The adhesion of organisms, especially bacteria, on the surfaces of materials is crucial in diverse fields such as ship hull fouling, on bridge piers, industrial cooling water systems, textiles, polymer membranes for water desalination, or aquaculture systems. Once adhered on a solid surface, bacteria form colonies which serve as a nutritional basis for higher organisms, and eventually a biofilm is formed. Antifouling coatings release toxic copper and other co-biocides to retard the growth of algae and encrusting organisms.
Current strategies for surface coatings to reduce bacterial adhesion rely either on biocides (cuprous oxide and organic co-biocides) or engineered surface topographies. New environmental regulations have motivated advancements in nontoxic chemical strategies to combat fouling. Making use of a natural defense mechanism of marine organisms would be an efficient and sustainable solution. Nature’s defense strategy against epibiont growth relies on vanadium-dependent haloperoxidases (V-HPOs) which catalyze the oxidative bromination of signaling compounds that impede bacterial quorum sensing.
We show that CeO2-x nanorods have an intrinsic biomimetic oxidative bromination activity that allows the formation of HOBr under seawater conditions (neutral pH and natural Br-/H2O2 concentrations). CeO2-x nanorods show an exceptional operational stability and catalytic activity compared to natural V-HPOs. Starting from the basic “enzyme kinetics” of CeO2-x nanoparticles we show step by step the antifouling activity of CeO2-x nanorods for E. coli in the presence of Br- and H2O2 and give experimental and computational evidence for the proposed radical reaction mechanism. The antifouling activity is retained even when CeO2-x nanorods are used as an additive (2 wt %) in antifouling paint formulations. CeO2-x nanorods have a comparable activity for blocking the adhesion and colonization of bacteria as cuprous oxide, the current gold standard, which, however, is added in amounts up to 50%. Different from vanadium oxide and molecular biocides ceria it is non-toxic and highly insoluble. This makes it a sustainable and also cost-efficient substitute for conventional inorganic/organic biocides.