Bandgap Widening of Titania through Semiconductor Support Interactions

Abstract

Silica-supported titania powders with 50, 36, 13 and 4 wt% of TiO2 (TiO2-50/SiO2, TiO2-36/SiO2, TiO2-13/SiO2 and TiO2-4/SiO2) were prepared by hydrolysis of TiCl4 in the presence of silica, followed by calcination at 500 degrees C. The formation of Ti-O-Si linkages was confirmed by diffuse reflectance infrared Fourier transform spectroscopy. Atomic force microscopy indicated the presence of titania crystals larger than 15 nm. All supported materials exhibited a blue-shift of the TiO2 absorption edge, which was attributed to an electronic semiconductor support interaction. Bandgap energies of TiO2-50/SiO2, TiO2-36/SiO2, TiO2-13/SiO2 and TiO(2)4/SiO2 were measured to be 3.28, 3.36, 3.40 and 3.42 eV, respectively, as compared to 3.15 eV for unsupported TiO2. From these values, and from the quasi-Fermi level of electrons, a high anodic shift of both the valence and the conduction band was estimated. X-ray photoelectron spectroscopy (XPS) measurements of oxygen 1s- and titanium 2p-binding energies confirmed the anodic shift of the band edges.

Titania-Supported Gold Catalysts: Comparison between the Photochemical Phenol Oxidation and Gaseous CO Oxidation Performances

“…The results are shown in Table 2. The value obtained for the TiO 2 P25 support is 3.0, close to that reported early [32,36] . Gold catalysts have lower band gap energies, a minimum values being detected for 0.24Au/Ti sample (Fig.…”

“…5. The strong absorption observed at wavelengths lower than 400 nm is assigned to the intrinsic band gap absorption of TiO 2 [14,31,32]. The absorption edge shifts toward higher wavelengths for the gold catalysts, pointing out a decrease in the band gap energy of TiO 2 when supporting gold.…”

The solid–solid interface: Explaining the high and unique photocatalytic reactivity of TiO2-based nanocomposite materials

“…In a recent study by Kisch and co-workers, the formation of covalent Ti-O-Si linkages in silica-supported TiO 2 powders was confirmed by FT-IR spectroscopy [128]. The supported materials exhibited a blue-shift of the TiO 2 absorption edge, which was attributed to an electronic semiconductor-support interaction mediated through surface Ti-O-Si bonds.…”

“…The supported materials exhibited a blue-shift of the TiO 2 absorption edge, which was attributed to an electronic semiconductor-support interaction mediated through surface Ti-O-Si bonds. It was observed that the nanocomposite materials have lowered reducing power and, thus decreased driving force for oxygen reduction, due to the anodic shift of the conduction bands [128]. Furthermore, the researchers suggested that the charge recombination was accelerated in the silica-supported materials as compared to unsupported TiO 2 .…”

“…Furthermore, the researchers suggested that the charge recombination was accelerated in the silica-supported materials as compared to unsupported TiO 2 . Consequently, the TiO 2 materials supported on silica demonstrated lower photoactivity than unsupported TiO 2 [128]. The effect of covalent attachment on the photoredox properties of composite photocatalysts has been studied and reviewed by Kisch and coworkers in several accounts [129][130][131].…”