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Purification of single-walled nanotubes using froth flotation.
A
method
for the purification of singlewalled carbon nanotubes (SWNTs) in four
sequential steps - oxidative pretreatment, acid treatment, silica
dissolution, and froth flotation - has been proposed by a team
from the Petroleum and Petrochemical College, Chulalongkorn University
(Bangkok, Thailand; edlinks.che.com/7368-536).
Team
leader Sumaeth Chavadej says the team used SWINTs synthesized
from the disproportionation of CO of Co-Mo/SiO2 catalyst.
The SWNTs are first oxidized at 250oC to convert
the metal catalysts into metal oxides, thereby increasing the
exposure surface. After that, the oxidized samples
are treated with HCl where 90% removal of the catalysts is achieved. In the silica
dissolution step, NaOH is applied to increase the carbon purity to 35% from
the original purity of 2.6%. Froth flotation is then used to separate the
SWNTs from silica with two surfactants: sodium dodecyl benzene sulfonate
(SDBS) and alcohol ethoxylate surfonic L24-7.
SDBS provided the highest
carbon purity, up to 69.3% at 0.5 critical micelle concentration (CMC) and
pH=5, compared with 64.8% at 0.75 CMC and pH=7 for Surfonic L24-7. The team
said under the optimum conditions with SDBS as a frother, the four
purification steps resulted in the highest purity of total carbon at 70%, and
the physical structure of the SWNTs was not damaged.
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