Application of dual inhibitor-loaded ZIF-8 decorated montmorillonite nanocomposite toward active corrosion resistance of waterborne epoxy coatings

Impregnation of multiple corrosion inhibitors within stimuli-responsive nanocontainers significantly enhances the active corrosion protection capabilities of anticorrosion coatings, thus extending their service life. This study introduces a novel nanocontainer, BTA-ZIF-8@Ce-MMT, for the active corrosion protection of carbon steel. In this design, zeolitic imidazolate frameworks (ZIF-8) containing 1H-benzotriazole are in-situ grown on cerium ion-intercalated montmorillonite. The dual inhibitor-loaded nanocontainers exhibit superior on-demand inhibitor release properties, where the cerium ions and BTA molecules effectively mitigate corrosion reactions at the cathodic and anodic sites, respectively. Potentiodynamic polarization measurements demonstrated that addition of 1 g/L of BTA-ZIF-8@Ce-MMT reduced the corrosion current density (i_corr) of Q235 carbon steel immersed in 3.5 wt% NaCl solution from 3.389 to 1.132 μA·cm⁻², resulting in a maximum inhibition efficiency of 67.6 %. Electrochemical impedance spectroscopy (EIS) analysis of the bare carbon steel surface further indicated that dual inhibitor system provided synergistic corrosion inhibition and enhanced interfacial corrosion resistance (R_ct). When incorporated into a waterborne epoxy matrix, BTA-ZIF-8@Ce-MMT nanocontainers significantly improved the anticorrosive stability of the coatings. After 28 d of immersion in a saline solution, the impedance modulus of the coating at 0.01 Hz (|Z|_{0.01 Hz}) remains at 5.12 × 10⁹ Ω cm², nearly two orders of magnitude higher than that of the pure epoxy coating. Additionally, the adhesion strength of the coating declined by only 50.8 % after two weeks of salt spray test. This enhanced performance is contributed by the synergistic effects of montmorillonite, cerium ions, and 1H-benzotriazole (BTA) molecules. Together, these components establish a robust anticorrosion mechanism, which includes an extended diffusion pathway for corrosive media via the flake-structured MMT, the formation of protective cerium hydroxide or cerium oxide films, and acid-responsive BTA release from the ZIF-8 frameworks. This study for the first time introduces a dual-inhibitor strategy for modifying montmorillonite with functional MOF structures, offering a promising approach to improving the corrosion protection of epoxy coatings on Q235 mild steel.