Abstract

Abstract The inhibition of the corrosion of mild steel in 0.1 M H2SO4 by 3-nitrobenzoic acid was studied using weight loss, electrochemical impedance spectroscopy (EIS), linear polarization resistant, potentiodynamic polarization, scanning electron microscopy, Fourier transformed infra-red spectroscopy and quantum chemical techniques. The results obtained indicated that 3-nitrobenzoic acid inhibited the corrosion of mild steel in solution of H2SO4. Maximum inhibition efficiency obtained from weight loss, potentiodynamic, linear polarization and EIS methods were 87.15, 90.51, 95.42 and 99.40% at inhibitor’s concentration of 0.01 M respectfully. The activation energies (which ranged from 26.02 to 59.02 J/mol) supported the mechanism of charge transfer from charged inhibitor to charged metal surface, which favours the mechanism of physical adsorption. The adsorption of the inhibitor was found to be exothermic and spontaneous. Although the adsorption characteristics of the inhibitor fitted the Langmuir adsorption model, the deviation of slope values from unity was explained by the existent of positive interaction parameters (attractive behaviour of the inhibitor’s molecules) according to the Frumkin model. 3-nitrobenzoic acid is dominantly a cathodic-type inhibitor and prevented the corrosion of mild steel by blocking the metal’s surface. Calculated values of the frontier molecular orbital energies and other semi-empirical parameters were in good agreement with those obtained for known and efficient corrosion inhibitors while Fukui function analysis indicated that the inhibitor is adsorbed unto the metal surface through the delocalization of electrons in the nitro oxygen bond, i.e. O(11)-N(10)-O(12).