title: Purification, separation and extraction of inner tubes from double-walled carbon nanotubes by tailoring density gradient ultracentrifugation using optical probes.
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.
authors.affiliation: Faculty of Physics, University of Vienna, Strudlhofgasse 4, 1090 Wien, Austria.
authors.forename: Philip
authors.initials: P
authors.lastname: Rohringer
authors.affiliation: Faculty of Physics, University of Vienna, Strudlhofgasse 4, 1090 Wien, Austria.
authors.forename: Lei
authors.initials: L
authors.lastname: Shi
authors.affiliation: Department of Physics, Chemistry and Biology (IFM), Linköping University, 58333 Linköping, Sweden.
authors.forename: Xianjie
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Physics, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachiouji, Tokyo 192-0397, Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Yanagi
authors.affiliation: Faculty of Physics, University of Vienna, Strudlhofgasse 4, 1090 Wien, Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Pichler
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