Regulation of the physical characteristics of Titania nanotube aggregates synthesized from hydrothermal treatment

Titania nanotube aggregates with different porosities were prepared from hydrothermal treatment on commercial TiO2 particles in NaOH followed by HCl washing. Pore structure analysis reflects that pores of smaller sizes are mainly contributed by the nanotubes while those of larger sizes are contributed by the interspace region of the aggregates. The hydrothermal treatment temperature, ranging within 110-150 degreesC, was shown to affect not only the extent of particle-to-sheet conversion, and thus the resulting structures of the nanotubes, but also the anatase-to-rutile transformation at high temperatures. The surface area of the nanotube aggregates increases with the treatment temperature to reach a maximum of ca. 400 m(2)/g at 130 degreesC, and then decreases with further increase of the temperature. In HCl washing, both the charge-removal rate and final state of the electrostatic charges on TiO2 affect the rolling of TiO2 sheets into nanotubes. This demonstrates that the nanotube structure can be regulated by adjusting the washing condition. Selective catalytic reduction of NO with NH3 has been conducted to prove that the vast surface of the nanotube aggregates is accessible to the interacting molecules.