Hydrothermal Stability of Ordered Surfactant-Templated Titania

In this study, we have investigated the hydrothermal stability of mesostructured titania having either amorphous or nanocrystalline walls. On the basis of Raman, XRD, and N-2 adsorption-desorption analysis, we have shown that the alteration of the mesostructure is mainly due to the appearance or the growth of anatase particles during the treatment into boiling water. Transformation of amorphous TiO2 into the anatase nuclei is catalyzed by water, which adsorbs to the titania surface to form bridges between surface OH groups of different octaedra. Then, the growth of the nuclei leads to a progressive loss of the mesopore ordering, which is accompanied by a decrease in the specific surface area. Consequently, the growth of the anatase particles involves a complete collapse of the mesostructure. A comparison of the characteristics of the materials with amorphous and nanocrystalline walls also provides evidence that the latter are more stable when treated with boiling water. Finally, the photocatalytic activity of the two kinds of titania materials, after different immersion times into boiling water, has been also tested on the photodegradation of methyl orange.