A high-efficiency corrosion inhibitor of N-doped citric acid-based carbon dots for mild steel in hydrochloric acid environment

Novel N-doped carbon dots (CDs) were obtained through pyrolysis of ammonium citrate at 180 °C for 1, 2 and 3 h, and their corrosion inhibition effect on Q235 steel in 1 M HCl solution were evaluated through electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (Tafel), scanning vibrating electrode technique (SVET) analysis. The changes of corrosion current density and impedance modulus of Q235 steel in inhibitor solutions showed that the as-prepared carbon dots presented a valid protective effect on steel in 1 M HCl solution. Meanwhile, the inhibition efficiency of three carbon dots exceeded 90% at 200 mg/L and the highest inhibitive efficiency was found for the carbon dots prepared at the reaction time of 2 h. The adsorption mechanism of all as-prepared carbon dots complied with the Langmuir adsorption model, containing chemical and physical adsorptions, which was also confirmed by X-ray photoelectronic spectroscopy (XPS) analysis.