Synthesis of high aspect ratio titanate nanotubes

Titanate nanotubes were synthesised using a hydrothermal method in a static and a rotating autoclave (end-over-end) over a range of rotation speeds (0-20 rpm). The control of the average length of the titanate nanotubes by the speed of rotation during their synthesis was revealed. As the rotation speed was increased, longer nanotubes (more than 1 mm at 20 rpm) were produced. This phenomenon was attributed to an increase in the mass transfer, facilitating the formation of longer intermediate titanate nanosheets. Long nanotubes self-assemble, forming secondary structures without transformation into nanowires as confirmed by the high specific surface area, pore size (inner nanotubes diameter) of 3.7 nm, XRD and Raman analyses. The initial phase of dissolution of the ends of the nanotubes was observed at higher rotation speeds. Pre-sonication treatment of the suspension of TiO2 precursor in NaOH solution resulted in a slight increase in the length of the nanotubes in the static synthesis, but did not have any effect in the rotating autoclave syntheses.