Environmental Engineering Reference
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Clean CNT
Unclean CNT
Carbopack TM
Time (min)
figure 14.9 Comparison of desorption profile from different CNTs and Carbopack. Reproduced with permission from Refs. [33, 34].
© RsC Publication.
producing a high signal to noise ratio for sensors. Figure 14.9 shows the desorption profile of naphthalene from CNT, unpuri-
fied CNT, and Carbopack™. Under the same conditions, the desorption band from sWNTs was much narrower than that from
either Carbopack™ or unpurified MWNTs. The purified MWNT was similar to the sWNT and is not presented here [33].
14.5
ChromatographiC appliCations of Cnms
Most recent work deals with CNMs used as separation media in GC, and in particular in the past 15 years various research
groups have been investigating the gas chromatographic properties of FUls and CNTs. Essentially two general approaches
have been practiced, that is, their usage in packed and in capillary columns. despite the lower efficiency of the former, simplicity
in preparation made packed columns attractive for easily studying the chromatographic behavior of the selected stationary
phase. different techniques have been considered to prepare open tubular columns based on CNMs, mostly entailing Cvd or
chemicals methods, the latter widely employed especially for FUls bonded stationary phases [3, 4, 13].
14.5.1
Chromatographic stationary phases with Cnts
li and yuan were the first who tested purified MWNTs in glass columns for different classes of compounds for the GC
stationary phase. Good separation was achieved compared to graphitized carbon especially in the case of polar analytes, due to
the low content of polar groups in CNTs. The role of sorbent morphology was elucidated by an analysis of selected probes: it
was observed that for the same surface area and amount of material packed in the columns, CNTs exhibited higher adsorption
than graphitized carbon (Carbopack b) due to their higher number of sorption sites in comparison with a planar carbon surface
in spite of the higher number of theoretical plates of the graphitized packing; on the other hand, porous material such as
activated charcoal demonstrated strong retention toward aromatics, making any separation unfeasible. such findings were also
substantiated in another work where pristine and purified MWNTs were compared with activated charcoal for the separation of
light alkanes and aromatic hydrocarbons. The pristine material was HCl-treated to remove metallic impurities, as these influ-
enced surface properties such as acceptor/donor characteristics and the dispersive component of the surface energy, without
altering their original structure due to the nonoxidative nature of HCl. Results clearly showed the outstanding chromatographic
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