The influence of aqueous and alcoholic extracts of Garcinia cambogia fruit rind in the management of mild steel corrosion in hydrochloric acid: Theoretical and electroanalytical studies

Abstract

The work focuses on the corrosion inhibition behavior of the aqueous and alcoholic extracts of Garcinia Cambogia fruit rind (GCW and GCA) for the mild steel in an acid environment. Garcinia cambogia is a medicinal plant, whose corrosion inhibition property is evaluating for the first time in this study. Since the plant is readily available, eco-friendly, and cost-effective is considered as a good candidate for corrosion inhibition. The fruit rind of Garcinia Cambogia is rich in cyanidin, garcinol, and many organic acids including hydroxy citric acid, malic acid, ascorbic acid and tartaric acid and hence the extracts are slightly acidic with a pH of around 5. Under this pH condition cyanidin shows a single peak at 287 nm. Cyanidins like other anthocyanins exists in various structural forms in aqueous solution depending on the pH of the solution and at a pH, about 5.5 it changes to the colorless hemiacetal form from flavylium cationic form, with a band around 280–290 nm. But the alcoholic extract shows an absorption maximum at 208 nm representing the presence of hydroxy citric acid in the extract. It also exhibits a shoulder peak at 284.49 nm confirming the presence of cyanidin in the alcoholic extract too. Hence the presence of these compounds was confirmed through the IR and UV spectral studies. The electronic spectra confirm the literature saying that the GCW is enriched with cyanidin while GCA contains mainly hydroxy citric acid as the major active constituent along with a smaller fraction of cyanidin, which make them efficient inhibitor systems. The inhibition efficiency of both GCW and GCA for mild steel in HCl was initially evaluated through theoretical calculations and then experimentally using impedance spectroscopy and polarization analysis. It is found that 4(V/V %) GCW has an efficiency of 91.50% at room temperature and the same concentration of GCA has 92.85% efficiency, validating the better inhibition ability of GCA than GCW in acidic medium. Tafel polarization studies recommend that the inhibition ability of GCW on mild steel corrosion is by retarding the cathodic evolution process of hydrogen while for GCA, the inhibition is through resisting the anodic dissolution process of the metal. Hence Tafel studies suggest mixed-type inhibition nature for the extracts towards mild steel corrosion. The adsorption active components of the extracts follow Langmuir monolayer adsorption. Theoretical studies support the effective role of the active constituents of the extract and their adsorption on the metal surface through co-ordinate type interaction and back donation of electrons from the metal to the inhibitor molecules. Surface studies support the inference that the adsorption of the active species of GCW and GCA on the metallic surface with greater tendency for GCA.