In this study, hydrothermally produced Fe-doped Co₃O₄ nanostructured particles are investigated as electrocatalysts for the water-splitting process and electrode materials for supercapacitor devices. The results of the experiments demonstrated that the surface area, specific capacitance, and electrochemical performance of Co₃O₄ are all influenced by Fe³⁺ content. The Fe_xCo_3-xO₄ with x = 1 sample exhibits a higher BET surface (87.45 m²/g) than that of the pristine Co₃O₄ (59.4 m²/g). Electrochemical measurements of the electrode carried out in 3 M KOH reveal a high specific capacitance of 153 F/g at a current density of 1 A/g for x = 0.6 and 684 F/g at a 2 mV/s scan rate for x = 1.0 samples. In terms of electrocatalytic performance, the electrode (x = 1.0) displayed a low overpotential of 266 mV (at a current density of 10 mA/cm²) along with 52 mV/dec Tafel slopes in the oxygen evolution reaction. Additionally, the overpotential of 132 mV (at a current density of 10 mA/cm²) and 109 mV with 52 mV/dec Tafel slope were obtained for x = 0.6 sample towards hydrogen evolution reaction (HER). According to electrochemical impedance spectroscopy (EIS) measurements and the density functional theory (DFT) study, the addition of Fe³⁺ increased the conductivity at the electrode–electrolyte interface, which substantially impacted the high activity of the iron-doped cobalt oxide. The electrochemical results revealed that the mesoporous Fe-doped Co₃O₄ nanostructure could be used as potential electrode material in the high-performance electrochemical capacitor and water-splitting catalysts.

The study reports the influence of rare-earth ion doping on the structural, magnetic, and magnetocaloric properties of ferrimagnetic Gd_3−xRE_xFe₅O₁₂ (RE = Y, Nd, Sm, and Dy, x = 0.0, 0.25, 0.50, and 0.75) garnet compound prepared via facile autocombustion method followed by annealing in air. X-Ray diffraction (XRD) data analysis confirmed the presence of a single-phase garnet. The compound’s lattice parameters and cell volume varied according to differences in ionic radii of the doped rare-earth ions. The RE³⁺ substitution changed the site-to-site bond lengths and bond angles, affecting the magnetic interaction between site ions. Magnetization measurements for all RE³⁺-doped samples demonstrated paramagnetic behavior at room temperature and soft-ferrimagnetic behavior at 5 K. The isothermal magnetic entropy changes (−ΔS_M) were derived from the magnetic isotherm curves, M vs. T, in a field up to 3 T in the Gd_3−xRE_xFe₅O₁₂ sample. The maximum magnetic entropy change ($-∆S_M^{max}$) increased with Dy³⁺ and Sm³⁺substitution and decreased for Nd³⁺ and Y³⁺ substitution with x content. The Dy³⁺-doped Gd_2.25Dy_0.75Fe₅O₁₂ sample showed $-∆S_M^{max}$~2.03 Jkg⁻¹K⁻¹, which is ~7% higher than that of Gd₃Fe₅O₁₂ (1.91 Jkg⁻¹K⁻¹). A first-principal density function theory (DFT) technique was used to shed light on observed properties. The study shows that the magnetic moments of the doped rare-earths ions play a vital role in tuning the magnetocaloric properties of the garnet compound.

A set of experiments was conducted to synthesize doped and undoped sodium tantalates with carbon and sulfur in energy efficient single-step hydrothermal process. Undoped sodium tantalate nanocubes were synthesized at 140 °C and doped one at 180 °C for 12 h in rich alkaline atmosphere. The sizes of undoped, carbon-doped, and sulfur-doped sodium tantalate nanocubes were 38 nm, 45 nm, and 40 nm, respectively. The morphological, elemental, compositional, structural, thermal, and photophysical properties of as-synthesized doped and undoped sodium tantalate (NaTaO₃) were characterized using scanning electron microscope (SEM), energy dispersive x-ray spectroscope (EDS), Raman spectroscopy, X-ray powder diffraction (XRD), thermal gravimetric analysis (TGA), Fourier transform infrared spectrophotometer (FTIR), and UV-vis spectrophotometer. The sulfur doped NaTaO₃ shows a higher photocatalytic activity in degradation of methylene blue than carbon doped and the undoped NaTaO₃. The band gaps of undoped NaTaO₃, carbon doped c-NaTaO₃, and sulfur doped s-NaTaO₃ were calculated to be 3.94 eV, 3.8 eV, and 3.52 eV, respectively using Tauc plot.

The study reports the synthesis and characterization of the magnetic and magnetocaloric effects of metal-oxide (MO) modified La_0.7Ca_0.3MnO₃ perovskites manganite. The powder composite samples, with a nominal composition of (1 − x)La_0.7Ca_0.3MnO₃-xMO (Wt.% x = 0.0, 2.5, 5.0), were prepared using the facile autocombustion method, followed by an annealing process. The phase purity and structure were confirmed by X-ray diffraction. Temperature and field-dependent magnetization measurements and Arrott analysis revealed mixed first- and second-order phase transition (ferromagnetic to paramagnetic) in composite samples. The phase transition temperature shifted to lower temperatures with the addition of MO in the composite. A large magnetic entropy change (4.75 JKg⁻¹K⁻¹ at 1T and 8.77 JKg⁻¹K⁻¹ at 5T) was observed in the La_0.7Ca_0.3MnO₃ (LCMO) sample and was suppressed, due to the presence of the MO phase in the composite samples. On the other hand, the addition of MO as a secondary phase in the LCMO samples enhanced their relative cooling power (RCP). The RCP of all composite samples increased with respect to the pristine LCMO, except for LCMO–5%NiO. The highest RCP value of 267 JKg⁻¹ was observed in LCMO–5%CuO samples, which was 23.4% higher than the 213 JKg⁻¹ observed for the pure LCMO at a magnetic field of 5T. The enhanced RCP of these composites makes them attractive for potential refrigeration applications.

Single-phase Gd₂O₃ nanostructures with different morphologies, such as nanoparticles, nanorods, nanospheres, and nanoplates, were synthesised. Gd₂O₃ 1D nanorods and 2D nanoplate architectures were prepared via the hydrothermal method, while 3D hollow nanospheres were synthesised via homogeneous precipitation. The magnetic and magnetocaloric properties of Gd₂O₃ nanostructured particles were studied as functions of temperature and field. The material demonstrated typical paramagnetic behaviour in the measured temperature range of 3–300 K. The magnetic entropy change (−ΔS _M ) was determined from the magnetic isotherms measured in the 3–38 K temperature range in the field up to 5 T. The maximum change in magnetic entropy Δ S M max value 11.2 J kg⁻¹ K⁻¹ for the nanoplate, 9.4 J kg⁻¹ K⁻¹ for the nanorod, 9.2 J kg⁻¹ K⁻¹ for the nanosphere, and 10.7 J kg⁻¹ K⁻¹ for the nanoparticle sample was observed at temperature 5 K for the magnetic field of 5 T. Owing to large Δ S M max , these Gd₂O₃ nanostructured particles would be considered promising materials for magnetic refrigeration at cryogenic temperatures.