Bottom-up synthesis of titanate nanoflakes with euhedral shapes by aqueous solution process

Abstract

A bottom-up synthesis of titanate nanoflakes with euhedral shapes was accomplished by an aqueous solution process. Crystal growth by bottom-up synthesis utilizing chemical reactions has a possibility to produce crystals with euhedral shapes. Close packing of nanoflakes with a euhedral shape and a uniform size in the in-plane direction would enable the fabrication of large polycrystalline nanosheet thin films. However, the bottom-up synthesis of metalate nanosheets that we have been studying is prone to yielding small and indistinct nanoflakes. In this study, it is revealed that both the removal of an amorphous phase and relatively large lateral sizes are required for the formation of euhedral shapes. The addition of organic ligands to reaction sols is useful for such a synthesis of titanate nanoflakes. The addition of lactic acid and triethanolamine yielded transparent aqueous sols containing titanium species by inhibiting the formation of insoluble amorphous phases. Moreover, the combination of triethanolamine as an organic ligand and tetrabutylammonium hydroxide as a base exhibited a high sol-state stabilization effect because of their interaction with the surface of formed titanate nanoflakes. Furthermore, further crystal growth of preformed titanate nanoflakes in a fresh reaction sol including both triethanolamine and tetrabutylammonium hydroxide provided many titanate nanoflakes with rhombic shapes, which are euhedral shapes.