Design of crystal structures, morphologies and functionalities of titanium oxide using water-soluble complexes and molecular control agents

Abstract

Nature produces materials with excellent physical and chemical properties using water as a medium under ambient temperature and pressure. The current need for more highly functional and compact materials makes the mimicking of natural processes to produce these materials a very interesting approach, not only to obtain highly functionalized materials but also to reduce the environmental impact. Our research group is engaged in the development of new stable water-soluble compounds that follow natural processes for the synthesis of materials using water as a medium. This paper summarizes a hydrothermal synthesis of rutile-type titanium oxide using water-soluble titanium complexes, controlling the crystal morphology by utilizing organic molecules as shape-control agents as well as their speculative formation mechanism and superior dielectric properties of unusually shaped titanium oxide crystals. By recapitulating our results, we indicate that control of the nano- and macro-structures and functional improvement are accomplished through the development of new precursor compounds. Titanium dioxide (TiO2) with highly controlled nano (polymorph) and macro (morphology) structures was synthesized from water by hydrothermal method using a series of unique water-soluble titanium complexes. Thanks to their high stability in water, a variety of organic molecules, which act as a shape-controlling agent, can coexist, resulting in the formation of anistropically grown rutile-type TiO2. The obtained rutile crystals exhibited greatly improved functions with respect to their dielectric or photocatalytic performance. The results suggest that the chemical design of metal-complex precursors leads to achievement of high functionalization of materials.