Abstract: To protect the cold-rolled steel (CRS) in aggressive sulfamic acid (H₂NSO₃H, SA) and sulfuric acid (H₂SO₄) environments, two highly effective biomass carbon dots (CDs)-derived corrosion inhibitors (JCDs and N, S-JCDs) were developed from Jatropha curcas fruit seeds meal (JFM). For the first time, 2-thiouracil was employed as a dopant to retard the high corrosion of H₂SO₄ by introducing additional N-and S-active sites. Both JCDs and N, S-JCDs spontaneously adsorb onto the CRS surface, forming a hydrophobic layer to block the diffusion of corrosive particles, thereby migrating 95.6 % (SA) and 92.6 % (H₂SO₄) of corrosion at 100 mg L^-1 dosage. Remarkably, these high inhibition efficiencies persist even under prolonged immersion and elevated corrosive medium concentrations. JCDs acts as a hybrid inhibitor but primarily inhibit the cathodic reaction, whereas N, S-JCDs functions as a typical mixed-type inhibitor. Both significantly reduce the corrosion current density and enhance polarization resistance. The potent interaction between the Fe atom and organic groups in JCDs or N, S-JCDs is the key for film formation, with the additional Fe-S bond in N, S-JCDs-inhibited system underscoring the importance of doping for achieving effective inhibition in H₂SO₄ medium. Furthermore, the intrinsic fluorescence of CDs serves as a probe, validating the adsorption behaviors of these two inhibitors. This study provides comprehensive functional and mechanistic insights into JFM-derived CDs as a corrosion inhibitor. It not only solidifies the potential of JFM as a promising raw material for green corrosion inhibitors, but also exploits a sustainable approach for valorizing Jatropha curcas fruit seed meal, thereby advancing the field of eco-friendly corrosion protection.

Key words: Corrosion inhibitor, Carbon dots, Hydrothermal synthesis, Steel, Adsorption