Experimental and theoretical investigation on the effect of N-substituent position on the inhibition performance of l-lysine derivatives for carbon steel in H2SO4 solution

The inhibitive effect and inhibition mechanism of l -lysine derivatives, namely α- N -benzyloxycarbonyl- l -lysine (α-NL) and ε- N -benzyloxycarbonyl- l -lysine (ε-NL), on the corrosion of carbon steel in 0.5 M H 2 SO 4 solution were investigated by electrochemical technique, weightlessness test, scanning electron microscope, atomic force microscope, infrared attenuated reflectance spectroscopy and quantum chemical calculation. The results showed that α-NL and ε-NL as moderate cathodic inhibitors mainly inhibited the cathodic reaction of carbon steel in 0.5 M H 2 SO 4 solution, and the terminal substituted ε-NL showed better corrosion inhibition than the α- N -benzyloxycarbonyl protected α-NL. Their inhibition efficiencies increased with the increase in inhibitor concentration, and the inhibition efficiency of α-NL and ε-NL with concentration of 10 mmol can reach 53.4% and 61.5%, respectively, but decreased with rising temperature. The adsorption of investigated inhibitors on the surface of carbon steel obeyed the modified Langmuir isotherm and El-Awady thermodynamic-kinetic model, and the thermodynamic and kinetic parameters were determined to discuss the mechanism of inhibition of α-NL and ε-NL. Moreover, Quantum chemical calculation gave further insight into the inhibition mechanism of α-NL and ε-NL and was employed to reveal the reasons for their differences in inhibition performance.