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

The reaction of 17O-labelled water with titanium n-propoxide [Ti(OPrn)4] proceeds rapidly to produce OTi3 and OTi4 environments that can be clearly identified from 17O magic-angle spinning NMR spectra. The gel structure is highly disordered but the quadrupolar interaction is shown to be small throughout (quadrupolar coupling constant, Cq < 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. 17O NMR and electron diffraction are also used to follow the conversion of anatase to rutile.