In the work, nanostructured Fe₃O₄/C composites based on natural raw materials (beet pulp and corn stalks) are synthesised in various ways. Iron chloride FeCl₃ is used as an activator. The synthesised composites are investigated using the following methods, scanning electron microscopy, X-ray diffractometry, nitrogen adsorption/desorption porometry, magnetometry, impedance and galvanostatic measurements. The presence of nanosized Fe₃O₄ magnetite in the synthesised carbon structures is disclosed. Based on the magnetic measurements, the particle size of Fe₃O₄ is on average 50 nm for the sample of the composite synthesised from beet pulp in one step, 30 nm for the sample of the composite synthesised from beet pulp in two steps, 33 nm for the composite synthesised from corn stalks in one step, and 29 nm for the composite synthesised from corn stalks in two steps. It is shown that the two-step synthesis using pre-carbonised raw materials gives the specific capacitance of the composite made with beet pulp at 96 F/g, and for the composite made with corn stalks at 95 F/g. The high coulombic efficiency (>95%) and the stability of the electrical capacitance during long-term cycling make it possible to use Fe₃O₄/C composites for the manufacture of supercapacitor electrodes with aqueous electrolytes.

This article presents the technology for the preparation of a nitrogen-containing nanoporous bio-carbon and investigates its properties. It has been shown that the synthesised bio-carbon is characterised by a high degree of homogeneity, which has been confirmed by energy dispersive spectroscopy. The obtained bio-carbon has a micromesoporous structure, which has been confirmed by the results of studies using the method of low-temperature nitrogen adsorption and desorption. It was found that the specific surface area of biochar is 1247 m²/g. The data on nitrogen adsorption and desorption were compared with the data on small-angle X-ray scattering, and it was found that the micropores in the synthesised bio-carbon are open pores, while mesopores remain closed. The energy dispersion analysis showed that the structure of the bio-carbon does not contain ferromagnetic atoms, but due to the addition of nitrogen, the synthesised bio-carbon in a magnetic field has the properties of a ferromagnet with a characteristic hysteresis of the specific magnetisation. It was found that this material has a saturation magnetisation σ_s of 1.4 A∙m²∙kg⁻¹ and a coercive force H_c of 10 kA/m. Symmetric supercapacitors were fabricated from the synthesised bio-carbon material with 30% aqueous KOH and 1 M Na₂SO₄ as electrolytes. It was found that for bio-carbon synthesised at 800 °C, the specific capacitance in a 30% aqueous solution of KOH is 180 F/g, and in a 1 M aqueous solution of Na₂SO₄, it is 124 F/g. The cyclic voltammetry of the fabricated supercapacitors at different rates of potential expansion was investigated and analysed. Impedance studies on these supercapacitors were carried out. The equivalent electrical circuits describing the electrochemical processes in the studied supercapacitors were constructed and characterised.

A two-step method for the synthesis of C/Ni/N nanocomposites based on hydrolysis lignin from wood chemical processing waste is proposed. These nanocomposites were found to have a well-developed porous structure with a wide pore size distribution. It was shown that doping hydrolysis lignin with urea-derived nitrogen leads to the appearance of ferromagnetic behavior in the carbon material. When nickel chloride was added during pyrolysis, the magnetic behavior of the C/Ni/N composite was provided by superparamagnetic Ni particles less than 30 nm in size and the magnetism of the carbon matrix. The addition of urea during the synthesis of the nanocomposite further promotes better integration of nickel into the carbon structure. According to the results of magnetic studies, the nickel content in the C/Ni/N nanocomposite was 19 wt.% compared to 15 wt.% in the C/Ni nanocomposite. The synthesized nanocomposite was demonstrated to have no residual magnetization, so its particles do not agglomerate after the external magnetic field is removed. Due to this property and the well-developed porous structure, C/Ni/N composites have the potential to be used as catalysts, active electrode materials for autonomous energy sources, and in environmental technologies as magnetically sensitive adsorbents.

In this paper, the porous structure of three types of β-cyclodextrin (β-CD) carbons was synthesized and investigated. The first carbon was obtained from pure β-CD, the second carbon was synthesized from β-CD using the KOH activator, and the third carbon was synthesized from pure β-CD with additional ultrasonic treatment in the non-cavitation mode at the last stage. It was found that the carbon from pure β-CD has a micromesoporous structure with a small specific surface area (~35 m2/g). Activation with KOH causes a significant increase in the specific surface area (~654 m2/g) due to an increase in the content of micropores with an average size of 1,25 nm. The ultrasonic treatment causes mechanical grinding and oxidation of the carbon surface. It has been shown that such treatment increases the mesopore content and significantly changes the mesopore size distribution. It has been established that the oxidation of the β-CD carbon surface after ultrasonic treatment causes an increase in its hydrophilicity of up to 83,1%. The increase in hydrophilicity will allow more efficient use of synthesized carbon and composites based on it in solving the problems of environmental safety in water environments.