Unraveling the Charge State of Oxygen Vacancies in ZrO_2–x on the Basis of Synergistic Computational and Experimental Evidence

Abstract

The functional properties of metal oxide semiconductors depend on intrinsic and extrinsic defects. The population of intrinsic defects is strongly affected by the synthesis method and subsequent treatments of the material, while extrinsic defects can originate from suitable doping. Stoichiometric ZrO 2 is a nonreducible oxide with a large band gap. Therefore, controlling and modulating its defect profile to induce energy states in the band gap is the sole possibility to make it a photocatalyst responsive to visible light. We report a method, based on low temperature sol−gel synthesis coupled with treatments performed in mild conditions, to obtain undoped visible light-responsive ZrO 2−x . The electronic structure of these materials is interpreted in relation to their oxygen vacancy defect population. On the basis of a wide set of experimental measurements (X-ray photoelectron, steady-state and time-resolved photoluminescence, electron paramagnetic resonance, and UV−visible diffuse reflectance spectroscopy) and supported by density functional theory calculations, we demonstrate, for the first time, the predominance of positively charged F-center oxygen vacancies that do not give rise to Zr 3+ species.

Photocatalytic hydrogen evolution by co-catalyst-free TiO2/C bulk heterostructures synthesized under mild conditions

“…Although the formation of oxygen vacancies during annealing of TiO 2 in inert or reducing atmosphere is oen accompanied by a partial reduction of Ti 4+ , the lack of Ti 3+ signal was also observed in some reduced TiO 2Àx samples. 40 On the other hand, it was recently shown that in reduced ZrO 2Àx a distribution of neutral and charged oxygen vacancies not associated to the presence of Zr 3+ species can be obtained, 41 and a similar behavior might occur in TiO 2 .…”

Highly Carbon-Resistant Y Doped NiO–ZrOm Catalysts for Dry Reforming of Methane

“…In order to understand the reduction of ZrO 2 , the Zr 3d peak is resolved into two peaks, which is shown in Figure 1B. The peaks at about 181.4 and 182.3 eV are ascribed to Zr 3+ and Zr 4+ , respectively [35,36]. which is very hard to be reduced.…”

Spontaneous Production of Ultrastable Reactive Oxygen Species on Titanium Oxide Surfaces Modified with Organic Ligands

“…) found in metal oxides, [23,24] also play a key role in the interaction with adsorbed molecules, including O 2 or H 2 O. [25,26] Therefore, Ti 3+ is not necessarily entailed in electron trapping or can be transiently involved.…”