A green strategy for nitrogen-doped polymer nanodots with high oxygen and chloride corrosion resistance in extremely acidic condition

Carbon dots as a specific type of carbon material require the connection of experiment to theory, exploration of new application, and development of new material. Here we present a new nitrogen-doped polymer nanodots (NPDs) from 3,4-dihydroxy-L-phenylalanine (L-DOPA) via the one-step synthesis of simultaneous self polymerization and carbonization process. This water-dispersible N-PDs, composed of poly-L-DOPA aggregates and embedded nitrogen-doped graphene patches, shows the zero-dimensional structure with an average diameter of 2.06 nm. In-depth investigation of the inhibition effect of as-prepared N-PDs demonstrates that N-PDs can suppress the oxygen and chloride corrosion of mild steel in extremely acidic condition through the dual effect of adsorption/assembly onto metal surface as a passivation film and strong covalent bonding with iron, resulting in an inhibition efficiency of 97.95% at the concentration higher than 200 mg/L within 6 h, the most efficient reported for carbon dots-based corrosion inhibitors. Furthermore, density-functional-theory calculations clearly reveal that the atoms present in unsaturated bonds of N-PDs play a dominant role in strengthening the interaction between corrosion inhibitor and metal substrate, which gives rise to the stable and homogeneous adsorption of N-PDs and then the effective protection for metal substrate against corrosion.