Search Results (238)

Reactive oxygen species (ROS) play a dual role in biological systems as indispensable signaling molecules and as key mediators of oxidative damage. Chronic wounds are often associated with excessive ROS formation, which impedes the healing process. Locally applied antioxidants may mitigate such imbalance and support tissue regeneration. The chitosan–hyaluronan (Ch/HA) composite membranes’ biocompatibility, moisture retention, and ability to maintain local redox balance rank these materials among the most promising next-generation wound dressings. The aim of this review is to summarize the Ch/HA composite membranes serving as reservoirs for locally applied antioxidants to accelerate the healing of full-thickness skin wounds in experimental animals. Composite Ch/HA membranes fortified with the selected antioxidants such as phosphatidylcholine dihydroquercetin and glutathione were evaluated in rats. A mitochondria-targeted derivative such as mitoquinone mesylate was evaluated in rats and rabbits, while l-(+)-ergothioneine has been examined in rabbits so far. This review demonstrates that smartly designed Ch/HA composite membranes represent a novel-generation wound dressing platform capable of smart antioxidant release and efficient stimulation of skin regeneration. Full article

Biogas upgrading to biomethane is an important route for increasing the energy value of renewable gas streams and enabling their wider use in fuel, heat, and power applications. In the present study, a two-stage membrane process for biogas upgrading was developed and validated using polysulfone (PSF) and polyetherimide (PEI) hollow-fiber membranes. The main original aspects of this work include the formulation of a PEI/DMF/IPA spinning dope composition (27/60/13 wt.%), the mixed-gas testing of PSF and PEI hollow-fiber membranes in a six-component model biogas mixture, and the combined simulation, experimental validation, and techno-economic evaluation of a two-stage membrane process. Mixed-gas permeation experiments with a six-component model biogas mixture were used as the basis for process simulation of four membrane-stage configurations. Only the PSF + PEI cascade simultaneously provided methane recovery above 90%, methane concentration in the product above 95 mol.%, and residual carbon dioxide content below 2 mol.%. Experimental verification confirmed the modeled process concept and demonstrated that the target biomethane quality was achieved at feed flow rates of 0.9–1.1 L min⁻¹, where methane recovery reached 93.5–95.2% and methane purity was 95.5–96.2 mol.%. A preliminary techno-economic analysis for a 100 m³ h⁻¹ unit indicated an upgrading penalty of USD 96.4 per ton of 95.5 mol.% CH₄. PSF membranes provided higher carbon dioxide permeance, whereas PEI membranes exhibited higher CO₂/CH₄ selectivity, which explains the efficiency of their combination in the two-stage scheme. The results show that the proposed PSF + PEI cascade is a promising membrane-based approach for energy-efficient biogas upgrading. Full article

Ceramic membranes show potential for high-temperature CO₂ extraction from flue gas; nevertheless, their performance under simultaneous heat and pressure stress is not well comprehended. This research addresses the temperature-dependent CO₂/N₂ separation characteristics of a commercial ceramic membrane (pore size ~0.1–1 µm) utilizing simulated flue gas (11.8% CO₂, 74.2% N₂, 2.5% O₂, remainder CH₄) at temperatures ranging from 60 to 140 °C and pressures between 4 and 6 bar. Calibrated GC-TCD was used to quantify permeate compositions across multiple operating valve openings. With a CO₂/N₂ selectivity (α) of 0.75 at 4 bars, the maximum CO₂ enrichment peaked at 80 °C (10.8 mol%), getting close to the Knudsen diffusion limit (0.80). Selectivity decreased dramatically beyond 100 °C—α = 0.61 (100 °C), 0.45 (140 °C)—and CO₂ dropped to 5.8% at 4 bar and 2.2% at 6 bars. Viscous flow dominance was shown by the strong pressure amplification—α decreased by more than 60% from 4 to 6 bar at all temperatures. These findings emphasize the possibility of performance collapse in hot, pressured flue streams and identify the limited operating window under which Knudsen-controlled transport can be maintained. The study provides quantitative evidence of a transition in transport regime under mixed flue-gas conditions. Full article

The global energy transition and the implementation of carbon capture, utilization, and storage (CCUS) strategies require energy-efficient and scalable CO₂ separation technologies. Mixed-matrix membranes (MMMs), combining polymer matrices with functional inorganic or hybrid nanofillers, have emerged as advanced separation platforms capable of surpassing the conventional permeability–selectivity trade-off observed in neat polymer membranes. This review critically evaluates recent developments in modern hybrid membranes for CO₂ separation from synthetic and industrial gas mixtures, including CO₂/N₂ (flue gas), CO₂/CH₄ (natural gas and biogas upgrading), and syngas systems. Particular emphasis is placed on MMMs incorporating covalent organic frameworks (COFs), metal–organic frameworks (MOFs), graphene oxide (GO), MXenes, transition metal dichalcogenides (TMDs), carbon nanotubes (CNTs), g-C₃N₄, layered double hydroxides (LDH), zeolites, metal oxides, and magnetic nanoparticles. Reported performance ranges include CO₂ permeability (P_CO2) typically between 100 and 800 Barrer, CO₂/N₂ selectivity up to 319, and CO₂/CH₄ selectivity up to 249, depending on filler chemistry, loading, and interfacial compatibility. The mechanisms governing gas transport—molecular sieving, selective adsorption, facilitated transport, and diffusion-pathway engineering—are systematically discussed. Key challenges addressed include filler dispersion, polymer–filler interfacial defects, physical aging, moisture sensitivity, oxidation (particularly in MXenes), and scalability toward industrial membrane modules. Future perspectives focus on sub-nanometer pore engineering, surface functionalization to enhance CO₂ affinity, controlled alignment of 2D nanosheets to promote directional transport, multifunctional core–shell and hollow structures, and the integration of computational modeling and machine learning for accelerated material design. Modern hybrid MMMs are identified as strategically important materials enabling high-efficiency CO₂ separation processes aligned with decarbonization and energy transition objectives. Full article

Polyetherimide (Ultem-1000) hollow-fiber membranes were developed for biogas purification with emphasis on the relationship between spinning conditions, membrane morphology, gas transport properties, and module performance. Hollow fibers were prepared from dope solutions based on dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP) at different conditions, followed by post-treatment with 1 and 3 wt.% silicone solution in n-heptane to reduce nonselective defects and improve selectivity toward the intrinsic behavior of dense PEI films. SEM analysis revealed that DMF-based fibers formed a more open, macrovoid-rich structure, whereas NMP-based fibers exhibited a more homogeneous sponge-like morphology with a better-defined selective layer. DMF-based fibers experienced faster demixing, which promoted macrovoid formation, increased pore connectivity of the substructure, lowered mass transfer resistance, and at the same time increased the probability of nonselective pathways and defect-related loss of selectivity. This structural evolution was reflected in gas transport properties: untreated DMF fibers showed high mixed-gas permeance but limited selectivity, while NMP fibers demonstrated lower permeance and selectivity values closer to those of the dense film. Silicone post-treatment significantly improved separation performance, with 3 wt.% coating being markedly more effective than 1 wt.% coating. The best compromise between permeance and selectivity was achieved for the DMF-based fibers treated with 3 wt.% silicone, which exhibited CO₂ and H₂S permeances of 39.4 and 47.12 GPU, respectively, together with selectivity values of 22.4, 26.8 and 20.2 for CO₂/CH₄, H₂S/CH₄ and CO₂/N₂. A membrane module containing 500 fibers was studied during the quasi-real biogas upgrading. With increasing stage-cut, the CH₄ concentration in the retentate increased from ~74 to 96 mol.%, while CO₂ decreased from ~21 to 2 mol.%. The results demonstrate that structure control combined with silicone post-treatment is an effective strategy for producing PEI hollow fibers suitable for simultaneous methane enrichment and removal of acid impurities from biogas. Full article

Conventional high-temperature calcination for activating MFI zeolite membranes is energy-intensive and prone to inducing defects. Here, we demonstrate that a rapid ozonation treatment at 200 °C for only 1 h effectively decomposes organic templates while preserving membrane integrity. The resulting membrane exhibits H₂/CH₄ and H₂/N₂ ideal selectivities of 10.3 and 6.5, respectively, at room temperature, with C₃H₈ and SF₆ permeances below the detection limit. These results confirm a dense, defect-minimized architecture and good molecular sieving performance of the zeolite membrane. In contrast, extending ozonation to 48 h leads to defect formation and a marked reduction in selectivity. For H₂/CH₄ mixture separation, the membrane achieves a selectivity of 23.8 at 100 °C, which is highly competitive among reported MFI membranes. In isopropanol dehydration, it achieves a water flux of 2.3 kg·m⁻²·h⁻¹ and a separation factor of 3278 at 70 °C with a 10 wt% water feed, while maintaining >99.5 wt% water content in the permeate over a broad operating temperature range (30–70 °C). This work establishes rapid ozonation as a scalable, energy-efficient activation method for high-performance MFI zeolite membranes in both gas and liquid separations. Full article

Renewable hydrogen purification is a critical yet often underemphasised step in enabling its use as a clean energy carrier. Hydrogen produced from biomass-based thermochemical and biological routes typically contains CO₂, CO, CH₄, H₂S, and other impurities that must be removed to meet stringent requirements for fuel cell, industrial, and grid-injection applications. This review provides a critical and up-to-date assessment of renewable hydrogen purification technologies, focusing on their suitability for variable and impurity-rich renewable hydrogen streams. Established benchmark technologies, including pressure swing adsorption and cryogenic separation, are described, with emphasis on their operating principles, material innovations, and process integration strategies. Recent advancements in inorganic, polymeric, and mixed-matrix membranes are highlighted, with particular focus on how advanced porous materials enhance selectivity, permeability, and flexibility. Additionally, a comparative techno-economic assessment is presented, evaluating each purification method based on technology readiness level, capital and maintenance costs, energy efficiency, and operational lifespan. By incorporating recent research trends, this approach facilitates the selection and design of purification systems that are not only efficient and scalable but also cost-effective, tailored to both decentralised and centralised renewable hydrogen production. Full article

Fabricating polyimide (PI) membranes with outstanding anti-plasticization ability and gas separation performance remains a challenge. In this study, two novel diamine monomers, DAMBO (methyl 3,5-diamino-4-methylbenzoate) and DAPGBO (3-hydroxypropyl 3,5-diamino-4-methylbenzoate), were synthesized through esterification reactions. Then, we copolymerized each of these two new monomers with 4,4′-diaminodiphenylmethane (DAM) and 4,4′-(Hexafluoroisopropylidene) diphthalic anhydride (6FDA) separately to yield two monoesterified PIs. Following this, we further prepared the ester-crosslinked PIs by inducing a transesterification crosslinking reaction within the PI-PGBO membrane via thermal treatment. As expected, we found that the formation of cross-linked structures can effectively regulate the microporous structure, enhance its sieving performance, and thus improve the membrane’s gas selectivity. Furthermore, the resulting network structure endowed the thermally treated PI membrane with excellent anti-plasticization ability. Physical characterization results show that after heat treatment, both the d-spacing and BET surface area of the PI membrane decreased, but the solvent resistance of the thermally treated PIs was significantly improved. Gas separation experiments revealed that the representative membrane (PI-PGBO-300) exhibited the optimal CO₂/CH₄ separation performance, with a CO₂ permeability of 371.05 Barrer, a CO₂/CH₄ selectivity of 28.11, and a CO₂ plasticization pressure exceeding 30 bar. This study provides valuable insights into the design of cross-linked polyimides (PIs) via transesterification reactions, which are capable of enhancing the performance of membrane-based gas separation processes. Full article

This work explores a novel and efficient synthetic approach to a new class of boron cluster derivatives via the nucleophilic addition of stabilized phosphorus ylides, Ph₃P=CHR² (R² = COOEt, CN), to a series of nitrilium salts of the closo-decaborate anion, [2-B₁₀H₉NCR¹]⁻ (R¹ = Me, Et, ⁿPr, ⁱPr, Ph). The reaction proceeds regio- and stereospecifically, affording a diverse range of iminoacyl phosphorane derivatives, [2-B₁₀H₉NH=C(R¹)C(PPh₃)R²]⁻, in high isolated yields (up to 95%). The obtained compounds (10 examples) were isolated as tetrabutylammonium or tetraphenylphosphonium salts and thoroughly characterized by multinuclear NMR (¹¹B, ¹H, ¹³C, ³¹P), high-resolution mass spectrometry, and single-crystal X-ray diffraction. The reaction feasibility was found to be strongly influenced by the steric hindrance of the R¹ group. Furthermore, the practical utility of these novel hybrids was demonstrated by employing the [2-B₁₀H₉NH=C(CH₃)C(COOC₂H₅)=PPh₃]⁻ anion as a highly effective membrane-active component in ion-selective electrodes. The developed tetraphenylphosphonium (TPP⁺) sensor exhibited a near-Nernstian response, a low detection limit of 3 × 10⁻⁸ M, and excellent selectivity over a range of common inorganic and organic cations, showcasing the potential of closo-borate-based ionophores in analytical chemistry. Full article

Polysulfone (PSU) membranes are widely recognized for their thermal stability, mechanical strength, and chemical resistance, making them suitable for diverse separation applications. This review highlights recent advances in PSU membrane development, focusing on fabrication techniques, structural modifications, and emerging applications. Phase inversion remains the predominant method for membrane synthesis, allowing precise control over morphology and performance. Functional enhancements through blending, chemical grafting, and incorporation of nanomaterials—such as metal–organic frameworks (MOFs), carbon nanotubes, and zwitterionic polymers—have significantly improved gas separation, and water purification., In gas separation, PSU-based mixed matrix membranes demonstrate enhanced CO₂/CH₄ selectivity, particularly when integrated with MOFs like ZIF-7 and ZIF-8. In water treatment, PSU membranes effectively remove algal toxins and heavy metals, with surface modifications improving hydrophilicity and antifouling properties. Despite these advancements, challenges remain in optimizing cross-linking strategies and understanding structure–property relationships. This review provides a comprehensive overview of PSU membrane technologies and outlines future directions for their development in sustainable and high-performance separation systems. Full article

The biogas dry reforming reaction offers a promising route for syngas production while simultaneously mitigating greenhouse gas emissions. Membrane reactors have proven to be an excellent option for hydrogen production and separation in a single unit, where conversion and yield can be enhanced over conventional processes. In this study, a Pd/YSZ membrane integrated with a Ru/CeO₂ catalyst was evaluated for biogas reaction under varying operating conditions. The selective removal of hydrogen through the palladium membrane improved reactant conversion and suppressed side reactions such as methanation and the reverse water–gas shift. Experiments were performed at temperatures ranging from 500 to 600 °C, pressures of 1–6 bar, and a gas hourly space velocity (GHSV) of 800 h⁻¹. Maximum conversions of CH₄ (43%) and CO₂ (46.7%) were achieved at 600 °C and 2 bar, while the maximum hydrogen recovery of 78% was reached at 6 bar. The membrane reactor outperformed a conventional reactor, offering up to 10% higher CH₄ conversion and improved hydrogen production and yield. Also, a comparative analysis between Ru/CeO₂ and Ni/Al₂O₃ catalysts revealed that while the Ni-based catalyst provided higher CH₄ conversion, it also promoted methane decomposition reaction and coke formation. In contrast, the Ru/CeO₂ catalyst exhibited excellent resistance to coke formation, attributable to ceria’s redox properties and oxygen storage capacity. The combined system of Ru/CeO₂ catalyst and Pd/YSZ membrane offers an effective and sustainable approach for hydrogen-rich syngas production from biogas, with improved performance and long-term stability. Full article

This research focuses on developing and optimizing mixed matrix membranes (MMMs) by incorporating graphene oxide (GO) into a polysulfone (PSF) matrix to enhance the separation performance of CO₂ and CH₄. The morphology and gas separation performance of the MMMs were systematically characterized. The incorporation of GO enhanced gas permeation and CO₂/CH₄ selectivity, as evaluated using a gas permeation setup. Notably, the PSF/GO-0.3 wt.% membrane exhibited superior performance, achieving a CO₂ permeability of 21.63 Barrer, among the highest reported for PSF-based MMMs. Additionally, the membrane demonstrated a CO₂/CH₄ selectivity of 14.32, highlighting its effectiveness in distinguishing between the two gases, which is essential for carbon capture and natural gas decontamination applications. The uniform distribution of GO within the polymer matrix contributed to the membrane’s enhanced performance. Furthermore, the MMMs exhibited outstanding resistance to CO₂ plasticization, with the PSF/GO-0.3 wt.% membrane maintaining its performance at pressures up to 10 bar, a significant improvement over the pristine PSF membrane, which failed at 4 bar. The improved plasticization resistance is ascribed to the reinforcing effect of GO, which stabilizes the polymer matrix, minimizing CO₂-induced swelling. The PSF/GO-0.3 wt.% membrane exhibited exceptional CO₂ permeability, selectivity, and plasticization resistance, making it a viable alternative for industrial gas separation applications and outperforming previously reported PSF-based MMMs. Full article

Biogas upgrading and bottling represent essential processes in transforming raw biogas produced via the anaerobic digestion of organic waste into high-purity biomethane (≥95% CH₄), a renewable energy source suitable for applications in cooking, transportation, and electricity generation. Upgrading technologies, such as membrane separation, pressure swing adsorption (PSA), water and chemical scrubbing, and emerging methods, like cryogenic distillation and supersonic separation, play a pivotal role in removing impurities like CO₂, H₂S, and moisture. Membrane and hybrid systems demonstrate high methane recovery (>99.5%) with low energy consumption, whereas chemical scrubbing offers superior gas purity but is limited by high operational complexity and cost. Challenges persist around material selection, safety standards, infrastructure limitations, and environmental impacts, particularly in rural and off-grid contexts. Bottled biogas, also known as bio-compressed natural gas (CNG), presents a clean, portable alternative to fossil fuels, contributing to energy equity, greenhouse gases (GHG) reduction, and rural development. The primary aim of this research is to critically analyze and review the current state of biogas upgrading and bottling systems, assess their technological maturity, identify performance optimization challenges, and evaluate their economic and environmental viability. The research gap identified in this study demonstrates that there is no comprehensive comparison of biogas upgrading technologies in terms of energy efficiency, price, scalability, and environmental impact. Few studies directly compare these technologies across various operational contexts (e.g., rural vs. urban, small vs. large scale). Additionally, the review outlines insights into how biogas can replace fossil fuels in transport, cooking, and electricity generation, contributing to decarbonization goals. Solutions should be promoted that reduce methane emissions, lower operational costs, and optimize resource use, aligning with climate targets. This synthesis highlights the technological diversity, critical barriers to scalability, and the need for robust policy mechanisms to accelerate the deployment of biogas upgrading solutions as a central component of a low-carbon, decentralized energy future. Full article

A hollow fiber-supported polymeric mixed-matrix membrane, consisting of a Pebax-1657 matrix and graphene nanoplatelet (GNP) fillers as the selective layer, was tested for CO₂/CH₄ gas separation at transmembrane pressures up to 30 bar(a). Using a custom, novel, membrane module, we simultaneously performed permeability/selectivity and in situ electric impedance spectroscopy measurements. This in situ technique is proposed here for the first time. Furthermore, stable mixed-gas selectivities, for 10% CO₂ in CH₄ gas, reaching up to 61.4 (M0) and 68.5 after heat treatment (M2) were observed at 20–30 bar(a), whereas the stressed state (M1) dropped to ~22. Throughout the whole procedure of the three (initial, degraded, and restored) membrane testing assessments, a gradual decline in gas permeability coupled with a corresponding increase in the membrane’s AC resistance, due to membrane compaction, was evident. More specific, the membrane’s AC resistance, R₁, increased from ~96–147 ΜΩ (M0) to ~402–435 ΜΩ (M1) and ~5390–5700 ΜΩ (M2), while the peak-phase frequency f_p decreased from ~1.25 kHz (M0) to ~340 Hz (M1) and ~115 Hz (M2). Overall, this work proposes a new tool/method for connecting membrane’s deterioration phenomena with AC resistance and demonstrates that a facile heat treatment can restore selectivity following compaction, despite the absence of full permeance recovery. Full article

Biomethane is one of the controllable Renewable Energy Sources. It may be derived from biogas, a multicomponent gas mixture, using, among others, membrane processes. The proper optimization of such a process requires the knowledge of the phenomena accompanying each specific biogas–membrane separation system. Therefore, the solubility, permeance and diffusion of CO₂, CH₄, O₂ and N₂ in a polyimide-based sample were described and analyzed using the Dual Mode Sorption and partial immobilization models. The parameters of the models were determined based on pure gas sorption isotherms measured gravimetrically and experimental permeances of the four gases. The membrane swelling caused by CO₂ was observed at temperatures of 293 and 303 K and for pressures higher than 3 bar. The adsorption of CH₄, O₂ and N₂ in the fractional free volume (FFV) has a dominant (>50%) share in their total solubility in the entire pressure range. This makes them sensitive to the presence of CO₂, whose affinity is the strongest towards the tested polyimide-based sample. The diffusion of O₂ is the fastest which makes it competitive with CO₂ in permeation through the membrane, despite its low solubility. The ideal CO₂/O₂ selectivity is thus relatively low (2.3–5.1). Methane, which is competitive in solubility compared to CO₂, was found to diffuse the slowest and as a result, it is also the slowest permeating gas. This translates into the very high CO₂/CH₄ ideal selectivity (33–95.7), which is, however, strongly dependent on temperature and pressure. Full article