Unveiling the adsorption and inhibition mechanism of thiadiazole derivatives for mild steel corrosion in hydrochloric acid based on experimental approaches and first-principles calculations

In this work, two eco-friendly thiadiazole derivatives, 5-amino-1,2,3-thiadiazole (AT) and N-phenyl-N-1,2,3-thiadiazol-5-yluree (thidiazuron, TDZ), were employed to alleviate the corrosion of mild steel in hydrochloric acid medium. Electrochemical tests show that compared to AT, TDZ exhibits a much better inhibitive effect with an inhibition efficiency of 98.95% at 0.6 mM. The introduced side chain with phenyl ring in TDZ molecule endues it with more adsorption sites, which facilitates the strong absorption of TDZ by the extra bonding of O atom and phenyl ring with steel surface. The DFT-based first-principles calculations indicate that AT and TDZ could adsorb on the steel surface through the thiadiazole ring, O atom and phenyl ring by forming Fe–S, Fe–N, Fe–O, and Fe–C bonds. The parallel adsorptions of AT and TDZ are more stable with more negative adsorption energy than their perpendicular adsorptions. Furthermore, the non-covalent interaction between AT/TDZ and H2O solvent molecules deteriorates their adsorptions on steel surface.