Lippia javanica leaf extract as an effective anti-corrosion agent against mild steel corrosion in 1 M HCl and its characterization by UHPLC/Q-TOF-MS spectroscopy and quantum chemical evaluation of its adsorption process on Fe(110)

A study was conducted to assess the anticorrosive potential of Lippia javanica leaf extract as a mild steel corrosion inhibitor in 1 M HCl acidic media. The chemical compositions of the acetone extract and its fractions were investigated by ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC/Q-TOF-MS) with C29H36O15 (verbascoside) identified as the major constituent of L. javanica. The anticorrosive assessment included weight loss measurements as well as an examination of thermodynamic parameters. According to weight loss data, 800 ppm of L. javanica at 303 K achieved a maximum inhibition efficiency of 98.01%. Temperature studies revealed that, in the presence of the extract, inhibition efficiency decreased, and activation energies increased as inhibitor concentration increased. The ability of L. javanica to maintain an inhibition efficiency of around 90% even at elevated temperatures, as supported by immersion time studies, indicates its effectiveness against mild steel corrosion. Electrochemical studies, open circuit potential (OCP), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) were conducted to study the inhibition mechanism of the extract. PDP results indicated that the cathodic polarization slope values were higher than anodic ones, indicating that the extract components act principally on the cathodic branch of the metal, suppressing the reduction of hydrogen ions. Impedance diagrams showed that increasing L. javanica concentration increased charge transfer resistance (Rct) and decreased double layer capacitance (Cdl). The morphology and the surface composition of the mild steel were examined by scanning electron microscopy with energy dispersive x-ray analysis (SEM/EDX) to verify the presence of inhibitor components. Water contact angle (WCA), UV–visible, and Fourier-transform infrared spectroscopy (FTIR) were carried out to establish the corrosion-inhibitive properties responsible for the inhibition capabilities of the plant extract. Adsorption of L. javanica components onto mild steel surfaces was modelled to acceptable parameters using the Langmuir adsorption isotherm for PDP, EIS, and weight loss data. In this work, quantum calculations were performed to study the adsorption of the main component on a clean Fe(110) surface using density functional theory (DFT) with the PBE exchange-correlation functional in the DMol3 program.