Cation-vacancy and electron-hole relaxation in single-walled aluminosilicate nanotubes: a linear-scaling Density Functional Theory study

We report a linear-scaling Density Functional Theory (DFT) study of cation-vacancy related defects in single-walled aluminosilicate nanotubes (AlSi NTs), based on the structures derived from solid-state Nuclear Magnetic Resonance.\footnote{G. Yucelen et al.,\textbf{J. Phys. Chem. C.},116, 17149, 2012} Defect geometry optimization leads to water condensation and modifications to the AlSi NT hydrogen network around the defect sites, leaving no dangling bond. Electronic structure analysis indicates that defect-states are highly localized in real-space and energy, with appearance of shallow and deep occupied defect states above the valence band (VB) edge of the pristine-NT. Electrostatic alignment of the defect states suggests energetically favourable separation of photo-generated electrons and holes on different defects, which may promote defect-centred photochemistry. The peculiar energy alignment of the defect-states is found to be qualitative unaffected by protonation of the defect-sites. These results should be a useful complement to ongoing experimental research in the potential of (alumino)silicate-based nano-porous materials for photocatalysis.\footnote{F. Sastre et al.,\textbf{J. Am. Chem. Soc.},133, 17257, 2011}.