Assessment of Caffeine Adsorption onto Mild Steel Surface as an Eco-Friendly Corrosion Inhibitor

The adsorption and corrosion-inhibition properties of caffeine as an eco-friendly corrosion inhibitor for mild steel in acid medium were investigated by electrochemical and spectroscopic techniques. Polarization experiments indicated that caffeine behaves as a cathodic-type inhibitor. Impedance data showed that surface coverage increased with caffeine concentration in the range of 1.0 to 10.0 mmol L-1. The maximum inhibition efficiency obtained was 92.4%. The adsorption of the corrosion inhibitor was consistent with the Frumkin adsorption isotherm with a free energy of adsorption of -66.1 kJ mol(-1). Contact angle measurements revealed the formation of a hydrophobic protective film, while scanning electron microscopy, energy dispersive spectroscopy and fluorescence experiments clearly verified the presence of caffeine on the surface.