Bottom-Up Synthesis of Titanate Nanosheets in Aqueous Sols and Their Morphology Change by the Addition of Organic Ligands and Dialysis

The size, shape, and stacking of titanate nanosheets synthesized by heating aqueous mixtures of titanium complexes and tetrabutylammonium hydroxide were dependent on the type and amount of organic ligands and the amount of tetrabutylammonium ion (TBA+). When titanium isopropoxide was used as the titanium source, most titanate crystals were smaller than 10 nm in lateral size. However, the use of titanium complexes provided a lateral size of about 100 nm. The titanate crystals were synthesized by the acid-base reaction of titanic acid and TBAOH. The decrease in titanic acid concentration by titanium complex formation led to larger titanate crystals by the inhibition of crystal nucleation. Moreover, the use of triethanolamine and lactic acid as an organic ligand provided round and hexagonal titanate crystals, respectively. However, when the concentration of organic ligands was decreased by the dialysis of the titanate sols, the form of titanate crystals was changed to a rhombic shape. Thus, the adsorption of organic ligands on the titanate crystals probably influenced the shape of the titanate crystals. Furthermore, the decrease in TBA+ concentration by the dialysis of the sols inhibited the stacking of the titanate nanosheets during the evaporation of the sols.