Nowadays, antimicrobial agents are currently being employed using noble metal nanoparticles such as gold and silver. NiO nanoparticles are a good alternative in this case, since they are less expensive than gold and silver. Antimicrobial agents are very important in textiles, water disinfection, medicine and food packaging. Most of these applications employ nanoparticles of specific shape, size and chemical composition. For these reason, present work focuses on synthesis of Nickel oxide nanoparticles by Chemical precipitation method. Obtained particles by this method were characterizes for their structural, optical, and antimicrobial properties after calcination process at various temperature of 400 °C, 600 °C, and 800 °C at 2 h. The Rietveld refinement was carried out to obtain the crystal structure and purity of synthesis was achieved. The analysis of peak broadening was performed to estimate the discrepancy in crystallite size and microstrain components of the nanoparticles with the calcination temperatures and were compared with Transmission Electron Microscope results. The calculated band gap value varies from 3.37 to 3.3 eV by increasing the calcination temperature. The emission peak at 490 and 580 nm affirmed the presence of defects in the NiO lattice. The formation of NiO was confirmed using FTIR for all the calcination at different temperatures nanoparticles. Antimicrobial activities of prepared nanoparticles were tested against selected four distinct pathogenic bacterial and three non-identical fungi species by the disc diffusion method. Results of the zone of inhibition values (mm) indicate that the test samples were exhibited significant antimicrobial activity.
