This work reveals a green combustion route for the synthesis of TiO₂, Fe₂O₃ and TiO₂-Fe₂O₃ nanocomposites as photocatalysts for decolorization of Titan Yellow (TY) and Methyl Orange (MO) dyes at room temperature in aqueous solution concentration of 20 ppm under UV-light irradiation. We observed that the TiO₂-Fe₂O₃ nanocomposite shows superior photocatalytic activity for TY dye compared to pure TiO₂ and Fe₂O₃. Rate constant (k) values of TiO₂, Fe₂O₃ and TiO₂–Fe₂O₃ for TY and MO are 0.0194, 0.0159, 0.04396 and 0.00931, 0.00772 0.0119 kmin⁻¹ respectively. The surface area and pore volume of TiO₂-Fe₂O₃ nanocomposite were found to be 71.56 m²/g and 0.076 cm³/g, respectively as revealed by BET studies. From the Barrett–Joyner–Halenda (BJH) plot, the mean pore diameter of TiO₂-Fe₂O₃ nanoparticles was found to be 2.43 nm. Further, the TiO₂-Fe₂O₃ nanocomposite showed good electrochemical behavior as an electrode material for supercapacitors when compared to pure TiO₂ and Fe₂O₃ nanoparticles resulted in stable electrochemical performance with nearly 100% coulombic efficiency at a scan rate of 10 mV/s for 1000 cycles. Interestingly, the novelty of this work is that the designed supercapacitors showed stable electrochemical performance even at 1000^th cycle, which might be useful for rechargeable supercapacitor applications. The electrochemical properties of the nanocomposites were compared by the data obtained by cyclic voltammograms, charge-discharge tests and electrochemical impedance spectroscopic studies. These results demonstrated that the TiO₂-Fe₂O₃ nanocomposite showed stable performance compared to TiO₂ and Fe₂O₃ nanoparticles at current density of 5 Ag⁻¹.

A simple and low‐cost and highly calibrated probe sonication method was used to prepare bismuth oxide nanoparticles (Bi₂O₃ NPs). The formation of a well‐crystalline sample at the end of the product has been further calcined at 600°C for 2 hrs. The powder X‐ray diffraction (PXRD) patterns of the NPs substantiated the monoclinic structure (space group P2₁/c), and the average crystallite size was found to be 60 nm, which was also confirmed by transmission electron microscopic (TEM) studies. Scanning electron microscopic (SEM) images depicted highly porous Bi₂O₃ NPs with little agglomeration. Utilizing diffused reflectance spectra (DRS) data, the energy bandgap (E_g) value of 3.3 eV was deduced for Bi₂O₃ NPs, and their semiconductor behavior has been confirmed. Two dyes, methylene blue (MB) and acid green (AG) were utilized for degradation studies using Bi₂O₃ NPs under UV light irradiation (from 0 to 120 min). The photocatalytic degradation was found to be maximum for MB (93.45%) and AR (97.80%) dyes. Cyclic voltammetric (CV) and sensor studies using the electrochemical impedance spectroscopy (EIS) were performed. The specific capacitance value of 25.5 Fg^-1 was deduced from the cyclic voltammograms of the Bi₂O₃ electrode in 0.1 N HCl with a scan rate of 10 to 50 mV/s. From the obtained EIS data, the Bi₂O₃ electrode showed pseudocapacitive characteristics. The prepared electrodes also exhibited high sensitivity towards the detection of ascorbic acid and lead. Hence, sonochemically synthesized Bi₂O₃ NPs are possibly hopeful for excellent photocatalytic and electrochemical sensing of biomolecules.

The biogenic/green silver nanoparticles (g-Ag NPs) were synthesised by using the extract of indigenous medicinal plant of Ethiopia,Hagenia abyssinica (Brace) JF. Gmel.leaf extract for the first time, to investigate the synergistic effect of biomolecules towards the enhancement of electrochemical properties of NPs. The synthesized g-Ag NPs were characterized by UV-visible, UV-DRS, FT-IR, XRD, SEM, EDXA, TEM, HRTEM and SAED techniques. The maximum absorbance,λ_maxwas found to be 461 nm for g-Ag NPs due to surface plasmon resonance. The energy gap, E_gof NPs, was found to be 2.31 eV. FTIR spectrum confirmed the presence of bioactive compounds responsible for possible capping and stabilisation of g-Ag NPs. The XRD analysis revealed that the g-Ag NPs are highly crystalline exhibiting sharp peaks for (111), (200), (220) and (311) planes in the diffraction pattern. SEM and TEM micrographs showed differently shaped Ag particles in addition to spherical shape. The average particle size of NPs was found to be 24.08 nm using imageJ analysis. EDX analysis confirmed the presence of Ag in the g-Ag NPs. In addition, the SAED pattern of g-Ag NPs presented concentric patterns for 4 major planes of crystalline silver. The d-spacing values of 0.2428 nm, 0.2126 nm, 0.1483 nm and 0.1263 nm corresponds to d₁₁₁Ag, d₂₀₀Ag, d₂₂₀Ag and d₃₁₁Ag lattice fringes respectively. The cyclic voltammetry (CV) results suggest that g-Ag NPs possess better electrochemical properties due to its lower charge transfer resistance value of 17 Ω. EIS studies too revealed better stability of g-Ag NPs as electrode materials.

The synthesis of optoelectrically enhanced nanomaterials should be continuously improved by employing time- and energy-saving techniques. The porous zinc oxide (ZnO) and copper-doped ZnO nanocomposites (NCs) were synthesized by the time- and energy-efficient solution combustion synthesis (SCS) approach. In this SCS approach, once the precursor-surfactant complex ignition point is reached, the reaction starts and ends within a short time without the need for any external energy. The TGA-DTA analysis confirmed that 500 °C was the point at which stable metal oxide was obtained. The doping and heterojunction strategy improved the optoelectric properties of the NCs more than the individual constituents, which then enhanced the materials' charge transfer and optical absorption capabilities. The porosity, nanoscale crystallite size (15-50 nm), and formation of Cu/CuO-ZnO NCs materials were confirmed from the XRD, SEM, and TEM/HRTEM analyses. The obtained d-spacing values of 0.275 and 0.234 nm confirm the formation of ZnO and CuO crystals, respectively. The decrease in photoluminescence intensity for the doped NCs corroborates a reduction in electron-hole recombination. On the Mott-Schottky analysis, the positive slope for ZnO confirms the n-type character, while the negative and positive slopes of the NCs confirm the p- and n-type characters, respectively. A diffusion-controlled type of charge transfer process on the electrode surface was confirmed from the cyclic voltammetric analysis. Thus, the overall analysis shows the applicability of the less expensive and more efficient SCS for several applications, such as catalysis and sensors. To confirm this, an organic catalytic reduction reaction of 4-nitrophenol to 4-aminophenol was tested. Within three and a half minutes, the catalytic reduction result showed the great potential of NCs over ZnO NPs. Thus, the energy- and time-saving SCS approach has a great future outlook as an industrial pollutant catalytic reduction application.