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, N2 adsorption, SANS contrast matching, solid-state 1H MAS NMR, IR, and UV-vis spectroscopies. It was found that titania forms well-dispersed isolated (TiO2)n clusters (n ∼ 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 Å 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 α-terpineol; however, product selectivity was low.