Highly-protective coating against corrosion through a dual-MOF microcapsule based self-responsive strategy

Inhibitor-loaded microcapsules play a promising role in mitigating metal corrosion through a smart fashion but challenges remain in their commercial implementations, including unexpected leakage of inhibitors, poor compatibility with coating matrices, and short effective lifespan. Herein, dual-MOF-based microcapsules (UiO-66 and ZIF-8) were prepared for carrying curcumin as inhibitor to address those issues via a Pickering emulsion template. Differing from loose single-MOF counterparts, size-complementary dual-MOF particles formed tightly packed barriers (smaller ZIF-8 filling gaps between larger UiO-66) that profoundly suppressed emulsion coalescence and enhanced mechanical resistance of the microcapsules to minimize uncontrolled leakage, achieving a three-time increment in loading rate of curcumin (18.4% vs 6.0%). The dual-MOF particles strengthened interfacial compatibility through multiple interactions with epoxy coating matrix. The resultant composite coating (epoxy + dual-MOF-based microcapsules) maintained a high low-frequency impedance after 40-day immersion in 3.5 wt% NaCl solution and 720-h neural salt spray tests. pH-triggered microcapsule decomposition rapidly released internal curcumin and key species (Zn 2+ /2-methylimidazole from ZIF-8 and Zr 4+ /terephthalic acid from UiO-66), collectively establishing a protective film upon steel substrates. Residual MOF particles provided continuous active protection, yielding the lowest corrosion current density after salt spray tests among all scratched coatings. Such a dual-MOF- based microcapsule strategy offers an alternative option for design and development of sustainable and high-efficiency protective coatings against corrosion for numerous engineering services, such as marine and pipeline industry. • A dual MOF-based microcapsule strategy was designed and prepared through polymerizing Pickering emulsion. • Synergism of dual-MOF particles enhances emulsion stability, increases loading rate of corrosion inhibitors, and improves the compatibility of microcapsules in coating. • Composite coating incorporating dual-MOF-based microcapsules exhibits excellent passive barrier performance and sustained active protection.