Hydrothermal synthesis and characterization of nanorods of various titanates and titanium dioxide.

The formation process of titania based nanorods during hydrothermal synthesis starting from an amorphous TiO2.nH2O gel has been investigated. Sodium tri-titanate (Na2Ti3O7) particles with a rodlike morphology were prepared by a simple hydrothermal process in the presence of a concentrated NaOH aqueous solution. The ion exchange reaction of the synthesized Na2Ti3O7 nanorods with HCl under ultrasonic treatment promotes a complete sodium substitution and the formation of H2Ti3O7 nanorods. Low-temperature annealing of the as-produced nanorods of Na2Ti3O7 and H2Ti3O7 leads to a loss of the layered crystal structure and the formation of nanorods of condensed framework phases-sodium hexa-titanate (Na2Ti6O13) and metastable TiO2-B phases, respectively. These transformations proceed without a significant change in particle morphology. The nanostructures were investigated by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), the Brunauer-Emmett-Teller (BET) method, thermogravimetric analysis (TGA), and Raman spectroscopy. The structural defects of the synthesized nanorods were investigated by high-resolution electron microscopy. The presence of planar defects can be attributed to the exfoliation of the zigzag ribbon layers into two-dimensional titanates as well as to the condensation of the layers of TiO6 octahedra into three-dimensional frameworks.