Formation Mechanism ofH2Ti3O7Nanotubes

Formation mechanism of ${\mathrm{H}}_2{\mathrm{T}\mathrm{i}}_3{\mathrm{O}}_7$ nanotubes by single-step reaction of crystalline ${\mathrm{T}\mathrm{i}\mathrm{O}}_2$ and NaOH has been investigated via transmission electron microscopy examinations of series specimens with different reaction times and extensive ab initio calculations. It was found that the growth mechanism includes several steps. Crystalline ${\mathrm{T}\mathrm{i}\mathrm{O}}_2$ reacts with NaOH, forming a highly disordered phase, which recrystallized into some ${\mathrm{H}}_2{\mathrm{T}\mathrm{i}}_3{\mathrm{O}}_7$ thin plates. H-deficiency on the top surface leads to an asymmetrical environment for the surface ${\mathrm{T}\mathrm{i}}_3{\mathrm{O}}_7^{2-}$ layer. The calculations of the surface tension, elastic strain energy, interlayer coupling energy, and Coulomb force indicated that the asymmetrical environment is the principal driving force of the cleavage of the single sheets of ${\mathrm{H}}_2{\mathrm{T}\mathrm{i}}_3{\mathrm{O}}_7$ from the plates and the formation of the multiwall spiral nanotubes.