Type of presentation: Poster

MS-10-P-2693 Investigation of the bonding behavior and chemical stability of silica-based nanotubes and their 3D mesocrystals

Dennenwaldt T.1,2, Sedlmaier S. J.1,3, Binek A.1, Schnick W.1, Scheu C.1,2
1Department of Chemistry and Center for NanoScience, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377 Munich, Germany, 2New address: Max Planck Institute for Iron Research, Max-Planck-Str. 1, 40237 Düsseldorf, Germany, 3New address: Department of Chemistry, University of Oxford, Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR, UK
t.dennenwaldt@mpie.de

Recently, we reported a template-free synthesis for amorphous silica-based nanotubes (SBNTs) through a solid-state chemistry approach.1 The SBNTs are amorphous in terms of diffraction and assemble to ordered 3D hyperbranched mesocrystals (Fig. 1). In the present study, the bonding behavior and the elemental distribution of these SBNTs were investigated at the nanoscale using energy dispersive X-ray diffraction (EDX) and electron energy loss spectroscopy (EELS) in a transmission electron microscope (TEM). The analysis of the walls and the interior of the SBNTs revealed chemical homogeneity along the SBNTs. A comparison of energy-loss near-edge structures (ELNES) of the Si-L2,3-edges of the SBNTs with the two amorphous bulk reference materials SiO2 and Si3N4 showed that the bonding situation of Si in the SBNTs is a mixture of the one in SiO2 and Si3N4 exhibiting a tetrahedral coordination with mostly O and N as bonding atoms (Fig. 2). By analyzing the low loss region of the EEL spectra the band gap energy was determined at 5.7 ± 0.2 eV and the plasmon maximum at 23 ± 0.2 eV indicating that the electronic structure of the SBNTs is indeed dominated by a mixture between SiO2 and Si3N4. In line with these results the SBNTs show a higher stability to extreme pH conditions than pure amorphous SiO2 nanotubes2 which is attributed to the incorporation of nitrogen as well as phosphorus. A correlation between nitrogen incorporation and enhancement of the basicity is known from the literature.3 The increased chemical stability of SBNTs is promising for potential applications in e.g. nanofluidic systems.

1 Sedlmaier, S. J.; Dennenwaldt, T.; Scheu, C.; Schnick, W. Template-Free Inorganic Synthesis of Silica-Based Nanotubes and Their Self-Assembly to Mesocrystals. J. Mater. Chem. 2012, 22, 15511.
2 Hu, K.-W.; Hsu, K.-C.; Yeh, C.-S. pH-Dependent Biodegradable Silica Nanotubes Derived from Gd(OH)3 Nanorods and Their Potential for Oral Drug Delivery and MR Imaging. Biomaterials 2010, 31, 6843.
3 Wang, J.; Liu, Q. Structural Change and Characterization in Nitrogen-Incorporated SBA15 Oxynitride Mesoporous Materials via Different Thermal History. Microporous Mesoporous Mater. 2005, 83, 225.

We kindly acknowledge C. Minke (Department of Chemistry, LMU) for the SEM analysis.

Fig. 1: Fig. 1. Scanning electron microscopy (SEM) images of SBNTs showing a) a 3D assembly and b) a zoom-in view of a network.

Fig. 2: Fig. 2. Comparison of the ELNES of the amorphous bulk compounds Si3N4 (blue), SiO2 (red) and of an individual SBNT (green). a) Si-L1,2,3- edges, b) N-K-edges and c) O-K-edges.