HYDROLYSIS CONDENSATION PROCESS OF BETA-DIKETONATES-MODIFIED CERIUM(IV) ISOPROPOXIDE

Acetylacetone-modified cerium(IV) isopropoxide precursors have been synthesized and structurally characterized by means of IR and EXAFS analyses. Their hydrolysis yields colloidal dispersions and gels. The morphology of these materials was analyzed with X-ray and light-scattering techniques. The complexation ratio acac/Ce = x (acac = acetylacetonato) is a key parameter for the system. Within the complexation range x = 0-2, hydrolysis of acetylacetone-modified precursors leads to three different domains. For x < 0.15, hydrolysis leads to precipitation. For 0.15 less-than-or-equal-to x < 1, sols are obtained. The mean hydrodynamic diameter of the particles can be modulated from 450 to almost-equal-to 15 angstrom when x goes from 0.15 to 1.0. These sols slowly turn into gels even for cerium concentrations as low as 0.05 M. For 1 less-than-or-equal-to x less-than-or-equal-to 2, small oligomeric species are formed and remain stable without any gelation. A simple model is proposed to account for the size control. It is based on the variation of the functionality of the precursor, which comes from the fact that acetylacetonato ligands are not removed upon hydrolysis. Other studies on acetylacetone-modified metal alkoxides show that this model can be generalized.