pH-responsive bimetallic Ce-ZIF-8 nanocontainer for the active corrosion protection of Al alloys

In this study, novel pH-sensitive bimetallic Ce-ZIF-8 nanocontainers are loaded with benzotriazole (BTA) corrosion inhibitors and then decorated with a polydopamine (PDA) shell. The applied PDA layer acts as an acid-responsive gatekeeper, controlling the intelligent release of the encapsulated inhibitors and also preventing their self-leakage. UV–vis and ICP-OES tests indicate that the BTA and cerium inhibitors release slowly in the neutral 3.5 wt% NaCl solution. Afterward, the designed pH-responsive Ce-ZIF-8-BTA-PDA nanocontainers are dispersed uniformly in the epoxy matrix as a novel intelligent filler. EIS results demonstrate that the incorporation of Ce-ZIF-8-BTA-PDA nanocontainers significantly improves the corrosion resistance of epoxy coatings, in which the low-frequency impedance is about three orders of magnitude higher than that of the pure epoxy coating after 60 days of immersion. Furthermore, the low-frequency value of the scratched Epoxy-Ce-ZIF-8-BTA-PDA coating increases from 5.05 × 105 Ω cm2 to 8.83 × 105 Ω cm2 after 8 h of exposure to the 3.5 wt% NaCl solution, confirming their outstanding self-healing performance. The excellent corrosion protection and self-healing ability are due to the incorporation of the Ce-ZIF-8-BTA-PDA nanocontainers, improving the surface compactness and therefore enhancing the physical barrier effect. Moreover, the intelligent release of the encapsulated corrosion inhibitors provides active corrosion protection performance by forming a dense protective film on the Al alloy surface when the coating is damaged. Meanwhile, the highly dispersed nanocontainers lengthen the diffusion path of corrosive ions and therefore extend the service life of the epoxy coatings in aggressive environments. This new type of acid-responsive smart coating based on the bimetallic Ce-ZIF-8 nanocontainers has the potential to broaden the future applications of active corrosion protection of metals.