Ultraviolet absorption spectra of CeO₂ nano-particles

Toluene suspensions containing surfactant coated CeO₂ (ceria) nano-particles of narrow size distributions (with mean deviation less than 20%) in the 1.8-3.8 nm diameter range are obtained from an original ceria aqueous sol having particle sizes extending over a wide range, by ultrafiltration and successive microemulsifications. These suspensions show clear blue shifts in ultraviolet absorption spectra. Two possibilities are presented in order to explain the size effect. A model for size fractionation by surfactants is proposed.