Surface and Electrochemical Investigation of a Novel Isoxazolone Inhibitor for Carbon Steel Corrosion: Adsorption and Inhibition Mechanism

A novel isoxazolone derivative, (E)-4-(4-(diethylamino)benzylidene)-3-methylisoxazol-5(4H)-one (DEAI), was synthesized via a one-pot, environmentally friendly protocol and characterized by spectroscopic techniques. Its corrosion inhibition performance toward carbon steel in 1 M HCl was investigated using electrochemical methods, including potentiodynamic polarization and electrochemical impedance spectroscopy, combined with surface analyses (AFM, XPS, UPS) and theoretical calculations. Electrochemical results indicate that DEAI acts as a mixed-type inhibitor with predominant cathodic behavior, achieving maximum inhibition efficiencies of 87.5% (303 K), 88.1% (308 K), 92.7% (313 K), 90.2% (318 K), and 86.7% (323 K) at 7.5 × 10–5 M. Impedance measurements reveal that the corrosion process is governed by charge transfer and that inhibition efficiency increases with inhibitor adsorption. UV–vis analysis suggested that the functional groups of DEAI form a complex with iron cations on the carbon steel surface. Surface characterization confirms the formation of a protective interfacial film. Atomic force microscopy (AFM) shows a significant reduction in surface roughness, while X-ray photoelectron spectroscopy (XPS) provides evidence of strong interactions between inhibitor molecules and the steel surface through Fe–O and Fe–N bonds. Ultraviolet photoelectron spectroscopy (UPS) reveals modifications in the electronic structure at the metal–inhibitor interface, indicating enhanced surface passivation and strong electronic coupling. Adsorption follows a modified Langmuir isotherm and involves both physical and chemical interactions. Density functional theory and molecular dynamics simulations further support strong adsorption of DEAI on the Fe(110) surface. These findings provide comprehensive insight into the mechanism of inhibition and highlight the key role of interfacial interactions in corrosion protection.