Water- and Acid-Sensitive CuO@Cu-MOF Nano Sustained-Release Capsules with Superior Antifouling Behaviors.

Marine biofouling is one of the technical bottlenecks restricting the development of the global marine economy. Among the commercial self-polishing antifouling coatings, cuprous oxide is an irreplaceable component because of its efficiency and broad-spectrum antibacterial activity. However, one of the biggest obstacles to achieving long-term antifouling is the "initial burst and final decay" of cuprous oxide in the coating. Here, we lock the copper ions by establishing an antifouling unit composed of CuO (core) and Cu-based metal-organic framework (Cu-MOF, shell). Cu-MOF is densely grown in situ on the periphery of CuO by acid proton etching. The shell structure of Cu-MOF can effectively improve the stability of the internal CuO and thus achieve the stable and slow release of copper ions. Furthermore, CuO@Cu-MOF nanocapsules can also achieve active defense by rapid and complete dissolution of CuO@Cu-MOF at local acidic microenvironment (pH ≤ 5) where the adhesion of fouling organisms occurs. Super-resolution fluorescence microscopy is used to explain the sterilization mechanism. Relying on the water- and acid-sensitive properties of Cu-MOF shell, the stable, controlled and efficient release of copper ions has been achieved for the CuO@Cu-MOF nanocapsules in the self-polishing antifouling coatings. Thus, these controlled-release nanocapsules make long-term antifouling promising.