Composite epoxy coating with dual-responsive Fe3O4@BTA-ZIF-8 nanocontainers for active corrosion protection: Magnetic field-directed distribution synergized with pH-controlled corrosion inhibitor release

The spatial distribution of functional nanofillers in anticorrosion coatings significantly influences their ability to seal micropores/cracks and enhance self-healing properties. In this study, a novel dual-responsive nanocontainer loaded with the corrosion inhibitor benzotriazole (BTA) was developed for active corrosion protection in waterborne epoxy coatings. The magnetic nanocontainers (Fe 3 O 4 @BTA-ZIF-8) were synthesized via the in-situ growth of BTA-encapsulated zeolitic imidazolate frameworks-8 (ZIF-8) on the surface of anion-modified Fe 3 O 4 nanoparticles. This unique structure endows the nanocontainers with pH responsiveness for controlled BTA release under corrosive conditions. Additionally, under an external magnetic field, the nanocontainers migrate toward the coating/metal interface, increasing the local inhibitor concentration and improving corrosion resistance. Potentiodynamic polarization tests revealed that the nanocontainers achieved an inhibition efficiency of 82.40 % on carbon steel surface after 24 h of saline immersion. Cross-sectional analysis of the composite coatings confirmed the magnetic-field-induced accumulation of nanocontainers at the coating/substrate interface, facilitating rapid and efficient inhibitor release. Electrochemical impedance spectroscopy results further revealed a low frequency impedance value (|Z| 0.01 Hz ) of 1.42 × 10 10  Ω·cm 2 for epoxy coating containing magnetically distributed Fe 3 O 4 @BTA-ZIF-8 nanocontainers after 35 d of saline immersion, over an order of magnitude higher than that of coating without magnetic modulation. Furthermore, the scratched composite coating after magnetic modulation exhibited an improvement efficiency (η) of 165.04 % after 6 h of immersion, compared to only 22.76 % for the non-modulated counterpart. These results confirm the long-term protective performance of Fe 3 O 4 @BTA-ZIF-8 within epoxy coatings under magnetic modulation. This study is the first to introduce a magnetic MOF-based nanomaterial for corrosion protection, demonstrating the potential of epoxy coatings with magnetically directed distribution and pH-responsive inhibitor release.