Issue

In this paper, a comparative analysis of methods for determining the surface area in relation to electrode materials was carried out on the example of commercial carbon felts of various structures. For a more complete analysis, scanning electron microscopy and Raman spectroscopy methods were additionally used. It is shown that electrochemical methods for determining the surface area are selective with respect to the edge plane of graphite, which can be both an advantage and a disadvantage, depending on the objectives of the study. It is revealed that the use of the classical method of low-temperature adsorption of gases is not always justified due to the complexity of selecting the correct model describing the system under study. Adsorption of dyes from aqueous solutions seems to be the most suitable method for determining the wetted surface of the material, however, it requires large amounts of sample and is characterized by a significant error.

The paper deals with the development of a graphene-containing sorbent material based on activated rapeseed biochar. The physicochemical properties of the sorbent and features of its morphological structure were determined. The nanocomposite was found to have amorphous properties with a graphene-like structure. The morphological analysis confirmed the formation of internal carbon framework and external three-dimensional multilayer graphene structure, which is excellent for mass transfer between pollutants and adsorbent surface. The research also aimed to determine the important parameters of sorption of organic compounds, i.e. synthetic dyes Congo Red (CR) and Malachite Green (MG), on the developed material from aqueous solutions in a limited volume. According to the kinetic studies, the experimental sorption capacity of the material on MG was 1860 mg⋅g–1 (sorption time – 60 min) and 642 mg⋅g–1 on CR (sorption time – 15 min). The theoretical maximum adsorption capacity of the sorbent calculated by the Langmuir model reached values of 769.23 mg⋅g–1 for CR and 3333.33 mg⋅g–1 for MG. It is found that the extraction of dye molecules is controlled by the second-order reaction according to the pseudo-second-order model and proceeds mainly by a mixed-diffusion mechanism. The activation energy has a value of 0.01 kJ⋅mol–1 for CR molecules and 0.02 kJ⋅mol–1 for MG, confirming the physical mechanism of dye adsorption. The high efficiency of adsorption of organic dyes on graphene-containing sorption material based on activated rapeseed biochar was demonstrated, indicating the feasibility of its practical application in wastewater treatment.

A new approach to carbon membranes fabrication by IR pyrolysis of the hollow fiber (HF) porous membranes from a homopolymer (PAN) and acrylonitrile copolymers with methyl acrylate (PAN-MA) and itaconic acid (PAN-IA) was developed. The method includes thermal stabilization of membranes at 250 °С, and subsequent IR pyrolysis. It was established that the HF membranes made from PAN-IA and PAN were the least susceptible to destruction with increasing temperature. However, for samples based on PAN-MA, the significant deformation of hollow fiber membranes after IR pyrolysis occurs at temperatures above 200–300 °C. Scanning electron microscopy study showed that the presence of glycerol as an impregnating agent in membranes (regardless of the chemical composition of acrylonitrile copolymers) leads to a less regular and more defective structure of the resulting carbon membranes. It was found that the thermal stabilization at 250 °C preserves structural integrity and contributes to the production of mechanically stable carbon membranes. FTIR spectra confirmed that IR radiation catalyzes transformations in the polymer structure. As a result, the time of thermal stabilization and pyrolysis was noticeably reduced. It was shown, that 15 min pretreatment and 5 min pyrolysis is enough for effective stabilization of membrane structure.

The paper examines the control of functional characteristics, particularly electronic transport properties, in inhomogeneous surface nanostructures of a topological class on a solid substrate, with a focus on enhancing electrical conductivity and controlling its modes in cluster-type metal-carbon composites. From the perspective of general solid-state physics, particularly for granular metals, the discussion centers on structural microcrystalline defects, specifically at the nanoscale in this case. The study involves the modeling of the formation of such systems with nanocluster structures within the context of digital materials science, demonstrating several experimental results. This is done under conditions of introducing nanotubes into a non-conductive matrix as additives with an optimal concentration, or conversely, introducing metal atoms (typically noble metals) into a nanotube system. A two-stage process is considered, involving laser ablation of various targets, including the initial stage of obtaining nanoparticles and nanoclusters with a sufficiently large number of atoms in colloidal systems in specific liquids. In the second stage, subsequent deposition onto a solid, usually dielectric, surface is implemented to create a matrix with the desired geometry and specified nanocluster topology. The studied effects and the possibility of controlling them using laser methods hold great promise for the development of micro- and nanoelectronics components and systems based on new physical principles. Trends and tendencies in the synthesis of hightemperature superconducting states in topological structures of various classes are also discussed.

The potassium polytitanates (PPT) modified in the aqueous solutions containing the mixtures of water soluble salts of Mn2+ and trivalent metals (R3+ = Fe3+, Cr3+ or Al3+) are used as intermediates to produce ceramic sinters consisting of hollandite-like solid solutions corresponding to the chemical composition of K1.3±0.1Mn1.5±0.1R0.2Ti6.3±0.1O16. It has been shown that an introduction of various trivalent metals into the salt compositions used to obtain Mn-containing powdered potassium polytitanate (PPT-Mn/R3+) makes it possible to produce single-phase ceramics based on the resulting products by sintering. The resulting ceramic materials are characterized with a colossal dielectric constant at low frequencies and ac-conductivity varied in a wide range of values depending R3+. The mechanism of relaxation processes occurring in the resulting ceramic materials and the prospects for their application are considered. The ceramics based on PPT-Mn/Cr intermediates is are characterized by relatively high ac-conductivity (10–7.5 Sm⋅cm–1) and permittivity | (108 at 10–2 Hz), and can be used in manufacturing of BLC electrode materials, whereas, the ceramics produced with the PPT-Mn/Fe intermediate and characterized by relatively low ac-conductivity (10-9.2 Sm/cm) and high permittivity (107.3 at 10–2 Hz) can be used as a dielectric material in manufacturing of ceramic capacitors.