The effect of pyrrolic nitrogen on corrosion inhibition performance of N-doped carbon dots

In this study, nitrogen-doped carbon dots (NCDs) were synthesized using a two-step hydrothermal method. Initially, carbon dots (CDs) were prepared from citric acid, followed by nitrogen doping with ammonia solution. By varying the heating temperature in the second step, three types of NCDs were synthesized containing amino-N, pyrrolic-N, or quaternary-N. The corrosion inhibition properties of these NCDs on Q235 carbon steel in 1 M HCl were investigated. The NCDs with the highest pyrrolic-N content (4.10 at.%) demonstrated superior corrosion inhibition, with an efficiency of 96.63 % at 200 mg/L, underscoring the vital role of pyrrolic-N. Quantum chemical calculations elucidated the underlying mechanism: NCDs adsorbed parallelly onto the carbon steel surface by donating their π-electrons to Fe atoms, and forming a protective film that segregated the steel from the acid solution. The delocalization of p-orbital electrons from pyrrolic-N into π-conjugation altered the energies of the π-electrons within the NCDs, enhancing their reactivity and electron-donation ability, thereby augmenting their adsorption capability.