Photocatalysis and Biomedical Applications of Phytofabricated Nickel Oxide Nanoparticles via Olive Leaf Extract

Phytosynthesis of nanoparticles (NPs) is a green, effective, and sustainable method that uses the phytochemicals in the biosynthesis of NPs as reducing and stabilizing agents. In this work, two forms of nickel oxide (NiO) have been synthesized and characterized using different physicochemical tools. The first NiO is NiO-1, which is photosynthesized using olive (Olea europaea L) leaf extract and nickel nitrate as a precursor of nickel ions. The second NiO is NiO-2, which is synthesized via the thermal treatment of NiO-1 at 550°C. The photocatalytic, antioxidant, and antimicrobial activities have been studied. The semiconducting properties of NiO-2 were higher than NiO-1, with energy band gap values of 3.4 eV and 5.2 eV, respectively. When exposed to natural sunlight, NiO-2 broke down 95% of 5 ppm crystal violet dye in 40 min, making it an effective and sustainable photocatalyst. The antioxidant activity has been studied using the 2,2-diphenyl-1-picrylhydrazyl assay and followed the order olive leaf extract > NiO-2 > NiO-1 with IC50 values of 2.3, 7.66, and 14.49, respectively. The antimicrobial activity has been evaluated against pathogenic microbes, Escherichia coli, Staphylococcus aureus, and Candida albicans. The best antimicrobial resulted from NiO-1, which showed more inhibition zones than the extract and NiO-2 against the tested microbes.