Synthesis and growth mechanism of titanate and titania one-dimensional nanostructures self-assembled into hollow micrometer-scale spherical aggregates

Three-dimensional, dendritic micrometer-scale spheres of alkali metal hydrogen titanate ID nanostructures (i.e., nanowires and nanotubes) have been generated using a modified hydrothermal technique in the presence of hydrogen peroxide and an alkali metal hydroxide solution. Sea-urchin-like assemblies of these ID nanostructures have been transformed into their hydrogen titanate analogues (lepidocrocite HxTi2-x/(4)square O-x/4(4) (x similar to 0.7, square: vacancy)) by neutralization as well as into their corresponding anatase TiO2 nanostructured counterparts through a moderate high-temperature annealing dehydration process without destroying the 3D hierarchical structural motif. The as-prepared hollow spheres of titanate and titania ID nanostructures have overall diameters, ranging from 0.8 to 1.2 mu m, while the interior of these aggregates are vacuous with a diameter range of 100 to 200 nm. The constituent, component titanate and TiO2 1D nanostructures have a diameter range of 7 +/- 2 nm and lengths of up to several hundred nanometers. A proposed two-stage growth mechanism of these hollow micrometer-scale spheres was supported by time-dependent scanning electron microscopy, atomic force microscopy, and inductively coupled plasma atomic emission spectrometry data. We have also demonstrated that these assemblies are active photocatalysts for the degradation of synthetic Procion Red dye under UV light illumination.