In recent years, the anti-corrosive properties of natural extracts as environmentally friendly inhibitors have gained considerable interest. This study evaluates the potential of Marjoram (Origanum majorana L.) essential oil (OML), collected from Salé, Morocco, as a corrosion inhibitor for mild steel in 1 M HCl medium. The protection performance of OML was assessed using various electrochemical techniques, including potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS), as well as the weight loss method. The influence of OML concentration and temperature on the inhibition performance were investigated. OML demonstrated pronounced inhibitory benefits via increasing the corrosion resistance of mild steel in the corrosive HCl solution, thus reducing the corrosion rate to 0.11 mg cm⁻² h⁻¹ and increasing the inhibition efficiency to 87.1% at an inhibitor concentration of 500 ppm. PDP confirmed that the inhibitor works as a mixed-type inhibitor with cathodic supremacy. EIS revealed that the charge transfer mechanism is the main controlling factor for the corrosion process. The thermodynamic parameters suggested a key role of OML physisorption in inhibition, following the Langmuir isotherm. Importantly, SEM and EDX analyses suggested the formation of a protective layer of the extract onto the steel surface, which shields the surface from corrosive species. This is owed to the functional group-rich phytochemicals of OML. Therefore, the development of bio-based corrosion inhibitors is not only a step towards more eco-friendly industrial practices, but also meets the growing demand for sustainable materials in a world with constrained resources.

Phytochemical-rich natural extracts have recently attracted intense attention as green corrosion inhibitors and costly benign coating components for the protection of metallic structures of immense commercial importance. Herein, various methods were applied to assess the corrosion protection efficiency of a methanolic extract of parsley (Petroselinum crispum) (PCE) on carbon steel C37 in 1 M HCl. Initially, the chemical profile of PCE was analyzed using gas chromatography/mass spectrometry (GC/MS), and myristicin and apiol were identified as the main components. The results from the weight loss, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) techniques revealed a substantial reduction in the corrosion rate upon the use of PCE, with a maximum inhibition efficiency of 92% at 1 g L⁻¹ PCE. To optimize the performance, the corrosion behavior was investigated over a temperature range of 303–333 K and for concentrations of 0.1–1 g L⁻¹. The inhibition effectiveness increased at higher concentrations of PCE, whilst it decreased when the temperature was elevated. The query suggests that the adsorption process involves both physical and chemical mechanisms. The adsorption of PCE onto C37 was well described by the Langmuir adsorption isotherm. The data were used to determine the activation energy and thermodynamic parameters. The PCE coating acted as a mixed-type inhibitor, hampering both cathodic and anodic corrosion reactions. SEM further confirmed the formation of a protective coating film on the steel surface when exposed to PCE. UV-Vis and XRD were implemented to understand the inhibition mechanism and formed products at the microscopic and spectroscopic levels. Hence, the green PCE inhibitor may potentially be applied in corrosion mitigation due to its high corrosion protection efficacy and its environmentally benign nature.

In this study, 1,5-diallyl-1H-pyrazolo [3,4-d] pyrimidin-4 (5H)-one (PPD) was evaluated as an anticorrosion agent for mild steel (MS) in 1 M HCl. The analysis was performed by weight loss (WL), potentiodynamic polarization measurement, and electrochemical impedance spectroscopy (EIS). The Tafel polarization showed that PPD is a mixed-type inhibitor and reaches 94% of the protective efficiency at 10⁻³ M. EIS results indicated that the resistance to charge transfer increases with increasing inhibitor concentration and the corrosion of MS is controlled by a charge transfer process. The inhibitor adsorption on the MS surface obeyed the Langmuir’s adsorption isotherm. Thermodynamic parameters were calculated to elaborate the corrosion inhibition mechanism. The micrographic analysis revealed the existence of a barrier layer on the electrode surface with the presence of PPD. Theoretical examinations performed by electronic/atomic computer simulations confirmed that the obtained results were found to be consistent with experimental findings.