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Purification, separation and extraction of inner tubes from double-walled carbon nanotubes by tailoring density gradient ultracentrifugation using optical probes.

Rohringer P, Shi L, Liu X, Yanagi K, Pichler T - Carbon N Y (2014)

Bottom Line: We found that by using a low sonication intensity before applying density gradient ultracentrifugation (DGU), only inner tube species with a diameter [Formula: see text]0.8 nm can be identified in absorption measurements.This is in stark contrast to the result after sonicating at higher intensities, where also bigger inner tubes can be found.This can be explained by extraction of inner tubes from their host outer tubes in a two-stage process: the different shearing forces from the sonication treatments result in some DWCNT to be opened, whereas others stay uncut.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Physics, University of Vienna, Strudlhofgasse 4, 1090 Wien, Austria.

ABSTRACT

We studied the effect of varying sonication and centrifugation parameters on double-walled carbon nanotubes (DWCNT) by measuring optical absorption and photoluminescence (PL) of the samples. We found that by using a low sonication intensity before applying density gradient ultracentrifugation (DGU), only inner tube species with a diameter [Formula: see text]0.8 nm can be identified in absorption measurements. This is in stark contrast to the result after sonicating at higher intensities, where also bigger inner tubes can be found. Furthermore, by comparing PL properties of samples centrifugated either with or without a gradient medium, we found that applying DGU greatly enhances the PL intensity, whereas centrifugation at even higher speeds but without a gradient medium results in lower intensities. This can be explained by extraction of inner tubes from their host outer tubes in a two-stage process: the different shearing forces from the sonication treatments result in some DWCNT to be opened, whereas others stay uncut. A subsequent application of DGU leads to the extraction of the inner tubes or not if the host nanotube stayed uncut or no gradient medium was used. This work shows a pathway to avoid this phenomenon to unravel the intrinsic PL from inner tubes of DWCNT.

No MeSH data available.


PL Line scans at two different excitation wavelengths for the DWCNT sample from Procedure A. Spectra normalized to their optical density at 900 nm. (A colour version of this figure can be viewed online.)
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f0010: PL Line scans at two different excitation wavelengths for the DWCNT sample from Procedure A. Spectra normalized to their optical density at 900 nm. (A colour version of this figure can be viewed online.)

Mentions: For checking the abundance of different species in the DWCNT sample, photoluminescence spectroscopy was performed. Fig. 2 shows the line scans of the DWCNT sample from Procedure A at two different excitation wavelengths, namely 569 nm to excite inner tubes with smaller diameter and 660 nm for bigger diameter inner tubes. The PL response shows that the line scans cover all non-zigzag semiconducting nanotube species with a diameter between 0.65 and 1 nm as also seen by Bachilo et al. [33] (PL emission of zigzag tubes could not be resolved which is most likely due to their lower PL quantum yield compared to semiconducting species with bigger chiral angles [34–36]). We also measured the Raman signal of this solution that gave us the same results as Kim et al. obtained while investigating on dispersed DWCNT [22] and additionally, the sample from Procedure A showed a much lower PL intensity when compared to the SWCNT reference sample (not shown). Combined with the result from the optical absorption measurement this highlights that the mild centrifugation from Procedure A is not affecting the diameter-distribution of inner and outer tubes within the sample and we can see no possible extraction of inner tubes.


Purification, separation and extraction of inner tubes from double-walled carbon nanotubes by tailoring density gradient ultracentrifugation using optical probes.

Rohringer P, Shi L, Liu X, Yanagi K, Pichler T - Carbon N Y (2014)

PL Line scans at two different excitation wavelengths for the DWCNT sample from Procedure A. Spectra normalized to their optical density at 900 nm. (A colour version of this figure can be viewed online.)
© Copyright Policy - CC BY-NC-ND
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4375560&req=5

f0010: PL Line scans at two different excitation wavelengths for the DWCNT sample from Procedure A. Spectra normalized to their optical density at 900 nm. (A colour version of this figure can be viewed online.)
Mentions: For checking the abundance of different species in the DWCNT sample, photoluminescence spectroscopy was performed. Fig. 2 shows the line scans of the DWCNT sample from Procedure A at two different excitation wavelengths, namely 569 nm to excite inner tubes with smaller diameter and 660 nm for bigger diameter inner tubes. The PL response shows that the line scans cover all non-zigzag semiconducting nanotube species with a diameter between 0.65 and 1 nm as also seen by Bachilo et al. [33] (PL emission of zigzag tubes could not be resolved which is most likely due to their lower PL quantum yield compared to semiconducting species with bigger chiral angles [34–36]). We also measured the Raman signal of this solution that gave us the same results as Kim et al. obtained while investigating on dispersed DWCNT [22] and additionally, the sample from Procedure A showed a much lower PL intensity when compared to the SWCNT reference sample (not shown). Combined with the result from the optical absorption measurement this highlights that the mild centrifugation from Procedure A is not affecting the diameter-distribution of inner and outer tubes within the sample and we can see no possible extraction of inner tubes.

Bottom Line: We found that by using a low sonication intensity before applying density gradient ultracentrifugation (DGU), only inner tube species with a diameter [Formula: see text]0.8 nm can be identified in absorption measurements.This is in stark contrast to the result after sonicating at higher intensities, where also bigger inner tubes can be found.This can be explained by extraction of inner tubes from their host outer tubes in a two-stage process: the different shearing forces from the sonication treatments result in some DWCNT to be opened, whereas others stay uncut.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Physics, University of Vienna, Strudlhofgasse 4, 1090 Wien, Austria.

ABSTRACT

We studied the effect of varying sonication and centrifugation parameters on double-walled carbon nanotubes (DWCNT) by measuring optical absorption and photoluminescence (PL) of the samples. We found that by using a low sonication intensity before applying density gradient ultracentrifugation (DGU), only inner tube species with a diameter [Formula: see text]0.8 nm can be identified in absorption measurements. This is in stark contrast to the result after sonicating at higher intensities, where also bigger inner tubes can be found. Furthermore, by comparing PL properties of samples centrifugated either with or without a gradient medium, we found that applying DGU greatly enhances the PL intensity, whereas centrifugation at even higher speeds but without a gradient medium results in lower intensities. This can be explained by extraction of inner tubes from their host outer tubes in a two-stage process: the different shearing forces from the sonication treatments result in some DWCNT to be opened, whereas others stay uncut. A subsequent application of DGU leads to the extraction of the inner tubes or not if the host nanotube stayed uncut or no gradient medium was used. This work shows a pathway to avoid this phenomenon to unravel the intrinsic PL from inner tubes of DWCNT.

No MeSH data available.