Synthesis and Photoactivity of Ordered Mesoporous Titania with a Semicrystalline Framework

Mesoporous titania with a high mesopore ordering and a high surface area have been synthesized by a new surfactant templating process that combined both the evaporation-induced self-assembly method and the liquid crystal templating pathway. The precipitation of titania in the hybrid mesophase is activated by an NH3 treatment. We have investigated the influence of the surfactant concentration and the surfactant/titanium precursor (TiOPr) molar ratio on the properties of mesostructured titania. The recovered materials have been characterized by SAXS measurements, nitrogen adsorption–desorption analysis, and Raman spectroscopy. Results clearly evidence that the lower the surfactant concentration, the better the mesopore ordering. The surfactant/TiOPr molar ratio also affects the structure of the recovered material. Indeed, the mesopore ordering is detected only for ratios lower than 0.0245. The optimal ratio has been found equal to 0.015. The obtained mesoporous titania exhibited high thermal stability, and the transformation of the amorphous titania walls into nanosized anatase walls occurred at 350 °C without the collapse of the mesostructure. The photocatalytic activity of the calcinated materials has been tested on the photodegradation of methyl orange. The results indicate that the photocatalytic activity considerably depends on the calcination temperature. The maximum methyl orange degradation (96% after 180 min) is observed at a calcination temperature of 450 °C. Despite the larger surface area of the materials calcinated at lower temperature, the higher degradation at a higher calcination temperature implies that crystallinity plays a major role in the photocatalytic activity.