In this study, we used multilayer graphene oxide (GO) obtained by anodic oxidation of graphite powder in 83% sulfuric acid. The modification of GO was carried out by its interaction with hexamethylenediamine (HMDA) according to the mechanism of nucleophilic substitution between the amino group of HMDA (HMDA) and the epoxy groups of GO, accompanied by partial reduction of multilayer GO and an increase in the deformation of the carbon layers. The structure and properties of modified HMDA-GO were characterized using research methods such as scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction spectroscopy and Raman spectroscopy. The conducted studies show the effectiveness of using HMDA-OG for modifying epoxy composites. Functionalizing treatment of GO particles helps reduce the free surface energy at the polymer–nanofiller interface and increase adhesion, which leads to the improvement in physical and mechanical characteristics of the composite material. The results demonstrate an increase in the strength and elastic modulus in bending by 48% and 102%, respectively, an increase in the impact strength by 122%, and an increase in the strength and elastic modulus in tension by 82% and 47%, respectively, as compared to the pristine epoxy composite which did not contain GO-HMDA. It has been found that the addition of GO-HMDA into the epoxy composition initiates the polymerization process due to the participation of reactive amino groups in the polymerization reaction, and also provides an increase in the thermal stability of epoxy nanocomposites.

Some solid solutions with the chemical composition K_xFe_yTi_8-yO₁₆ (KFTO) and a hollandite-like structure were successfully synthesized by modified sol–gel method. The obtained powders were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ceramic pellets based on KFTO powders were obtained by compressing and sintering at 1080 °C for 4 h. The sinters were characterized by X-ray and impedance spectroscopy. XRD results show that KFTO powders have a mono-phase tetragonal structure at x = 1.4–1.8 and y = 1.4–1.6. However, it was recognized that the hollandite-like phase could be broken during sintering to form TiO₂ and Fe₂TiO₅ crystals distributed throughout the volume of the ceramics. A frequency dependency of dielectric properties for the sinters was studied by impedance spectroscopy. It was found that an increase in the TiO₂ (rutile) phase during the sintering contributes to a decrease in dielectric losses. At the same time, the KFTO ceramics with reduced content of potassium had increased permittivity. The contribution of electron-pinned defect dipoles (EPDD) and internal barrier layer capacitance (IBLC) in the permittivity of the obtained ceramics was estimated using the Havriliak–Negami equation. It is shown that the KFTO ceramics have the polydisperse characteristic of dielectric relaxation. The observed grain and grain boundary dipole relaxation times were 1.03 × 10⁻⁶ to 5.51 × 10⁻⁶ s and 0.197 to 0.687 s, respectively.

Электрохимическим методом синтезированы образцы многослойного оксида графена в электролитах на основе H₂SO₄. Результаты дифференциальной сканирующей калориметрии и термогравиметрического анализа полученных образцов выявляют эндотермический пик в интервале сканирования до 100 °С, сопровождающийся потерей массы порядка 7%. Этот эффект может быть обусловлен десорбцией и испарением некоторого количества удерживаемой воды в образцах. Другой эндотермический пик появляется при 252 °С на кривой ДТА и потерю массы 15%, можно объяснить разложением лабильных гидроксильных, эпоксидных и карбоксильных кислородсодержащих функциональных групп. Термическая эксфолиация при 250 °С многослойного оксида графена приводит к удалению кислородсодержащих функциональных групп, значительному увеличению размера частиц (K_V = 1490 см³·г^-1) и формированию червеобразных структур с большим количеством V-образных пор с размером 1-10 мкм и толщиной полиграфеновых плоскостей до 0,01 мкм. Удельная поверхность порошка термовосстановленного оксида графена составляет 400-500 м²г^-1, диапазон распределения частиц в воде составляет 0,3-1400 мкм, модальный размер 211 мкм. При ультразвуковом воздействии на водную дисперсию оксида графена размер частиц дисперсной фазы значительно уменьшается до 0,2-400 мкм, с модальным размером 143 мкм. По ИК спектрам термовосстановленного оксида графена установлено наличие sp²-гибридизации C=C в структуре графена (пик при 1627 см^-1), эпоксигрупп -C-O-C- (полоса между 1106 см^-1 и 1005 см^-1), карбоксильных групп -СООН- (полоса при 1384 см^-1). Пик при 2300 см^-1 соответствует пику поглощенных молекул СО₂. После экспонирования термовосстановленного оксида графена в растворах, содержащих катионы меди, на ИК спектрах в области 690 - 1130 см^-1 наблюдаются полосы поглощения, которые можно рассматривать как колебания группировок, образовавшихся на поверхности в результате взаимодействия катионов меди с атомами кислорода в составе функциональных групп. Изотермы адсорбции Cu²⁺ на термовосстановленном оксиде многослойного графена имеют вид характерный для изотерм класса H₂ и характеризуются прямолинейным крутовосходящим начальным участком, что свидетельствует о большом сродстве адсорбата к адсорбенту и образовании химичсеких соединений. Вероятно, происходит взаимодействие ионов Cu²⁺ с карбоксильными функциональными группами, что подтверждается незначительным понижением pH раствора. Изотерма аппроксимирована прямой линией, что позволяет использовать для описания процесса адсорбции модель Ленгмюра. Максимальная сорбционная способность термовосстановленного оксида многослойного графена к Cu²⁺ составила ≈ 25 мг г^-1, что заметно выше, чем сорбционная способность активированных углеродных волокон.

Developing polymer composites with improved mechanical and thermal properties requires strategies to overcome the problem of agglomeration and weak interfacial interactions of carbon nanofillers. This paper presents an effective strategy for the covalent functionalization of graphene oxide (GO) with melamine to create high-performance epoxy nanocomposites. The functionalization results in the formation of nitrogen-containing heterocyclic structures on the GO surface, as confirmed by FTIR and Raman spectroscopy. The addition of the obtained modified filler (mel-GO) into the epoxy matrix provides a synergistic effect: the melamine amino groups catalytically accelerate curing, reducing the gelation time from 146 to 48 min and increasing the maximum self-heating temperature from 94 to 122 °C, thus indicating enhanced interfacial interaction. This interaction results in a remarkable overall improvement in mechanical properties: tensile and flexural strengths increase by more than 20%, and elastic moduli by 31% and 58%, respectively, compared to the composite containing unmodified GO. At the same time, impact strength (from 14 to 23 kJ/m²) and hardness (up to 87 Shore D) increase. A key achievement is a dramatic increase in thermal and thermal-oxidative stability: the onset temperature of decomposition (T₅%) increases by 27 °C, the half-decomposition temperature (T₅₀%) by 45 °C, and the thermal stability index (THRI) increases from 119.3 to 128.9 °C. A more than twofold increase in coke residue yield (to 9.29%) and an increase in the Vicat softening point to 175 °C confirm the formation of an effective thermally stabilizing barrier layer due to the combined action of nitrogen-containing groups and dispersed graphene flakes. The proposed approach to functionalizing graphene oxide with melamine opens the way for the creation of next-generation epoxy composites with a record-breaking combination of strength, impact toughness, and thermal stability for applications in aerospace, electronics, and composite structures operating under extreme conditions.

The results of the study of the electrochemical reduction of multilayer graphene oxide in the potentiostatic mode are presented and the possibility of using alkaline electrolyte (KOH) with the concentration below 0.1 M is shown. The identification of the electrochemically reduced graphene oxide was carried out using the XRD, FTIR and Raman-spectroscopy methods. Applying the method of Raman spectroscopy the increase in the intensity of the G and 2D bands, indicating the formation of few-layer forms of reduced graphene oxide was found. The surface morphology of the electrochemically reduced graphene oxide was studied by means of the SEM method.