Pre-edge Features of Ti K-edge X-ray Absorption Near-edge Structure for the Local Structure of Sol-Gel Titanium Oxides

Abstract

Titanium K-edge X-ray absorption near-edge structure (XANES) spectroscopy is used to examine the local Ti environments in the sol, gel, and xerogels of titanium oxide prepared by a sol-gel method. The xerogels were prepared by heat treatment at 200, 300, 400, 500, and 600 degrees C (denoted xero-200, xero-300, xero-400, xero-500, and xero-600), and the xerogels were doped with Fe(II), Ni(II), and Cu(II) ions (xero-Fe, xero-Ni, and xero-Cu). The local structures of the samples are compared using the pre- and post-edge features of the XANES spectra. Further analysis of the pre-edge features using Gaussian functions provides the energy and height of each peak, and the intensity ratios between peaks. Based on the resulting data, the samples can be classified into three groups: a weak Ti-Ti interaction group, an anatase-like structure group, and an anatase group. The sol, gel, xerogel, and xero-Ni are in the weak Ti-Ti interaction group, and the xero-200, xero-Fe, and xero-Cu are in the anatase-like structure group. The remaining samples are in the anatase group.

X-ray absorption spectroscopy studies of phase transformations and amorphicity in nanotitania powder and silica–titania core–shell photocatalysts

“…According to Grunes (1983) and Farges et al (1997), the more intense A 2 and A 3 peaks are consistent with lower coordination and the absence of a centre of symmetry in a solid figure described as 'tetrahedral'. A reduction in the intensity of A 1 -A 3 at higher temperatures (673 and 873 K) matches the spectrum of the anatase (I4 1 =amd) reference and is therefore ascribed to octahedral coordination with 4 4m2 point symmetry, while from 973 K the pre-edge features gain intensity due to removal of the centre of inversion (mmm point symmetry) in rutile (P4 2 =mnm) (Matsuo et al, 2005). For the third common polymorph, brookite, the point symmetry of Ti is the identity (1); therefore, the intensity is predicted to be higher than for anatase and rutile.…”

“…The subsequent development of multiplescattering theory provided a unified treatment for both extended X-ray absorption fine structure (EXAFS) spectra and XANES, with contemporary methods including a Debye-Waller factor ( 2 ) and anharmonic corrections in EXAFS simulations providing more nearly quantitative spectral interpretations (Rehr & Albers, 2000). Recent studies of titania have emphasized the pre-edge and XANES features of 'amorphous' (Matsuo et al, 2005;Chen et al, 1997) and nanostructured forms (Yoshitake et al, 2003;Yeung et al, 2002;Ferná ndez-García et al, 2007), together with EXAFS of metal-doped titanias (Chen et al, 1997;Bryan et al, 2004;Heald et al, 2005;Li et al, 2005;Zhu et al, 2007). The titanium pre-edge and XANES regions, which arise from 1s !…”

“…3d and 1s ! 4p (Grunes, 1983;Wu et al, 1997;Farges et al, 1997) transitions, respectively, provide characteristic fingerprints of coordination number, chemical state and geometric distortions (Matsuo et al, 2005;Chen et al, 1997;Yoshitake et al, 2003;Yeung et al, 2002;Ferná ndez-García et al, 2007). In metal-doped titanias, the short-range coordination environment of the dopant can be deduced from EXAFS (Yoshitake et al, 2003;Yeung et al, 2002;Ferná ndez-García et al, 2007).…”

XAS spectra of mechanically milled TiO2

“…The ratio I A1 /I B and I A3 /I B are independent of milling time, while I A2 /I B shows an almost linear increase with milling time. A marked increase in the peak A 2 has been reported in both nanocrystalline anatase and amorphous phases of TiO 2 [5,7]. It is also observed in a perovskite PbTiO 3 that the distortion of Ti atoms from O octahedron increases the central peak [15].…”

“…They have been investigated experimentally and theoretically because of their interesting chemical and electronic properties [1][2][3][4][5][6][7][8][9][10]. X-ray absorption spectroscopy (XAS) such as x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) is one of the powerful techniques for probing these properties and the local structural environment around a specific element.…”