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

Abstract

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 S_BET of the mesoporous Bi_0.2Ce_0.8O_1.9 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 Bi_0.2Ce_0.8O_1.9 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.