Self-Healing Epoxy Composite Coatings Enabled by a pH-Responsive Ce-ZIF-8 Nanocontainer System

A pH-responsive MBT/Ce-ZIF-8@TA nanocontainer system was developed to enhance the corrosion resistance of epoxy coatings. Porous Ce-ZIF-8 cores loaded with 2-mercaptobenzothiazole (MBT) were encapsulated by a functional tannic acid (TA) shell. In this system, TA acts as a “gatekeeper,” preventing premature leakage in neutral environments while triggering inhibitor release under corrosive stimuli. Release kinetics reveal a distinctive “on-demand” mechanism: while stable at neutral pH, a rapid burst release (87.84% in 24 h) occurs at pH 3.0, ensuring immediate delivery of inhibitors to passivate defects. The nanocontainers are uniformly dispersed in the epoxy matrix, significantly enhancing long-term corrosion protection. After 60 days of immersion in 3.5 wt % NaCl, the composite coating exhibits an impedance modulus 3 orders of magnitude higher than that of pure epoxy. Notably, scratched coatings demonstrate superior active self-protection, with Rc recovering from 7.76 × 109 Ω·cm2 to 1.58 × 1010 Ω·cm2 within 24 h. This enhanced performance is attributed to the synergistic combination of physical barrier reinforcement and pH-triggered chemical passivation by the released inhibitors.