In this work, the effect of applying layers of polyethyleneimines with different molecular weights (1300 and 25 000 Da), polystyrene sulfonic acid or sodium polyacrylate on the surface of the heterogeneous membrane MK-40 on the selectivity to singly charged ions was investigated. It is shown that the modification leads to an increase in the selectivity coefficients P(Na+/Ca2+) and P(Li+/Mg2+), and in membranes based on polyethyleneimine with a molecular weight of 1300 Da this effect is more pronounced. For a couple of Na+/Ca2+, the highest selectivity value (3.95) was obtained using a membrane with two layers of polyethyleneimine with a molecular weight of 1300 Da and polystyrene sulfonic acid.
In this work, asymmetric flat-sheet membranes based on the commercial polyetherimide–siloxane copolymer Siltem, whose gas permeability is one order of magnitude higher than that of polyetherimide Ultem 1000, were first obtained. Based on the solubility analysis and Hansen solubility parameters, N‑methyl-2-pyrrolidone was selected as the principal solvent, as it provides the best thermodynamic compatibility with both polymers. It was shown that Siltem STM1700 is soluble in a significantly wider range of organic solvents, including tetrahydrofuran and N-butylpyrrolidone. Furthermore, solutions of Siltem in N‑methyl-2-pyrrolidone exhibit substantially lower viscosity compared to those of Ultem, which allows the preparation and processing of polymer solutions at concentrations up to 36 wt
This work investigates the competitive transport of acetic and citric acids from model solutions containing both salt and molecular forms of the acids. The study examines two membrane systems: a Ralex AMH heterogeneous membrane with a total concentration of 0.1 mol-eq/L of each acid and a Ralex AMH/MF-4SK bilayer membrane with a total concentration of 0.5 mol-eq/L of each acid. Experiments were conducted at solution pH values of 1.0, 4.8, and 9.0. The separation of organic acids by electromembrane processes is a key challenge when these acids are obtained from mixtures. The results show that electrodialysis extraction of citric acid from solution containing 0.1 mol-eq/L of organic acid ions and molecules, using Ralex AMH membrane at current density of about 3 A/dm2 and pH 9.0, yields a specific selective permeability coefficient PCit/Ac equal to 4 for citric acid compared to acetic acid. Electrodialysis removal of acetic acid from solution containing 0.5 mol-eq/L of organic acid ions and molecules using the Ralex AMH/MF-4SK membrane at current density of 0.17 A/dm2 and pH 9.0 results in PCit/Ac value of 0.025.
A series of composite ion-exchange membranes based on the heterogeneous anion-exchange strongly basic membrane MA-41 and polyaniline was obtained via oxidative polymerization of aniline. This was achieved through sequential diffusion of an oxidizer (ammonium persulfate) and a monomer (aniline sulfate) through the membrane into water with varying contact times with the monomer solution (from 2 to 6 h). The penetration depth of the modifier into the membranes was determined to be independent of the polyaniline synthesis time and to be 30–35
Mixed ionic-electronic conductors (MIECs) are essential for high-temperature electrochemical devices, such as solid oxide fuel cells and oxygen separation membranes. While it is difficult to optimize both ionic and electronic transport simultaneously in single-phase materials, composite systems offer a promising strategy by separating these functionalities into distinct and percolating phases. This study reports the functional properties of the nominal composition BaCe0.5Fe0.5O3 – δ (BCF), which forms a dual-phase composite due to the mismatch in ionic radii between the Ce4+ and Fe3+/4+ cations. The BCF material was synthesized via a single-step citrate-nitrate combustion route to ensure a homogeneous dual microstructure state consisting of an orthorhombic BaCeO3-based phase and a cubic BaFeO3-based phase. This was confirmed by Rietveld refinement and electron microscopy analyzes. Electrical characterization revealed moderate total conductivity at 300–750°C, which did not exceed 1 S cm–1. Despite its restricted electronic conductivity, the composite exhibited acceptable oxygen permeation fluxes, reaching 2.0 × 10–3 mL min–1 cm–2 at 750°C for a 650 µm-thick membrane. The calculated specific oxygen permeation flux exhibited thermally activated behavior with an activation energy ( 0.75 eV) comparable to that of similar iron-containing perovskite systems. A comparative analysis with literature data showed that the BCF performance is acceptable for the 600–750°C range. These results highlight the effectiveness of the in situ formed composite, in which the Ce-rich phase facilitates ionic transport and compensates for the moderate electronic conductivity of the Fe-rich phase. Consequently, the BCF composite can be considered a promising material for oxygen transport membranes.
It is proposed for the first time to use non-integer order moments for the analysis of the sorption kinetics of gases and liquids by membranes and adsorbents. An analytical formula for the moment of the gas sorption kinetic curve by a homogeneous membrane of any non-negative order has been obtained. It is shown that the first and second order moments obtained using this formula coincide with known analytical expressions for these moments. An expression has been derived for calculating the diffusion coefficient using a non-integer order moment. Through mathematical modeling, it has been demonstrated that the error in determining the diffusion coefficient depends on the total measurement time of the sorption kinetic curve and the order of the kinetic curve moment.
Ceramic microfiltration membranes based on fly ash microspheres were used for the separation of diesel fuel (DF) in water emulsions. The membranes were characterized by an average pore size of 0.451 µm and a water permeability of 0.255 m3/(m2 h bar). Filtration experiments in a dead-end configuration were conducted for emulsions with hydrocarbon phase concentrations from 100 to 1000 mg/L at a transmembrane pressure of 3 bar. The steady-state DF rejection was 97–98
This work presents a comprehensive study on hydrogen recovery from a CO2-containing mixture (75/25 mol
New copolyimides based on phosphorus-containing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), oxidianiline (ODA), and 4,4'-(4,4'-isopropylidenediphenoxy)bis-(phthalic anhydride) (BPADA) containing 50, 60, and 70 mol
In this work, we propose a novel ultrafiltration ceramic membrane based on support from fly ash microspheres and selective layer from alumina nanofibers with carbon coating. The membrane is characterized by the average pore size of 19 nm and water permeability of 46 L/m2 h bar. The filtration experiments with aqueous solutions of anionic dyes are performed in cross-flow mode. The membrane demonstrates high rejection of 96–97 and 99.8
Anion-exchange membranes were synthesized via radiation-induced graft polymerization of vinylbenzyl chloride or styrene (with subsequent chloromethylation) onto polyvinylidene fluoride and poly(ethylene-tetrafluoroethylene) films. The introduction of quaternary ammonium functional groups into the grafted polymer structure was carried out by treatment with a trimethylamine solution. The use of various preparation methods allows tuning the ionic conductivity in the range from 0.2 to 15.2 mS/cm and the potentiometric anion transport numbers in the range from 0.84 to 0.95. The possibility of using such membranes in ion separation by electrodialysis was demonstrated for the first time. The selectivity coefficients of the obtained membranes for the transport of monovalent ions relative to divalent ones reach 1.75 and 2.27 for the Cl^ - /SO_4^2 - and NO_3^ - /SO_4^2 - pairs, respectively.
Various oligomers and infinite chains of pure and phosphoric acid-doped poly(2,5-benzimidazole) (ABPBI) were studied by a quantum-chemical method within the framework of the cluster approximation with the functional ωB97XD and basis 6-31G**, taking into account periodic boundary conditions with the functional PBE and the basis of the projector-augmented plane waves PAW, and also by the molecular dynamics method MD-VASP. It was found that random orientations of ABPBI units and the presence of free rotation around a single bond connecting two monomeric segments of ABPBI lead to a minimal possibility of p–p interactions. ABPBI has a form wavy chain i.e. it has local curvatures and with energies of ∼0.1 eV can rotate around single bonds. In the case of doping with phosphoric acid, an acid-base reaction can occur in some monomer segments of ABPBI between the imidazole moieties in the polymer chain and phosphoric acid to form dihydrogen phosphate ions and protonated imidazolium cations ABPBIH+. When the temperature increases from 0 to 600 K, in addition to protons, acid molecules, acid residues, formed OH-fragments, and released intrastructural water also actively participate in the transport process. However, the structure of the fragments depends on the speed and uniformity of heating.
Fouling of ion-exchange polymeric membranes during operation is one of the problems that reduces the efficiency of devices based on them. Potentiometric membrane sensors are no exception. The approaches ensuring the long-term stability of their characteristics during the analysis of real media may be similar to those for protecting membranes in electrodialysis units. This work studies the electrode-active properties of homogeneous membranes based on a commercial copolymer of tetrafluoroethylene with sulfonated perfluorovinyl ether and novel grafted membranes based on a copolymer of polyvinylidene fluoride and sulfonated polystyrene in potentiometric sensors for the analysis of pharmaceuticals, artificial saliva solutions, and real samples of oral fluid. The patterns of change in the equilibrium and transport characteristics of the grafted membranes depending on the grafting degree and the conditions for polyaniline synthesis in them have been established. The results were compared with those for perfluorinated membranes. It was shown that polyaniline as a modifier of homogeneous and grafted sulfonated membranes increased their resistance to fouling due to its “cross-linking” effect on hydrophilic clusters and hydrophilization of the surface. The effect was achieved by suppressing the absorption of low-molecular-weight cations of drugs and metabolites with nitrogen-containing proton-acceptor groups, as well as the adsorption of high-molecular-weight components of physiological fluids.
Anion-exchange membranes based on cardo polybenzimidazole and zinc(II) ions with various molar ratios of metal ions (0, 0.05, 0.25, 0.50, and 1.00) were prepared by casting solutions of metal–polymer complexes. The introduction of zinc(II) ions into the structure of cardo polybenzimidazole is accompanied by the formation of a cross-linked polymer matrix due to the coordination of metal ions to the pyridine nitrogen atoms of the monomer unit (–N=) and the appearance of anion-conducting properties. Increasing the metal content leads to an increase in the ionic conductivity of the membranes in the nitrate form from 1.8 × 10–8 to 8.3 × 10–6 S/cm. It is shown that the obtained materials demonstrate preferential transfer of monovalent anions (chloride, fluoride, nitrate) compared to divalent anions (sulfate) during electrodialysis. The selectivity coefficients reach 9.7 and 14 for chloride–sulfate and nitrate–sulfate pairs, and 5.7 and 9.1 for chloride–fluoride and nitrate–fluoride pairs, respectively. The obtained selectivity coefficient values exceed the corresponding values for the commercial Neosepta AMX anion-exchange membrane. At the same time, long-term cycling of the obtained membranes in galvanostatic mode leads to their degradation with leaching of zinc ions.
This work investigates the influence of natural juices on the specific conductivity and current–voltage curves of monopolar heterogeneous membranes of domestic (MK-40, MA-41) and foreign (Ralex CMHPES, Ralex AMHPES) production. It was found that storage in juices leads to a decrease in the conductivity of anion-exchange membranes by up to 80
In this study, membranes based on palladium and its alloy with copper, capable of selectively transmitting hydrogen in the range of 25–500°C, were manufactured. Modification of the membrane surface by applying a nanostructured coating significantly expanded the operating capabilities of Pd membranes to low temperatures unattainable by analogs. This result was achieved by accelerating the limiting surface stages and, accordingly, shifting the influence of the diffusion stage toward lower temperatures. The obtained results were confirmed by data on the activation energy of the processes, according to which, due to surface modification, the activation energy was reduced by up to 2 times, compared to uncoated membranes. These results formed the basis for the mathematical model of hydrogen transport through Pd membranes at low temperatures developed in this study. This model takes into account the membrane surface roughness factor, which is an important criterion for the selected temperature range, where surface processes limit hydrogen transport. The obtained results suggest that the developed model is promising for predicting the efficiency of Pd-based membranes.
Water is essential for life, but contamination has become a significant global problem, particularly with groundwater, which serves as a vital source of drinking water for millions. One of the pollutants is fluoride, which, when present in high concentrations, can lead to serious health problems such as dental and skeletal fluorosis. Electrodialysis (ED) is an efficient and sustainable method to remove fluoride from contaminated water. This study investigated the application of electrodialysis (ED) under different electric current conditions to optimize fluoride removal efficiency. The study aims to evaluate fluoride removal both in monocomponent solutions, such as sodium fluoride (NaF), and in multicomponent solutions, represented by a real water sample collected from the Bambuí Aquifer in Bahia, Brazil. This dual approach allows for a better understanding of the electrodialysis performance in simplified systems, and in complex naturally occurring water matrices. The applied currents included both the conventional value commonly adopted in the literature, corresponding to 80
Selective electrodialysis with monovalent-ion-selective membranes has shown high efficiency for separating mono- and multivalent ions. However, the separation mechanism is not yet fully understood. This work studies two cation-exchange membranes from Astom, Japan: a standard-grade CSE membrane and a monovalent-cation-selective CIMS membrane. Based on the results of measurements of exchange capacity, water uptake, zeta potential, contact angle, specific electrical conductivity, and diffusion permeability of both membranes, it is suggested that the selective permeability of CIMS towards monovalent cations is provided both by an electrostatic barrier due to the presence of a selective layer with fixed amino groups and by its denser structure and smaller pore size. The latter necessitates partial dehydration of multivalent cations for their access to the pore space. The dependencies of Li+ and Mg2+ ion flux densities through CIMS on current density were studied during the electrodialytic extraction of Li+ ions from a solution simulating the composition of the natural lithium-containing brine of the Angara–Lena basin. The experimental results indirectly confirmed a significant contribution of the dehydration mechanism to the selective transport of Li+. Based on the values of the CIMS selective permeability coefficient ( P_Li^ + /Mg^2 + ), energy consumption, and Li+ extraction degree, the range of optimal current densities in the vicinity of half the partial limiting current density of lithium ions was determined.
In the production of levulinic acid (LA) from biomass, creating an efficient separation method is essential to isolate LA from unreacted reactants and unwanted byproducts. One promising approach is the use of a supported liquid membrane (SLM). This study examined the performance of LA separation using a hybrid graphene/polyethersulfone hollow fiber SLM by varying the liquid membrane impregnation time from 1 to 24 h. Additionally, the hollow fiber membranes used in the SLM were fabricated at different coagulation bath temperatures (CBT), ranging from 32°C (room temperature) to 60°C, under high relative humidity (86
