Experimental and Computational Study on Inhibitory Effect and Adsorption Properties of N-Acetylcysteine Amino Acid in Acid Environment

Abstract

Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) were applied to study the inhibitory effect of N-acetylcysteine (NAC) on corrosion inhibition of carbon steel in hydrochloric acid solution. N-acetylcysteine influenced the iron dissolution to a greater extent than the hydrogen evolution reaction acting as a mixed inhibitor, predominantly anodic. The charge transfer resistance (Rct) gradually increased with the inhibitor concentration. From both methods, the inhibition efficiency (IE) reached a value of 89 ± 1% and NAC adsorption followed the Temkin isotherm. The value of adsorption Gibbs energy (ΔGadso), around −35 kJ mol−1, indicated a spontaneous adsorption and mixed action mechanism, with NAC chemical adsorption prevailing over physical one. New data will be reported by the computational study, that was performed using the density functional theory (DFT) method in aqueous phase. Quantum chemical descriptors were determined by B3LYP theory level with 6–31G+(d) basis set. Metropolis Monte Carlo atomistic simulation was used to reveal the adsorption configuration and interactions between acetylcysteine molecules and the carbon steel surface. Theoretical results were consistent with the experimental data, showing that the inhibitor action mechanism consisted of mainly chemisorption of its molecules on the carbon steel surface accompanied by van der Waals forces and electrostatic interactions.

New Inhibitor Based on Hydrolyzed Keratin Peptides for Stainless Steel Corrosion in Physiological Serum: An Electrochemical and Thermodynamic Study

“…On the other hand, the R ct decreases with the increase in temperature caused by, generally, an increase in the number of active sites (unprotected sample) or the desorption of peptides, leading to the appearance of additional free places on which the corrosion processes can be intensified. Consequently, at the same inhibitor concentration, R ct reaches higher levels at a low temperature, and, at both 25 °C and 45 °C, R ct increases with an increase in the HKER concentration, in agreement with the literature data [ 32 , 35 ].…”

“…The environment temperature from the electrochemical cell was continuously controlled with a specific thermometer. The electrochemical assembly was also reported in our previous studies [ 5 , 6 , 7 , 8 , 32 ].…”

“…The Nyquist plots obtained for 304L stainless steel immersed in physiological serum with and without different concentrations of HKER at 25 °C and 45 °C, respectively, are shown in Figure 2 a,b. The capacitive loops are easily deviated from a semicircular shape due to surface defects and/or heterogeneities [ 20 , 32 , 33 , 34 ] caused by the randomly agglomeration of chemical species at the metal/electrolyte interface. Moreover, for the same studied system, more extensive capacitive loops were recorded at 25 °C ( Figure 2 a) compared to those at 45 °C ( Figure 2 b).…”

“…The charge transfer resistance ( R ct ) was used to calculate the HKER inhibition efficiency, (IE), according to Equation (1) [ 6 , 32 , 40 ]. where represents the charge-transfer resistance obtained after the corrosion of 304L stainless steel in a physiological serum blank solution; R ct is the charge-transfer resistance of 304L of stainless steel corroded in physiological serum containing various HKER concentrations.…”

“…The following conclusions can be deduced from Table 1 : (i) R ct increases considerably with the increase in the HKER concentration, both at 25 °C and at 45 °C; (ii) the inhibition efficiency (IE) at 25 °C is higher than that obtained at 45 °C, probably due to the occurence of a more even and coherently organized upper layer, ensuring an effective inactivation of the active surface sites at a lower temperature; (iii) the decrease in R s and C dl , can be attributed to the ability of HKER molecules to replace pre-adsorbed molecules of water and/or other ions [ 32 , 35 ], such as chloride anions.…”