Solution-phase grafting of titanium dioxide onto the pore surface of mesoporous silicates: Synthesis and structural characterization

Titanium dioxide, a large-bandgap semiconductor and versatile photocatalyst, has been grafted onto the pore surface of MCM-41 and FSM-16 (a mesoporous material derived from kanemite) by reacting TiCl4 in hexanes with the as-synthesized mesostructured silicate. The products have been extensively characterized by powder XRD, TEM, SEM, EDS, XPS, N-2 adsorption, SANS contrast matching, solid-state H-1 MAS NMR, IR, and UV-vis spectroscopies. It was found that titania forms well-dispersed isolated (TiO2)(n) clusters (n similar to 30-70) within the channel structure. These are attached to the silicate walls via Si-O-Ti bonds. A minor second phase consisting of anatase crystallites ca. 100-250 Angstrom in diameter on the external surface of the mesoporous silicate crystals was sometimes obtained. It is concluded that an organic moiety, such as the surfactant present in the pores, or a physical constraint, such as the pore walls, is necessary to prevent the creation of large TiO2 agglomerates and enable the formation of nanosized TiO2 clusters. The titania-grafted MCM-41 samples exhibited good catalytic activity for photobleaching of rhodamine-6G and for oxidation of alpha-terpineol; however, product selectivity was low.