Abstract
Producing compact monoliths of mesoporous uranium oxide that are free from surface active components and able to be wet by highly radioactive solutions is of great interest for future nuclear technologies. In this direction, metastable colloidal sols of UO2 using U(IV) as precursor and carboxylic surfactants (Polyoxyethylene(9) oleyl ether carboxylic acid C16/18:1E9COOH and Polyoxyethylene(10) lauryl ether carboxylic acid C12E10COOH) have been successfully prepared by indirect precipitation for 6 pH 8 with a molar ratio between uranium and surfactant U/S < 0.3. The self-assembly of this colloidal system results in micelles and U(IV) species partitioned as different forms: U-C16/18:1E9COOH/U-C12E10COOH complexes forming multi-lamellar vesicles with interdigitated bilayers, UO2 nanocrystallites (nc-UO2) within the vesicles and nc-UO2 forming aggregates attached on the surface of the vesicles with a relative proportion of 61 %:28 %:11 %. We showed that using an amphiphilic molecule having carboxylic head group, U(IV) species can be complexed and form multi-lamellar vesicles as supporting gel. The competition between the U(IV) species complexation by surfactant molecules and their hydrolysis prevents the rapid condensation of U (1 and makes the colloidal sol-gel process controllable. The principle shown here that results in partitioning the uranium into molecules, nanoparticles and aggregates could be useful in the design of molecularly dispersed Uranium and Plutonium coming from sol-gel chemistry.