Incorporating of Lawsonia inermis as a bio-template for synthesising of NiO nanoparticles: a potential antibacterial agent

This work details the synthesis of NiO nanoparticles, one of the most abundant metal oxides, under varying conditions. A green hydrothermal route utilizing Lawsonia inermis (henna) as a bio-template was employed. By adjusting the hydrothermal temperature from 140 °C to 180 °C, three distinct samples (Ni-140, Ni-160, and Ni-180) were produced. The XRD patterns showed excellent agreement with the standard NiO phase. Based on the XRD data, the structural parameters of NiO samples have been analyzed, too. Morphological analysis via FESEM indicated discrete nanoparticles for Ni-140 and Ni-180, whereas the Ni-160 sample was agglomerated. Optically, the transmittance at 550 nm was measured at 62%, 46%, and 47%, leading to band gap energies of 3.78 eV, 3.82 eV, and 3.90 eV, respectively. These band gap values are consistent with previously reported data. According to calculations, the crystallite size for all samples was about 14 nm. The efficacy of metallic oxide nanoparticles as antibacterial agents is attributed to their innate nanoscale dimensions and their increased capacity for interaction with biological structures.