Microwave-assisted green synthesis, characterization, and <i>in vitro</i> antibacterial activity of NiO nanoparticles obtained from lemon peel extract

<jats:title>Abstract</jats:title>
<jats:p>In the realm of nanotechnology, the synthesis of nanoparticles using environmentally benign methods, such as using plant extracts, has garnered significant attention. This work reports a simple and eco-friendly approach for the synthesis of nickel oxide nanoparticles (NiO NPs) utilizing microwave irradiation in the presence of lemon peel extract as a green reducing agent and Ni(CH<jats:sub>3</jats:sub>COO)<jats:sub>2</jats:sub>·2H<jats:sub>2</jats:sub>O as a precursor. Numerous analytical techniques were employed to determine the optical, morphological, and structural properties of the green-synthesized NiO NPs. The findings revealed that the resulting NiO NPs are pure, with an average size of 34 nm and a spherical geometry, possessing a face-centered-cubic crystalline structure. The antibacterial activities of the NiO NPs were preliminarily investigated against Gram-positive bacteria (<jats:italic>Bacillus subtilis</jats:italic> and <jats:italic>Staphylococcus aureus</jats:italic>) and Gram-negative bacteria <jats:italic>(Klebsiella pneumoniae</jats:italic> and <jats:italic>Salmonella typhimurium</jats:italic>). The morphological changes in <jats:italic>B. subtilis</jats:italic> and <jats:italic>S. typhimurium</jats:italic> were also evaluated by FE-SEM analysis, which showed that some cells were partially damaged and distorted in shape upon treatment with NiO NPs, thus demonstrating their promising antibacterial activities.</jats:p>