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The copper oxide nanoparticles (CuO NPs) were synthesized via solution combustion approach with Bengal gram powder as a fuel. The XRD analysis confirms the monoclinic structure of CuO NPs. FT-IR spectrum reveals the formation of CuO NPs. SEM studies show that the NPs are nearly spherical, and the elemental composition was confirmed by EDAX. The absorption spectra revealed a direct optical band gap of 1.50 eV. DFT calculations were performed to determine the HOMO–LUMO energy bandgap and found to be 1.72 eV, which is in good agreement with the experimental value. The Z-scan technique was used to investigate the third-order nonlinear optical (NLO) characteristics using DPSS continuous wave laser (532 nm, 200 mW). A high reverse saturation absorption and negative nonlinear refractions were observed. Third-order NLO parameters β , n 2 and χ (3) were found to be 1 9. 6 × 1 0 − 5 cm/W, − 1. 1 2 × 1 0 − 8 cm2/W and 5. 9 7 × 1 0 − 7 esu, respectively. The CuO NPs also displayed strong optical limiting behavior with a limiting threshold of 2.11 kW/cm2. [ABSTRACT FROM AUTHOR]

The trimanganese tetraoxide (Mn3O4) nanoparticles (NPs) belong to transition metal oxides and play a vital role in decaying the organic pollutants by harvesting light. The Mn3O4 is synthesized by solution combustion method for different metal-to-fuel ratios. The variation of crystallite sizes of Mn3O4 NPs with changes in the fuel ratio was studied by powder X-ray diffraction. The d-spacing of the HR-TEM image's lattice fringes perfectly match the (200) plane of the XRD pattern. The surface chemistry and composition of samples was confirmed by XPS data. Absorption spectroscopy was used to estimate the optical bandgap of the prepared samples. The BET analysis revealed the decrease in surface area with the increase in crystallite size. The photocatalytic degradation of Rhodamine B (RB) with crystallites of various shapes and sizes of Mn3O4 NPs was investigated. The degradation of RB increased with the enhancement in crystallinity of the sample. The proportion of RB dye degradation was found to be 99.75% in 2 h. The oxidizer-to-fuel ratio–dependent electrochemical investigations of Mn3O4 NPs were carried out using a three-electrode setup. Mn3O4 NPs were observed to be a better supercapacitor material with a specific capacitance of 58.91 F/g at 1 A/g. Hence, the prepared Mn3O4 samples can be used in cost-effective energy storage device applications. [ABSTRACT FROM AUTHOR]