Biogenic nickel oxide nanoparticles for the catalytic reduction of nitrobenzene derivatives and their anticancer and antioxidant activities

With the increasing focus on environmental sustainability, green synthesis methods are being increasingly recognised for their simplicity and eco-friendly nature. This study presents an innovative approach for synthesising nickel oxide (NiO) nanoparticles from the aqueous leaf extract of Ricinus communis. The synthesised nanoparticles were extensively characterised using various techniques. X-ray Diffraction (XRD) confirmed the crystalline nature of the nanoparticles with an average size of 6.35 nm, while Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) revealed their spherical morphology. The Fourier Transform Infrared Spectroscopy (FTIR) indicated the involvement of phytochemicals in the synthesis and stabilisation of the nanoparticles. The UV–Visible Spectroscopy (UV–Vis) showed a distinct absorption at 270 nm. The zeta potential of -19.8 mV showed moderate colloidal stability, and a polydispersity index (PDI) of 0.390 suggested a moderately uniform size distribution of the nanoparticles. Their elemental composition was confirmed through X-ray Photoelectron Spectroscopy (XPS) and Energy Dispersive X-ray (EDX) technique. The nanoparticles demonstrated promising catalytic activity in the reduction of hazardous nitrobenzene compounds to their corresponding aniline derivatives under sustainable reaction conditions. The reactions gave a good yield of products in brief reaction times. The nanocatalyst exhibited good stability and was effectively reusable for up to five consecutive cycles. Moreover, the nanoparticles showed significant anticancer activity against the A549 human lung cancer cell line, with 84.57 % cytotoxicity at 250 µg/mL concentration and an observed IC₅₀ value of 53.16 µg/mL. The nanoparticles also displayed a dose-dependent free radical scavenging activity, with a maximum scavenging of 73.38 % found at 200 µg/mL concentration. This work contributes to the advancement of green nanotechnology and highlights the potential of Ricinus communis-based NiO nanoparticles in catalytic and biomedical applications.