Quantitative XAFS/EELS analyses of nitrogen species in titanium oxide photocatalysts

Abstract

With a view to rational designing of a highly functional visible‐light TiO2 photocatalyst, nitrogen atoms were doped into TiO2 samples by an ion implantation technique which enables to control the depth and concentration of dopants. Although the absorbance in the visible‐light region of the sample increased by the nitrogen doping, photocatalytic activity of the sample was not directly connected with the photo‐absorbance. The N K‐edge X‐ray absorption near edge structure (XANES) spectrum of the photocatalytic active sample (A‐cat) showed a characteristic double peak at 398 and 401 eV, and the XANES spectrum of the inactive sample (I‐cat) a distinct single peak around 401 eV. These features of the XANES spectra were well reproduced by theoretical simulations based on the model where an O atom in TiO2 was replaced by N ((N)s) for A‐cat, and that of quasi NO2 molecule ((NO2)s) for I‐cat. Therefore, we have concluded that the nitrogen atom occupying the oxygen site of TiO2 is photocatalytic active species effective for visible light photocatalysis. In addition, the quantitative XANES/ELNES analysis has revealed that the photo‐absorbance ratio of I‐cat to A‐cat corresponds well to the ratio of total doped nitrogen concentration rather than photocatalytic active nitrogen ((N)s) concentration. This result indicates that not only (N)s but also (NO2)s also absorb the visible light. Thus, the absorbance in the visible‐light region is not necessarily an indication of the visible‐light response of a photocatalyst.

Ion‐Implantation in Titania‐Based Plasmonic Photo‐anodes: A Review

“…Yoshida et al have researched on the photo‐catalytic decomposition of methylene blue by visible light in N implanted TiO 2 . [ 264 ] The results indicate that nitrogen implanted into TiO 2 results in attachments as Ti ((N)s) and NO 2 ((NO 2 )s), and the former is believed to dominate in the active sample, and the latter in the inactive sample. Wu et al have substantially extended the range of light harvesting of TiO 2 NW by nitrogen implantation.…”

Scrutinizing metal–ligand covalency and redox non-innocence via nitrogen K-edge X-ray absorption spectroscopy

“…There are however, studies in the literature using N K-edge energy loss near edge structures spectra to investigate N containing transition metals. This technique can enable further interpretation of features seen in the X-ray absorption near edge structure (XANES) spectra and allow for investigation of the electronic structure and bonding of these species 25–27. In addition, studies using N K-edge on solids has been shown to provide information on changes in the local structure surrounding N atoms in these materials.…”

TiOxNy/TiO2 Photocatalyst for Hydrogen Evolution under Visible Light Irradiation II Degradation of Photocatalytic Activity of TiOxNy/TiO2 with Mild Oxidation

“…The characteristic double-peaked structure appeared at around 396–402 eV in TiO x N y decreased with the oxidation temperature. Instead, a sharp single peak at 400 eV appeared which was attributed to the formation of O–N–O in TiO x N y . With higher temperature oxidation (see O X TON-673 K (2%) in Figure ), the double-peaked structure changed to the single peak.…”

“…Instead, a sharp single peak at 400 eV appeared which was attributed to the formation of O−N−O in TiO x N y . 19 With higher temperature oxidation (see O X TON-673 K (2%) in Figure 4), the double-peaked structure changed to the single peak. As N K-edge XANES in the total electron yield mode gives information on depth within 10 nm from the surface, the oxidation changed the boding of O−Ti−N near the surface of TiO x N y to O−N−O.…”