Facile preparation of transparent monolithic titania gels utilizing a chelating ligand and mineral salts

Highly homogeneous transparent titania gels have been successfully prepared from titanium alkoxide by a sol–gel method utilizing chelating agent, ethyl acetylacetate (EtAcAc), in the presence of strong acid anions. Only catalytic amount of a strong acid anion suppress the rapid hydrolysis of titanium alkoxide by blocking the nucleophilic attack of HO⁻ and H₂O, and the resultant moderate sol–gel reactions thus afford homogeneous gelation, leading to transparent monolithic titania gels. Gelation time can be widely controlled by changing amounts of water, chelating agent and salt. The ability of salts to suppress the too abrupt sol–gel reactions is strongly dependent on the electronegativity of anions and valence of cations. With employing NH₄NO₃ as a suppressing electrolyte, the obtained titania gels can be converted to pure TiO₂ by simple washing and heat-treatment, and transformations to anatase and rutile structures were found to start at 400 and 600 °C, respectively.