Bifunctional N,O,S-Codoped Carbon Dots for High-Efficiency Corrosion Inhibition and In Situ Fluorescence Monitoring of N80 Steel in HCl.

Designing intelligent anticorrosion systems that couple robust protection with real-time corrosion visualization remains a formidable challenge in industrial safety and infrastructure longevity. Here, a one-step hydrothermal condensation of 2-aminothiazole and citric acid yields a multifunctional carbon dot (CD) whose surface is densely terminated with N-, O-, and S-bearing functionalities. These heteroatom-rich groups furnish abundant coordination anchors for metal substrates. Electrochemical assays and gravimetric measurements reveal that the CD delivers a corrosion inhibition efficiency of 95.18% for N80 steel in 1 M HCl at a dosage of 200 mg/L. Adsorption conforms to the Langmuir isotherm with a Gibbs free energy of -31.66 kJ/mol, indicating a spontaneous mixed physical-chemical adsorption mechanism dominated by chemisorptive interactions from Fe-N, C-S, and S═O linkages. Surface analyses confirm a compact, adherent protective film that strongly retards both anodic dissolution and cathodic hydrogen evolution. Capitalizing on the intrinsic blue fluorescence of the CD, the system additionally accomplishes in situ reporting of corrosion progression: fluorescence quenching occurs synchronously with Fe3+/Fe2+ release as the film degrades. This work establishes a single-component "protect-and-report" platform, offering an effective and conceptually innovative strategy for next-generation corrosion management.