Solids, Volume 5, Issue 2 (June 2024) – 6 articles

Using the solid-state reactions method Na_0.55(Co,M)O₂ (M = Cr, Ni, Zn, W, and Bi) ceramics were prepared and their crystal structure, microstructure, electrophysical, thermophysical, and thermoelectric properties were studied. Doping of Na_0.55CoO₂ by transition or heavy metal oxides led to the increase in the grain size of ceramics, a decrease in electrical resistivity and thermal diffusivity values, and a sharp increase in the Seebeck coefficient, which resulted in essential enhancement of their thermoelectric properties. The largest power factor (1.04 mW/(m·K²) at 1073 K) and figure of merit (0.702 at 1073 K) among the studied samples possessed the Na_0.55Co_0.9Bi_0.1O₂ compound, which also demonstrated the highest values of the Seebeck coefficient (666 μV/K at 1073 K). The obtained results show that the doping of layered sodium cobaltite by different metal oxides allows for improving its stability, microstructure, and functional properties, which proves the effectiveness of the doping strategy for developing new thermoelectric oxides with enhanced thermoelectric performance. Full article

A comprehensive study of the thermoelectric properties of CuCr_0.99Ln_0.01S₂ (Ln = La…Lu) disulfides was carried out in a temperature range of 300 to 740 K. The temperature dependencies of the Seebeck coefficient, electrical resistivity, and thermal conductivity were analyzed. It was found that the cationic substitution of chromium with lanthanides in the crystal structure of layered copper–chromium disulfide, CuCrS₂ resulted in notable changes in the thermoelectric performance of CuCr_0.99Ln_0.01S₂. The cationic substitution led to an increase in the Seebeck coefficient and electrical resistivity and a thermal conductivity decrease. The highest values of the thermoelectric figure of merit and power factor corresponded to the praseodymium-doped sample and an initial CuCrS₂-matrix at 700–740 K. The cationic substitution with lanthanum, cerium, praseodymium, samarium, and terbium allowed for an enhancement of the thermoelectric performance of the initial matrix at a temperature range below 600 K. The cationic substitution of CuCrS₂ with lanthanum and praseodymium ions appeared to be the most promising approach for increasing the thermoelectric performance of the initial matrix. Full article

This research investigates the influence of synthesis kinetics on the structural and photocatalytic properties of chitosan–clay nanocomposites (Cs/MMT) and chitosan–hectorite nanocomposites (Cs/HET), employing an optimized initial stoichiometry of 1:3. Utilizing a variety of analytical techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FTIR), the study explores the structural evolution of the nanocomposites and their photocatalytic performance using semiconductor catalysts TiO₂ and ZnO. The findings emphasize the significant impact of reaction kinetics, particularly after 3 h of reaction time, on the structural features of the nanocomposites. Notably, Cs/MMT demonstrates greater crystalline stability compared to Cs/HET due to variations in octahedral cavity occupancy in the initial clays. FTIR and TEM analyses depict the progressive evolution of the nanocomposites during the reaction, shedding light on how reaction kinetics drive the formation of specific bonds within the nanocomposites. In terms of photocatalytic activity, this study provides insights into the complex dynamics of photocatalytic degradation, with a specific focus on the performance of TiO₂ and ZnO under diverse experimental conditions. The superior efficacy of TiO₂ as a catalyst, particularly when integrated with Cs/MMT nanocomposites, is unequivocally demonstrated, with degradation rates exceeding 80%. This preference stems from TiO₂ consistently exhibiting higher degradation rates compared to ZnO, attributed to structural disparities between montmorillonite and hectorite, influencing catalyst–support interactions. The findings underscore the critical importance of selecting suitable catalyst and support matrix combinations for optimizing performance in specific applications. Full article

Taking advantage of fact that the surface electrons of metallic nanoparticles (NPs) can be effectively released even at a low voltage bias, we demonstrate an improvement in the electrochemical performance of nanosized Prussian Blue (PB)-based secondary batteries through the incorporation of bare Ag or Ni NPs in the vicinity of the working PB NPs. It is found that the capacity for electrochemical energy storage of the 17 nm PB-based battery is significantly higher than the capacity of 10 nm PB-based, 35 nm PB-based or 46 nm PB-based batteries. There is a critical PB size for the highest electrochemical energy storage efficiency. The full specific capacity C_F of the 17 nm PB-based battery stabilized to 62 mAh/g after 130 charge–discharge cycles at a working current of I_W = 0.03 mA. The addition of 14 mass percent of Ag NPs in the vicinity of the PB NPs gave rise to a 32% increase in the stabilized C_F. A 42% increase in the stabilized C_F could be obtained with the addition of 14 mass percent of Ag NPs on the working electrode of the 35 nm PB-based battery. An enhancement in C_F was also found for electrodes incorporating bare Ni NPs but the effect was smaller. Full article

The charge properties and regularities of mutual influence of the electro-physical parameters in a metal (M)/insulator (I)/two-dimensional crystal heterostructure were studied. In one case, the transition metal dichalcogenide (TMD) MoS₂ was considered as a two-dimensional crystal, and in another the Weyl semi-metal (WSM) ZrTe₅, representative of a quasi-two-dimensional crystal was chosen for this purpose. By self-consistently solving the electrostatic equations of the heterostructures under consideration and the Fermi–Dirac distribution, the relationship between such parameters as the concentration of charge carriers, chemical potential, and quantum capacitance of the TMD (WSM), as well as the capacitance of the I layer and the interface capacitance I–TMD (WSM), and their dependence on the field electrode potential, have been derived. The conditions for the emergence of charge instability and the critical phenomena caused by it are also determined. Full article

In the quest to combat global warming, traditional thermal chemistry processes are giving way to selective photocatalysis, an eco-friendly approach that operates under milder conditions, using benign solvents like water. Benzaldehyde, a versatile compound with applications spanning agroindustry, pharmaceuticals, and cosmetics, serves as a fundamental building block for various fine chemicals. This study aims at enhancing benzaldehyde production sustainability by utilizing photooxidation of benzyl alcohol. Gold nanoparticle-based catalysts are renowned for their exceptional efficiency in oxidizing bio-based molecules. In this research, Au nanoparticles were anchored onto three distinct supports: $\mathrm{T}\mathrm{i}{\mathrm{O}}_2$, $\mathrm{Z}\mathrm{r}{\mathrm{O}}_2$, and graphitic carbon nitride (g-${\mathrm{C}}_3{\mathrm{N}}_4$). The objective was to investigate the influence of the support material on the selective photocatalysis of benzyl alcohol. In the preparation of g-${\mathrm{C}}_3{\mathrm{N}}_4$, three different precursors—melamine, urea, and a 50:50 mixture of both—were chosen to analyze their impact on catalyst performance. After 4 h of irradiation at 365 nm, operating under acidic conditions (pH = 2), the Au photocatalyst on graphitic carbon nitride support synthesized using urea precursor (Au@g-${\mathrm{C}}_3{\mathrm{N}}_{4\left(urea\right)}$) displayed the optimal balance between conversion (75%) and selectivity (85%). This formulation outperformed the benchmark Au@TiO₂, which achieved a similar conversion rate (80%) but exhibited lower selectivity (55%). Full article