Experimental and theoretical studies on the inhibitory potential of Lippia javanica leaf extract for aluminium corrosion in 1M HCl medium

Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), and gravimetric analysis techniques were used to evaluate the ability of Lippia javanica leaf extract to inhibit aluminium (Al) corrosion in 1 M HCl solution. The formation of the protective film was confirmed using Ultraviolet-visible spectroscopy (UV–Vis), Fourier transform-infrared spectroscopy (FTIR) and contact angle studies. According to EIS, the presence of L. javanica extract in the acidic solution decreased the corrosion current density (icorr) and the double-layer capacitance (Cdl) due to the formation of a protective adsorption layer on the Al surface. PDP curves revealed anodic polarization passivation of the Al substrate, a well-known property of a highly entropic alloy like Al. Gravimetric results showed that the maximum protective efficacy of the L. javanica extract was 91.89% when the optimal concentration of the extract was 800 ppm. The contact angle increased to 123° in the presence of ALJPE, indicating the hydrophobic nature of the Al surface due to the formation of a protective film. The FTIR spectra revealed the involvement of C=O, C=C, O–H, =C–O–C, S=O, and C–H during the adsorption process, leading to the formation of ALJPE–Al3+ protective complexes. It was discovered that the adsorption mechanism of the extract on the Al surface follows the Langmuir adsorption isotherm description process. Using density functional theory (DFT), different dsorption positions were studied, finding that verbascoside preferentially binds to the Al(111) surface via the phenylethanoid group, with the oxygen atom close to the Al surface, leading to a binding energy of 114.620 kcal/mol.