Environmentally benign synthesis of NiO nanoparticles: Potential catalysts for Knoevenagel condensation with promising anti-cancer and anti-diabetic activities

With rising environmental awareness, there is an increasing demand for sustainable practices, leading to the growing popularity of green synthetic methodologies that focus on simplicity and non-toxicity. The study presents an efficient eco-friendly route for synthesizing nickel oxide nanoparticles using the Punica granatum L. fruit juice extract. The synthesized nanoparticles were characterized by Ultraviolet–visible Diffuse Reflectance Spectroscopy (UV–Vis DRS), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Dynamic Light Scattering (DLS), Zeta potential and Brunauer-Emmett-Teller (BET) analyses. The nanoparticles exhibited a face-centered cubic phase, with an average crystallite size of 10 nm and a nearly spherical shape. The specific surface area of the nanoparticles was found to be 113.73 m²/g. The nanoparticles served as highly effective, heterogeneous, and sustainable catalysts for the Knoevenagel condensation reactions involving various substituted aromatic aldehydes and active methylene compounds under non-toxic and moderate conditions. The reactions proceeded smoothly with excellent product yields in short time frames with convenient work-up procedures, and easy catalyst recovery, exhibiting high Turnover Number (TON) and Turnover Frequency (TOF). The catalytic performance of the nanoparticles remained consistent over five reaction cycles. The nanoparticles showcased significant cytotoxicity against the human liver cancer cell line (HepG2), achieving a 70.28 % inhibition at a concentration of 112.5 μg/mL. Moreover, the nanoparticles exhibited notable anti-diabetic properties by inhibiting the action of alpha-amylase enzyme. An enzyme inhibition of 52.04 % was attained at a nanoparticle concentration of 500 µg/mL, thereby promoting the hypoglycemic effect. Overall, this study showcases innovative applications of NiO nanoparticles synthesized from Punica granatum L. fruit juice extract, including their use as catalysts for the Knoevenagel condensation reactions, as anti-cancer agents against HepG2 cells, and as anti-diabetic agents through alpha-amylase inhibition.