Electrochemical and surface investigations of N, S codoped carbon dots as effective corrosion inhibitor for mild steel in acidic solution

Mild steel is a versatile, inexpensive, highly flexible, and easily weldable material widely used in construction, pipelines, transportation, shipping, and other industries. However, it is also extremely susceptible to corrosion processes under the influence of weather phenomena, posing a significant threat to society and human health. In this work, we investigated the corrosion inhibition capacity of a new type of N, S codoped carbon dots (N, S-CDs) on Q235 carbon steel in the acidic medium. The goal product was synthesized by hydrothermal method using ophenylenediamine and amidinothiourea as precursors. Combined with electrochemistry, Fourier transform infrared (FTIR) spectroscopy, scanning electrochemical microscopy (SECM), and theoretical calculations, the inhibition properties of N, S-CDs on Q235 carbon steel in HCl solution were evaluated. The potentiodynamic polarization (PDP) curves and electrochemical impedance spectroscopy (EIS) results indicated that the corrosion inhibition efficiency reached 90.3 % and 92.4% at 100 mg/L concentration, respectively. Indeed, the presence of N, S-CDs reduced the electric double-layer capacitance, increased the thickness of the adsorption film on the carbon steel surface, and reduced the corrosion current density, resulting in a delay of corrosion. X-ray photoelectron spectroscopy (XPS) analysis and surface characterization confirmed the successful doping of N, S and the formation of adsorption films, the Langmuir adsorption isotherm also confirmed the superior inhibition of N, S-CDs on the surface of Q235 carbon steel through physical and chemical adsorption mechanisms. At the same time, quantum chemical calculations and molecular dynamics (MD) simulations revealed its inhibition mechanism at the molecular/atomic level.