Selective synthesis of TiO₂ polymorphs by hydrothermal method using new water-soluble titanium complexes

A panel of new stable and water soluble complexes of titanium (IV) with natural hydroxy-carboxylic acids such as citric, tartaric, lactic or glycolic acid as ligands was developed. A typical structure of these complex ions includes a peroxo-group, and a hydroxy-carboxylic acid molecule attached to the metal ion by carboxylic and hydroxylic groups to form stable species. The tight coordination and negative charge of complex ions are responsible for stability of these new compounds in water solutions in a wide range of temperatures and pH. Use of natural non-toxic ligands and ammonium as counterions make such titanium compounds convenient reagents for "green" synthesis of titanium containing materials by aqueous solution methods. The architecture of titanium complexes includes structural motifs of different polymorphic forms of TiO₂, which allows for application of these compounds as building blocks (tecton) for synthesis of titania with different crystal structures by a simple hydrothermal processes. In this way anatase, rutile, TiO₂(B) and brookite were prepared in a reproducible and highly selective way. For the first time TiO₂(B) and brookite were synthesized as single phase nano-crystals by a "one-pot" hydrothermal process, and their outstanding photo-catalytic activities were revealed.