A hybrid thiophene-oxadiazole compound as a potent copper corrosion inhibitor: An integrated SEM, RSM, and DFT investigation

Abstract

Corrosion of copper in sulfuric acid environments poses persistent challenges across numerous industrial applications, necessitating the development of effective and mechanistically well-understood inhibitors. This work presents a comprehensive evaluation of 5-(5-(4-nitrophenyl) thiophen-2-yl)-1,3,4-oxadiazole-2(3H)-thione (NPT-OxT) as a corrosion inhibitor for copper immersed in 0.5 M H₂SO₄, employing an integrated experimental-computational methodology. Gravimetric measurements, optimized through Response Surface Methodology, yielded exceptional model reliability (R² = 0.999) and revealed a maximum protection efficiency of 97% under optimized conditions. Thermodynamic analysis of the adsorption process disclosed a dual physisorption-chemisorption character, with Gibbs free energy values between −39.64 and −40.48 kJ · mol⁻¹ , indicative of thermodynamically favorable and robust interfacial binding. Activation energy data further substantiated inhibitor efficacy, rising from 7.36 kJ · mol⁻¹ in uninhibited solution to 40.38 kJ · mol⁻¹ upon NPT-OxT addition, reflecting the formation of a stable protective barrier. Surface morphological examination via SEM confirmed a marked transition from extensive corrosion damage to a uniform, compact film in inhibitor-containing media, while EDX profiling evidenced suppressed oxidation and sulfur incorporation alongside a dominant copper signal. Quantum chemical calculations using DFT revealed a HOMO-LUMO energy gap of 3.084 eV, a negative electron-transfer parameter (∆N = −0.139), and an electrophilicity index of 7.659 eV, collectively affirming strong electron-donation capacity and favorable adsorption onto copper. These findings establish NPT-OxT as a highly efficient corrosion inhibitor with clear industrial applicability in aggressive acidic conditions.