Environmental Engineering Reference
In-Depth Information
2
3
4
1
5
6
7
1
2
3
Time (min)
4
figure 14.11
Chromatographic separations using a CNT-coating column: methanol (1), ethanol (2), carbon tetrachloride (3), acetonitrile
(4), xylene (5), phenol (6) and naphthalene (7). Reproduced with permission from Ref. [39]. © ACs Publications.
to column performance; specifically, by increasing CNMs (from 3 to 6 wt%), retention and selectivity were enhanced, although
efficiency did not improve. bonding of C60 imparted a certain polarity to the siloxane phase, resulting in a column with higher
polarity than commercial sE-30 and similar to that of ov-3. To enhance FUls selectivity for separation of both polar and apolar
analytes, different stationary phases based on FUls but with mixed composition have been prepared. Crown ethers and Cds
were selected as “model modifiers” with hydrophilic and hydrophobic cavities, respectively. A synergistic effect of FUls and
crown ethers was considered to explain the complete separation of structural isomers of butanol on the C60-(dibenzo-24-C8)
sorbent, not achieved on the nonmixed phases. Also, increased retention of heterocyclic compounds containing nitrogen or
sulfur was observed. FUls coupled with Cds were prepared to separate aromatic hydrocarbons, based on the ability of Cds to
yield inclusion complexes, due to hydrophobic and stacking interactions [42, 43].
14.5.3
high-pressure liquid Chromatography
The use of CNMs for designing novel stationary phases for high-pressure liquid chromatography (HPlC) is a current trend in
analytical chemistry. The synthesis of hybrid materials is very promising, in which CNTs or FUls play the role of active modifiers
responsible for retention and selectivity, while the bulk material in which they are incorporated just acts as the support (i.e., silica),
not taking part in the separation process. This is an approach especially adopted for packed-column liquid chromatography. Also,
CNT embedment in polymeric monoliths has been undertaken by chemical and physical methods [44, 45].
However, one of the main troubles encountered in this application is the preparation of sorbent phases with suitable chemical
stability—mandatory for long-term high-quality performance in particular with regard to the chemical route used for grafting
the nanomaterials. An alternative approach is the preparation of nanostructured stationary phases. overall, it is has to be con-
sidered that the chromatographic behavior of the sorbent would be heavily affected by some major factors, such as support
particle size, porosity, homogeneity of functionalization, and nanomaterials [46].
14.6
membranes appliCations of Cnms
The natural characteristics of CNMs such as high porosity and surface area make them attractive for the preparation of mem-
branes. CNTs-based membranes have been used to distinguish between molecules based on their size; additionally, functional-
ized CNTs have been used to influence molecular transport. because of this, the fabrication of CNTs-based membranes has
dramatically increased in recent years, particularly for their use in gas separation [3]. several physicochemical studies have
