pH-Triggered Tannic Acid Release from ZIF-8@ZIF-L for Intelligent Self-Healing Epoxy Coatings in Marine Environments

Marine infrastructures suffer from accelerated corrosion under coupled saline, humid, and biofouling-prone environments, where even minor coating defects can rapidly evolve into underfilm corrosion and catastrophic failure. Here, a self-healing TA@ZIF-8@ZIF-L/EP composite coating was developed by incorporating tannic acid-loaded ZIF-8@ZIF-L microcapsules into an epoxy resin (EP) matrix for enhanced corrosion protection in marine environments. The core-shell ZIF-8@ZIF-L structure was synthesized via a facile stirring method and served as a pH-responsive carrier for Tannic acid (TA). Upon mechanical damage, the local corrosive microenvironment triggers rapid TA release, followed by interfacial coordination with Fe³⁺ to form an adherent metal-polyphenol complex film that passivates exposed steel and suppresses corrosion reactions. Meanwhile, lamellar ZIF-L creates a tortuous diffusion pathway, and imidazolate species promote network densification, collectively enabling synergistic, multilevel protection. The result shows that |Z|_0.01Hz of TA@ZIF-8@ZIF-L/EP (6.88 × 10¹⁰ Ω·cm²) remain far higher than that of EP (2.47 × 10⁹ Ω·cm²) after 60 days of immersion in 3.5 wt % NaCl. Scratched-coating tests demonstrate autonomous self-healing at pH = 3, achieving a self-healing efficiency of 158.14% after 48 h due to rapid TA release and Fe³⁺-mediated reconstruction of a protective interfacial film at damaged sites. This work provides a scalable strategy to integrate container-enabled on-demand inhibition with interfacial passivation for durable marine anticorrosion coatings.