α-Zirconium Phosphate Hybrid Intercalated by Carbon Dots with High Anticorrosion Efficiency for Waterborne Epoxy Resin Composite Coating

In recent years, waterborne epoxy resin (WE) has garnered attention due to its lower environmental pollution compared to solvent-based coatings. However, their poor barrier properties severely limit their practical applications. In order to enhance the corrosion resistance of water-based epoxy resin coating, a highly efficient strategy of combining the barrier effect of lamellar structured zirconium phosphate (α-ZrP) and the inhibitor effect of special carbon dots by the intercalation method was proposed in this work. A mixture of l-tyrosine and 3-amino-1,2,4-triazole-5-thiol as carbon sources led to carbon dot LCDs carrying many functional groups on the surface, such as –SH, –OH, –NH2, –COOH, and so on. When α-ZrP was exfoliated by tetramethylammonium hydroxide (TMAH) to expand its interlayer spacing, it could conveniently receive the insertion of LCDs through an intercalation reaction, thereby producing an LCDs-ZrP hybrid. Due to its hydrophilicity, the LCDs-ZrP hybrid had good compatibility with waterborne epoxy resin, consequently greatly enhancing the density of the LCDs-ZrP/WE coating with less defects. The prepared LCDs-ZrP was characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. The corrosion resistance of the LCDs-ZrP/WE coating was tested using various techniques such as electrochemical impedance spectroscopy, three-dimensional optical microscopy, laser scanning confocal microscopy, Raman spectroscopy, etc. It was found that the main lamellar structure of the LCDs-ZrP hybrid easily extended the diffusion path of chloride ions and other corrosive substances through a maze effect. Besides, the LCDs-ZrP contained coordinated groups of –SH, –OH, –NH2, and –COOH, which could cause coordination interaction with the steel bottom plate to form a protective effect, thereby inhibiting steel corrosion. Under the comprehensive corrosion protection mechanisms, the impedance value of the LCDs-ZrP/WE after 28 days of immersion was 9.97 × 109 Ω.cm2, significantly higher than that of WE (4.74 × 106 Ω.cm2), markedly improving the corrosion resistance of WE.