Abstract
Amorphous TiO2 nanotubes with diameters of 8-10 nm and length of several nanometers were synthesized by high pressure treatment of anatase TiO2 nanotubes. The structural phase transitions of anatase TiO2 nanotubes were investigated by using in-situ high-pressure synchrotron X-ray diffraction (XRD) method. The starting anatase structure is stable up to ∼20GPa, and transforms into a high-density amorphous (HDA) form at higher pressure. Pressure-modified high- to low-density transition was observed in the amorphous form upon decompression. The pressure-induced amorphization and polyamorphism are in good agreement with the previous results in ultrafine TiO2 nanoparticles and nanoribbons. The relationship between the LDA form and α-PbO2 phase was revealed by high-resolution transmission electron microscopy (HRTEM) study. In addition, the bulk modulus (B0 = 158 GPa) of the anatase TiO2 nanotubes is smaller than those of the corresponding bulks and nanoparticles (180-240 GPa). We suggest that the unique open-ended nanotube morphology and nanosize play important roles in the high pressure phase transition of TiO2 nanotubes.
Highlights
Nanotubes have attracted considerable attention because of their interesting electronic, mechanical, and structural properties.[1,2,3] Among the different classes of nanotubes, TiO2 nanotube is one of the most typical model which exhibit promising applications in photocatalysis, gas sensors, lithium-ions battery, and so on.[3,4,5,6] Highly ordered transparent TiO2 nanotube arrays showed superior electron lifetimes and provided excellent pathways for electron percolation in dye-sensitized solar cells.[7]
There exist a number of defects in the nanotubes that maybe caused by the dehydration process of the heat treatment during the transition from the intermediate hydrogen titanate nanotubes to the anatase TiO2 nanotubes.[24]
We suggest that the reduced bulk modulus of nanotubes can be attributed to their nanotube morphology in which the large shell spacing maybe plays an important role in the high pressure phase transition
Summary
Nanotubes have attracted considerable attention because of their interesting electronic, mechanical, and structural properties.[1,2,3] Among the different classes of nanotubes, TiO2 nanotube is one of the most typical model which exhibit promising applications in photocatalysis, gas sensors, lithium-ions battery, and so on.[3,4,5,6] Highly ordered transparent TiO2 nanotube arrays showed superior electron lifetimes and provided excellent pathways for electron percolation in dye-sensitized solar cells.[7]. Amorphous nanomaterials exhibited interesting physicochemical properties and attracted more and more attention. High pressure provides a potential route for preparing nanostructured amorphous materials from the corresponding crystal nanomaterials by using their pressure-induced amorphization. TiO2 nanomaterials show unique size- and morphology-dependent phase transition behaviors under high pressure, especially for their pressure-induced amorphization in ultrafine nanoparticles[19,20,21] and nanostructures.[13] This motivates us to study the phase transition behaviors and synthesize amorphous TiO2 nanotubes under high pressure. The high pressure behaviors of the TiO2 nanotubes were studied by in-situ highpressure synchrotron XRD and HRTEM techniques. We discussed the effects of morphology and size on the high pressure phase transition behaviors for the TiO2 nanotubes
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