Nature of Corona in Tio2sba-15-like Mesoporous Nanocomposite

TiO2@SBA-15 mesoporous nanocomposite are of increasing interest as materials for photocatalytic applications. We report here an investigation on the characteristics of TiO2@SBA-15 prepared by introducing titanium by a grafting technique. The samples, having TiO2 loadings of 10%, have been characterized by XRF, XRD, FT-IR (CO adsorption), porosimetry, SEM, HRTEM, and UV-Visible diffuse reflectance. Three different titanium species were evidenced to be present. The first two derive from the reaction of titanium with silanol groups in the corona area of inner SBA-15 walls leading to the formation of either TiO4 tetrahedral sites (by reaction by hydroxyl nests of surface defect sites) and/or pseudo-octahedral surface sites anchored by two (or more) Si or Ti ions through bridging oxygen. The third species derives from the reaction of titanium in the regions with high sylanol density, e.g. in the micropores located in the corona of SBA-15 channels, leading to the formation of TiO2-like nanoareas with dimensions of around 1-2 nm maximum, but having characteristics different from those of crystalline titania as shown by FTIR data.