Effect of OH position on adsorption behavior of Schiff-base derivatives in corrosion inhibition of carbon steel in 1 M HCl

In this work, we have synthesized two new Schiff-bases from 2,2-dimethylpropane-1,3-diamine and n-hydroxy-nmethoxybenzaldehyde. The synthesized Schiff-bases were characterized by 1H NMR, 13C NMR. The anticorrosive property of the compounds were investigated using weight loss, polarization and EIS techniques against 1 M HCl solution. For additional support for this work, DFT studies also carried out for Schiff-bases. The surface morphology was examined by AFM and SEM to determine this inhibition mechanism. Schiff-base derivatives were found to successfully suppress steel corrosion. EIS studies showed that charge transfer resistance occurs because of the presence of an inhibitor. Moreover, increasing Schiff-bases concentration decreased the double-layer capacitance (Cdl) value because less charged species were attracted to the metal surface. Polarization measurements clearly showed that the inhibitors suppressed both anodic and cathodic reactions. In conclusion, this study demonstrates that these compounds inhibit corrosion via chemisorption of organic compounds. By studying the effects of hydroxyl groups in ortho-, para- positions, the best one as inhibitor was found to be ortho position of OH in Schiff base (i.e., 6-SH).