Abstract
Various morphologies of one-dimensional (1-D) nanostructured titanate materials including nanosheets, nanotubes, nanowires and nanoribbons have been synthesized by the alkaline hydrothermal method. However, the morphology and microstructure of the TiO2-derived nanostructured material are highly dependent on the preparation conditions. In this study, the effect of preparation conditions in terms of hydrothermal temperature, duration, nature of raw materials, alkaline concentration, ratios of TiO2 to caustic concentrations, washing step and post-heat treatment on the change in morphology, dimension and surface area of the nanostructured materials synthesized by conventional hydrothermal and microwave-assisted methods was systematically investigated. Three different TiO2 raw materials, Degussa P-25, ST-01 and sol-gel-derived TiO2 particles serving as the starting materials were added in 3-10 M NaOH solution at hydrothermal temperature of 60-230 □C for 1-3 d using pressure bomb system and at 90-180 □C for 1-2 h using microwave-assisted method. The morphology changed from nanoparticles/nanosheets, nanotubes, nanowires and then to nanoribbon as the hydrothermal temperatures increased from 60 to 230 □C. ST-01 has a relatively high reactivity than that of P-25 and sol-gel-derived TiO2 nanoparticle to form nanostructured material under mild conditions. In addition, the 1-D nanostructured materials have phase transformation during post-heat treatment process when calcination temperature was higher than 300 □C and the crystalline phase transferred from titanante H2Ti¬3O7¬ nanotubes to TiO2 (B) and then to anatase phase. Bandgaps of hydrothermal products have also been characterized using UV-Vis. The bandgaps of 1-D titanate nanomaterials are generally larger than TiO2 nanoparticles and increased upon increasing hydrothermal temperature. Hydrothermal products with large surface area (> 500 m2/g) have also been fabricated in this study. 1-D titanate nanomaterials have a promising potential to be applied in catalysis, gas sensor, DSSC, and biomaterial.