Membranes and Membrane Technologies最新文献

The possibility of obtaining a composite track membrane (TM) is investigated. The TM surface was modified by the method of planar magnetron deposition of titanium. The parameters of the magnetron installation operation, such as the deposition rate, the working pressure in the chamber and the magnetron current, have been optimized. The features of the structure and morphology of the 80 nm thick titanium layer have been studied using a combination of methods such as atomic force microscopy, scanning and transmission electron microscopy. X-ray photoelectron spectroscopy revealed that the titanium nanosheet has a complex composition including titanium, titanium oxide, titanium nitride and titanium carbide. The Scratch test showed high adhesion of Ti to TM, which is associated with the formation of an interfacial layer of titanium carbide. It is established that magnetron deposition of Ti does not worsen the operational parameters of TM and reduces the marginal angle of water wetting to a value of about 33° ± 2°. Study of survival and growth rate of fibroblasts of Chinese hamster (V79 line) on PET TM and PET TM with Ti, a slight decrease in the survival rate of fibroblasts on metallized membranes was shown. Titanium sputtering suppresses autofluorescence of the TM surface, which makes it possible to use PET TM with Ti as a substrate for microscopic examination of fluorescent biological objects both in vivo and in vitro. The resulting PET TM with Ti can be used as the basis of skin prostheses and membrane-sorption materials of a new generation. The conducted studies show that magnetron sputtering is a promising approach to the manufacture of metal polymer membrane material.

Mobility of alkaline metal cations Li⁺, Na⁺, Cs⁺ in membranes based on polyethylene and sulfonated grafted polystyrene has been investigated by NMR relaxation technique. The kinetic curves of longitude recovery and transverse decay magnetizations of ⁷Li, ²³Na, ¹³³Cs nuclei were recorded. It was indicated that spin relaxation is due to interaction of nuclear quadrupole moment with electric field gradient generated by cation hydrated water molecules and sulfonate groups. The correlation times and activation energies of translational cation mobility have been calculated from spin-lattice (T₁) and spin-spin (Т₂) relaxation temperature dependences. Cation mobility increases in the next sequence Li⁺ < Na⁺ < Cs⁺. Diffusion coefficients calculated from NMR relaxation have been compared with macroscopic diffusion coefficients measured by pulsed field gradient NMR and impedance spectroscopy techniques. On the basis of this comparison, a model of heterogeneous membrane ionic transfer is discussed. It has been shown that membrane conductivity is restricted by ionic transfer in narrow pores with low functional group concentration.

Samples of two-layer ceramics based on polydisperse powder of the pearlite mineral and foam silicates possessing high compressive strength up to 50 MPa, thermal stability up to 1150°C, and water permeability of 272 m³/h m² bar have been obtained. According to the X-ray powder diffraction analysis, the supporting substrate material is X-ray amorphous. The average pore size of the supporting substrate is 40 µm, while the average pore size of the modifying layer is 17 µm according to the bubble method and electron microscopy. The obtained materials are promising for use as substrates of microfiltration, ultrafiltration, and nanofiltration membranes.

A procedure has been developed for determining the water transport numbers in an ion-exchange membrane by the gravimetric method. Based on a comparative study of this characteristic by the volumetric and gravimetric methods, the experimental conditions (current density, duration of the experiment, and the concentration range of the electrolyte solution) have been found under which the water transport numbers differ by no more than 5%. The electroosmotic permeability, water content, and electrical conductivity of a heterogeneous cation-exchange membrane MK-40 have been studied in a wide range of concentrations of sodium chloride and sulfate solutions. The influence of the nature of the coion on the equilibrium and dynamic hydration characteristics of a heterogeneous membrane has been evaluated. Using the representation of the membrane as a two-phase system, the structure of the hydrated fixed ion–counterion complex has been quantitatively characterized and the hydration numbers of the sulfo group, the sodium counterion, and the sulfate ion in solution have been calculated.

The characteristic features of the mass transport of the components through the ion-exchange membranes during conventional electrodialysis of a ternary aromatic amino acid–disaccharide–mineral salt solution with inert spacers are studied. The mutual influence of the components of the system during the transport through MA-41 and MK-40 heterogeneous membranes is revealed. It is shown that the fluxes of phenylalanine through the membranes reach lower values at a higher concentration of sucrose in the feed solution. Here, lower values of the degree of desalination are observed when compared to the lower concentration of the carbohydrate in the mixture. It is found that most losses of sucrose during desalination are due to its mass transport through the cation-exchange membrane, while phenylalanine, through anion-exchange. The application of an electrodialysis scheme with bipolar and anion-exchange membranes at the next stage provides effective separation of the aromatic amino acid and disaccharide from the preliminary demineralized solution due to the conjugated transport of phenylalanine through the anion-exchange membrane with the hydroxyl ions generated at the inner interface of the bipolar membrane.

An analytical expression is obtained for the differential resistance of a four-layer electromembrane system consisting of a bilayer ion-exchange membrane with an uncharged layer and a layer with a constant through the thickness exchange capacity and two diffusion layers with the same thicknesses. The degree of influence of the diffusion layers on the electrical resistance of the system is determined. An algebraic expression for the electrical resistance of a surface-modified ion-exchange membrane depending on the physicochemical characteristics of the layers of the bilayer membrane is obtained for the first time.

The current–voltage characteristics of a Ralex AMH anion-exchange membrane and a Ralex AMH/MF-4SK double-layer membrane in solutions of acetic and malonic acids and the permselectivity coefficients of these acids across the two membranes in a pH range of 1–8 at an electric current density of 0–5 A/dm² have been measured. It has been shown that the Ralex AMH anion-exchange membrane exhibits a preferential selectivity with respect to malonic acid in the entire ranges of pH and current densities. The Ralex AMH/MF-4SK double-layer membrane is selective with respect to acetic acid at all pH values and at current densities lower than the limiting electrodiffusion current. At currents above the limiting current, this membrane is selective with respect to malonic acid. The permselectivity coefficient value is explained by the occurrence of two competing processes: the dissociation of water molecules, which accelerates at membrane currents above the limiting current, and the protonation–deprotonation process involving ions and molecules of malonic and acetic acids.

This work provides an overview of the processes of fouling, the deposition of substances on the surface or in the pores of membranes, leading to deterioration of their performance. Degradation and fouling phenomena in various membrane materials, as well as the mechanisms of these processes, are considered. It is shown that, despite the difference in the chemical composition, morphology of membranes, ion exchangers, and the phenomena in which they are used, the phenomena leading to clogging of their surface and pores are largely similar. Among the main substances that contaminate membranes are organic molecules, polyelectrolytes, crystals of inorganic substances formed from ions contained in a solution, as well as colloidal particles, and biological organisms. The binding strength of foulants essentially depends on their nature and on the chemical composition of the membranes. At the same time, many fouling phenomena have their own characteristics. For example, in the processes of electricity generation in fuel cells or hydrogen production in electrolyzers, the formation of oxides or metal particles is observed in the membrane pores due to the electrolysis processes. The consequences of the processes of fouling and methods of their control are also considered. It should be noted that cleaning of membranes is still the main method of preventing fouling. At the same time, in recent years, research has been intensively developed in the field of inhibition of corrosion processes, as well as the creation of integrated approaches that integrate various processing processes, including both membrane and other technologies.

Novel dynamic nanocomposite membranes for hydrophilic pervaporation, in which the selective layer is formed by the ultrafiltration of a dispersion of SiO₂ nanoparticles in a polyvinyl alcohol solution in the dead-end mode through porous membrane substrates based on poly(acrylonitrile-co-methyl acrylate), have been developed. The effect of the silica nanoparticle concentration in the selective layer of polyvinyl alcohol on the structure, transport properties, and stability of the dynamic nanocomposite membranes in the pervaporation of an ethanol–water mixture has been first revealed. It has been found that nanocomposite membranes obtained with the introduction of 10 wt % SiO₂ are characterized by the maximum selective layer thickness. It has been shown that the surface roughness and hydrophilicity of the nanocomposite membranes increases upon the introduction of SiO₂ nanoparticles into the selective layer. The transport properties of the nanocomposite membranes and their stability in the pervaporation have been studied in the separation of ethanol–water mixtures of various concentrations. It has been found that the nanocomposite membranes exhibit a lower flux than that of the unmodified PVA/poly(AN-co-MA) membrane; however, they are characterized by a significantly higher selectivity and higher stability in the ethanol dehydration.

The surface properties and chemical structure of nanosized coatings deposited on the surface of poly(ethylene terephthalate) track-etched membranes using methods based on the plasma polymerization of organic compounds and the magnetron sputtering and electron-beam dispersion of polymers in a vacuum have been studied. It has been shown that the application of these methods using low surface energy compounds as precursors for modification provides the formation of hydrophobic coatings on the membrane surface. It has been shown that the deposition of coatings on the surface of track-etched membranes by the plasma polymerization and magnetron sputtering methods leads to the smoothing of structural heterogeneities. Coating deposition by the electron-beam dispersion of polymers, conversely, causes an increase in the surface roughness. The observed differences in the morphology of the surface layer of the composite membranes are attributed to the size of the deposited polymer nanostructures. It has been found that the chemical structure of the coatings deposited by the electron-beam dispersion of polymers is more similar to the structure of the original polymers than the structure of the coatings formed by plasma polymerization and high-frequency magnetron sputtering.