Limits...
Confined conversion of CuS nanowires to CuO nanotubes by annealing-induced diffusion in nanochannels.

Mu C, He J - Nanoscale Res Lett (2011)

Bottom Line: Copper oxide (CuO) nanotubes were successfully converted from CuS nanowires embedded in anodic aluminum oxide (AAO) template by annealing-induced diffusion in a confined tube-type space.The spreading of CuO and formation of CuO layer on the nanochannel surface of AAO, and the confinement offered by AAO nanochannels play a key role in the formation of CuO nanotubes.

View Article: PubMed Central - HTML - PubMed

Affiliation: Functional Nanomaterials Laboratory and Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Zhongguancun Beiyitiao 2, Haidianqu, Beijing 100190, China. jhhe@mail.ipc.ac.cn.

ABSTRACT
Copper oxide (CuO) nanotubes were successfully converted from CuS nanowires embedded in anodic aluminum oxide (AAO) template by annealing-induced diffusion in a confined tube-type space. The spreading of CuO and formation of CuO layer on the nanochannel surface of AAO, and the confinement offered by AAO nanochannels play a key role in the formation of CuO nanotubes.

No MeSH data available.


TEM images of CuO nanowires and nanotubes obtained by annealing at 650°C for varying periods of time: (a) 1 h, (b) 4 h, (c) 10 h, and (d) 20 h. The scale bars in (a-d) are 20 nm. (e) Schematic illustration of the growth process of CuO nanotubes.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3211201&req=5

Figure 4: TEM images of CuO nanowires and nanotubes obtained by annealing at 650°C for varying periods of time: (a) 1 h, (b) 4 h, (c) 10 h, and (d) 20 h. The scale bars in (a-d) are 20 nm. (e) Schematic illustration of the growth process of CuO nanotubes.

Mentions: A hypothesis for the formation mechanism of CuO nanotubes from CuS nanowires was that, at elevated temperature, CuO was formed by oxidation of CuS, and might be spread on the pore surface of AAO template. It was previously reported that CuO could form a monolayer spontaneously on the Al2O3 surface at a temperature much lower than its melting point [18,19]. Once a CuO layer is formed on the pore surface of AAO template, further spreading of CuO would become possible, which would eventually result in the formation of CuO nanotubes. To examine this hypothesis for the formation mechanism of CuO nanotubes, CuS nanowires embedded in AAO template were annealed in muffle furnace at 650°C for varying periods of time. Figure 4a,b,c,d shows TEM images of CuO nanostructures obtained by annealing CuS nanowires embedded in AAO for 1, 4, 10, and 20 h, respectively. After 1-h annealing, the CuS nanowires of smooth surface were converted to CuO nanowires of rough surface, which consist of small aggregated CuO particles. This is in sharp contrast to the single crystal structure of precursor CuS nanowires. After annealing for 4-20 h, the CuS nanowires turned to tube-type CuO nanostructures. The wall thickness of tube-type CuO nanostructure became thinner with increase of annealing time, and for extended annealing (e.g., 20 h), the exterior surface of AAO template was found to be covered by a thin CuO layer. This clearly indicated that CuO had spread on the channel surface and exterior surface of AAO template. Figure 4e schematically illustrates the process of CuO nanotube growth. In contrast, nanowires without the support of AAO template would break under different heat-treatment conditions, leading to the formation of nanoparticles instead of nanotubes [20,21]. Thus, the spreading of CuO and formation of CuO layer on the nanochannel surface of AAO and the confinement offered by AAO nanochannels play a key role in the formation of CuO nanotubes. While the surface CuO layer acts as a nucleation center, the AAO nanochannels help the CuO nanowires maintain their 1 D morphology at elevated temperatures.


Confined conversion of CuS nanowires to CuO nanotubes by annealing-induced diffusion in nanochannels.

Mu C, He J - Nanoscale Res Lett (2011)

TEM images of CuO nanowires and nanotubes obtained by annealing at 650°C for varying periods of time: (a) 1 h, (b) 4 h, (c) 10 h, and (d) 20 h. The scale bars in (a-d) are 20 nm. (e) Schematic illustration of the growth process of CuO nanotubes.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211201&req=5

Figure 4: TEM images of CuO nanowires and nanotubes obtained by annealing at 650°C for varying periods of time: (a) 1 h, (b) 4 h, (c) 10 h, and (d) 20 h. The scale bars in (a-d) are 20 nm. (e) Schematic illustration of the growth process of CuO nanotubes.
Mentions: A hypothesis for the formation mechanism of CuO nanotubes from CuS nanowires was that, at elevated temperature, CuO was formed by oxidation of CuS, and might be spread on the pore surface of AAO template. It was previously reported that CuO could form a monolayer spontaneously on the Al2O3 surface at a temperature much lower than its melting point [18,19]. Once a CuO layer is formed on the pore surface of AAO template, further spreading of CuO would become possible, which would eventually result in the formation of CuO nanotubes. To examine this hypothesis for the formation mechanism of CuO nanotubes, CuS nanowires embedded in AAO template were annealed in muffle furnace at 650°C for varying periods of time. Figure 4a,b,c,d shows TEM images of CuO nanostructures obtained by annealing CuS nanowires embedded in AAO for 1, 4, 10, and 20 h, respectively. After 1-h annealing, the CuS nanowires of smooth surface were converted to CuO nanowires of rough surface, which consist of small aggregated CuO particles. This is in sharp contrast to the single crystal structure of precursor CuS nanowires. After annealing for 4-20 h, the CuS nanowires turned to tube-type CuO nanostructures. The wall thickness of tube-type CuO nanostructure became thinner with increase of annealing time, and for extended annealing (e.g., 20 h), the exterior surface of AAO template was found to be covered by a thin CuO layer. This clearly indicated that CuO had spread on the channel surface and exterior surface of AAO template. Figure 4e schematically illustrates the process of CuO nanotube growth. In contrast, nanowires without the support of AAO template would break under different heat-treatment conditions, leading to the formation of nanoparticles instead of nanotubes [20,21]. Thus, the spreading of CuO and formation of CuO layer on the nanochannel surface of AAO and the confinement offered by AAO nanochannels play a key role in the formation of CuO nanotubes. While the surface CuO layer acts as a nucleation center, the AAO nanochannels help the CuO nanowires maintain their 1 D morphology at elevated temperatures.

Bottom Line: Copper oxide (CuO) nanotubes were successfully converted from CuS nanowires embedded in anodic aluminum oxide (AAO) template by annealing-induced diffusion in a confined tube-type space.The spreading of CuO and formation of CuO layer on the nanochannel surface of AAO, and the confinement offered by AAO nanochannels play a key role in the formation of CuO nanotubes.

View Article: PubMed Central - HTML - PubMed

Affiliation: Functional Nanomaterials Laboratory and Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Zhongguancun Beiyitiao 2, Haidianqu, Beijing 100190, China. jhhe@mail.ipc.ac.cn.

ABSTRACT
Copper oxide (CuO) nanotubes were successfully converted from CuS nanowires embedded in anodic aluminum oxide (AAO) template by annealing-induced diffusion in a confined tube-type space. The spreading of CuO and formation of CuO layer on the nanochannel surface of AAO, and the confinement offered by AAO nanochannels play a key role in the formation of CuO nanotubes.

No MeSH data available.