Figure 1

(a) Schematic diagram of the synthesis procedure of NiO nanoparticles. The details are given in the text. (b) X-ray diffraction spectra of cleaned NiO nanoparticles. The high-intensity peaks have been identified at 2\(\theta\) = 36.9\(^{\circ }\), 42.97\(^{\circ }\) are indexed to (111) and (200) crystallographic planes. (c) The UV–vis spectra converted into a Tauc plot indicate an optical energy gap of 3.72 eV.