Tuning hydrated nanoceria surfaces: experimental/theoretical investigations of ion exchange and implications in organic and inorganic interactions.

Long-term stability and surface properties of colloidal nanoparticles have significance in many applications. Here, surface charge modified hydrated cerium oxide nanoparticles (CNPs, also known as nanoceria) are synthesized, and their dynamic ion exchange interactions with the surrounding medium are investigated in detail. Time-dependent zeta (zeta) potential (ZP) variations of CNPs are demonstrated as a useful characteristic for optimizing their surface properties. The surface charge reversal of CNPs observed with respect to time, concentration, temperature, and doping is correlated to the surface modification of CNPs in aqueous solution and the ion exchange reaction between the surface protons (H(+)) and the neighboring hydroxyls ions (OH(-)). Using density functional theory (DFT) calculations, we have demonstrated that the adsorption of H(+) ions on the CNP surface is kinetically more favorable while the adsorption of OH(-) ions on CNPs is thermodynamically more favorable. The importance of selecting CNPs with appropriate surface charges and the implications of dynamic surface charge variations are exemplified with applications in microelectronics and biomedical.