New green inhibitor of Olax subscorpioidea root for J55 carbon steel corrosion in 15% HCl: theoretical, electrochemical, and surface morphological investigation

Abstract

The corrosion inhibition performance of Olax subscorpioidea (OS) root extract on J55 carbon steel corrosion in acidizing solution stimulated with 15% HCl was studied using weight loss and electrochemical techniques as well as surface morphological study. The weight loss study showed a decrease in corrosion rate and an increase in inhibition efficiency by increasing the OS concentration. Potentiodynamic polarization measurements indicated that the OS extract is a mixed-type corrosion inhibitor but predominantly of anodic type. Electrochemical impedance spectroscopy (EIS) studies revealed that the introduction of OS in the 15% HCl solution increases the charge transfer resistance and simultaneously decreases the double-layer capacitance, enhancing an adsorbed film formation on the steel surface. Maximum inhibition efficiency of 89.7% was obtained with EIS study in the presence of 2.0 g/L of extract. The Fourier-transform infrared spectroscopy (FTIR) results indicated that the mechanism of inhibition is an absorption process through the functional groups present in OS molecules. The adsorption of OS onto the J55 steel surface followed the Langmuir adsorption model. Scanning electron microscopy (SEM), energy-dispersive X-ray spectra (EDS) analysis, and atomic force microscopy (AFM) confirm the formation of an adsorbed protective film of the OS molecules on the J55 steel surface. Quantum chemical calculations performed by density functional theory (DFT) on the major phytochemicals present in the OS root extract supported the experimental results and explained the adsorption behavior of the extracts.