Novel green synthesis of ZnO, CaO, and ZnO-CaO hybrid nanocomposites using extract of Foeniculum vulgare (Fennel) stalks : characterization, mechanical stability, and biological activities

Abstract Plant-mediated synthesis of nanoparticles is considered an eco-friendly and cost-effective approach to developing safer and more effective treatment strategies. The current study employed Foeniculum vulgare (FV) waste extract to mediate the green synthesis of Zinc oxide (ZnO) and Calcium oxide (CaO) nanoparticles (NPs) as well as their hybrid NPs (ZnO-CaO). The biosynthesised NPs were characterized using ultraviolet-visible (UV-Vis) spectroscopy, Fourier-transform infra-red (FTIR) spectroscopy, energy-dispersive X-ray analysis (EDX), X-ray diffraction (XRD), dynamic light scattering (DLS), and scanning electron microscopy (SEM). The influence of zeta potential, size, and turbidity on the NPs stability was studied. The synthesised NPs were also evaluated for their antioxidant, anti-inflammatory, and antibacterial activities. UV-visible spectroscopy confirmed the synthesis of FV-ZnO, FV-CaO, and FV-ZnO-CaO hybrid NPs using a surface plasmon resonance peak at 271.5, 269.5, and 269 nm, respectively. FTIR analysis indicated that the plant extract contains phytochemicals that aid in the bio-reduction and stabilization of the NPs. EDX confirmed the elemental composition, and XRD showed crystallinity of the NPs. FV-ZnO revealed a hexagonal crystalline structure, FV-CaO showed a cubic lattice structure, and FV-ZnO-CaO showed a mixed ratio of crystalline and cubic phase. SEM revealed distinct characteristics for the NPs with FV-ZnO-CaO showing spherical morphology. FV-ZnO-CaO and FV-ZnO NPs exhibited low turbidity and high zeta potentials, indicating better dispersion and more stable suspensions. FV-ZnO-CaO exhibited better antibacterial activity against Methicillin-resistant Staphylococcus aureus than their monometallic oxide forms. Mild to moderate scavenging activities were observed for the NPs. FV-ZnO-CaO showed a 91% ability to mitigate against albumin protein denaturation. The antibacterial, free radical scavenging and anti-albumin denaturation potentials of the FV-mediated NPs can be prospectively explored for more effective treatment options. Graphical Abstract