Molecular Dynamics Simulations of Silica Nanotube： Structural and Vibrational Properties Under Different Temperatures

Four-, six-, and eight-membered ring silica nanotubes at temperatures from 300 K to 1600 K are relaxed by classical molecular dynamics simulations with three potential models. The simulation results indicate that the stability of the end rings of the three silica nanotubes gradually decreases with increase in temperature. The validity of the vibrational features of silica nanotubes is shown by the vibrational density of states. Infrared spectra on the silica nanotubes under different temperatures are investigated. A detailed assignment of each spectral peak to the corresponding vibrational mode of the three nanotubes has been addressed. The results are in good agreement with the other theoretical and experimental

Functionalization of Semi-terminated Silica Nanotubes

The semi-terminated silica nanotubes with 80-100 nm porous diameter were prepared with AI/Al2O3 （AAO） template by the sol-gel method, and then were functionalized by 3-aminopropyltriethoxysilane （APTES）. The functionalized silica nanotubes were characterized by transmission electron microscope （TEM）, fourier transform infrared spectroscopy （FT-IR）, nuclear magnetic resonance （1H-NMR and 29Si-NMR）. The results indicated that APTES was successfully functionalized onto the internal surface and the mouth of the silica nanotubes. It would provide the material base for silica nanotubes corking and delivery drug.

Cobalt catalysts supported on silica nanotubes for Fischer-Tropsch synthesis

Silica nanotubes(SNT) have been synthesized using carbon nanotubes(CNT) as a template.Silica-coated carbon nanotubes(SNT-CNT) and SNT were loaded with a cobalt catalyst for use in Fischer-Tropsch synthesis(FTS).The catalysts were prepared by incipient wetness impregnation and characterized by N2 physisorption,X-ray diffraction(XRD),hydrogen temperature programmed reduction(H2-TPR) and transmission electron microscopy(TEM).FTS performance was evaluated in a fixed-bed reactor at 493 K and 1.0 MPa.Co/CNT and Co/SNT catalysts showed higher activity than Co/SNT-CNT in FTS because of the smaller cobalt particle size,higher dispersion and stronger reducibility.The results also showed that structure of the support affects the product selectivity in FTS.The synergistic effects of cobalt particle size,catalytic activity and diffusion limitations as a consequence of its small average pore size lead to medium selectivity to C5+ hydrocarbons and CH4 over Co/SNT-CNT.On the other hand,the Co/CNT showed higher CH4 selectivity and lower C5+ selectivity than Co/SNT,due to its smaller average pore size and cobalt particle size.

A chirality indicator for the walls and the surfaces of silica nanotubes

Single-handed helical silica nanotubes were prepared according to the literature procedures,using the self-assemblies of a pair of chiral cationic low-molecular-weight gelators as the templates.A chirality indicator,4,4＇-bis（triethoxysilyl）-1,1＇-biphenyl,was developed to determine the chirality of the silica nanotubes.The chirality of the surfaces and the bulky walls of the silica nanotubes were understood from the twist of the biphenylene rings.