Synthesis of novel metal alkoxides and preparation of porous oxide materials from the synthesized metal alkoxides via sol-gel technolog

Abstract

The synthesis of novel metal alkoxides and preparation of porous oxide materials using the corresponding metal alkoxide precursors have been investigated. Examples of materials synthesized on account of the versatility of the oxide one-pot synthesis process, including sodium tris(glycozirconate), cerium glycolate complex and alumatrane precursors are presented and discussed. Metal alkoxides are useful and clean oxide-precursors because alcohol groups used as ligands do not participate in subsequent processes or can be easily removed from the solution. Simple metal alkoxides with usual ligands are commercially available for a large number of metals. However alkoxides are thermodynamically unstable in aqueous solution, they usually react with water to form precipitates. Generally more hydrolytically stable metal alkoxides are in fact the reason for which the chemistry of sol-gel process could be exploited. It is known that the alkoxides inertness increases as both the size of the steric effect and the number of alcohol groups in the ligands. In this work, we focused on the use of triisopropanolamine and ethylene glycolate ligands. Our synthetic approach is based on the hydrolytic stability of the obtained products toward water. The most outstanding feature of theatranes and ethylene glycolate complexes, with respect to simple metal alkoxides, is their moisture inertness towards hydrolysis during the sol-gel process. The other contribution of this approach lies in the use of atranes and ethylene glycolate complexes as precursors to obtain porous oxides. All the porous materials reported are chemically homogeneous. In addition, the final porous oxides are unimodal pore size distributions. To obtain homogeneous nanoscale macromolecular oxide networks by the sol-gel technique, control of hydrolysis is crucial. The properties and nature of the resulting products are controlled by many factors including the chemical characteristics of particular metal alkoxide precursor employed, the solvent, acid or base content, and other processing conditions (e.g. hydrolysis ratio and temperature). Moreover, one other parameter which can be deligerately accounted for designing porous materials is the temperature of heat treatment. Too low temperature leads to incomplete decomposition of organic residues and too high temperature causes phase transformation or loss of surface areas.