Anticorrosion Improvement of Waterborne Epoxy-Acrylate Coatings by Constructing g‑C₃N₄ Functionalized by Polyaniline-Coated Zinc Phosphate

In response to the poor anticorrosion properties of waterborne coatings, g-C₃N₄ coated with zinc phosphate and polyaniline (PANI) was synthesized by in situ polymerization. Added to water-based epoxy-acrylate (WEP) emulsions, this new composite is used as an anticorrosive agent to protect metal substrates. The PANI film on the surface of g-C₃N₄ (denoted as CA) guarantees excellent g-C₃N₄ dispersion owing to the hydrophilic groups. The addition of zinc phosphate was to improve the corrosion protection ability of the composite (denoted as CAZP). The structure and chemical composition of the CAZP composite were analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Transmission electron microscopy was used to monitor the morphological changes of the composites and scanning electron microscopy to characterize the topography of different coatings. By applying these analyses, the successful formation of CAZP was confirmed. The anticorrosion performance of g-C₃N₄, CA, and CAZP coatings on Q235 carbon steel in 3.5 wt % NaCl solution was evaluated by electrochemical impedance spectroscopy and dynamic potential polarization curves. The results show that even after prolonged immersion (60 days) in the NaCl solution, the |Z_0.01Hz| of CAZP/WEP was still as high as 1.69 × 10⁹ Ω·cm². The corrosion rate was reduced to 9.590 × 10^–6 mpy, 3 orders of magnitude lower than that of the blank coating. This indicates that CAZP/WEP has excellent corrosion protection properties.