Experimental and computational studies of the corrosion inhibitive effects of Zingiber officinale rhizomes on mild steel corrosion in acidic solutions

The study investigates the anticorrosion potentials of Zingiber officinale (ZO) on mild steel induced in 1.0 M HCl and 0.5 M H2SO4 acid solution respectively using structural characterization (gas chromatography-mass spectroscopy, GC-MS and Fourier transform infrared spectroscopy, FTIR) and electrochemical (electrochemical impedance spectroscopy, EIS and potentiodynamic polarization, PDP) techniques respectively and theoretical simulations. The structural characterization was performed to identify chemical constituents and functional groups present in the plant extract whereas electrochemical techniques and theoretical computations were used to examine the anticorrosion potentials of the extract and validate the experimental results. The GC-MS result revealed the presence of twenty-three (23) compounds within the extract and out of which three (1-(1,5-dimethyl-4-hexenyl)-4-methyl-, dodecanoic acid and 9-Octadecenoic acid (Z)-2-hydroxy-1-(hydroxymethyl)ethyl ester) were selected for computational simulation and the results of FTIR revealed the presence of the following functional groups (O-H, C=C, C=O, C-C and C-H) in the ZO extract. The results of EIS revealed that extract of ZO exhibited corrosion inhibition efficieny of 82.7% and 93.6 % for mild steel in 1 M HCl and 0.5 M H2SO4 solution respectively at maximum inhibitor concentration of 1000 mg/L for mild steel. Also, PDP results revealed that ZO extract functioned as mixed inhibitor because both the anodic and cathodic reaction process was altered. The quantum chemical calculation results revealed that 9- Octadecenoic acid (Z)-2-hydroxy-1-(hydroxymethyl) ethyl ester had a good energy gap (\Delta E) compared to other two compounds, indicating its better adsorption interaction with the metal surface in sulfuric acid environment. This was further confirmed by its good adsorption energy of -355.55 Kcal/mol with mild steel surface in H2SO4 environment compared with -167.81Kcal/mol in HCl environment from the molecular dynamic simulation.