Preparation and crystallization characteristics of mesoporous TiO2 and mixed oxides

Mesoporous TiO2 and mixed Ti oxides are prepared by a modified sol-gel method using a block copolymer as a mesoporous template. Calcination of the material at 400 °C for template removal is shown to induce crystallization of pure TiO2, resulting in the destruction of the original mesoporous structure and the development of larger pores (7.5 nm) as inter-particle voids. The addition of tri-, tetra- and penta-valent metals (Al, Zr and Nb) to Ti oxide in the amorphous phase in the ratio Ti : M = 1 : 2 (M = Al, Zr or Nb) increases the thermal stability of the material by elevating the crystallization temperature above that for pure TiO2. The formation of Al2TiO5, TiZr2O6 and TiNb2O7 crystal phases without phase separation is confirmed in these materials, demonstrating the homogeneous mixing of TiO2 and the additive element at the atomic level. The mixed mesoporous oxides are thermally stable at 400 °C, although the porous structure is still destroyed due to crystallization. Thus, a homogeneous mixture of Ti with another element (Al, Zr or Nb) in mesoporous amorphous Ti-mixed oxide is observed.