Hollow ZIF-8 microcapsules loaded with tannic acid for smart self-healing anticorrosion coatings

Zeolitic imidazolate framework-8 (ZIF-8) has been widely investigated as a nanocontainer for corrosion inhibitors in anticorrosion coatings. However, its limited internal space usually restricts inhibitor encapsulation. In this work, ethyl cellulose (EC) microspheres were prepared via solvent evaporation and served as sacrificial templates for the fabrication of hollow ZIF-8 microcapsules (H-ZIF-8). After template removal, tannic acid (TA) was encapsulated into H-ZIF-8 to obtain TA@H-ZIF-8 microcapsules. The resulting TA@H-ZIF-8 exhibited pH-responsive release behavior, providing both active corrosion inhibition and barrier protection for Q235 carbon steel. When incorporated into an epoxy (EP) matrix, the microcapsules endowed the coating with multifunctional properties, including self-warning, self-healing, and long-term anticorrosion performance. Electrochemical impedance spectroscopy (EIS) demonstrated that the EP coating containing 5 wt.% TA@H-ZIF-8 maintained an impedance modulus above 108 Ω·cm2 after 50 days of immersion, an increase of approximately 17 times. This study demonstrates that TA-loaded hollow ZIF-8 microcapsules are promising candidates for the development of intelligent anticorrosion coatings.