TiO₂@CeO_x Core–Shell Nanoparticles as Artificial Enzymes with Peroxidase-Like Activity

Abstract

The Ce 4+ ↔ Ce 3+ redox switch is at the basis of an all-inorganic catalytic cycle that is capable to mimic the activity of several natural redox enzymes. The efficiency of these artificial enzymes (nanozymes) strongly depends on the Ce 4+ /Ce 3+ ratio. By capitalizing on the results obtained on oxide/oxide model systems, we implemented a simple and effective procedure to obtain conformal TiO 2 @CeO x core-shell nanoparticles whose thickness is controlled with single layer precision. Since the Ce 3+ species are stabilized only at the interface by the electronic hybridization with the TiO 2 states, the modulation of the shell thickness offers a simple method to tailor the Ce 4+ /Ce 3+ ratio and therefore the catalytic properties. The activity of these nanoparticles as artificial peroxidase-like enzymes was tested, showing exceptional 2 performances, even better than natural horseradish peroxidase enzyme. The main advantage with respect to other oxide/oxide nanozymes is that our nanoparticles, having a tunable Ce 4+ /Ce 3+ ratio, are efficient already at low H 2 O 2 concentrations.

An Operando Investigation of (Ni–Fe–Co–Ce)Ox System as Highly Efficient Electrocatalyst for Oxygen Evolution Reaction

“…65,66 By measuring the core level binding energy (BE) shift of the elements present in the liquid layer (e.g. O 1s or K 2p peaks) as a function of the applied potential at the WE, it is possible to achieve full potential control at the solid/liquid interface and monitor the ion-supported electrical connection between the electrolyte layer on the sample surface and the bulk liquid phase, as reported in Figure S2a [67][68][69][70] reported in Figure 3a indicates the presence of Ce(III) in the pristine sample (green shaded areas), which is partially re-oxidized upon exposure to water vapor (hydrated conditions), with the Ce(III) fraction decreasing from 19% to 11%. The remaining Ce(III) is completely oxidized after dipping the WE into the electrolyte, as no Ce(III) can be detected in the OCP measurement.…”

Electrospun ceria-based nanofibers for the facile assessment of catalyst morphological stability under harsh HCl oxidation reaction conditions

“…This has been demonstrated first for flat single crystalline films [59] but recently also of TiO 2 nanoparticles which are coated by an ALD type method with CeO 2 . [60] For both systems, the redox activity was significantly increased.…”

Highly Dispersed CeO2 on TiO2 Nanotube: A Synergistic Nanocomposite with Superior Peroxidase-Like Activity

“…For pure CeO 2 , the peaks at V 0 , V′, U 0 , and U′ (881.6, 884.7, 899.4, and 902.5 eV) represented the presence of Ce 3+ while characteristic peaks of Ce 4+ presented at V, V″, V‴, U, U″, and U‴ (882.9, 888.9, 897.9, 900.9, 907.2, and 916.2 eV). 38,48,49 In comparison with those of pure CeO 2 , the characteristic peaks of Ce 3d in CeO 2 / TiO 2 @0.1 shifted to lower binding energy positions, which is due to the different types of screening that TiO 2 (band gap 3 eV) and CeO 2 (band gap 6 eV) can provide in the final state of the photoemission process or most probably to the presence of band bending in CeO 2 /TiO 2 @0.1. 37 The calculated concentrations of Ce 3+ were 28.1%, 57.6%, 36.3%, 31.2%, and 29.8% in pure CeO 2 , CeO 2 /NT-TiO 2 @0.1, CeO 2 /NR-TiO 2 @0.1, CeO 2 /NP-TiO 2 @0.1, and CeO 2 /NW-TiO 2 @0.1 (Table 3), respectively.…”

“…More recently, TiO 2 @CeO x core−shell nanoparticles have been reported as artificial enzymes with peroxidase-like activity which is tailored by CeO 2 shell thickness. 38 Therefore, it is deduced that different TiO 2 supports maybe potentially affect the peroxidase-like activity of CeO 2 −TiO 2 . Recently, the TiO 2 nanotube has been found to be a promising support because of its special structural characteristics and physicochemical properties.…”