Correlation between photoluminescence and positron annihilation lifetime spectroscopy to characterize defects in calcined MgO nanoparticles as a first step to explain antibacterial activity

Many studies discussed the potential antibacterial activity of MgO nanoparticles; however, there is no clarity about ideal calcination temperature for MgO nanoparticles. Therefore, the present work shows low cost preparation of MgO nanoparticles bysol-gel method followed by exposing to different annealing temperatures to determine the optimal calcination temperature for the highest antibacterial activity. MgO nanoparticle properties were investigated via X-ray diffraction (XRD), high resolution scanning electron microscope (SEM) and transmission electron microscope (TEM). The obtained results emphasized the formation of cubic structure of MgO nanoparticles. Moreover, the average particle size was directly increased with calcination temperature. Antibacterial activity of calcined MgO nanoparticles was examined against gram-positive Bacillus cereus. Our results show that 100% inhibition was observed in case of MgO nanoparticles calcined at 500 degrees C. Moreover, Photoluminescence (PL) and Positron annihilation lifetime spectroscopy (PALS) were employed to determine the defects in calcined MgO nanoparticles in order to explain the antibacterial activity. The results show correlation between PL and PALS where the oxygen vacancies defects had the maximum with calcined MgO nanoparticles at 500 degrees C. Consequently, this sample of MgO nanoparticles exhibited the highest ability to generate reactive oxygen species (ROS) which consequently reacts with the bacterial cells causing cell death. (C) 2019 Elsevier B.V. All rights reserved.