Insights into the physicochemical aspects from natural halloysite to silica nanotubes

Silica nanotubes (SiNTs) were synthesized by acid-leaching the natural halloysite nanotubes (HNTs). Transmission electron microscopy (TEM) and scanning electron microscope (SEM) images showed that SiNTs retained the morphology of HNTs. The specific surface area (183.6 m2/g) and pore volume (0.74 cm3/g) of SiNTs were three times higher than those of HNTs, which indicated more active groups on the surface of SiNTs than HNTs. The 29Si nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR) were used to trace the variations of chemical structures. NMR spectroscopy demonstrated the disappearance of Q2 structure (Si(OSi)2(OH)2) and Q4 framework structure (Si(SiO)4), and the partial chemical shift of Q3 structure (Si(SiO)3(OH)) from HNTs to SiNTs. Photoluminescence (PL) analysis showed the higher blue PL intensity of SiNTs than that of HNTs, which indicated that the as-synthesized SiNTs could have potential application in the fields of light localization and optical devices.