Stable Cu(I) release from multivalent Cu-MOFs: Achieving long-lasting antifouling performance in marine coatings

Modulating the release of Cu(I) ions from copper-based antifoulants is of notable engineering and scientific importance. However, this approach remains challenging because of a lack of valence-stabilizing protection strategies for Cu(I) sites and the poorly characterized releasing behavior of Cu(I) ions. To address these issues, a novel multivalent antifoulant Cu(I, II)-metal–organic framework (Cu(I, II)-BTC; BTC: 1,3,5-benzenetricarboxylate) was synthesized via an in situ reduction of Cu(II)-BTC under mild conditions. The framework structure of Cu(I, II)-BTC was examined in detail using X-ray diffraction, N 2 sorption analysis, and transmission electron microscopy–selected-area electron diffraction. For the first time, the release behavior of Cu(I) from Cu(I, II)-BTC submerged in seawater was characterized by ultraviolet–visible spectrophotometry. The chemical state of the copper sites in the Cu(I, II)-BTC complex was determined before and after submersion in fresh seawater to investigate whether the framework structure facilitated the retention of Cu(I) ions. Further, the bactericidal activity of Cu(I, II)-BTC was evaluated by measuring the intracellular reactive oxygen species levels to reveal the biocidal effect of the released Cu(I) ions. Finally, the antifouling performance of the resulting Cu(I, II)-BTC-based antifouling coating was comprehensively evaluated via laboratory bioassays (using fouling bacteria and barnacle larvae as test organisms) and long-term marine field trials. This study offers viable avenues for designing novel antifoulants and developing an in-depth understanding of the copper-mediated antifouling process.