Exploring olive leaf-derived carbon-quantum-dots as an innovative anti-corrosion sustainable agent for carbon-steel in 1.0 M HCl

Olive leaf-derived carbon quantum dots (OCQDs) were prepared via thermal pyrolysis decomposition reaction and characterised using Fourier transform infrared spectroscopy, energy dispersive X-ray spectrometry, transmission electron microscopy, UV-Vis, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction techniques to verify different functional groups, chemical composition, morphology/particle size, transition type, bonds and chemical structure and amorphous nature, respectively. Steel corrosion inhibition effect by OCQDs in HCl 1.0 M was assessed at 30 °C through mass loss, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarisation techniques. Mass loss indicates that after adding OCQDs, the corrosion rates significantly decreased compared to the blank solution to demonstrate that OCQDs potent protective activity. The EIS results indicate R _p increase and C _dl decrease as OCQDs concentration increases, revealing 90.9% optimal inhibition effectiveness at 500 mg L ⁻¹ OCQDs. The potentiodynamic outcomes declared that OCQDs is a mixed-type inhibitor. Effectiveness and mechanism of steel corrosion inhibition by OCQDs in HCl 1.0 M solution were examined using SEM, EDX, contact angle, XPS and XRD techniques. Furthermore, adsorption mechanism of OCQDs on the steel surface was explored. Assessment of isotherms of adsorption indicated that Flory–Huggins, Langmuir as well Kinetic thermodynamic model offer the most appropriate interpretations of the adsorption mechanism. A calculated Δ G ^o _ads −25.86 kJ mol ⁻¹ suggests a physical/chemical adsorption mechanism.