Influence of autogeneous pressure under hydrothermal reaction on the structural and thermal stability of nanostructured titanates

Synthesis of four different morphologies of nanostructured titanates (sphere (TNS), sponge (TNSp), tube (TNT) and wire (TNW)) by hydrothermal reaction was investigated under the presence/absence of autogeneous pressure. Starting from 5 m2/g anatase TiO2 particles (com–TiO2), TNS and TNSp products with surface area >200 m2/g were obtained under atmospheric pressure at 150 and 200 °C, respectively. On the other hand, TNT (192 m2/g) and TNW (23 m2/g) were synthesized at 150 and 200 °C under autogeneous pressure in a Teflon line autoclave reactor, respectively. After annealing at 600 °C, TNS, TNSp, and TNT transformed back into anatase TiO2 but their surface areas were still much higher than the original one (60–70 m2/g). Annealing of the TNW resulted in metastable form TiO2 under similar conditions with no significant change of the surface area.