Abstracts

The titanium oxide nanotubes have become a very attractive material with potential applications in biomedicine, photocatalysis, energy etc. Their properties depend mostly on morphology which is relatively easy to change by controlling the conditions of the anodization like the type of electrolyte used, the voltage and the time of anodization. There is a direct linear relation between the anodization voltage and the average diameter of the formed nanotubes, as the voltage increases the diameter of nanotubes also increases [1,2].  The possibility of the preparation of nanotubes with different size, shape and wall thickness leads to the control of their geometric surface area and specific surface area, which is an important parameter in the development of new substrates for example in heterogeneous catalysis. Nanotube surface functionalization with platinum nanoparticles is a way to fabricate active material for catalysis of oxidation reaction of methanol. Such nanostructured complex materials demand advanced methods for characterization and visualization of real structure, therefore application of TEM and electron tomography techniques is desired.

In this work titania nanotubes were obtained by electrochemical oxidation of pure titanium at voltage of 10 and 25 V, that resulted in creation of TiO₂ nanotubes with 40 and 110 nm in diameter, respectively. After anodization the heat treatment was performed at 450^oC for 1h to change amorphous structure of TiO₂ nanotubes into crystalline anatase structure. A suitable amount of Pt – 0.2 mg/cm² on the surface of the nanotubes was deposited using magnetron sputtering.  FIB prepared specimens were analyzed in a Hitachi HD-2700 dedicated STEM (Scanning Transmission Electron Microscopy).

Fig. 1 shows cross-section SEM images of TiO₂ nanotubes with 0.2 mg/cm² Pt deposit on the top. The platinum nanoparticles tend to choose the edges of TiO₂ nanotubes and side walls. A high amount of Pt fills the interior of the nanotubes as shown in Fig. 1b. As nanotubes diameter increases from 40 to 110 nm the depth of deposition into nanotubes also increases (Fig. 1c). Morphology of prepared structures was characterized by scanning transmission electron microscopy tomography. This method provides three-dimensional structural information at nanoscale based on two dimensional projections acquired at different tilt angles. High angle annular dark field (HAADF) imaging was used for 2D projections. The results have shown distribution of platinum nanoparticles inside the nanotubes. The variations in platinum content introduced into different diameter nanotubes were also examined. Segmented volume of nanotubes was analyzed in terms of specific surface area and volume fraction.

References

[1] Roguska, A., Pisarek, M., Andrzejczuk, M., Dolata, M., Lewandowska, M., & Janik-Czachor, M. (2011) Materials Science and Engineering C, 31(5), 906-914

[2] M. Pisarek, A. Roguska, A. Kudelski, M. Andrzejczuk, M. Janik-Czachor, K.J. Kurzydłowski, Materials Chemistry and Physics, 139 (1), (2013) 55-65.

Acknowledgments

This work was supported by The National Science Centre through the research grant UMO-2014/13/D/ST8/03224

Figures:

Fig. 1. Cross-section STEM images of TiO2 nanotubes with 0.2 mg/cm2 Pt deposit (a) Overview HAADF-STEM image of the prepared sample with visible bright layer of platinum (b) BF-STEM image of 40 nm in diameter nanotubes with deposited Pt (c) BF-STEM image of 110 nm in diameter nanotubes with deposited Pt.

Fig. 2. STEM tomography image of 110 nm in diameter nanotubes with visible platinum deposit on the top.

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EMC Abstracts - https://emc-proceedings.com/abstract/stem-electron-tomography-of-titanium-oxide-nanotubes-surface-functionalized-by-pt-nanoparticles/