A pH-responsive cerium-imidazole decorated ZIF-8 to achieve self-healing barrier property for epoxy coating on Al alloy by controlled release

Ce-based imidazole complex (Ce-IM/ZIF-8) nanoparticles (NPs) were fabricated by doping cerium ions (Ce3+ /Ce4+) in zeolite imidazolate framework-8 (ZIF-8) through a one-pot co-precipitation method. The stimuli-responsive release of Ce3+/Ce4+ species from the Ce-IM/ZIF-8 NPs under acidic conditions was confirmed by UV–Vis spectroscopy. Electrochemical impedance spectroscopy and scanning electron microscope were applied to evaluate the corrosion inhibition efficiency of Ce-IM/ZIF-8 NPs on bare aluminum alloy, and it demonstrates that the released Ce3+/Ce4+, Zn2+ ions and imidazole could absorb on the surface of Al alloy by chelating effect, forming a compact corrosion barrier on the Al substrate. Furthermore, the Ce-IM/ZIF-8 NPs were encapsulated into epoxy (EP) resin to obtain a composite coating, and it is found that when the NPs addition amount was 1 wt%, the EP-based composite coating exhibits excellent corrosion barrier and promising self-healing ability, with its impedance at 0.01 Hz maintaining 2.2 × 108 Ω·cm2 even after 6 cycles of aging tests (720 h), which could be ascribed to the synergistic inhibition of released Ce ions and imidazole molecules on Al substrate beneath the defective coating.