Correlation of the Catalytic Activity for Oxidation Taking Place on Various TiO₂ Surfaces with Surface OH Groups and Surface Oxygen Vacancies

Abstract

Three catalytic oxidation reactions have been studied: The ultraviolet (UV) light induced photocatalytic decomposition of the synthetic dye sulforhodamine B (SRB) in the presence of TiO(2) nanostructures in water, together with two reactions employing Au/TiO(2) nanostructure catalysts, namely, CO oxidation in air and the decomposition of formaldehyde under visible light irradiation. Four kinds of TiO(2) nanotubes and nanorods with different phases and compositions were prepared for this study, and gold nanoparticle (Au-NP) catalysts were supported on some of these TiO(2) nanostructures (to form Au/TiO(2) catalysts). FTIR emission spectroscopy (IES) measurements provided evidence that the order of the surface OH regeneration ability of the four types of TiO(2) nanostructures studied gave the same trend as the catalytic activities of the TiO(2) nanostructures or their respective Au/TiO(2) catalysts for the three oxidation reactions. Both IES and X-ray photoelectron spectroscopy (XPS) proved that anatase TiO(2) had the strongest OH regeneration ability among the four types of TiO(2) phases or compositions. Based on these results, a model for the surface OH group generation, absorption, and activation of molecular oxygen has been proposed: The oxygen vacancies at the bridging O(2-) sites on TiO(2) surfaces dissociatively absorb water molecules to form OH groups that facilitate adsorption and activation of O(2) molecules in nearby oxygen vacancies by lowering the absorption energy of molecular O(2). A new mechanism for the photocatalytic formaldehyde decomposition with the Au/TiO(2) catalysts is also proposed, based on the photocatalytic activity of the Au-NPs under visible light. The Au-NPs absorb the light owing to the surface plasmon resonance effect and mediate the electron transfers that the reaction needs.

Liquid-Phase Cyclohexene Epoxidation with H2O2 over RuO2-Loaded Mesoporous-Assembled TiO2 Nanocrystals: Catalyst Preparation and Recyclability

“…It can also be observed that at calcination temperatures of 500 and 550°C, the surface OH density of the RuO 2 /TiO 2 (SSSG) was somewhat higher than that of the RuO 2 /TiO 2 (IWI). This evidence is in agreement with a recent study [30], which reported that anatase TiO 2 not only has high surface OH density but also has high ability to generate OH group compared to other types of TiO 2 phases.…”

Atmospheric-pressure O2 plasma treatment of Au/TiO2 catalysts for CO oxidation

“…6a and b. The fringes with a spacing of 0.23 nm could be assigned to the (1 1 1) plane of the face-centered cubic gold crystal [44,52,53]. on the low-coordinated sites (e.g., corners, edges, etc.)…”

Highly reliable bipolar resistive switching in sol-gel derived lanthanum-doped PbTiO3 thin film: Coupling with ferroelectricity?

“…The peaks correspond respectively to the perovskite lattice oxygen at 529.89 eV (pink line), the oxygen vacancies at 530.76 eV (blue line) and the surface absorbed oxygen at 532.16 eV (green line) [33][34][35][36], indicating complicated states of oxygen in the film. The abundant surface absorbed oxygen would possibly act as an absorption source to absorb water, oxygen and even other small molecules from its surroundings [37], supplementing oxygen vacancies to the film. Therefore, the XPS result evidences the existence of large amounts of oxygen vacancies on the film surface, which can provide large quantity of trapping sites for electrons and contribute to the formation of conductive filament.…”