Electrochemical and Quantum Chemical Studies of Phytochemical Isolated from the Seeds of Cola nitida as a Green Corrosion Inhibitor of Mild Steel in Acidic Medium
摘要
Mature seeds of Cola nitida were subjected to comparative extractions using methanol, ethyl acetate, ethanol, hexane and dichloromethane (DCM) solvents. DCM fraction was found to be the most active in retarding corrosion and was put through isolation and characterization processes from which 1, 3, 7-trimethylpurine-2, 6-dione (TMPD) was elucidated. Corrosion inhibition of mild steel in 1.0 M HCl by TMPD was studied using weight loss and electrochemical methods. The inhibition efficiencies obtained from weight loss, potentiodynamic polarization and impedance spectroscopic methods converged at 77% with 0.0005 g/L and at 303 K. Results obtained from temperature variation studies revealed a marked increase in activation energy and Arrhenius constant at the introduction of TMPD confirming physical adsorption. Formation of a dense organic film on the metal was observed using scanning electron microscopy. ∆Ecorr 25.2 mV/SCE with a shift of icorr to lower values, Rct increased from76.550 Ω cm− 2 to 332.83 Ω cm− 2, n increased from 0.753 to 0.860, and phase angle maximum ranges from − 54o to -67o at the introduction of TMPD. With ∆Ecorr ˂ 85 mV, the inhibitor is a mixed-type. TMPD was protonated and optimized using the Gaussian 09 program package. The interaction energy of TMPD on Fe(110) surface is 100.433 kcal mol− 1. Mulliken atomic charges reveal the primary atoms in TMPD responsible for adsorption to include: N7, O11 and O13. C8 serve as an electrophilic site. Other atoms that facilitate adsorption are N1, N5 and N9. TMPD has better adsorption capacity than its protonated form. Therefore, TMPD is an effective green corrosion inhibitor of mild steel in an acidic medium.