Synthesized novel carbon dots as green corrosion inhibitor for mild steel in hydrochloric acid: Gravimetric, electrochemical and morphological studies

Carbon dots (CDs), mainly heteroatom-doped CDs, have been recognized as efficient eco-friendly corrosion inhibitors due to their low cost, excellent chemical stability, good water solubility, and nontoxic properties. Inspired by this, in present investigation a pair of nitrogen-doped eco-friendly CDs (CD1 and CD2) have been synthesized using a one-step hydrothermal technique, and their anticorrosion performance for the mild steel (MS) in 15 % HCl solution has been studied. The synthesized CD1 and CD2 have been characterized by Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible spectroscopy, photoluminescence (PL), and high-resolution transmission electron microscopy (HRTEM). The anticorrosion proficiency of the CD1 and CD2 have been studied using weight-loss, electrochemical impedance spectroscopy (EIS) and potentiodynamic studies and it was found that obtained results are in agreement with each other at all concentrations. Corrosion inhibition efficiency of both inhibitors increases with increasing concentration and reaching 96.8 % (CD1) and 94.7 % (CD2) after 6 h immersion at 150 ppm concentration. The adsorption of inhibitors CD1 and CD2 on MS obeyed Langmuir adsorption isotherm and physical adsorption process. Potentiodynamic polarization study suggested that CD1 and CD2 act as mixed type inhibitor and alter the rates of anodic dissolution of MS and cathodic hydrogen evaluation reaction simultaneously. The field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) and XPS studies confirmed the formation of protective film of inhibitor molecules at the MS surface.