Sequential Release From Hierarchical MOF-on-MOF Architectures for Programmable Self-Healing and Self-Warning Coatings

Stimuli-responsive micro/nanocontainers play a vital role in targeted delivery for protective coatings. Achieving precise functions necessitates a new generation of materials capable of stepwise-controlled release of multiple payloads. However, co-encapsulating diverse active agents poses challenges, particularly in achieving sequential release, critical for advancing complex protective strategies. Herein, hierarchical MOF-on-MOF core-shell containers were constructed by mild epitaxial growth to spatially accommodate corrosion inhibitors and warning agents. The ZIF-67@ZIF-8 system showed a two-stage release profile, with preferential MBT release from the less stable ZIF-67 core followed by delayed BTA release from the ZIF-8 shell. Comparatively, the parallel ZIF-8@ZIF-8 architecture exhibited largely overlapped release profiles. This observation suggests that core-shell construction alone does not guarantee staged release and that framework stability contrast is an important factor in regulating temporal delivery. When incorporated into epoxy coatings, the inhibitor-loaded containers enhanced defect-site corrosion protection on Cu and Al substrates, while Phen-containing containers enabled colorimetric warning on Fe-based substrates. This work demonstrates a stability-gradient strategy for temporally programmed delivery in multifunctional corrosion-protective coatings.