Defect Structures in Aluminosilicate Single-Walled Nanotubes: A Solid-State Nuclear Magnetic Resonance Investigation

We report a detailed investigation of the defect structures in aluminosilicate single-walled nanotubes via multiple advanced solid-state NMR techniques. A combination of H-1-Si-29 and H-1-Al-27 FSLG-HETCOR, H-1 CRAMPS, and H-1-Si-29 CP/MAS experiments were employed to evaluate the proton environments around Al and Si atoms in the final nanotube structure. The H-1 CRAMPS spectra of dehydrated aluminosilicate nanotubes revealed the proton environments in great detail. Integration of these results with the findings from the H-1-Si-29 and H-1-Al-27 FSLG-HETCOR and H-1-Si-29 CP/MAS data allows the structural assignment of all the chemical shifts and the identification of various types of defect structures in the aluminosilicate nanotube wall. In particular, we identify five main types of defect structures arising from specific atomic vacancies in the nanotube structure. It is estimated that similar to 16% of Si atoms in the nanotube inner wall are involved in a defect structure. The characterization of the detailed structure of the nanotube wall is expected to have significant implications for its chemical properties and applications.