Surface-driven interactions for enhanced corrosion resistance and chemical durability of metal alloys using triazole-based inhibitors: Synthesis, characterization, and computational perspectives

This study investigates the potential of environmentally friendly corrosion inhibitors by focusing on two newly synthesized heterocyclic compounds, namely 5-pentylsulfanyl-3-phenyl-1,2,4-triazole (PTri-C₅H₁₁) and 5-pentylsulfanyl-3-undecyl-1,2,4-triazole (UTri-C₅H₁₁). These novel 1,2,4-triazole-5-thione derivatives were synthesized via solid-liquid phase transfer catalysis at ambient temperature conditions. The synthesis involved the alkylation of precursor triazole-thione compounds using iodopentane as the alkylating agent. The structural features of the synthesized compounds were confirmed by spectroscopic techniques, while their corrosion inhibition performance was evaluated through a combination of experimental and theoretical approaches. Results indicated that the inhibition efficiency followed the order: PTri-C₅H₁₁ > UTri-C₅H₁₁, attributed to the donor-acceptor capability of the benzene ring and conjugated π-electrons forming coordination complexes with the carbon steel (CS) surface. At a concentration of 10⁻³ M, the tested compounds significantly enhanced corrosion resistance, achieving inhibition efficiencies of 92.98 % and 91.96 % for PTri-C₅H₁₁ and UTri-C₅H₁₁, respectively. To gain molecular-level insights, density functional theory (DFT) and density functional tight binding (DFTB) calculations were employed to explore the quantum chemical properties, adsorption characteristics, and interfacial interactions of the studied inhibitors Surface adsorption studies further revealed the formation of strong covalent bonds between the inhibitors and the CS surface, confirmed by the electron density analysis. Theoretical modeling showed that both inhibitors could adsorb in a parallel orientation via C, S, and N atoms, which maximizes the surface coverage. In this orientation, C–Fe, S–Fe, and N–Fe bond distances ranged, for both inhibitors, from 1.98 Å to 2.40 Å. Thus, experimental and theoretical findings are consistent, confirming that heteroatoms (1,2,4-triazole-5-thione group) and benzene ring (for PTri-C₅H₁₁) serve as primary adsorption sites on the CS surface. Overall, these findings demonstrate the promising potential of these 1,2,4-triazole derivatives as effective corrosion inhibitors for CS in acidic environments.