Multi-techniques investigation of mesoporous zinc and tungsten titanates materials

Abstract

We have investigated the preparation of zinc and tungsten mesoporous titanates materials from a sol–gel method using a block copolymer as amphiphile. The mesoporous network is created through a soft templating method. Samples have been characterized by SAXS, XRD, nitrogen adsorption–desorption, XPS, TEM, EDX, Raman and UV–Vis spectroscopies. The presence of tungsten induces the formation of orthorhombic crystal phase WO3 besides the titania network and inhibits the formation of anatase, which is the predominant structure in the Zn–TiO2 materials. No trace of ZnO is detected by XRD and Raman. However XPS suggests the presence of zinc ions in the mesoporous network and their linkage with oxygen atoms. The zinc oxide could therefore either be randomly dispersed or amorphous on the material surface. XPS and EDX also reveal that the tungsten clusters are located at the surface of the tungsten mesoporous titanates. Studies of the Kubelka–Munk function showed that at low Zn content, the band gap energy is in the range of the anatase one and the photocatalytic efficiency of the corresponding zinc titanates is similar to the one of the pure titania mesoporous material. Beyond the addition of 1mol.% of tungsten, the titanates present a band gap energy in the range 2.7–2.8eV, close to the value of the orthorhombic WO3. For both kinds of titanates, the decrease of the band gap reduces their capacity for the photodegradation of methyl orange.