Nitrogen-doped carbon quantum dots for effective corrosion inhibition of Q235 steel in concentrated sulphuric acid solution

In recent years, steel corrosion, an issue affecting a trillion-dollar industry, is being addressed with nanotechnology technologies. Small clusters and nanoparticles, as well as numerous molecules, are viable solutions, with carbon quantum dots (CQDs) being among the best and most promising. However, the complexity and duration of the CQDs purification process, as well as a few other issues, limit their practical applications as corrosion inhibitors. Therefore, in this study, a new type of nitrogen-doped CQDs (N-CQDs) with an average size of 2.5 ± 0.8 nm were synthesized via hydrothermal reaction of amino-guanidine and citric acid using a robust purification process. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) techniques were used to evaluate the new inhibitor's corrosion mitigation effect on Q235 steel in 0.5 M H2SO4 solution. X-ray photoelectronic spectroscopy (XPS) and FTIR analyses were employed for the chemical composition investigation of as-prepared N-CQDs and surface characterization of Q235 steel samples. The analysis of the impedance module and the current density of Q235 steel in the corrosive solution validates the effective protective performance of the inhibitor. The results showed that the maximum inhibition efficiency of 95.3% was achieved at the concentration of 200 mg/L. Moreover, it was found that the formation of the protective layer on the steel samples results from the Physico-chemical adsorption of the inhibitor on the steel surface and follows the Langmuir adsorption isotherm that was also confirmed via XPS. The quantum chemical calculations show that CQD nitrogen doping has an effect on corrosion inhibition performance. Overall, the corrosion inhibition efficiency of the carbon dots inhibitor is higher at the same concentration than that of most other similar inhibitor types.