Cerium oxide particles as functional haloperoxidase mimics to combat biofouling

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Surfaces in aqueous habitats are usually colonized by microorganisms. A textbook example is the settlement of bacteria, unicellular organisms, algae or shells on ships or port facilities. A current strategy to reduce this so-called biofouling is the addition biocides in paints. Microorganisms enter into synergistic communities in the formation of biofilms and co-ordinate film formation through signaling via signaling molecules ("quorum sensing"). A defense mechanism of marine organisms is based on disrupting cell-to-cell communication of epibionts by enzymatic formation of halogenated - and thus ineffective - signaling molecules. The proposed project uses CeO2-x nanoparticle (NP) enzyme (haloperoxidase) mimics, which - analogously to natural haloperoxidases - catalyze the oxidation of ubiquitous halides by hydrogen peroxide (generated in daylight). The resulting hypohalous acid (HOX) intermediates react with organic substrates in follow-up to form the halogenated signal molecules. The metal oxide particles can be immobilized on surfaces as a constituent of paints and resins without losing their effect. The catalytic halogenation of a halogenated signal compound has been demonstrated in laboratory experiments. The project aims to achieve the following objectives by pooling the expertise of both project partners:1. Unraveling the sequence of the halogenation reactions: Does the reaction proceed via short-lived HOBr/HOCl intermediates, or are other reactive intermediates involved? Which halogenated signaling compounds are formed in natural waters (i.e., in the field)? What is the stability of these halogenated primary intermediates and in what concentrations are they formed? Which other compounds are formed?2. The catalytic activity of CeO2-x NP in halogenation reactions is determined by defects. By increasing the defect concentration in different solid state solution series (e.g., CeO2-M2O3, (M = La, Y, Bi, etc.) the activity should be improved.3. Alternative halogenation catalysts: Besides the halogenation properties of CeO2-x and its substituted variants, the halogenation activity of Ce perovskites (BaCe1-xO3-y etc.), Ce-substituted silica compounds (Ce-TUD-1), delafossite-type composites (CuCrO2-CeO2), or Mn oxides will be tested.4. The use of CeO2-x NP (and possible alternatives) in antifouling applications requires the availability in sufficient amounts. The synthesis must be scaled up to the kg scale.5. Analytical examination and optimization of the resistance of the coatings and their surface properties: The particles should be integrated into films or coatings for use under application oriented conditions. The surface properties must be optimized, the bacterial and algae growth on the films and the leaching of the particles (environmental compatibility) and the released products will be determined.