Search Results (171)

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

Anion exchange membranes are utilised in cutting-edge energy technologies including electrolysers and fuel cells. Recently, these membranes have also emerged as a promising tool in CO₂ capture techniques, such as moisture-driven direct air capture and the separation of CO₂ from other gases, leveraging the moisture-induced sorption/desorption and diffusion of CO₂ in its ionic forms. In this study, we examine the absorption and permeation of CO₂ and CH₄ in two commercially available anion exchange membranes, Fumasep^® and Sustainion^®, under dry conditions. With the exception of CO₂ sorption in Fumasep^®, these measurements have not been previously reported. These new data points are crucial for evaluating the fundamental separation capabilities of these materials and for devising innovative CO₂ capture strategies, as well as for the simulation of novel combined processes. In a dry state, both materials demonstrate similar CO₂ absorption levels, with a higher value for Sustainion^®. The CO₂ solubility coefficient decreases with pressure, as is typical for glassy polymers. Fumasep^® exhibits higher CO₂/CH₄ ideal solubility selectivity, equal to ~10 at sub-ambient pressures, and higher diffusivity. The CO₂ diffusion coefficient increases with the CO₂ concentration in both membranes due to swelling of the matrix, varying between 0.7 and 2.2 × 10⁻⁸ cm²/s for Fumasep^® and between 1.6 and 9.0 × 10⁻⁹ cm²/s for Sustainion^®. CO₂ permeability exhibits a minimum at a pressure of approximately 2–3 bar. The CO₂ permeability in the dry state is higher in Fumasep^® than in Sustainion^®: 3.43 and 0.72 Barrer at a 2-bar transmembrane pressure, respectively. The estimated perm-selectivity was found to reach values of up to 40 at sub-ambient pressures. The CO₂ permeability and CO₂/CH₄ estimated perm-selectivity in both polymers are of a similar order of magnitude to those measured in fluorinated ion exchange membranes such as Nafion^®. Full article

The enrichment of ⁶Li isotopes from a natural stage of 7.6% to above 59% is required for the development of next-generation green technologies capable of sustaining climate change mitigation and energy-mix targets. In this study, we developed two categories of custom laboratory-made organic membranes, membranes that were non-impregnated before electromigration (AI-1) and membranes impregnated with LiNTf₂ (AI-2), to evaluate their performance in lithium isotope separation. Both types of membranes were exposed in synthesis to ionic liquid and crown ether. The objective of the study was to test the performance of membranes in separating lithium isotopes from a lithium-loaded organic phase in an aqueous solution with variable potentials and time intervals. The results show that the impregnated AI-2 membranes increased the enrichment of ⁶Li in the early stages, and the effect decreased after 25 h. The efficiency of lithium isotope enrichment was positively related to the potential profile applied, migration time, and concentration of organic solution in the anode chamber. The 0.5 mol/L Bis-(trifluoromethane) sulfonimide lithium salt (Li[NTf₂]) with 0.1 M tetra butyl ammonium perchlorate (TBAP) in acetonitrile (CH₃CN) ionic solution significantly improved Li isotope separation compared with an aqueous environment with higher salt concentrations. The maximum isotopic separation coefficient (α) for AI-1.2 (15-crown-5 ether and 1 mol/L LiNTf₂ in TBAP solution after 48 h of electromigration) gradually increased to 1.0317. Our results demonstrated that in the laboratory-made setup described, the migration efficiency and Li isotope separation in the catholyte environment needed a minimum of 9 V and a migration time of 6 h, respectively; these values varied with the concentration of the organic solution in the anode chamber. The ability of laboratory-engineered membranes to impart isotope selectivity and enhance permselectivity or selectivity towards singly charged ions was demonstrated through the functionality of single-collector inductively coupled plasma mass spectrometry (ICP-MS). This technology is particularly valuable and commercially feasible for future lithium isotope research in nuclear technology. Full article

Innovations for separation via membranes are extremely energy-efficient, and through the previous decade, attention to this technology has spiked tremendously. Biopolymers are becoming widely recognized as membrane materials since they are sustainable. Furthermore, the second most common biopolymer, chitin, is the source of chitosan, which has several benefits that make it ideal for the construction of membranes. This review article presents an evaluation of current developments in the utilization of chitosan membranes. The applications of interest in this review are nanofiltration, pervaporation and ion exchange. The chitosan based nanofiltration membranes are comprehensively reviewed with respect to various factors (e.g., solvent, pH resistant, etc.). The development of water permselective, organic permselective, and organic-organic separation films, as well as its permeability and segregation properties, are addressed in pervaporation (PV) section. Full article

For industrial CO₂ utilization, the supply of concentrated CO₂ within a continuous, high-volume stream at high temperatures remains a substantial requirement. Membrane processes offer a simple and efficient method to provide CO₂ in this form. While several organo-silica-based membranes have been developed for CO₂/N₂ separation under these conditions, there is no standardized framework guiding comparability and optimization. Therefore, we present these membranes in a Robeson-like plot across various temperatures. Utilizing a standard 1,2-bis(triethoxysilyl)-ethane (BTESE) precursor and a simplified sol–gel method, we prepared a microporous membrane layer and characterized it for an exemplary comparison. This characterization includes key parameters for mixed-gas applications: (1) temperature-dependent single- and mixed-gas permeances to observe interactions, (2) the impact of the driving forces in mixtures (vacuum and concentration) to distinguish between permselectivity and the separation factor clearly, and (3) influence of the support structure to enable permeability calculations at elevated temperatures. Furthermore, a quick interpretation method for assessing the membrane’s microstructure is presented. A qualitative microstructure assessment can be achieved by analyzing the temperature dependencies of the three major diffusion mechanisms that simultaneously occur—Knudsen, surface, and activated diffusion. Full article

NaZSM-5 powder and membranes were hydrothermally prepared. Their (1) steam (H₂O) adsorption properties and (2) the permeation and separation of gas and H₂O were evaluated before and after the cation exchange of Na⁺ to K⁺ or Cs⁺. The quantity of adsorbed H₂O decreased as the size of the cation increased, indicating that the micropore volume and effective pore size of ZSM-5 decreased after cation exchange. The H₂ and N₂ permeances after cation exchange were less than 5% of the values before cation exchange, indicating a significant reduction in gas permeability. In contrast, the reduction of the H₂O permeance values of the ZSM-5 membranes before and after K⁺ or Cs⁺ exchange was lower than that of H₂, resulting in improved H₂O/H₂ separation performance. Compared with the NaZSM-5 membrane, the K⁺- or Cs⁺-exchanged ZSM-5 membranes exhibited superior H₂O permselectivity, particularly at dilute H₂O concentrations (<1 vol%). Full article

Biogas, one of the important controllable renewable energy sources, may be split into two streams: bio-CH₄ and bio-CO₂ using, among others, membrane processes. The proper optimization of such processes requires the knowledge of phenomena accompanying each specific CH₄–CO₂–membrane system (e.g., competitive sorption or swelling). The phenomena were analyzed for the polysulfone-based membrane used in a developed adsorptive–membrane system for biogas separation. The Dual Mode Sorption and partial immobilization models were used to describe the solubility and diffusion of CO₂, CH₄ and their mixtures in this material. The parameters of the models were determined based on pure-gas sorption isotherms measured gravimetrically and permeances of CO₂/CH₄ mixture components from our previous studies. It was found, among other things, that the membrane swelling caused by CO₂ was observed for pressures higher than 5 bar. The real selectivity (permselectivity) of CO₂ vs. CH₄ is significantly lower than the selectivity of pure gases (ideal selectivity), while the solubility selectivity of CO₂ vs. CH₄ in the mixture is higher than that of pure gases. This is due to the better affinity of CO₂ towards the tested polysulfone membrane, making CO₂ the dominant component in competitive sorption. The reduction in the permselectivity is mainly due to an approximately two-fold decrease in the CO₂ diffusion rate in the presence of CH₄. It was also found that the fraction of solubility in the fractional free volume (FFV) is dominant for both gases, pure and mixed, reaching 65–73% of the total solubility. Moreover, in CO₂/CH₄ mixtures, the mobility of methane in FFV disappears, which additionally confirms the displacement of methane by CO₂ from FFV. Full article

This work addressed the fine dispersion of Multiwalled Carbon Nanotubes (MWCNTs) in a polymer matrix to obtain Mixed Matrix Membranes (MMMs) suited for gas separation. Not-purified MWCNTs were effectively loaded within a polyether block amide (Pebax^®2533) matrix, up to 24 wt%, using ultrasonication as well as a third component (polysorbate) in the dope solution. The obtained flexible thin films were investigated in terms of morphology, thermal properties, characterized by SEM, FT-IR, DSC, TGA, and gas permeation tests. The response to temperature variations of gas permeation through these nanocomposite specimens was also investigated in the temperature range of 25–55 °C. Defect-free samples were successfully obtained even at a significantly high loading of CNTs (up to 18 wt%), without a pre-treatment of the fillers. A remarkable enhancement of gas permeability upon the nanocarbons loading was reached, with a threshold value at a loading of ca. 7 wt%. The addition of polysorbates in the ternary MMMs further improves the dispersion of the filler, enhancing also the permselectivity of the membrane. Full article

Stimuli-responsive polysulfone (PSf) ultrafiltration (UF) membrane was developed via surface modification with tethered hydrophilic polyacrylic acid (PAA) chains of length greater than the native membrane pore size. The surface nano-structured (SNS) membrane was synthesized via atmospheric pressure plasma-induced graft polymerization (APPIGP) to form a surface tethered PAA brush layer. The SNS-PAA-PSf UF membrane demonstrated hydraulic permeability and selectivity in the ranges of 0.74–2.29 × 10¹³ m⁻¹ and 1.8–15.0 kDa, respectively, in response to changes in pH (3–11) and ionic strength (~0.02–547 mM). Membrane performance characterization showed that, for the above ranges of pH and salinity, the SNS-PAA-PSf UF membrane can overcome the typical membrane perm-selectivity tradeoff. The above performance is attributed to the swelling of the tethered PAA chains, upon ionic strength decrease or pH increase, which provides a less hindered transmembrane solute transport path, but increased hydraulic resistance. Conversely, at high ionic stress or low pH tethered chain collapse leads to lower molecular weight cutoff (MWCO) but with hydraulic resistance below that of the swollen state. The study results suggest that there is merit for further tailoring and improving the performance of stimuli-responsive UF membranes, developed via APPIGP, for applications over selected ranges of pH and ionic strength. Full article

Electroosmosis reduces the available energy from ion transport arising due to concentration gradients across ion-exchange membranes. This work builds on previous efforts to describe the electroosmosis, the permselectivity and the apparent transport number of a membrane, and we show new measurements of concentration cells with the Selemion CMVN cation-exchange membrane and single-salt solutions of HCl, LiCl, NaCl, MgCl₂, CaCl₂ and NH₄Cl. Ionic transport numbers and electroosmotic water transport relative to the membrane are efficiently obtained from a relatively new permselectivity analysis method. We find that the membrane can be described as perfectly selective towards the migration of the cation, and that ${\mathrm{Cl}}^{-}$ does not contribute to the net electric current. For the investigated salts, we obtained water transference coefficients, $t_w$, of 1.1 ± 0.8 for HCl, 9.2 ± 0.8 for LiCl, 4.9 ± 0.2 for NaCl, 3.7 ± 0.4 for KCl, 8.5 ± 0.5 for MgCl₂, 6.2 ± 0.6 for CaCl₂ and 3.8 ± 0.5 for NH₄Cl. However, as the test compartment concentrations of LiCl, MgCl₂ and CaCl₂ increased past 3.5, 1.3 and 1.4 mol kg⁻¹, respectively, the water transference coefficients appeared to decrease. The presented methods are generally useful for characterising concentration polarisation phenomena in electrochemistry, and may aid in the design of more efficient electrochemical cells. Full article

Membrane capacitive deionization (MCDI) is an electrochemical ion separation process that combines ion-exchange membranes (IEMs) with porous carbon electrodes to enhance desalination efficiency and address the limitations of conventional capacitive deionization (CDI). In this study, a cation-exchange membrane (CEM) embedded with a metal–organic framework (MOF) was developed to effectively separate monovalent and multivalent cations in influent solutions via MCDI. To fabricate CEMs with high monovalent ion selectivity, ZIF-8 was incorporated into sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) at various weight ratios. The resulting membranes were systematically characterized using diverse electrochemical methods. The ZIF-8-embedded CEMs demonstrated a sieving effect based on differences in ion size and hydration energy, achieving excellent permselectivity for monovalent ions. MCDI tests using the prepared CEMs showed a Na⁺ ion removal rate exceeding 99% in Na⁺/Mg²⁺ and Na⁺/Ca²⁺ mixed feed solutions, outperforming a commercial membrane (CSE, Astom Corp., Tokyo, Japan), which achieved a removal rate of 94.1%. These findings are expected to provide valuable insights for advancing not only MCDI but also other electro-membrane processes capable of selectively separating specific ions. Full article

This study proposes a new dense membrane for selectively separating CO₂ and O₂ at high temperatures and simultaneously producing syngas. The membrane consists of a cermet-type material infiltrated with a ternary carbonate phase. Initially, the co-doped ceria of composition Ce_0.9Zr_0.05Y_0.05O_2−δ (CZY) was synthesized by using the conventional solid-state reaction method. Then, the ceramic was mixed with commercial silver powders using a ball milling process and subsequently uniaxially pressed and sintered to form the disk-shaped cermet. The dense membrane was finally formed via the infiltration of molten salts into the porous cermet supports. At high temperatures (700–850 °C), the membranes exhibit CO₂/N₂ and O₂/N₂ permselectivity and a high permeation flux under different CO₂ concentrations in the feed and sweeping gas flow rates. The observed permeation properties make its use viable for CO₂ valorization via the oxy-CO₂ reforming of methane, wherein both CO₂ and O₂ permeated gases were effectively utilized to produce hydrogen-rich syngas (H₂ + CO) through a catalytic membrane reactor arrangement at different temperatures ranging from 700 to 850 °C. The effect of the ceramic filler in the cermet is discussed, and continuous permeation testing, up to 115 h, demonstrated the membrane’s superior chemical and thermal stability by confirming the absence of any chemical interaction between the material and the carbonates as well as the absence of significant sintering concerns with the pure silver. Full article

New homogeneous bilayer membranes with a thin anion-exchange layer have been developed based on the copolymer of N,N-diallyl-N,N-dimethylammonium chloride (DADMAC) and ethyl methacrylate (EMA) on the surface of a membrane substrate made from polyfluorosulfonic acid (PFSA). The overall and partial current–voltage characteristics, as well as external and internal diffusion-limiting currents, were theoretically and experimentally investigated. Parameters such as specific conductivity, sorption, and diffusion permeability of individual membrane layers were determined, along with effective transport numbers and specific permselectivity of the bilayer homogeneous membranes in mixed solutions of calcium chloride and sodium chloride. It was found that applying a thin anion-exchange layer of DADMAC and EMA to the homogeneous membrane allows for the creation of a charge-selective bilayer membrane with enhanced selectivity toward monovalent metal cations. The specific selectivity of the bilayer membrane for sodium cations increases more than 6-fold (from 0.8 to 4.8). Verification of the obtained experimental data was performed within a four-layer mathematical model with quasi-equilibrium boundary conditions for the diffusion layer (I)/modifying layer (II)/membrane substrate (III)/diffusion layer (IV) in ternary NaCl+CaCl₂ solutions. Full article

The present work details the development of carbon fiber-reinforced epoxy membranes with excellent rejection of small-molecule dyes. It is a proof-of-concept for a more sustainable membrane design incorporating carbon fibers, and their recycling and reuse. 4,4′-methylenebis(cyclohexylamine) (MBCHA) polymerized with either bisphenol-A-diglycidyl ether (BADGE) or tetraphenolethane tetraglycidylether (EPON Resin 1031) in polyethylene glycol (PEG) were used to make monolithic membranes reinforced by nonwoven carbon fibers. Membrane pore sizes were tuned by adjusting the molecular weight of the PEG used in the initial polymerization. Membranes made of BADGE-MBCHA showed rejection of Rose Bengal approaching 100%, while tuning the pore sizes substantially increased the rejection of Methylene Blue from ~65% to nearly 100%. The membrane with the best permselectivity was made of EPON-MBCHA polymerized in PEG 300. It has an average DI flux of 4.48 LMH/bar and an average rejection of 99.6% and 99.8% for Rose Bengal and Methylene Blue dyes, respectively. Degradation in 1.1 M sodium hypochlorite enabled the retrieval of the carbon fiber from the epoxy matrix, suggesting that the monolithic membranes could be recycled to retrieve high-value products rather than downcycled for incineration or used as a lower selectivity membrane. The mechanism for epoxy degradation is hypothesized to be part chemical and part physical due to intense swelling stress leading to erosion that leaves behind undamaged carbon fibers. The retrieved fibers were successfully used to make another membrane exhibiting similar performance to those made with pristine fibers. Full article

This study investigated the effect of different synthesis parameters including pre- and post-hydrothermal treatment on the formation of a high-quality SSZ-13 membrane layer. The membranes were identified initially by the gas tightness test, then were characterized by single gas permeation measurements applying H₂, He, CO₂, N₂, CH₄, and SF₆ at room temperature. The results showed how each parameter affects the performance of the membrane, including structural defects in the formed selective layer, CO₂ permeance, and the ideal CO₂/CH₄ permselectivity. This work focused on optimizing these parameters. An ideal CO₂/CH₄ permselectivity of up to 122 with CO₂ permeance of ~3.72 × 10⁻⁶ [mol/(m²sPa)] and CO₂/CH₄ selectivity of 111 with CO₂ permeance of 8.5 × 10⁻⁷ [mol/(m²sPa)] in an equimolar mixture at room temperature and pressure drop of 0.15 MPa was achieved. This is one of the highest performances compared to other publications for SSZ-13 or all-Si membranes. Full article