Green Synthesis of ZrO₂ Nanoparticles from Cynodon dactylon: Structural Characterization, Antioxidant Performance,...

Zirconia (ZrO₂) nanoparticles (NPs) were biosynthesized using Cynodon dactylon leaf extract via an environmentally benign route and evaluated for antioxidant activity and corrosion protection of mild steel in acidic media. X-ray diffraction confirmed nanocrystalline tetragonal ZrO₂, while Fourier transform infrared spectroscopy evidenced phytochemical functionalities that cap and stabilize the particle surface. Scanning electron microscope and transmission electron microscopy revealed agglomerated morphologies composed of nanoscale primary particles; consistent with this, dynamic light scattering showed micrometer-scale hydrodynamic diameters arising from aqueous aggregation. NP formation and aggregation were strongly governed by alkaline pH, reaction time, temperature, and extract concentration, which collectively modulate nucleation, growth, and surface stabilization. Electrochemical and gravimetric assessments (potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and weight loss) demonstrated dose-dependent inhibition, achieving a maximum protection efficiency of 82.5%. EIS responses showed enlarged Nyquist semicircles and increased charge transfer resistance, indicating development of a compact barrier layer on steel. Weight-loss measurements yielded inhibition efficiencies of ∼23.5% after 24 h and ∼64.7% after 48 h. Antioxidant performance of C. dactylon extracts was quantified using 2,2-diphenyl-1-picrylhydrazyl and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays, with methanolic extracts exhibiting the highest radical-scavenging activity. Collectively, these results establish C. dactylon-derived ZrO₂ as multifunctional nanoadditives with coupled antioxidant and mixed-type anticorrosive behavior supported by adsorption-based mechanistic interpretation. This integrated study connects synthesis optimization to corrosion and antioxidant performance.