sol–gel auto-combustion method and incorporated into PES membranes through mixed-matrix embedding (1 wt% and 3 wt%) and surface coating. X-ray diffraction confirmed the cubic spinel structure of the composite nanoparticles, which followed the second order kinetic reaction during the photodegradation–adsorption of crystal violet. The mixed-matrix membranes displayed a remarkable 170% increase in water flux and a 25% improvement in mechanical strength, accompanied by a slight decrease in contact angle at 1 wt% of nanoparticle loading. In contrast, the surface-coated membranes demonstrated a significant reduction in contact angle to 18°, indicating a highly hydrophilic surface and increased roughness. All membranes achieved high dye removal rates of 98–99%, but only the coated membrane system exhibited approximately 50% photocatalytic degradation, following mixed kinetics. These results highlight the critical importance of surface modification in advancing PES membranes, as it significantly reduces fouling and enhances water–material interaction qualities essential for future filtration and photocatalytic applications. Exploring hybrid strategies that combine both embedding and coating approaches may yield even greater synergies in membrane functionality. Full article