Xerogel-Sequestered Transition Metal Catalysts for the Activation of Hydrogen Peroxide in Antifouling Applications: Stability and Possible Mechanism of Catalytic Oxidation

The accumulation of microorganisms, plants, algae, or animals on wetted structures is known as marine fouling or biofouling. Marine biofouling increases the surface roughness of submerged structures. This added roughness corresponds to an increased hydrodynamic drag, which significantly impedes the efficient movement of a vessel through water. Additional fuel expenditures to counteract the inefficiencies brought on by drag prompt increased greenhouse gas emissions. Furthermore, organismal attachment to sea bound vessels impose substantial ecological threats by introducing invasive species into various waterways.;The majority of mainstream antifouling technologies employed are paints that utilize topographical variations or the slow leach of biocides to deter organismal settlement. These formulations, however, commonly involve arduous application procedures and/or produce biocidal leachates that may accumulate in marine organisms and environments. The potential to generate biocides in situ presents a promising alternative for the control of biofouling. By utilizing naturally occurring chemicals in seawater to produce environmentally benign deterrents, fouling may be controlled without employing detrimental biocides or costly multifaceted topographical paints.;Although a kinetically slow process, naturally occurring aqueous halide salts in seawater may be oxidized in the presence of H2O2 to generate hypohalous acids in situ. These oxidized halide species may then act as negative settlement cues, deterring the settlement of marine fouling organisms on submerged surfaces. Silica based xerogel coatings introduce an excellent platform for the sequestration of catalysts to be used for the oxidation of aqueous halide species in seawater. By incorporating a catalyst into the silica matrix of a xerogel coating, the continuous production of oxidized halide species on the surface generates a biocide from naturally occurring reagents, thus eliminating the need for coatings that rely on the production of toxic biocidal leachates.;Transition metal catalysts sequestered into the inorganic framework of silica xerogels have shown immense promise for the catalytic oxidation of aqueous halides. Kinetic evaluation of these catalysts has demonstrated improved rates for the oxidation of bromide, in addition to evidence for the first catalytic oxidation of chloride utilizing a xerogel sequestered catalyst at ambient conditions. Elucidation of the stability, identity, and mechanism of catalysis for titanium and tungsten sequestered xerogel catalysts for their use as antifouling coatings is discussed within.