Membranes and Membrane Technologies最新文献

Modern studies in the field of lithium metal batteries focus on the development of safe and stable electrolytes with high ionic conductivity and electrochemical stability. In this context, promising materials are gel polymer electrolytes based on perfluorosulfonic acid cation-exchange membranes modified with inorganic fillers and solvated with aprotic solvents. This study addresses Nafion® composite membranes containing surface-sulfonated zirconia (sZrO₂) and solvated with binary mixtures of ethylene carbonate (EC) with dimethylacetamide (DMAc), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) at a 1 : 1 ratio by volume. The presented systems demonstrate the dependence of ionic conductivity on the nature of the solvent, following the series: EC–DMAc > EC–DMF > EC–DMSO, with the maximum conductivity (2.2 mS/cm at 25°C) being achieved for the Nafion@sZrO₂–EC–DMAc composition. The resulting electrolytes are electrochemically stable up to 4.2 V (vs. to Li⁺/Li), which makes them compatible with cathode materials such as LiFePO₄ (LFP). However, DMSO slowly interacts with lithium metal to form a low-conductivity SEI layer, whereas EC–DMAc and EC–DMF systems provide stable operation of Li|Li cells for >1000 h at a current density of 0.1 mA/cm². Cyclic tests of Li|LFP cells with Nafion@sZrO₂–EC–DMAc and Nafion@sZrO₂–EC–DMF electrolytes show an initial discharge capacity of ∼155 mA h/g (0.1C) and high stability—capacity loss after 50 cycles at 0.5C is 4.7 and 2.0%, respectively. The obtained results confirm the potential of using Nafion^®-based composite gel polymer electrolytes solvated with amide solvents in new generation lithium metal batteries.

This work presents an optimized bead-milling approach for producing monodisperse cesium dihydrogen phosphate nanoparticles (100–200 nm), while preserving their P2₁/m crystal structure, as confirmed by X-ray diffraction and particle size characterized by scanning electron microscopy and Rietveld refinement (125 ± 10 nm crystallites). The obtained nanoparticles demonstrated high proton conductivity (∼1.8 × 10^–2 S cm^–1 at 240°C) due to the bulk transport mechanism predominance, which allowed them to be successfully applied in the first tests in fuel cell electrodes (OCV 0.96 V, current density ∼120 mA/cm² at 235°C). The developed mechanical processing method enables precise particle size control, facilitating the fabrication of electrode materials with enhanced three-phase boundary characteristics for improved fuel cell performance.

A method for producing electrically conductive ceramic membranes based on a fly ash microsphere substrate and a selective layer of alumina nanofibers with a carbon coating is proposed. The formation of a carbon layer by chemical vapor deposition reduces the average pore size from 28 to 19 nm and decreases the water permeability of the membranes from 207 to 45 L/m² h bar. A setup for an electro-baromembrane process was developed, based on a tangential filtration cell with radial flow and the capability of applying a potential to the membrane relative to a counter electrode. Experiments on the ultrafiltration of an aqueous solution of the ionic dye Berillon II showed that the rejection increases from 60 to 82% over time and is provided by the electrostatic interaction of negatively charged dye molecules with the pore surface. Applying a positive potential of +800 mV to the membrane increases the rejection by 20–25% at the beginning of the process and by 13% in the steady state due to enhanced sorption of dye molecules on the membrane surface. Applying a negative potential of –800 mV ensures a stable rejection of 93–96% and a flux of 160 L/m² h at a pressure difference of 5 bar due to the enhanced Donnan exclusion of negatively charged dye molecules in the membrane pores. The obtained results can be used to improve the efficiency of separation, concentration, and purification processes of aqueous solutions of ionic dyes.

This study investigated the physicochemical characteristics and treatment methods for finely dispersed oil-containing wastewater with a dispersed phase particle size of less than 100 nm. For this purpose, both novel composite membranes developed by the authors and commercially available analogs were used. The novelty of the work lies in the development of a method for producing composite membranes comprising a micro-mesh support and a surface layer of cellulose acetate. The developed ultrafiltration membranes consisted of a micro-mesh coated with a layer of cellulose acetate. Nylon was chosen as the base material for the micro-mesh due to its strength and chemical resistance. The pore size of the developed ultrafiltration membranes ranged from 0.05 to 0.1 μm, which allowed for effective separation of oil particles sized 82–86 nm present in the emulsions. Compared to the commercial UPM-100 membrane, the developed membranes demonstrated higher performance and fouling resistance.

Fundamental barrier properties of biomimetic membranes have to be similar to those of biological membranes. Previously, this was demonstrated on many examples for nitrocellulose ultrafilters impregnated with esters of fatty acids. We also discovered that when the filters were impregnated with fatty acids, transmembrane potential starts spontaneous oscillations at or near the melting point of the fatty acid. This effect was observed even when the membrane separated two acidic aqueous solutions with the same ionic composition and without a concentration gradient. Here we describe current oscillations near the melting point, discuss their mechanisms, possible applications and relations to biological channel oscillations.

Increasing the mass transfer rate in electrodialysis allows for a reduction in the area of expensive membranes and, in some cases, lowers the cost of the final product. It has been experimentally established that an increase in the concentration of a KCl solution (from 0.02 to 0.75 M) in the concentrate chamber of a flow-through electrodialysis cell (c_c) leads to a significant growth in the limiting current density (i_lim) through the MA-41P anion-exchange membrane, provided that the desalination chamber contains a solution with a constant concentration (0.02 M KCl). This growth (36% at c_c = 0.5 M) significantly exceeds the value (4%) that could be expected due to the increase in diffusion and electromigration transport of co-ions through the membrane caused by the increase in c_c. As the experiment shows, an increase in c_c leads, on the contrary, to a decrease in the rate of H⁺ and OH^– ion generation at the solution/membrane boundaries, which could also contribute to an increase in the limiting and overlimiting current density. Using voltammetry, chronopotentiometry, and pH-metry, it is shown that the observed growth in i_lim may be associated with the emergence of unstable equilibrium electroconvection, the possibility of which was theoretically predicted in the works of Rubinstein and Zaltzman.

The effect of a natural biocide based on forest chemical raw materials as an additive to cellulose acetate (CA) casting solutions on the structure and properties of the resulting membranes was studied. The NMR method was used to determine the component composition of rosin and turpentine, from which rosin terpene maleic adduct (RTMA) was obtained. Successful modification of the AC-membranes was confirmed by the results of FTIR-spectroscopy. The operational properties of AC-membranes were studied (electron microscopy, atomic force microscopy, study of the transport properties of membranes). It was shown that the introduction of 1.5–2.0 wt % RTMA into the casting solutions does not affect the transport properties of the membranes, but decrease the surface roughness of the selective layer. At the same time, modified membranes are characterized by increased antibacterial resistance and resistance to fungal fouling.

The process of selective recovery of ammonium nitrogen from a multicomponent feed solution (({text{NH}}_{4}^{ + }), K⁺, Cl^–, ({text{HPO}}_{4}^{{2 - }}), pH 9.3) into a stripping solution (HCl, pH 3.0) has been studied using a liquid–liquid membrane contactor. The feed and stripping solutions were separated by experimental polysulfone hollow fiber membranes with fundamentally different structures. One of them had a large-pore substrate and a dense nonporous layer on its surface (skin layer), and the other had an isotropic structure with uniformly distributed pores of about 50 nm in diameter. Two more asymmetric membranes made of polyetherimide or polyvinyltrimethylsilane were used for comparison. It has been shown that the ammonia nitrogen transfer coefficients through asymmetric membranes with a dense skin layer facing the feed solution are several times lower than those achieved in the case of a symmetric membrane. In the studied range of ammonium nitrogen concentrations in the feed solution (200–400 mmol/L), these coefficients reach values of (1–4) × 10^–3 m/h, which are comparable with the characteristics of the best hollow fiber gas separation membranes made of other materials presented in the scientific literature. A hypothesis is proposed to explain both the observed differences in behavior between membranes with different structures and the increase in the mass transfer coefficient of ammonia nitrogen upon dilution of the feed solution.

Membrane fouling is a major challenge in practical membrane applications, which cannot be completely avoided but can be minimized. A promising approach to membrane modification is the introduction of hydrophilic polymers or polyelectrolytes into the coagulation bath (CB) during membrane fabrication via the phase inversion method. This study systematically investigates the influence of polyacrylic acid (PAA) molecular weight (100 000, 250 000, and 450 000 g mol^–1) on the structure, surface physicochemical properties, transport characteristics, and fouling resistance of polysulfone (PSf) membranes modified with the amphiphilic block copolymer polyethylene glycol-polypropylene glycol (Synperonic F108). Aqueous PAA solutions (0.4–2.0 wt %) were used as the CB. The results demonstrate that ultrafiltration PSf/Synperonic F108/PAA membranes exhibit significantly enhanced surface hydrophilicity (water contact angle decreases from 53° to 10°–32°), reduced surface roughness, and a more negatively charged surface compared to unmodified membranes. The use of PAA solutions in the CB leads to a denser membrane structure, characterized by a decrease in the average pore size and number of pores in the selective layer. As a result, the pure water permeability declines from 195 to 21–66 L m^–2 h^–1, while selectivity improves substantially. The rejection coefficients increase from 56 to 76–94% for polyvinylpyrrolidone (PVP K30, M_n = 40 000 g mol^–1) and from 55 to 92–94% for lysozyme. The modified membrane structure and permeability also significantly enhance fouling resistance during filtration of a humic acid model solution: the flux recovery ratio (FRR) improves from 74 to 92–100%, and the total flux decline (DT) decreases from 30 to 0–5%, while maintaining high efficiency in iron and color removal.

The transport and separation characteristics of the composite membrane with a selective layer based on a copolymer of polydecylmethylsiloxane and polymethylpentafluoropropylsiloxane (50F5) were studied during the pervaporation recovery of n-butanol from aqueous mixtures. It was shown that the membrane with the selective layer of copolymer (M-50F5 exhibits a high separation factor for n-butanol/water (35) and a total permeate flux of 0.31 kg/(m² h). For the first time, an analysis of the impact of concentration polarization on the efficiency of n-butanol recovery from a model fermentation mixture was conducted, including the calculation of the concentration polarization modulus and the thickness of the diffusion boundary layer. It was revealed that increasing the flow rate of the feed mixture above 30 cm/s eliminates concentration polarization effects, as evidenced by a reduction in the boundary layer thickness to zero. Optimization of the hydrodynamic regime allowed for the minimization of mass transfer limitations caused by concentration polarization, particularly at low butanol concentrations. The obtained results substantiate the potential of using 50F5-based membranes for the pervaporation recovery of butanol from fermentation broths and open new opportunities for improving separation technologies for multicomponent systems.