Application of Magic-Angle Spinning NMR to Examine the Nature of Protons in Titanate Nanotubes

Systematic magic-angle spinning (MAS) 1 H NMR studies of protonated titanate nanotubes (produced by alkaline hydrothermal treatment of TiO 2 with NaOH) have revealed that there are several types of protons incorporated into their wall structure, including crystallographic water molecules and ion-exchangeable OH groups. Each type (a) has a characteristic chemical shift and (b) disappears at a different rate during annealing in air. The evolution of protons in titanate nanotubes during crystallographic and morphological transformation in the sequence H 2 Ti 3 O 7 · x H 2 O, H 2 Ti 3 O 7, H 2 Ti 6 O 13, TiO 2 (B), TiO 2 (anatase) during calcination, at temperatures from 140 to 500 °C, has been studied using MAS NMR and Raman spectroscopies together with thermogravimetric analysis (TGA), X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The irreversible disappearance of ion-exchangeable OH groups has been observed, even under low temperature treatment.