Investigating the mixed valence states of Ce⁴⁺(CeO₂) and Ce³⁺(Ce₂O₃) nanoparticles in a soluble bioactive borate glass

A soluble bioactive borate glass was used to synthesize cerium oxide nanoparticles (nanoceria) with two main valence states Ce⁴⁺ (CeO₂) and Ce³⁺ (Ce₂O₃) through a reversible ceric–cerous redox equilibrium reaction. By controlling the melting parameters, a series of glasses were developed with varied Ce³⁺/Ce⁴⁺ ratios of nanoceria. Further, these mixed valence nanoceria were extracted from the glass through dissolution. The extracted nanoceria was investigated using Transmission Electron Microscopy (TEM). TEM imaging of the extracted nanoceria confirmed the existence of the two main valence states, Ce⁴⁺ and Ce³⁺. The results showed that the Ce⁴⁺ valence state typically holds the cubic fluorite structure while the hexagonal and rhombic structures contribute to the Ce³⁺ valence state. The Fourier Transform Infrared spectroscopy results showed a significant change in the stretching vibrational bonds of O-Ce-O and Ce-O-Ce with respect to the Ce³⁺/Ce⁴⁺ ratio in the glass as well as that of the extracted nanoceria. Further, Raman and X-ray Diffraction spectroscopy were used to investigate the structural changes of the nanoceria embedded within the glass as well as that of the extracted.