Psidium guajava L. extract as corrosion inhibitor for mild steel in an acidic environment: Experimental and computational insights

The current research investigates the inhibitory effect of Psidium guajava leaf extract (PGLE) on mild steel (MS) in acidic solution, thus ameliorating the high demand for development of sustainable corrosion inhibitors. Herein, Psidium guajava leaf extract was considered for this research owing to its inherent chemical compositions such as flavonoids, tannins and vitamins which are responsible for its antioxidants and antimicrobial activity. The methodologies used in this work integrates detailed experimental validation based on gravimetric, combined electrochemical approach alongside computational studies. The gravimetric result demonstrated that the inhibition efficiency of the extract increased with its concentration, reaching a value of 89.4 % at 0.9 g/L and 303 K which further corroborates with impedance data. However, the inhibition efficiency decreased with an increase in temperature, highlighting the thermal degradation of the extract's active constituents at elevated temperatures which led to poor surface coverage by the extract. The adsorption of Psidium guajava leaf extract on the mild steel surface was evaluated using three adsorption models. Evidently, the best adsorption model fit was obtained via the Langmuir isotherm model. This type of model entails the formation of a barrier film layer over the mild steel thereby impeding the permeation of corrosive moieties reaching the metal surface. The morphological analysis based on SEM confirmed the formation of a protective organic film on the mild steel surface. In addition, the computational studies based on Density Functional Theory (DFT) and molecular dynamics simulation (MD) unveil the active sites and adsorption orientation of the inhibitor. As evidenced from the MD studies, the Psidium guajava leaf extract exhibited a flat adsorption coordination over the mild steel surface, thus corroborating with the experimental findings. Thus, this study provides invaluable insights into the emergence of inhibitors derived from renewable sources and shed more light on the Psidium guajava leaf extract potentials, while helping to ameliorate agricultural derived waste management problems.