Bonding Behavior and Chemical Stability of Silica-Based Nanotubes and Their 3D Assembly

Abstract

Recently discovered amorphous silica-based nanotubes (SBNTs) forming 3D hyperbranched assemblies were studied with transmission electron microscopy. The chemical composition and the element distribution in these template-free synthesized SBNTs were analyzed in depth at the nanoscale with energy-dispersive X-ray and electron energy loss spectroscopy. Furthermore, the bonding behavior of the elements Si, O, N, and P was examined. The SBNTs show a better resistance to extreme pH conditions than pure amorphous silica nanotubes. This is most likely due to the incorporation of N and P in the SBNTs.

Insight in the 3D morphology of silica-based nanotubes using electron microscopy

“…Independent from the synthesis temperature and SiCl 4 precursor concentration, EDX and EELS analyses reveal that the SBNTs and the hollow particles are predominantly containing Si, O and N, whereas the flakes have a higher amount of P and N. This is in good agreement with our former study of SBNTs synthesized at a temperature of 700 °C and a low SiCl 4 precursor concentration (Dennenwaldt et al, 2014;Sedlmaier et al, 2012). Analyzing the SBNTs synthesized at different temperatures with varying amounts of SiCl 4 precursor, we found that the chemical composition averaged over all reaction products is very similar (Si : O : N : P = 28 : 40 : 25 : 3 at.%), independent from these two parameters.…”

“…Analyzing the SBNTs synthesized at different temperatures with varying amounts of SiCl 4 precursor, we found that the chemical composition averaged over all reaction products is very similar (Si : O : N : P = 28 : 40 : 25 : 3 at.%), independent from these two parameters. Also, like in previous studies the tip and walls of the SBNTs have the same chemical composition (Dennenwaldt et al, 2014;Sedlmaier et al, 2012). Electron energy-loss near-edge structure (ELNES) analysis of the Si-L 2,3 -edge in the EELS spectra of the samples prepared with a high SiCl 4 precursor concentration reveal that Si is predominantly tetrahedrally coordinated with O and N. The ELNES data of the Si-L 2,3 -edge are in good agreement with those synthesized with a low SiCl 4 precursor content.…”

“…It should be noted that around 130 eV the P-L2,3-edge occurs which overlaps with the Si-L 1 -edge. In addition to the Si-L 2,3 -edge, the ELNES of the P-L 2,3 -, N-and O-Kedges measured at SBNTs prepared by a high SiCl 4 precursor concentration do also not vary from those taken at samples synthesized with a low SiCl 4 precursor concentration (Dennenwaldt et al, 2014).…”

“…In the recently reported novel template-free approach for SBNTs phosphoryl triamide, OP(NH 2 ) 3 , (Klement and Koch, 1954) thiophosphoryl triamide, SP(NH 2 ) 3 , (Schnick, 1989) and silicon tetrachloride, SiCl 4 , were mixed under inert gas atmosphere, sealed in silica glass ampoules and heated to different temperatures ranging from 3 200 to 700 °C (Sedlmaier et al, 2012). We obtained the reaction products, flakes and NTs as well as hollow particles as side product, consisting all of Si, P, O, and N which were amorphous in X-ray and electron diffraction (Dennenwaldt et al, 2014;Sedlmaier et al, 2012). The SBNTs exhibit a bamboolike structure.…”

“…With electron energy loss spectroscopy (EELS) in the TEM on the nanoscale we found that the bonding behavior of the elements and the electronic structure of the SBNTs is a mixture of silicon dioxide (SiO 2 ) and silicon nitride (Si 3 N 4 ) (Dennenwaldt et al, 2014). Furthermore, the SBNTs show a much higher stability against bases (Dennenwaldt et al, 2014) compared to SNTs reported in the literature (Hu et al, 2010). In the present work, the 3D arrangement, the internal morphology, diameter and length of these SBNTs is elucidated with focused ion beam (FIB) microscopy, TEM and STEM-HAADF tomography and correlated to the synthesis conditions.…”