Structural and Electronic Properties of Sol−Gel Titanium Oxides Studied by X-ray Absorption Spectroscopy

Abstract

X-ray absorption spectroscopy (XAS) has been used to study the local Ti environment in titania xerogel samples containing nanoparticles of different sizes. The xerogels were prepared by hydrolysis of titanium isopropoxide followed by peptization with HNO3 and size control was achieved through calcination in air at different temperatures. An amorphous precipitate obtained by hydrolysis of titanium isopropoxide prior to peptization with HNO3 has also been studied. The X-ray absorption near edge structure (XANES) of the precipitate possesses a characteristic preedge that is dominated by a transition designated as A2 at 4970.7 eV, and assigned to five coordinate Ti. This A2 component is detected in all of the studied xerogels. Its intensity decreases as the surface-to-volume ratio of the titania particles decreases, suggesting that it is associated with surface layers of the anatase particles. Other changes observed in the XANES of the xerogels as a function of particle size include broadening of 1s → np transitions in the postedge region. EXAFS shows that the smallest particles contain Ti in distorted coordination with contracted Ti−O bonds and probably reduced coordination number.

Investigation of titanium dioxide nanoparticles toxicity and uptake by plants

“…The intensity of A2 peak is related to the distortion of the octahedral TiO 6 unit, particularly the distortion observed on the surface of NP. The intensity of this peak is thus related to the size of the particle: the smaller the NP, the higher this A2 peak [15]. Meanwhile, the intensity of the A1 peak also decreases as the particle size decreases [16].…”

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.…”

Investigation of TiO2nanoparticles translocation through a Caco-2 monolayer

“…The intensity of A2 peak is related to the distorsion of the octahedral TiO6 unit, particularly the distorsion observed on the surface of NP. The intensity of this peak is thus related to the size of the particle: the smaller the diameter, the higher this A2 peak [11]. Meanwhile, the intensity of the A1 peak also decreases as the particle size decreases [12].…”