Effect of the thermodynamic properties of W/O microemulsions on samarium oxide nanoparticle size

Abstract

In this work, we report the preparation of the Sm 2O 3 nanoparticle precursors (Sm(OH) 3) via a simple W/O microemulsion process, in which microemulsions of cetyltrimethylammonium bromide (CTAB)/alkanol/1-octane/Sm(NO 3) 3 aqueous solution were added into sodium hydroxide (NaOH) aqueous solutions. The Sm 2O 3 nanoparticles were then prepared by calcining the precursors at 900 °C. Particularly, Δ G c → i , which is the change in standard Gibbs free energy for transferring cosurfactant from the continuous phase to the microemulsion interface and can be used to estimate the thermodynamic properties of microemulsions, was determined using the dilution method. The effects of alkanol carbon chain length (1-pentanol, 1-hexanol, 1-heptanol and 1-octanol) and the reaction temperatures (298, 308, 318 and 328 K) on both Δ G c → i and Sm 2O 3 nanoparticle size have been investigated. Specifically, the Sm 2O 3 nanoparticle size, when calcined at 900 °C, was found to be mainly controlled by Δ G c → i , and was thereby affected by the thermodynamic properties of microemulsions. The obtained products were characterized by DSC–TGA, XRD, TEM and UV–Vis. The results showed that Δ G c → i decreased with the increase in both the length of alkanol carbon chain and the reaction temperature, and the average size of Sm 2O 3 nanoparticles decreased as Δ G c → i decreased. The effect of microemulsion thermodynamic properties on Sm 2O 3 nanoparticle size reported here can provide some insights in controllable preparation of other rare earth oxide nanoparticles via the microemulsion route.