Size of Ceria Particles Influences Surface Hydroxylation and Hydroxyl Stability

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 degrees 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.

Automated summary

Understanding the surface chemistry of ceria nanoparticles in a water environment is crucial for catalysis and biology/biochemistry. The size of the particles is critical for their pro- and antioxidant activity, with smaller particles acting as scavengers and larger particles causing oxidative distress. The stability and concentration of surface hydroxyl groups are correlated with the size of ceria nanoparticles, with smaller particles showing higher hydroxyl group density and stability compared to larger ones.