Enhanced corrosion resistance and adhesion of epoxy coating by two-dimensional graphite-like g-C₃N₄ nanosheets

Graphene is usually used to enhance the corrosion protection of epoxy (EP) coating. Graphite-like C₃N₄ (g-C₃N₄) nanosheets can be a substitute for graphene to perform good barriers for the penetration of corrosive ions. Herein, g-C₃N₄ nanosheets were obtained via calcining melamine at 520 °C for 3 h (bulk g-C₃N₄) and exfoliating bulk g-C₃N₄ by supersonic stirring for 10 h. The EP coatings with different levels of g-C₃N₄ nanosheets performed better corrosion protection for Q235 steel. Compared with pure EP coating, the maximum enhancement of corrosion resistance was achieved by the addition of 2 wt% g-C₃N₄ in EP coating, with an increase of electrochemical impedance by two orders of magnitude in 3.5 wt% NaCl solution and an order of magnitude in 0.1 M H₂SO₄ solution, as well as a decrease of corrosion current by nearly two orders of magnitude and an order of magnitude in above-mentioned electrolyte solutions, respectively. The immersion test demonstrates the good durability of 2 wt% g-C₃N₄/EP coating against corrosion. Also, it is interesting to note that the addition of g-C₃N₄ nanosheets enhanced the adhesion of EP coating from 3B to 5B rating thanks to the formation of hydrogen bonds between C₃N₄ nanosheets and EP as well as steel surface.