Effect of preparation variables on morphology and anatase–brookite phase transition in sonication assisted hydrothermal reaction for synthesis of titanate nanostructures

The hydrothermal process coupled with sonication pretreatment has been employed to synthesize titanate nanostructures, including nanotubes and nanowires. By varying size of raw TiO2 powder (400 nm and 1 μm), reaction temperature (90–180 °C), and sonication power (0–38 W), morphology of titanate nanostructures, length of titanate nanotube, and phase of titanate nanowire could be adjusted. Transmission electron microscope (TEM), nitrogen adsorption, and X-ray diffraction (XRD) were employed to analyze structure, specific surface area, and crystalline phase of the synthesized products. The titanate nanostructures transformed from the smaller TiO2 particles provided higher specific surface area and shorter tube-length than those transformed from the larger ones. Morphology of titanate product transformed from TiO2 spherical particle to titanate nanosheet, nanotube and nanowire with the gradual increase in the reaction temperature. The surface area of the samples corresponded well with the amount of titanate nanotube (hollow) and nanowire (non-hollow), whilst the length of titanate nanotube became longer with the applying sonication pretreatment. Interestingly, the formation of brookite phase was observed for the titanate nanowire synthesized at 180 °C with sonication pretreatment.