Ceria nanoparticles serve as important catalysts and nanozymes accompanied with a strong affinity for harmful substances. Acting as scavengers, ceria particles are known for their enzyme-like behaviour and exhibit significant nanozymatic activity. Here, we studied the interactions of ceria with relevant molecules in the presence of strain, with particular focus on water, hydrogen peroxide and carboxylic acids including formic, carbonic, acetic, glycolic, glyoxylic and oxalic acid. We demonstrated the impact of strain on water (Chapter 3), with tensile strain enhancing surface stability as evidenced by an increased desorption temperature, while the opposite is observed for compressive strain. The thermodynamic approach confirmed that molecular adsorption of water desorbs at lower temperature compared to that of dissociative water. This behaviour is generally independent from the surface water coverage. The shape of ceria nanoparticles as a function of temperature and water pressure depends on strain, with tensile strain and dissociative water favouring cuboidal and truncated octahedral shapes, while octahedral shape is dominant for stoichiometric nanoparticles. Oxygen deficient nanoparticles predominantly express octahedral shapes at all coverages and strains. This is important as water is a ubiquitous molecule present in all reactions occurring at the surface of ceria nanozymes. We continued the study of the impact of strain on the adsorption of hydrogen peroxide on ceria facets (Chapter 4) while highlighting the impact of dissociative hydrogen peroxide species including hydroxyl, peroxide and superoxide, on surface morphologies. OH radicals converted to OH ions due to electron transfer with the surface Ce3+. We found that the peroxide ion has higher stability than the superoxide radical across most conditions. Tensile strain stabilizes superoxide and lowers reduction energies, while compressive strain does the opposite. The desorption temperature of molecular hydrogen peroxide is lower as compared to dissociative hydrogen peroxide species, with strain impacting desorption of such species on stoichiometric surfaces more compared to oxygen deficient surfaces. Despite these differences, adsorbed molecular and dissociative hydrogen peroxide do not affect the shape of nanoparticles significantly and produce predominantly octahedral shaped nanoparticles. This is important as these nanoparticles can control Peroxidase activity and be central to nanozymatic research. Finally, we studied the interactions of various carboxylic acids including formic, carbonic, acetic, glycolic, glyoxylic and oxalic acid on ceria surfaces under strain (Chapter 5). The adsorption modes i.e. monodentate, bidentate and chelate can all be possible, however bidentate adsorption is generally favourable. The adsorption energies are more negative on oxygen deficient compared to stoichiometric surfaces. The presence of adsorbed carboxylic acids lowers the reduction energy of all surfaces by facilitating the formation of oxygen vacancies. Desorption temperature are higher for oxygen deficient surfaces as compared to stoichiometric surfaces, indicating a stronger anchoring of acids on oxygen deficient surfaces. Morphology of oxygen deficient ceria favour octahedral nanoparticle shapes with exposed {111} facets. Stoichiometric ceria nanoparticles show variation in shapes across different acids and strain with truncated octahedra exposing {110} and {100} for formic, acetic and glycolic acid, while octahedra carbonic, glyoxylic and oxalic acid. This is important information as such acids may be used as capping agents to control the growth of specific shapes of ceria nanoparticles.
| Date of Award | 6 Oct 2025 |
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| Original language | English |
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| Supervisor | Marco Molinari (Main Supervisor) |
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