High-performance copper corrosion protection by novel pyrazole derivatives: a combined electrochemical,...

The development of efficient and mechanistically well-understood organic inhibitors for copper protection in strongly acidic environments remains a critical challenge for industrial corrosion control. In this work, three structurally related pyrano[2,3-c]pyrazole derivatives bearing electron-donating (-OCH₃), neutral (-H), and electron-withdrawing (-Cl) substituents, namely 6-amino-4-(4-methoxyphenyl)-3-methyl-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (AMMC), 6-amino-3-methyl-4-phenyl-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (AMPC), and 6-amino-4-(4-chlorophenyl)-3-methyl-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile (AMCC) were systematically investigated as corrosion inhibitors for copper in 0.5 M H₂SO₄. Electrochemical impedance spectroscopy and potentiodynamic polarization measurements revealed outstanding inhibition efficiencies exceeding 95% at 1.0 mM, with AMMC exhibiting the highest performance. Adsorption followed the Langmuir isotherm, and negative Gibbs free energies confirmed a spontaneous mixed adsorption mechanism with a dominant chemisorption contribution. SEM and AFM analyses showed the formation of compact and homogeneous protective films, leading to a pronounced reduction in surface roughness compared with uninhibited copper. Density functional theory calculations clarified substituent-induced electronic effects, showing that AMMC has the smallest energy gap, the highest softness, and the most favorable donor-acceptor balance. Molecular dynamics simulations, explicitly accounting for water and sulfate species, confirmed stable quasi-planar adsorption geometries and strong interaction energies on the Cu(111) surface. Overall, the combined electrochemical, surface-analytical, and atomistic results establish clear structure-property-performance relationships and provide mechanistic guidance for the rational design of high-efficiency, environmentally compatible copper corrosion inhibitors for acidic industrial applications.