Chitosan-derived nitrogen-doped carbon dot modified waterborne PU electrodeposited nanocomposite coatings for corrosion protection

In this work, we report a high-performance polyurethane (PU) nanocomposite cathodic electrodeposition (CED) coating, which has been reinforced with nitrogen-doped carbon dots (NCDs) obtained from the hydrothermal treatment of shrimp shells derived chitosan. The synthesized NCDs show a quasi-spherical shape with an average diameter of around 4–6 nm, confirmed by FT-IR, XRD, and TEM analysis. The incorporation of the NCDs into the PU polymer results in strong interfacial interactions between the polymer chains and the NCDs, resulting in a better and more adherent film formation. The NCDs provide nano-roughness to the coating surface, resulting in an increased water contact angle via enhanced nano-roughness. The incorporation of the NCDs also results in the filling up of the microvoids created in the film during solvent evaporation and results in the formation of longer diffusion paths for the corrosive species. EIS analysis exhibits that the incorporation of the NCDs into the nanocomposite coating enhances the charge transfer resistance, showing better anti-corrosion properties of the coated samples. However, higher dosage of NCD solution cause agglomeration and reduction in film property. Overall, bio-derived NCDs provide a minimalistic, scalable, and environmentally benign route to electrodeposited PU coatings with superior anticorrosion performance.