Characterisation of titania gels by 17O nuclear magnetic resonance and electron diffraction

Abstract

The reaction of '70-labelled water with titanium n-propoxide [T~(OPT")~] proceeds rapidly to produce OTi, and OTi, environments that can be clearly identified from 1 7 0 magic-angle spinning NMR spectra. The gel structure is highly disordered but the quadrupolar interaction is shown to be small throughout (quadrupolar coupling constant, C,< 1.5 MHz). Organic fragments, which can be monitored by 13C NMR, remain right up until crystallisation of anatase at 300 "C. Crystallisation is confirmed by electron diffraction, and electron microscopy determines the crystallite size to be ca. 3 nm. 170 NMR and electron diffraction are also used to follow the conversion of anatase to rutile. Keywords Sol-gel processing ; Titania ; 1 7 0 MAS NMR ; Electron diffraction Sol-gel processing is becoming increasingly important in the formation of oxide precursors for the manufacture of dense ceramics' and high-surface-area samples.2 Hydrolysis of metal alkoxides can be controlled carefully to produce very fine Paper 3/01282D;

Solid State NMR Interaction Parameters of Oxygens Linking Titanium and Silicon in Crystalline Cyclic Titanodiphenylsiloxanes

“…Hence it is extremely difficult to deconvolve these influences and interpret 29 Si MAS NMR spectra from amorphous and disordered TiO 2 -SiO 2 based materials to be able to understand the structural effects. 17 O NMR holds significant promise for characterizing the chemical environment of oxygen in such materials and probes directly Ti-O-Si linkages. Indeed, oxygen-17 (nuclear spin, I = 5/2) has already been used to study the local structure of a variety of inorganic solids (e.g., [13,14]).…”

“…Hence the coordination and bonding of oxygen can be distinguished through the 17 O isotropic chemical shift (δ iso ), which spans a large range ≈ 1500 ppm, and quadrupolar coupling parameters (C Q the quadrupole coupling constant and η the asymmetry parameter). Studies of connectivity between different metallic atoms in transition metal-oxo systems using 17 O NMR have recently been reported [15][16][17][18] but little work has been published on Si-O-Ti containing systems in the solid state [19][20][21]. The main drawback of 17 O NMR is its poor sensitivity due to its low natural abundance (0.037%).…”

A new experimental procedure to obtain titania powders as anatase phase by a sol-gel process

“…It is worth noting that the samples are crystalline as synthesized, without needing any previous or further treatment such as heating or hydrothermal aging, as observed for other sol-gel derived titania powders 7,8 . This phenomenon is probably related with the formation of TiO 3 groups, which could favour the formation of the anatase phase, with a localized structure with four edges shared by TiO 6 octahedral units, rather than the amorphous phase, with only two shared edges [9][10][11][12] . All peaks, including that one around 25°, confirm that anatase is the crystalline phase formed 7,8 .…”

A study of Li2TiOSiO4 and Li2TiOGeO4 by X-ray powder and electron single-crystal diffraction, 17O MAS NMR and O K-edge and Ti L 2,3-edge EELS

“…Four peaks can be immediately identi®ed at $40, 372, 406 and 595 parts in 10 6 . From the 17 O NMR shift data that already exist, the peak at 595 parts in 10 6 can be immediately identi®ed as rutile (Bastow et al, 1993) and the peaks at 372 and 406 parts in 10 6 as Li 2 TiO 3 . The resonance at $40 parts in 10 6 has second-order quadrupolar structure and the decrease in width from the SiÐOÐSi linkage is indicative of a nonbridging silicate unit, and given the stoichiometry is probably a lithium silicate.…”

“…Recently there have been extensive 17 O NMR studies of sol±gel produced oxides, e.g. TiO 2 (Bastow et al, 1993) and HfO 2 . One of the main advantages of NMR is that it is sensitive to short-range structure so that similar information is obtained from both crystalline and amorphous compounds.…”