Selenocyanates and selenotetrazoles derivatives: A detailed experimental and theoretical evaluation as corrosion inhibitors for mild steel in aggressive environment

This work presents the selenocyanates ESCA and ESCP and their derivatives selenotetrazoles ETSP and ETSA, which were synthesized with good to excellent yields. The compounds were designed and studied as corrosion inhibitors for mild steel in 1 mol L−1 HCl. Weight loss experiments showed that ESCP, ESCA, ETSP, and ETSA mitigate corrosion from 81.1 to 92.8 % at 2.00 mmol L−1 (298 K). At higher temperatures (338 K), those values go from 85 to 95 %. EIS shows that the mechanism of corrosion is by charge transfer and that the organic compounds act by adsorbing in the surface and blocking the active sites. Polarization curves and EFM prove that the corrosion density is significantly lower in the presence of the four molecules, and they all are mixed-type corrosion inhibitors. AFM depicted the topography of the metallic surface and point to the formation of an adsorbed protective film. Atomistic simulations using ab initio DFT were employed to investigate the interactions between selenocyanates and selenotetrazoles with an Fe(110) metal surface, elucidating the adsorption geometries and electronic properties. Our findings demonstrated that the adsorption geometries and resultant bonds, particularly those involving oxygen (O), selenium (Se), and nitrogen (N) atoms, critically influence the corrosion inhibition capabilities of these molecules. ESCA and ETSP showed bond rupture of C-Se while ESCP had no covalent bonding with iron atoms, which can explain their lower inhibitive performance compared to more energetically stable ETSA.