Stability and Size Effect of Silica Nanotube

The structure and infrared vibration of silica nanotubes with anhydrous structure (SiO2-NTs) and hydrogen-capped structure (SiO2-WNTs) were investigated using density-functional theory (DFT). It was found that the average binding energy was all the same for SiO2-WNTs with the same layer number or length. SiO2-WNTs were energetically more favorable than the SiO2-NTs and two-membered ring (2MR) molecular chains structure. The IR spectrum of 4MR-WNTs was in well accord with the experimental data, and the vibrations of oxygen atoms, which were in directions parallel or normal to the axis of nanotubes, showed a strong size effect. The results indicated that SiO2-WNTs is an appropriate structure model for one-dimensional silica nanotube.