Synthesis, experimental and theoretical studies of sesquiterpenic thiosemicarbazone and semicarbazone as organic corrosion inhibitors for stainless steel 321 in H2SO4 1M

In this work, the compounds thiosemicarbazone and semicarbazone sesquiterpene (TSC and SMC, respectively) were synthesized from sesquiterpene cz,fi-unsaturated ketone and investigated for their anti-corrosion behavior and electrochemical activity. Various spectroscopic analyses were performed (FT-IR, H-1 NMR,C- 13 NMR and HRMS) to characterize these molecules. The inhibitory performance of these inhibitors on corrosion of stainless steel 321 in 1 M H2SO4 medium was studied using the potentiodynamic polarization (PDP) method that indicated that these compounds acted as mixed-type inhibitors with dominant cathodic inhibition. Cyclic voltammetry (CV) was performed to assess the electrochemical activity and calculate the experimental band of the tested molecules. The values of the band gap of SMC and TSC were comparable (similar to 0.52 eV). The electrochemical findings agree quite well with the functional density theory (DFT) and Monte Carlo (MC) theoretical studies. The strong adsorption of the tested molecules and stainless steel surface, through nitrogen groups, is demonstrated. No significant difference resulting from (C=S) and (C=O) groups on the electrochemical and theoretical behaviors is noted. The nitrogen sites present an important reactivity for the metal/inhibitor interaction as evidenced by Mullikan negative charges and HOMO/LUMO spacial distributions. (C) 2021 Elsevier B.V. All rights reserved.