Structure Analysis of Nanotubes Synthesized from Hydrothermal Treatment on TiO2

• Main Authors: Chien-Cheng Tsai, 蔡建成
• Other Authors: Hsisheng Teng
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/54029425766614577790

博士 === 國立成功大學 === 化學工程學系碩博士班 === 93 === 　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 by the interspace region of the aggregates. The hydrothermal treatment temperature, ranging within 110-150°C, 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 m2/g at 130°C, 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 affects 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. 　We demonstrated that nanotubes synthesized from NaOH treatment on TiO2 with subsequent acid washing could proceed with repeatable crystalline-structure transformation through a simple acid/base washing step. By providing the unit cell parameters, a divalent-salt titanate (Na2Ti2O5·H2O) with layered structure was identified to be the structure formed after the NaOH treatment. With the increase of the acidity in the post-treatment acid washing, the layered titaniate transformed into nanotube through Na+/H+ substitution and eventually transformed into anatase TiO2. Crystalline-structure analysis has shown the feasibitity of this titanate/titania transformation through a simple structure rearrangement. A complete scheme for the formation and transformation of nanotubes caused by the NaOH treatment and the post-treatment washing was proposed.