3D visualization of TiO2 nanocrystals in mesoporous nanocomposite using energy filtered transmission electron microscopy tomography

摘要

Mesoporous silica, SBA-15, is one of the best candidate for the supporting material of catalytic nanoparticles because of its relative large and controllable pore size and large specific surface area [1]. So far, various nanoparticles, such as Au, Pt and Pd, have been introduced into the pore for catalytic application [2]. The size of nanoparticles supported inside SBA-15 is restricted by that of the pore, and they are usually ranging from 2 nm and 50 nm in space.It is necessary to anchor the nanoparticles within pores to avoid segregation / sintering of them. However, it is difficult to anchor them within pores in the case of use of deposition-precipitation method due to extreme low iso-electric point (IEP) of silica (∼2). Therefore, TiO2 nanocrystals (IEP 6-8) were then introduced to anchor AuNPs [3].In this study, EFTEM tomography was applied to examine the effectiveness of TiO2 for AuNPs. Materials and methodAu/TiO2-SBA-15 was embedded into epoxy resin for electron microscopy and microtomed to about 30 nm thickness. EFTEM-tomography was operated at 120 kV and using Ti-L ionization edge via three-window method. Prior to EFTEM, STEM-HAADF tomography was also carried out for visualizing AuNPs and for comparison. Result and discussionFigure 1 shows 3D-volume of AuNPs and TiO2 nanocrystals from EFTEM-tomography. TiO2 nanocrystals in the porous material were successfully visualized using EFTEM -tomography, and local relationship between AuNPs and TiO2 nanocrystals were revealed. A large number of TiO2 nanocrystals were randomly distributed in the SBA-15. It was found that most AuNPs were directly on the exposed TiO2 nanocrystals. It implies that TiO2 nanocrystals were exposed on the surface of the pore and anchored AuNPs inside the pores.jmicro;63/suppl_1/i27/DFU081F1F1DFU081F1Fig. 1.3D volume of AuNPs and TiO2 nanocrystals.