Green synthesis, characterization, and thermal stability of Albizia adianthifolia leaf–mediated CaO nanoparticles for anticorrosion applications

This study presents the first report on the green synthesis of ultrasmall calcium oxide nanoparticles (AA–CaO NPs) using Albizia adianthifolia leaf extract and provides a systematic evaluation of their corrosion inhibition performance in 1 M HCl solution. Transmission electron microscopy revealed predominantly quasi-spherical nanoparticles with an exceptionally narrow size distribution of 1–3 nm (average diameter 2.45 ± 0.81 nm), which is significantly smaller than the particle sizes typically reported for plant-mediated oxide systems.UV–Vis spectroscopy showed an absorption edge at 309 nm (4.0 eV), indicative of wide band-gap behavior, while FTIR analysis confirmed phytochemical surface functionalization through the presence of hydroxyl and C–O/C–O–C functional groups. Thermogravimetric analysis demonstrated high thermal stability, with ≥ 99% mass retention up to 184 °C.Corrosion inhibition performance was evaluated using gravimetric, atomic absorption, and thermometric techniques. A maximum inhibition efficiency of 97.20% at 298 K (gravimetric) and 88.96% at 318 K (thermometric) was achieved at optimal concentrations of 1.0–1.5 g·L⁻¹ . The inhibition efficiency exhibited adsorption-controlled behavior, with a slight decline at higher concentrations due to surface-site saturation.Significant reductions in weight loss and Fe dissolution confirmed effective suppression of metal dissolution kinetics. The enhanced corrosion protection is attributed to a synergistic dual mechanism involving adsorption-mediated barrier formation by phytochemical capping ligands and localized acid neutralization through CaO hydration to Ca(OH)₂. Furthermore, the ultrasmall particle size enhances adsorption density and promotes the formation of a compact, low-permeability protective film, resulting in thermally stable and highly efficient corrosion inhibition.Overall, these findings establish AA–CaO nanoparticles as a viable, high-performance, and environmentally sustainable alternative to conventional synthetic inhibitors for use in aggressive chloride environments.