Novel green corrosion inhibitor for carbon steel: A comprehensive analysis of the effect of nitrogen content on corrosion inhibition performance

Nitrogen-doped carbon dots (NCDs) serve as promising green corrosion inhibitors for carbon steel in acidic environments. However, the influence of nitrogen doping levels on their inhibition performance remains unclear. This study synthesizes five NCDs with varying nitrogen contents (8.34 %, 10.98 %, 13.04 %, 18.52 %, and 19.64 %) through a controlled method and confirms their long-term colloidal stability. Corrosion inhibition efficiencies are evaluated in 1 mol/L HCl using electrochemical measurements. More importantly, the inhibition mechanism is elucidated from both molecular-level calculations and microscopic characterization. The results show a non-monotonic relationship between nitrogen content and inhibition efficiency, with NCDs-4 (18.52 % N) exhibiting the highest performance, reaching 95.27 % efficiency at 100 mg/L. Adsorption isotherm analysis, surface morphology characterization, and quantum chemical calculations reveal the inhibition mechanism. The superior performance of NCDs-4 is attributed to its balanced electron-donating ability and favorable molecular geometry, which promote strong parallel adsorption on the steel surface. This work clarifies the role of nitrogen content in modulating NCD performance and provides guidance for their rational design as corrosion inhibitors.