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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.


Line scans of the PL signal from the different centrifugated samples with an excitation wavelength of 569 nm, comparing the PL intensity from samples being treated by DGU (Procedure B) or not (Procedure A and D). Spectra normalized to their optical density at 900 nm. (A colour version of this figure can be viewed online.)
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f0030: Line scans of the PL signal from the different centrifugated samples with an excitation wavelength of 569 nm, comparing the PL intensity from samples being treated by DGU (Procedure B) or not (Procedure A and D). Spectra normalized to their optical density at 900 nm. (A colour version of this figure can be viewed online.)

Mentions: The follow-up question is, whether applying DGU is essential for the extraction process or if inner and outer tubes are already separated before the centrifugation process. It has been mentioned in previous works that sonication alone can lead to extraction of inner tubes from DWCNT due to simultaneous opening of the host nanotube and ’shaking’ of the DWCNT, where the inner tube is extracted since the frictional force between inner and outer tube is insignificant small [17,41]. In that case, centrifugation at high speeds without a gradient medium as in the DGU process should be sufficient to remove remaining DWCNT, bundles, etc. due to their highly different buoyancies, leaving a sample consisting only of SWCNT. These, in return, should show (at least) a similar PL intensity than the extracted tubes from the DGU process. However, this is not the case. Applying the same centrifugation technique from the HiPco SWCNT sample to the DWCNT sample (Procedure D) leads only to a minor amplification of the PL intensity when compared to the pristine DWCNT sample (Procedure A), as seen in Fig. 6.


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)

Line scans of the PL signal from the different centrifugated samples with an excitation wavelength of 569 nm, comparing the PL intensity from samples being treated by DGU (Procedure B) or not (Procedure A and D). 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

f0030: Line scans of the PL signal from the different centrifugated samples with an excitation wavelength of 569 nm, comparing the PL intensity from samples being treated by DGU (Procedure B) or not (Procedure A and D). Spectra normalized to their optical density at 900 nm. (A colour version of this figure can be viewed online.)
Mentions: The follow-up question is, whether applying DGU is essential for the extraction process or if inner and outer tubes are already separated before the centrifugation process. It has been mentioned in previous works that sonication alone can lead to extraction of inner tubes from DWCNT due to simultaneous opening of the host nanotube and ’shaking’ of the DWCNT, where the inner tube is extracted since the frictional force between inner and outer tube is insignificant small [17,41]. In that case, centrifugation at high speeds without a gradient medium as in the DGU process should be sufficient to remove remaining DWCNT, bundles, etc. due to their highly different buoyancies, leaving a sample consisting only of SWCNT. These, in return, should show (at least) a similar PL intensity than the extracted tubes from the DGU process. However, this is not the case. Applying the same centrifugation technique from the HiPco SWCNT sample to the DWCNT sample (Procedure D) leads only to a minor amplification of the PL intensity when compared to the pristine DWCNT sample (Procedure A), as seen in Fig. 6.

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.