Development of self-healing sol-gel anticorrosion coating with pH-responsive 1H-benzotriazole-inbuilt zeolitic imidazolate framework decorated with silica shell

Zeolitic imidazolate framework-8 (ZIF-8)-based pH-responsive nanocontainers present a new pathway to endowing sol-gel anticorrosion coatings with self-healing ability. The organic nature of the ZIF-8-based nanocontainers, however, makes them less compatible with the inorganic sol-gel coating matrix, thus ineffective in protection against corrosion. In this paper, a novel pH-responsive corrosion inhibitor release system (BTA-ZIF-8@SiO2) based on ZIF-8 for self-healing sol-gel anticorrosion coating was reported. A facile one-step self-assembly procedure was used to create the 1H-benzotriazole (BTA)-encapsulated ZIF-8 core, on which a layer of silica was subsequently coated using a standard sol-gel method. The silica shell can provide better compatibility of the nanocontainers with the sol-gel matrix, thus improving the overall corrosion protection. Characterizations of the BTA-ZIF-8@SiO2 nanocontainers via X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, Brunauer−Emmett−Teller, scanning electron microscopy/energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy confirmed the successful synthesis of ZIF-8-based nanocontainers with high loading content of BTA and mesoporous SiO2 shell. Inhibitor release studies revealed the pH-responsive smart release of inbuilt BTA at both acidic and alkaline media. The anticorrosion performance of sol-gel coating incorporating the nanocontainers was investigated by electrochemical impedance spectroscopy, scanning Kelvin probe, and salt spray test, and the results indicated that BTA-ZIF-8@SiO2 could effectively enhance the corrosion protection properties of the coating and exhibit excellent self-healing performance, in which the |Z|0.01Hz was >2 orders of magnitude higher and coating resistance and oxide layer resistance were >3 orders of magnitude higher than these of pure sol-gel coating after 28 d of immersion. This could be attributed to the synergistic effect of enhanced passive protection, improved nanocontainer compatibility with the sol-gel matrix, and corrosion inhibitor film formed on metal surface.