Hydrothermal Synthesis and Characterization of Nanorods of Various Titanates and Titanium Dioxide

摘要

The formation process of titania based nanorods during hydrothermal synthesis starting from an amorphous TiO_2 centre dot nH_2O gel has been investigated.Sodium tri-titanate (Na_2Ti_3O_7) 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 Na_2Ti_3O_7 nanorods with HCl under ultrasonic treatment promotes a complete sodium substitution and the formation of H_2Ti_3O_7 nanorods.Low-temperature annealing of the as-produced nanorods of Na_2Ti_3O_7 and H_2Ti_3O_7 leads to a loss of the layered crystal structure and the formation of nanorods of condensed framework phases-sodium hexa-titanate (Na_2Ti_6O_(13)) and metastable TiO_2-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 TiO_6 octahedra into three-dimensional frameworks.