Highly efficient and eco-friendly acid corrosion inhibitor for mild steel: Experimental and theoretical study

Murraya koenigii Linn (Curry leaves) was established as an eco-friendly acid corrosion inhibitor (ECI) for mild steel (MS) in 5 M HCl by experimental and theoretical techniques. The weight loss, polarization, and impedance spectroscopy techniques were used to find corrosion rate and inhibition efficiency. The theoretical study includes DFT and molecular dynamic simulation (MDS) investigation. The different theoretical parameters were investigated to find the nature of interaction and mechanism of inhibition provided by the ECI. Frequency calculation was performed to obtain theoretical IR spectra. SEM, metallurgical microscopy, DFT, Langmuir, and Frumkin adsorption isotherm studies confirm the physiochemisorption of ECI on MS. Increase in charge transfer resistance supports physio-chemisorption of ECI on MS. A very high negative value of interaction energy, i.e., -185.23 kcal/mol and significant adsorption energy (8.76 kJ/mol) further supports strong physio-chemisorption of ECI. No pits and cracks were observed in presence of ECI. A maximum of 98.13% inhibition efficiency was achieved in 5 M HCl at 4 g/L of ECI. The biochemical and chemical oxygen demand of wastewater were found within an acceptable limit. (C) 2021 Elsevier B.V. All rights reserved.