Self-healing epoxy composite coating based on polypyrrole@MOF nanoparticles for the long-efficiency corrosion protection on steels

In this work, a simple strategy was applied to modify zeolitic imidazolate framework-8 (ZIF-8) by the conductive polypyrrole (PPy) through in-situ polymerization. The synthesized PPy@ZIF-8 composite material as an active filler has been added into epoxy resin (EP) to produce a long-term anti-corrosion coating. The corrosion resistance of PPy@ZIF-8/EP coating was evaluated by electrochemical impedance spectroscopy (EIS) test and salt-spray test. The results showed that the introduction of the filler significantly improved the anti-corrosion performance of EP. After 30-day immersion in 3.5 wt% NaCl solution, the PPy@ZIF-8/EP coating showed a high impedance modulus of |Z|0.01 Hz (3.7 × 108 Ω cm2), which was four orders of magnitude higher than the neat EP. The improvement in corrosion protection could be attributed to the synergistic combination of passive and active corrosion resistance mechanisms. The PPy@ZIF-8 particles could not only be used as a passive nanofiller against corrosion media but also display a self-healing behavior due to the formation of the passivation iron oxide and Zn(OH)2 deposition layer on the steel substrate by electrochemical reactions, after the corrosion media reached the metal. This study provides new insight into the development of multifunctional anti-corrosion coatings for engineering applications.