Size of Ceria Particles Influences Surface Hydroxylation and Hydroxyl Stability
Manoj Kumar Ghosalya, Xiansheng Li, Arik Beck, Jeroen A. van Bokhoven, Luca Artiglia
Abstract
Understanding the surface chemistry of ceria nanoparticles in a water environment is of fundamental interest for several research fields and notably in catalysis and biology/biochemistry. Particularly, regarding pro- and antioxidant activity, the size of the ceria nanoparticle plays a critical role. Large ceria particles (>5 nm) usually cause oxidative distress, resulting in the formation of reactive oxygen species, whereas small particles (<5 nm) act as reactive oxygen scavengers. It is generally believed that the activity depends on the Ce3+/Ce4+ ratio. However, biological reactions typically happen in aqueous media at room temperature, so other hypotheses were considered, in particular the degree of surface hydroxylation. By means of ambient pressure X-ray phototelectron spectroscopy, we demonstrate that Ce4+ does not reduce up to 300 °C. The surface concentration and thermal stability of hydroxyl groups correlate with the size of ceria nanoparticles. In particular, small ceria nanoparticles (<5 nm diameter) show a higher hydroxyl group density than larger ones. Finally, hydroxyl groups are thermally more stable on small ceria particles compared to large ones.