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Single-crystalline nanoporous Nb2O5 nanotubes.

Liu J, Xue D, Li K - Nanoscale Res Lett (2011)

Bottom Line: Dense nanopores with the diameters of several nanometers were created on the shell of Nb2O5 tubular structures, which can also retain the crystallographic orientation of Nb2O5 precursor nanorods.The present chemical etching strategy is versatile and can be extended to different-sized nanorod precursors.Furthermore, these as-obtained nanorod precursors and nanotube products can also be used as template for the fabrication of 1 D nanostructured niobates, such as LiNbO3, NaNbO3, and KNbO3.

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Affiliation: State Key Laboratory of Fine Chemicals, Department of Materials Science and Chemical Engineering, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, People's Republic of China. dfxue@dlut.edu.cn.

ABSTRACT
Single-crystalline nanoporous Nb2O5 nanotubes were fabricated by a two-step solution route, the growth of uniform single-crystalline Nb2O5 nanorods and the following ion-assisted selective dissolution along the [001] direction. Nb2O5 tubular structure was created by preferentially etching (001) crystallographic planes, which has a nearly homogeneous diameter and length. Dense nanopores with the diameters of several nanometers were created on the shell of Nb2O5 tubular structures, which can also retain the crystallographic orientation of Nb2O5 precursor nanorods. The present chemical etching strategy is versatile and can be extended to different-sized nanorod precursors. Furthermore, these as-obtained nanorod precursors and nanotube products can also be used as template for the fabrication of 1 D nanostructured niobates, such as LiNbO3, NaNbO3, and KNbO3.

No MeSH data available.


TEM characterizations of single-crystalline nanoporous Nb2O5 nanotubes: (a) low-magnification TEM image of nanoporous Nb2O5 nanotubes; (b, c) high-magnification TEM images of nanoporous Nb2O5 nanotubes showing that these nanotubes have a nanoporous shell. The inset of Figure 5b shows the SAED pattern taken from an individual nanotube indicating that these nanotubes are single-crystalline; (d) HRTEM image of the porous shell of a single nanotube revealing (001) lattice planes. The red circles indicate that the shell of these nanotubes densely distributes nanopores.
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Figure 5: TEM characterizations of single-crystalline nanoporous Nb2O5 nanotubes: (a) low-magnification TEM image of nanoporous Nb2O5 nanotubes; (b, c) high-magnification TEM images of nanoporous Nb2O5 nanotubes showing that these nanotubes have a nanoporous shell. The inset of Figure 5b shows the SAED pattern taken from an individual nanotube indicating that these nanotubes are single-crystalline; (d) HRTEM image of the porous shell of a single nanotube revealing (001) lattice planes. The red circles indicate that the shell of these nanotubes densely distributes nanopores.

Mentions: The morphology and structure of the finally nanoporous nanotubes were first evaluated by SEM observation. The representative SEM image in Figure 4a reveals the presence of abundant 1 D rod-like nanostructure, implying the finally formed nanotubes well resemble the shape and size of Nb2O5 nanorod precursors. The detailed structure information is supported by the high-magnification image shown in Figure 4b, which shows some typical nanotubes with thin walls. For accurately revealing the microstructure of these nanotubes, TEM observation was performed on these nanotubes. Figure 5a shows a typical TEM image of these special nanostructured Nb2O5. These nanotubes have a hollow cavity and two closed tips. A magnified TEM image of some Nb2O5 nanotubes is presented in Figure 5b. It can been see that the nanotube surface is highly nanoporous and coarse, composed of dense nanopores. SAED pattern obtained from them by TEM shows they are single-crystalline, as seen in the typical pattern in Figure 5b (inset). The nanoporous characterization of these single-crystalline nanotubes was further verified by a higher-magnified TEM image (Figure 5c). The single-crystalline nature of the nanotubes is further indicated by the Nb2O5 lattice which can be clearly seen in the HRTEM image of the surface of a nanoporous nanotube. Though it is difficult to directly observe by TEM, since the observed image is a two-dimensional projection of the nanotubes, Figure 5d shows dense nanopores around which the Nb2O5 lattice is continuous. The diameter of the nanopores appears to be 2-4 nm, and the growth direction of these nanoporous nanotubes is [001], just the same as nanorod precursors. During the hydrothermal process of Nb2O5 nanorod precursors, the formation of single-crystalline nanoporous nanotubes can be ascribed to preferential-etching of single-crystalline nanorods. In hydrothermal aqueous NH4F solution, HF were formed by the hydrolysis of NH4+ and were further reacted with Nb2O5 to form soluble niobic acid. The etching of nanorods in this study preferentially begins at the central site of the nanorod, which might be because the central site has high activity or defects both for growth and for etching. Further etching at the center of nanorod leads to its splitting, and the atom in the (001) planes are removed at the next process, causing the formation of the tubular structure. Furthermore, during the etching process, these newly generated soluble niobic acid diffused into the reaction solution from the central of the precursor nanorods, leaving dense nanopores on the shell of nanotubes with closed tips. For verifying such preferential-etching formation mechanism, HF solution as an etching reagent was directly adopted. Figure 6 shows the morphology and structure of Nb2O5 products, which exhibit that hollow tuber-like nanostructures can also be achieved. However, the as-obtained Nb2O5 products are broken or collapsed nanotubes, which is ascribed to the fast etching rate of HF reagent. The diameter of nanoporous nanotubes can be tunable by adjusting the diameter of precursor nanorods. We can thus obtain different diameters of Nb2O5 nanotubes, which could meet various demands of nanotubes toward practical applications. For example, when Nb2O5 nanorods with a smaller diameter (approximately 200 nm) were adopted as precursors, the corresponding Nb2O5 nanotubes with similar sized nanotubes were achieved (Figure 7).


Single-crystalline nanoporous Nb2O5 nanotubes.

Liu J, Xue D, Li K - Nanoscale Res Lett (2011)

TEM characterizations of single-crystalline nanoporous Nb2O5 nanotubes: (a) low-magnification TEM image of nanoporous Nb2O5 nanotubes; (b, c) high-magnification TEM images of nanoporous Nb2O5 nanotubes showing that these nanotubes have a nanoporous shell. The inset of Figure 5b shows the SAED pattern taken from an individual nanotube indicating that these nanotubes are single-crystalline; (d) HRTEM image of the porous shell of a single nanotube revealing (001) lattice planes. The red circles indicate that the shell of these nanotubes densely distributes nanopores.
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Figure 5: TEM characterizations of single-crystalline nanoporous Nb2O5 nanotubes: (a) low-magnification TEM image of nanoporous Nb2O5 nanotubes; (b, c) high-magnification TEM images of nanoporous Nb2O5 nanotubes showing that these nanotubes have a nanoporous shell. The inset of Figure 5b shows the SAED pattern taken from an individual nanotube indicating that these nanotubes are single-crystalline; (d) HRTEM image of the porous shell of a single nanotube revealing (001) lattice planes. The red circles indicate that the shell of these nanotubes densely distributes nanopores.
Mentions: The morphology and structure of the finally nanoporous nanotubes were first evaluated by SEM observation. The representative SEM image in Figure 4a reveals the presence of abundant 1 D rod-like nanostructure, implying the finally formed nanotubes well resemble the shape and size of Nb2O5 nanorod precursors. The detailed structure information is supported by the high-magnification image shown in Figure 4b, which shows some typical nanotubes with thin walls. For accurately revealing the microstructure of these nanotubes, TEM observation was performed on these nanotubes. Figure 5a shows a typical TEM image of these special nanostructured Nb2O5. These nanotubes have a hollow cavity and two closed tips. A magnified TEM image of some Nb2O5 nanotubes is presented in Figure 5b. It can been see that the nanotube surface is highly nanoporous and coarse, composed of dense nanopores. SAED pattern obtained from them by TEM shows they are single-crystalline, as seen in the typical pattern in Figure 5b (inset). The nanoporous characterization of these single-crystalline nanotubes was further verified by a higher-magnified TEM image (Figure 5c). The single-crystalline nature of the nanotubes is further indicated by the Nb2O5 lattice which can be clearly seen in the HRTEM image of the surface of a nanoporous nanotube. Though it is difficult to directly observe by TEM, since the observed image is a two-dimensional projection of the nanotubes, Figure 5d shows dense nanopores around which the Nb2O5 lattice is continuous. The diameter of the nanopores appears to be 2-4 nm, and the growth direction of these nanoporous nanotubes is [001], just the same as nanorod precursors. During the hydrothermal process of Nb2O5 nanorod precursors, the formation of single-crystalline nanoporous nanotubes can be ascribed to preferential-etching of single-crystalline nanorods. In hydrothermal aqueous NH4F solution, HF were formed by the hydrolysis of NH4+ and were further reacted with Nb2O5 to form soluble niobic acid. The etching of nanorods in this study preferentially begins at the central site of the nanorod, which might be because the central site has high activity or defects both for growth and for etching. Further etching at the center of nanorod leads to its splitting, and the atom in the (001) planes are removed at the next process, causing the formation of the tubular structure. Furthermore, during the etching process, these newly generated soluble niobic acid diffused into the reaction solution from the central of the precursor nanorods, leaving dense nanopores on the shell of nanotubes with closed tips. For verifying such preferential-etching formation mechanism, HF solution as an etching reagent was directly adopted. Figure 6 shows the morphology and structure of Nb2O5 products, which exhibit that hollow tuber-like nanostructures can also be achieved. However, the as-obtained Nb2O5 products are broken or collapsed nanotubes, which is ascribed to the fast etching rate of HF reagent. The diameter of nanoporous nanotubes can be tunable by adjusting the diameter of precursor nanorods. We can thus obtain different diameters of Nb2O5 nanotubes, which could meet various demands of nanotubes toward practical applications. For example, when Nb2O5 nanorods with a smaller diameter (approximately 200 nm) were adopted as precursors, the corresponding Nb2O5 nanotubes with similar sized nanotubes were achieved (Figure 7).

Bottom Line: Dense nanopores with the diameters of several nanometers were created on the shell of Nb2O5 tubular structures, which can also retain the crystallographic orientation of Nb2O5 precursor nanorods.The present chemical etching strategy is versatile and can be extended to different-sized nanorod precursors.Furthermore, these as-obtained nanorod precursors and nanotube products can also be used as template for the fabrication of 1 D nanostructured niobates, such as LiNbO3, NaNbO3, and KNbO3.

View Article: PubMed Central - HTML - PubMed

Affiliation: State Key Laboratory of Fine Chemicals, Department of Materials Science and Chemical Engineering, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, People's Republic of China. dfxue@dlut.edu.cn.

ABSTRACT
Single-crystalline nanoporous Nb2O5 nanotubes were fabricated by a two-step solution route, the growth of uniform single-crystalline Nb2O5 nanorods and the following ion-assisted selective dissolution along the [001] direction. Nb2O5 tubular structure was created by preferentially etching (001) crystallographic planes, which has a nearly homogeneous diameter and length. Dense nanopores with the diameters of several nanometers were created on the shell of Nb2O5 tubular structures, which can also retain the crystallographic orientation of Nb2O5 precursor nanorods. The present chemical etching strategy is versatile and can be extended to different-sized nanorod precursors. Furthermore, these as-obtained nanorod precursors and nanotube products can also be used as template for the fabrication of 1 D nanostructured niobates, such as LiNbO3, NaNbO3, and KNbO3.

No MeSH data available.