Computational modelling and theoretical calculations on hydroxy citric acid and mangostine and comparing the corrosion inhibition effect of aqueous and alcoholic extracts Garcinia cambogia leaves for mild steel in hydrochloric acid

Abstract

The utility of Garcinia cambogia leaves aqueous and alcoholic (GCLW and GCLA) extracts were used as a green candidate for mitigating the mild steel corrosion in 0.5N HCl solution. The protective efficiency was monitored electrochemically and theoretically using different soft wares including Gaussian09, Biovia material studio, and also with Fukui function analysis procedure from D Mol 3 calculations. The preliminary phytochemical screening of active components of the extracts were done using IR and UV-Visible spectral studies. Mangostine and hydroxy citric acid (HCA) were identified as the active constituents of the extracts and their presence on the metal surface after inhibition is confirmed using XPS elemental analysis. The increased activity of the aqueous extract may be due to the increased percentage of HCA in the water extract than the alcoholic counterpart. 4V/V% GCLW has 84 % efficiency at room temperature whereas the same volume percentage alcoholic extract has only 81% efficiency. The inhibition efficiency decreases with rise in temperature suggesting the physical mode of adsorption of the inhibitor system on the metal surface. But the results of computational modelling suggest chemisorption resulted from the donation of electron pairs from O22, H46, and H38 of mangostine and O12 of HCA. This bond is strengthened by the back acceptance of electron pairs from the filled metal orbital to C2 of mangostine and O3 of HCA. Tafel extrapolation studies suggest mixed type inhibition nature for both GCLW and GCLA with anodic prominence. Thermodynamic adsorption suggests the Langmuir monolayer model for GCLW and Temkin model for GCLA.