A study on the structure and thermal stability of titanate nanotubes as a function of sodium content

TiTanate NanoTubes (TTNT) were synthesized by hydro. thermal treatment of TiO2 anatase in 10 M NaOH at 120 degrees C followed by repeated water washing, with and without ion exchanging by HCl 0.1 M. Samples with different contents of remnant sodium in nanotubes were characterized, as synthesized and after heat-treatment, by X-ray diffraction, transmission electron microscopy, thermal analysis and N-2 adsorption. It was demonstrated that TTNT consisted of a trititanate structure with general formula NaxH2-xTi3O7 center dot nH(2)O, where 0 < x < 2 and n < 1.2, depending on the degree of proton exchange after washing. As-synthesized nanotubes retained interlayer water in its multi-walled structure. The removal of sodium reduced the amount of this intercalated water and increased the specific surface area, while thermal stability was reduced. The mechanism through which TTNT dehydrated and converted into their condensed titanates and/or TiO2 polymorphs after thermal treatment as a function of the sodium content was discussed and a schematic picture of the thermal transformations was proposed. (c) 2006 Elsevier SAS. All rights reserved.