Green synthesis of Co/TiO ₂ nanoparticles using <i>Mentha spicata</i> extract for adhesion-driven corrosion protection of carbon steel in acidic media

This work presents the sustainable synthesis of cobalt-doped titanium dioxide nanoparticles (Co/TiO
2
NPs) using
Mentha spicata
extract and their application as an adhesion-enhancing protective layer against carbon steel corrosion in 0.5 M HCl. Structural characterizations UV-Vis spectroscopy (UV-Vis), fourier transform infrared spectroscopy (FTIR), High-resolution transmission electron microscopy (HRTEM), scanning electron microscope (SEM) confirmed the nanoscale morphology and successful Co incorporation. Electrochemical analyses, including potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS), revealed a substantial decrease in corrosion current density from 281 to 8.10 µA cm
-2
at a nanoparticle concentration of 400 ppm resulting in a maximum inhibition efficiency of 97.1%, indicating mixed-type inhibition behavior and enhanced charge-transfer resistance. The Langmuir adsorption isotherm indicated stable monolayer coverage of the Co/TiO
2
nanoparticles on the steel surface, while atomic force microscopy (AFM) and SEM analyses revealed the formation of a smooth, adherent nanoparticle film on the steel surface. Density functional theory calculations highlighted strong donor–acceptor interactions and a low energy gap, validating synergistic physisorption-chemisorption adhesion. Overall, these findings establish Co/TiO
2
NPs as a promising green nanomaterial for eco-friendly and durable surface protection in corrosive environments.