M. Crocker et al., H-1-NMR SPECTROSCOPY OF TITANIA - CHEMICAL-SHIFT ASSIGNMENTS FOR HYDROXY-GROUPS IN CRYSTALLINE AND AMORPHOUS FORMS OF TIO2, Journal of the Chemical Society. Faraday transactions, 92(15), 1996, pp. 2791-2798
Citations number
52
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
H-1 magnetic-angle spinning (MAS) NMR measurements have been performed
on a number of crystalline titanias, and on amorphous silica-supporte
d titania and titania-silica, with the aim of measuring the characteri
stic proton chemical shifts of hydroxy groups bound to titanias of dif
ferent crystalline form. in the case of anatase, signals observed at d
elta = 2.3 and 6.7 ppm correspond to terminal and bridging hydroxy gro
ups, the results of deuterium exchange experiments (using D2O) and IR
data supporting these assignments. For rutile, signals observed at del
ta = 2.2 and 5.3 ppm are similarly assigned. Hydroxy groups bound to a
morphous titania supported on silica (containing tetrahedrally coordin
ated Ti-IV) are found to possess a characteristic chemical shift of de
lta = 3.3 ppm. Deconvolution of H-1 NMR spectra of titania-silica (con
taining 8 wt% Ti) indicate the presence of a signal at delta approxima
te to 3.3 ppm, which is similarly assigned to hydroxy groups bound to
tetrahedrally coordinated Ti-IV, together with signals assigned to ana
tase and silanol groups. These observations are consistent with litera
ture reports indicating the presence of two main titania phases in tit
ania-silicas: an amorphous phase containing isolated Ti sites tetrahed
rally coordinated by Si-O and OH groups, and segregated nanodomains of
TiO2 (anatase or rutile).