Detailed experimental and quantum chemical investigation on polysaccharide derived from Gellan Gum as a potent and green corrosion inhibitor for mild steel in 15 % HCl.

The polysaccharide derived from Gellan Gum, coded as GGP, has been tested as an inexpensive, highly efficient and greener corrosion inhibitor for acidic corrosion (15 % HCl) of mild steel (MS). Characterization of GGP was done by FTIR, APC, and NMR studies. Gravimetric, EIS, and PDP studies were exploited to predict the corrosion inhibition efficacy of the inhibitor. The Gravimetric study conducted for GGP at the temperature points 303 K, 313 K, 323 K and 333 K marked maximum corrosion inhibition efficiency (%η) of 94.76 % at an elevated temperature of 333 K, signifying the chemisorption mechanism of adsorption of inhibitor GGP on MS surface. The immersion test signified the stability of the inhibitor. The %η calculated from the gravimetric, EIS, and PDP studies was found to be coherent. During the EIS study, Rct values obtained from the Nyquist plot increased from 5.49 Ω in the case of blank solution to 56.55 Ω in the presence of optimum concentration (400 ppm) of GGP in 15 % HCl due to the inhibition of the charge transfer process by the development of GGP protective layer on MS surface. The PDP results suggested that GGP is a mixed-type inhibitor. The simultaneous decrease in corrosion rate from 64.8mmy-1 in the blank to 6mmy-1 with 400 ppm GGP solution showed the effectiveness of the inhibitor. The FTIR, HRXRD, and XPS analysis of the inhibited sample confirmed the adsorption of GGP on the MS surface. Morphological studies, such as FESEM, Optical profilometry, and AFM, showed the smooth and protected surface of MS in the presence of the GGP inhibitor. The adsorption of GGP on the MS surface followed the Langmuir adsorption isotherm. The derived DFT parameters further substantiated the experimental findings whereas; Monte Carlo (MC) simulations further complemented the adsorption of inhibitor GGP on the MS surface.