Abstract:

Microfibrous TiO₂−sepiolite and TiO₂/SiO₂−sepiolite nanocomposites were prepared following a colloidal route based on the controlled hydrolysis of alkoxides in the presence of cetyltrimethylammonium−sepiolite gel. In this way, titanium(IV) isopropoxide and tetramethoxysilane were used as titania and silica precursors, respectively, being incorporated within the organophilic layer developed on the surface of the silicate microfibers and further hydrolyzed in this region. The hydrolysis of the precursor gives highly viscous colloidal systems leading to a spontaneous heterocoagulation process of the colloidal system. Drying and thermal treatments of the resulting gels ensure the elimination of water and organic matter, driving to the formation of TiO₂ nanoparticles homogeneously distributed on the surface of the sepiolite microfibers. The nanocomposites were characterized by chemical analyses, transmission electron microscopy, field emission scanning electron microscopy, X-ray diffraction, thermogravimetric/differential thermal analysis, and N₂ adsorption. They were tested as photocatalysts in the photo-oxidation of phenol in an aqueous medium, showing the efficiency of the anatase containing nanocomposites in the removal of this selected pollutant model molecule. Thiourea was incorporated to increase the TiO₂ anatase phase stability, improving in this manner the photocatalytic activity of the TiO₂−sepiolite nanocomposites. It has been shown that sepiolite has a positive synergistic effect on the TiO₂ photocatalysis.