Environment-mediated structure, surface redox activity and reactivity of ceria nanoparticles

Abstract

Nanomaterials, with potential application as bio-medicinal agents, exploit the chemical properties of a solid, with the ability to be transported (like a molecule) to a variety of bodily compartments. However, the chemical environment can change significantly the structure and hence properties of a nanomaterial. Accordingly, its surface reactivity is critically dependent upon the nature of the (biological) environment in which it resides. Here, we use Molecular Dynamics (MD) simulation, Density Functional Theory (DFT) and aberration corrected TEM to predict and rationalise differences in structure and hence surface reactivity of ceria nanoparticles in different environments. In particular we calculate reactivity 'fingerprints' for unreduced and reduced ceria nanoparticles immersed in water and in vacuum. Our simulations predict higher activities of ceria nanoparticles, towards oxygen release, when immersed in water because the water quenches the coordinative unsaturation of surface ions. Conversely, in vacuum, surface ions relax into the body of the nanoparticle to relieve coordinative unsaturation, which increases the energy barriers associated with oxygen release. Our simulations also reveal that reduced ceria nanoparticles are more active towards surface oxygen release compared to unreduced nanoceria. In parallel, experiment is used to explore the activities of ceria nanoparticles that have suffered a change in environment. In particular, we compare the ability of ceria nanoparticles, in an aqueous environment, to scavenge superoxide radicals compared to the same batch of nanoparticles, which have first been dried and then rehydrated. The latter show a distinct reduction in activity, which we correlate to a change in the redox chemistry associated with moving between different environments. The reactivity of ceria nanoparticles is therefore not only environment dependent, but is also influenced by the transport pathway or history required to reach the particular environment in which its reactivity is to be exploited.

Structure of Surface Entrance Sites for Li Intercalation into TiO2 Nanoparticles, Nanosheets, and Mesoporous Architectures with Application for Li-Ion Batteries

“…21 In this present study, our images of nanostructured TiO 2 are in close accord with experiment ( Figure 4(a,b) and Figure 7(a,b)). The close comparison with HRTEM acts as a validation of the model.…”

Ceria Nanoshapes—Structural and Catalytic Properties

“…In the anion Frenkel type defect, an oxygen ion is displaced from its lattice position to an interstitial position, hence creating a vacancy at its original position and a defect at the interstitial site [39][40][41]. In general, the formation of these defects does not influence Figure 1 Fluorite structure of ceria.…”

“…In the past years, several studies based on atomistic calculations have also suggested the presence of additional defects in the ceria lattice, such as interstitial and Schottky disorder [29,41,45]. An interstitial defect is the displacement of both a cerium and two oxygen ions to form interstitial sites, for example, Figure 2 Possible types of point defects in the CeO 2 lattice.…”

Structure and properties of cerium oxides in bulk and nanoparticulate forms

“…The water dissociation on (111) surface was found to be much less stable than on (100) one, and water is predicted to recombine and leave the surface above 300K [96]. Further simulations predicted higher activities of ceria nanoparticles towards oxygen release, when immersed in water because the water quenches the coordinative unsaturation of surface ions [97].…”