Eco-friendly Click-Synthesized Phthalazinone-Triazole Inhibitors for Mild Steel Protection in Acidic Media: Experimental and Multiscale Theoretical Insights

In this study, a new class of phthalazinone-triazole derivatives was rationally designed and synthesized using an eco-friendly click-chemistry approach to develop efficient and sustainable corrosion inhibitors for mild steel in acidic media. The chemical structures of the synthesized compounds were unambiguously confirmed by 1 H/ 13 C NMR spectroscopy and high-resolution mass spectrometry. Their corrosion inhibition performance was systematically investigated in 1 M HCl using electrochemical techniques, including open-circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy. Electrochemical results revealed that all compounds act as highly effective mixed-type inhibitors, significantly reducing both anodic metal dissolution and cathodic hydrogen evolution reactions. At an optimal concentration of 10 -4 M, inhibition efficiencies exceeding 97% were achieved, accompanied by a pronounced increase in charge-transfer resistance and the formation of a compact, protective adsorbed film on the steel surface. To gain molecular-level insight into the inhibition mechanism, comprehensive multiscale theoretical investigations were performed using DFT, conceptual DFT, Monte Carlo, and molecular dynamics simulations. Theoretical results demonstrated strong and stable adsorption of the inhibitors on the Fe(110) surface through multiple Fe - N, Fe - O, and Fe - C interactions, in excellent agreement with experimental observations. Adsorption thermodynamics followed the Langmuir isotherm model, confirming spontaneous chemical adsorption.