Preparation of P-CDs functionalized α-ZrP flake fillers and enhancing anti-corrosion properties of epoxy coating

2D nanofillers can effectively improve coatings' barrier and anti-corrosion properties but are less compatible with coatings and prone to agglomeration. In this paper, glucose-derived phosphorus-doped carbon dots (P-CDs) were prepared as dispersants, and functionalized α-zirconium phosphate (α-ZrP) was prepared by combining with α-ZrP through π-π interactions, which showed good dispersion and compatibility in waterborne epoxy (WEP). The corresponding modified WEP coating is prepared on Q235 substrates through the scrape coating method. The effect of fillers on the physical and chemical properties of the coating was studied by electrochemical impedance spectroscopy (EIS), neutral salt spray test, and immersion test. The results of the electrochemical test show that the |Z|_{0.01 Hz} value of the coating prepared by P-CDs@ZrP as the filler after soaking in 3.5 wt% NaCl solution for 30 d is three orders of magnitude higher than that of the WEP coating, and the corrosion resistance is greatly improved. The salt spray and soaking tests prove that the prepared P-CDs@ZrP coating has excellent barrier properties and corrosion resistance. Besides, P-CDs can also act as an effective passivation agent, which could adsorb on the surface of the Q235 substrate and form a passivation film, preventing further corrosion of the substrate. This study provides a new way to enhance the corrosion resistance of the coating.