Surfactant-directed synthesis of mesoporous titania with nanocrystalline anatase walls and remarkable thermal stability

A synthesis route to mesoporous titania with remarkable thermal stability was developed using an amine or cetyltrimethylammonium-templating procedure. By a treatment of the titania hybrids in aqueous ammonia, a method has been developed to overcome the lack of thermal stability above 350 degreesC. As for most mesoporous titanias described in the literature, this thermal instability originates from the uncontrolled phase transformation of amorphous template-free titania into massive anatase grains. In situ Raman spectroscopy, X-ray Diffraction, Differential Scanning Calorimetry and Thermogravimetrical Analysis demonstrated that parts of the amorphous titania walls of the NH3-treated titania hybrids were transferred into walls built up of rutile nanobuilding blocks before the template was thermally removed. We further found that, after a subsequent increase of temperature to remove the template, the remaining amorphous particles were transformed into anatase in such a way that this crystallographic transformation is accompanied by a retention of the pore structure without massive segregation of anatase nuclei. This leads to ordered high surface area (up to 600 m(2) g(-1)) mesostructured titania having pore volumes up to 0.28 cm(3) g(-1). XRD and N-2 adsorption:-desorption data showed an outstanding thermal stability; the mesoscale order of NH3-treated titanias was retained after thermal treatment up to 600 degreesC.