Synthesized NiO nanostructures via sol–gel: unveiling the role of annealing conditions on structural and antioxidant properties

NiO octahedral nanoparticles with a face-centered cubic (fcc) structure were successfully synthesized via the sol–gel method, and the effects of annealing temperature and time on their structural, morphological, and antioxidant properties were systematically investigated. X-ray diffraction (XRD) results revealed that all samples crystallized in the fcc phase, except for the sample annealed at 300 °C. The lattice constant was calculated from XRD data, showing that increasing annealing temperature led to enhanced nanoparticle growth. Moreover, prolonging the annealing time initially resulted in a reduction of crystallite size, followed by stabilization at longer durations. Morphological and bonding characteristics were further confirmed by SEM and FTIR analyses. The antioxidant activity of the synthesized NiO nanoparticles was evaluated using the DPPH radical scavenging assay. Among all samples, the NiO nanoparticles annealed at 400 °C for 24 h exhibited the highest antioxidant activity (76.12 ± 3.43%), demonstrating that thermal treatment plays a critical role in controlling both the structural evolution and functional performance of NiO nanomaterials.