Surfactant-Directed Synthesis of Mesoporous Titania with Nanocrystalline Anatase Walls and Remarkable Thermal Stability

Abstract

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 °C. 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 m2 g-1) mesostructured titania having pore volumes up to 0.28 cm3 g-1. XRD and N2 adsorption−desorption data showed an outstanding thermal stability; the mesoscale order of NH3-treated titanias was retained after thermal treatment up to 600 °C.