Experimental and theoretical study on amino acid derivatives as eco-friendly corrosion inhibitor on mild steel in hydrochloric acid solution

Amino acid derivatives, namely, 2-(2-oxo-2-phenothiazin-10-yl)ethylamino)-3-mercaptopropanoic acid (OPEM) and 2-(2-oxo-2-phenothiazin-10-yl)ethylamino)acetic acid (OPEA) were synthesized and investigated as inhibitors for mild steel corrosion in 15% HCl solution using the weight loss, polarization, and electrochemical impedance spectroscopy (EIS) techniques. The inhibition efficiency of both the inhibitors increased with increasing the temperature and concentration of inhibitor. The inhibitors OPEM and OPEA show corrosion inhibition efficiency of 97.5 and 95.8%, respectively, in 200 ppm concentration, at 333 K. Polarization studies showed that both studied inhibitors were of mixed type in nature. The adsorption of inhibitors on the mild steel surface obeys Langmuir adsorption isotherm and the surface of inhibited and uninhibited specimens were analyzed by scanning electron microscopy (SEM). The semiempirical AM1 method was employed for theoretical calculations and the obtained results were found to be consistent with the experimental findings.