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 degrees 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. (C) 2020 Elsevier Inc. All rights reserved.