Thermal-induced effects on the structural and photocatalytic properties of Nickel Oxide nanoparticles for Indigo Carmine dye removal

Abstract In this study, NiO nanoparticles were formed using the chemical precipitation method, and the calcination process induced structural parameters and optical bandgap. The research was carried out using a variety of techniques such as XRD, FTIR, and SEM. The XRD analysis reveals that the formed NiO crystallized in an fcc crystal structure, and that the calcination process influences the microstrain, dislocation density, and average surface area. The optical bandgap and crystal structure parameters are significantly affected by increasing the calcination temperature and/or time. The formation of a Ni–O stretching vibration mode is revealed by FTIR, and the broadness of the absorption band confirms that the NiO samples are nanocrystals. The morphology of the prepared NiO reveals the formation of spherical nanoparticles for samples calcined at 700 °C and dodecahedron-like shapes for samples calcined at 800 and 900 °C. Depending on the calcination temperature and time, the optical band gap ranged from 3.33 to 3.71 eV. The photocatalytic performance of NiO nanoparticles as catalysts for the degradation of indigo carmine (IC) dye is investigated under UV-visible irradiation for up to 3 h. The best degradation efficiency was found to be 76% for NiO calcined at 800 °C for 4 h, which revealed the smallest crystallite size of 19.13 nm, and the highest surface area of 47.02 m2/g. A mechanism for the degradation process was proposed, and the reaction rate constants for various NiO catalysts were estimated, with the maximum value of 4.51×10–3/min calculated for NiO calcined at 800 °C for 4 h.