TEM 3D Tomography of Noble Metal Nanowires Growth inside SiO 2 Mesoporous Aggregates
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TEM 3D Tomography of Noble Metal Nanowires Growth inside SiO2 Mesoporous Aggregates J. Arbiol 1,2, E. Rossinyol 1, A. Cabot 1, F. Peiró 1, A. Cornet 1, J. R. Morante 1 1 Enginyeria i Materials Electrònics, Departament d’Electrònica, Universitat de Barcelona, C/. Martí i Franqués, 1, Barcelona, E-08028 (Spain). 2 SCT, Universitat de Barcelona, Lluís Solé i Sabarís, 1-3, Barcelona, E-08028 (Spain). Contact e-mail: [email protected] URL: http://nun97.el.ub.es/~arbiol/ ABSTRACT The use of bright-field transmission electron microscopy 3-D tomographic reconstruction allowed us to localize the synthesized nanostructures within the pores of mesoporous nanotemplates. Using this technique, we found that noble metal impregnation resulted in the inclusion of metal nanostructures within the SBA-15 mesoporous silica hexagonal pores (from nanoclusters to nanowires). The method allowed corroborating if the nanostructures were synthesized inside the pores or if they were alternatively on the nanotemplate aggregates exterior surface.
INTRODUCTION Development of new catalytic systems by using nanostructured mesoporous materials is nowadays having much attention [1, 2]. Noble metal addition in order to modify these mesoporous materials has improved their physical and chemical properties [3-6]. One of the most used mesoporous molecular sieves (MMS) is the well-known SBA-15 matrix family, with hexagonal pores. In the present work we use SBA-15 mesoporous silica due to its long range order, large monodispersed mesopores and thicker walls, which make it more thermally and hydrothermally stable than other mesoporous materials. By selecting the growth conditions, we can control the mesoporous aggregates pore size (from 3 to 10 nm). Therefore, the final width of the noble metal nanowires synthesized inside the pores is also under control, as we use the mesoporous materials as controllable nanotemplates. Once these nanowires have been synthesized, we would like to know whether the nanowires growth has occurred inside the pores or on the aggregates external walls. At this point, it is not enough to study the 2-D morphology of these nanostructures (e.g. using conventional TEM images) in order to demonstrate that the metal nanowires grow inside the pores [7, 8, 9]. We need some extra 3D information about our materials. To solve this problem, we have used a technique rarely used in materials science such as TEM 3D Tomographic Reconstruction. In the present work, we present those 3D reconstructions demonstrating how, effectively, metal nanowires grow inside mesoporous nanotemplates.
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EXPERIMENTAL DETAILS SBA-15 mesoporous silica was synthesized following the procedure reported by Zhao et al. [10, 11] using pluronic P123 triblock copolymer (EO20PO70EO20) as the structure-directing agent. Noble metal additives were introduced into mesoporous silica by impregnation of the SBA-15 silica with 0.01M aqueous solution of palladium chloride and ammonium tetrachloroplatinate, followed by slow evaporation of water. For TEM observations, mesopo
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