Combined Gravimetric, Electrochemical, and Computational Research on Benzothiophene Derivatives as Effective Corrosion Inhibitors for Mild Steel

Four benzothiophenes, thianaphthene (BT‐1), 3‐bromothianaphthene (BT‐2), benzo[b]thiophene‐2‐carboxaldehyde (BT‐3), and benzo[b]thiophene‐2‐carbonitrile (BT‐4), were tested as mild steel corrosion inhibitors in 1‐M HCl. The compounds have the similar benzothiophene core but differ in the substituents bound to the ring. The effect of the ‐Br, ‐CN, and ‐HCO groups on the inhibition performance of thianaphthene was investigated. The PDP and EIS results showed that the derivatives all had significant inhibition strength in the following order: BT‐4 > BT‐2 > BT‐3 > BT‐1. PDP analysis results revealed that the inhibitors were primarily mixed‐type in nature, and EIS confirmed the formation of a protective adsorbed layer on the steel surface. The Langmuir isotherm was used to determine the adsorption of the BTs derivatives, and the results of calculating Gibbs free energy values revealed a mixed mechanism of physisorption and chemisorption. Spectroscopic studies revealed that aromatic rings and heteroatoms play an active role in the formation of the Fe‐inhibitor complex. The results of DFT calculations and molecular dynamics simulations were consistent with the experimental results.