CeO₂ nanocrystals from supercritical alcohols: new opportunities for versatile functionalizations?

The fast and controlled synthesis of surface-modified cerium oxide nanoparticles was carried out in supercritical {ethanol + alcohol derivative} mixtures. The newly found ability of supercritical alcohols to graft onto cerium oxide nanocrystals (CeO2 NCs) during their synthesis was exploited to control their surface chemistry via the addition of three aminoalcohols: ethanolamine, 3-amino-1-propanol and 6-amino-1-hexanol. Although the ethanol to aminoalcohol ratio was consistent (285:1), the successful grafting of these alcohol derivatives onto CeO2 NCs was identified based on Fourier transform infrared (FTIR) and thermogravimetric analysis-mass spectrometry (TGA-MS) measurements. Smaller crystallite size of CeO2 NCs synthesized in the presence of aminoalcohols, compared to those synthesized in supercritical ethanol alone, were also noticed and attributed to a possible intervention of amine groups helping the grafting of the alcohols, allowing one to stop the growth of the CeO2 NCs faster. The use of supercritical alcohol mixture-ethanol with hexanol, dodecanol, or octadecanol, with a 285:1 ratio-was also investigated. Such mixtures allow accessing a finer control in CeO2 NCs crystallite size compared to pure alcohols, according to calculation made from X-ray diffraction measurements. Finally, fluorescent molecules (fluorescein isothiocyanate) were grafted onto amine-modified CeO2 NCs. The powders displayed a fluorescent behavior under UV light, confirming the suitability and interest of CeO2 NCs surface modification by such technique.