Hydrothermal synthesis and formation mechanism of the single-crystalline Bi₄Ti₃O₁₂nanosheets with dominant (010) facets

Single-crystalline bismuth-layered perovskite Bi4Ti3O12 nanosheets with a thickness of about 20 nm and a lateral size over several micrometers have been synthesized by a PVA assisted hydrothermal route. The as-prepared Bi4Ti3O12 nanosheets were characterized by means of X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy (TEM) and high-resolution TEM. The as-prepared Bi4Ti3O12 nanosheets have (010) dominated surface facets. Time-dependent experiments reveal that the layered K2Ti6O13 nanofibers formed in the initial stage of the hydrothermal treatment play a key role in the synthesis of Bi4Ti3O12. In the proceeding hydrothermal treatment, the Bi3+ ions substitute for the K+ ions in the layered K2Ti6O13 and peel off the TiO6 octahedron lamellae from the lattice of K2Ti6O13, which then serves as a template for the formation of lamellar Bi4Ti3O12 by reaction with the dehydrated Bi3+ ions. Finally, the lamellar Bi4Ti3O12 species crystallize and grow to single-crystalline Bi4Ti3O12 nanosheets under the effect of the preferential adsorption of PVA on the (010) planes. In addition, the band gap and the optoelectronic properties of the single-crystalline Bi4Ti3O12 nanosheets were investigated by measuring their UV-vis absorption and photoluminescence spectra, respectively.