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Structural and morphological investigations of titanate nanotubes modified for catalytic applications

Titanium dioxide (TiO2) is one of the most important transition metal oxides for sustainable energy and other environmental applications. Its remarkable chemical and physical properties, biological inertness, non-toxicity, photostability and cost effectiveness commend it for use for photocatalysts as well as for gas sensors, photochromic devices and dye-sensitized TiO2 solar cells. Generally, a large specific surface area is crucial to achieve high photocatalytic activities. Nanotubes have a particular advantage in the way they achieve high surface areas with three- dimensional mechanically coherent architectures that provide gas and radiation access. We studied modified and doped titanate nanotubes for application in catalysis. The aim is to prepare doped titanate nanoutubes with ferromagnetic properties for easier manipulation with the nanostructure and use them as the catalyst carrier. Catalytic properties can be achieved by modification of nanotubes’ surface. In this work magnetic material was inbuilt in the structure of the titanate nanotubes by doping. On the other hand, the surface of nanotubes is modified for catalyst carrier. We studied the stability of doped and modified nanotubes with the aim of further processing. Titanate nanotubes (TiNT-H) were synthesized by hydrothermal method. Doped titanate nanotubes (Fig. 1a) were synthesized by treating H2Ti3O7 nanotubes with NiSO4 solution. Chemical modification of TiNT-H surface was performed through the reaction of surface –OH groups with (3-aminopropyl) triethoxy silane (APTES) (Fig. 2a). The structure and morphology of surface modified and doped nanotubes were studied by transmission electron microscopy (TEM) and Raman spectroscopy. High temperature behavior and structural changes was examined by in situ at high temperature by Raman spectroscopy. It was observed that the structure of TNT- H was not distorted during processing the by NiSO4, but the nanotubes were occasionally stacked together in the bundles (Fig. 1b). It could be clearly observed that some nanoparticles of Ni were inbuilt inside the nanotubes. TEM images indicate that the morphology of the nanotubes was not changed during the modification (Fig. 2b), while the observation of the CH stretching region and the NH2 scissoring mode of vibration [1] in the Raman spectrum (Fig. 2c) prove that the nanotubes were successfully modified by APTES. During in situ Raman spectroscopy of modified nanotubes we observed that hydrogen titanate crystal structure were stable up to 400 °C, while the organic part starts to decompose at temperatures higher than 150 °C. We were successfully doped and modified titanate nanotubes, while the next step will be the modification of doped nanotubes by APTES and attachment of the catalyst. Reference: [1] L. Bistričić, V. Volovšek, V. Danačić, I. Movre Šapić, Spectrochimica Acta A 2006 ; 64: 327- 337.

titanate nanotubes; hydrothermal synthesis; surface modification; catalytic applications

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