Overlooked impact of surface hydroxylation on the solubility of less-soluble compounds: a case study of CeO2

Abstract

Unexpectedly, the solubility of CeO₂ nanoparticles (NPs) at 25 °C does not depend on particle size, but is significantly affected by the sample's thermal pre-treatment. The classical interpretation of NPs' solubility proposed by the Gibbs–Thompson or Kelvin equations fails to describe the experimental data on CeO₂ solubility obtained in this study. Thermal treatment did not change the samples' morphological characteristics, while slightly affecting NP hydroxylation and local crystallinity. The differences in the solubility of dried and non-treated CeO₂ particles were most noticeable at pH < 4, and dissolved cerium concentration was much lower in the case of the dried sample. After prolonged storage (up to 4.5 years) of CeO₂ NPs in aqueous media, the solubility of dried samples gradually increased, while for non-treated samples it remained unchanged. Based on the example of CeO₂, the dissolution laws of other less soluble nanomaterials should be reconsidered.