In situ generation of H₂O₂ using CaO₂ as peroxide storage depot for haloperoxidase mimicry with surface-tailored Bi-doped mesoporous CeO₂ nanozymes

Designing the size, morphology and interfacial charge of catalyst particles at the nanometer scale can enhance their performance. We demonstrate this with nanoceria which is a functional mimic of haloperoxidases, a group of enzymes that halogenates organic substrates in the presence of hydrogen peroxide. These reactions in aqueous solution require the presence of H2O2. We demonstrate in situ generation of H2O2 from a CaO2 reservoir in polyether sulfone (PES) and poly(vinylidene fluoride) (PVDF) polymer beads, which circumvents the external addition of H2O2 and expands the scope of applications for haloperoxidase reactions. The catalytic activity of nanoceria was enhanced significantly by Bi3+ substitution. Bi-doped mesoporous ceria nanoparticles with tunable surface properties were prepared by changing the reaction time. Increasing reaction time increases the surface area SBET of the mesoporous Bi0.2Ce0.8O1.9 nanoparticles and the Ce3+/Ce4+ ratio, which is associated with the ζ-potential. In this way, the catalytic activity of nanoceria could be tuned in a straightforward manner. H2O2 required for the reaction was released steadily over a long period of time from a CaO2 storage depot incorporated in polyether sulfone (PES) and poly(vinylidene fluoride) (PVDF) beads together with Bi0.2Ce0.8O1.9 particles, which may be used as precision fillers and templates for biological applications. The spheres are prepared as a dry powder with no surface functionalization or coatings. They are inert, chemically stable, and safe for handling. The feasibility of this approach was demonstrated using a haloperoxidase assay.