Environmental Engineering Reference
In-Depth Information
8.5.3
vertically aligned Cnt membranes
Vertically aligned CNT membranes are composed of highly organized CNTs arranged in a vertical orientation. Among CNT-
based membranes, those that are vertically aligned fully exploit the advantages of the inner cavity of CNTs as flow channels.
However, obtaining high-quality CNTs in vertical arrays poses a significant challenge in the production of vertically aligned
CNT membranes. To date, most vertically aligned CNTs are produced by CVD, where forests of aligned CNTs are grown on
either a silicon or a quartz substrate [83]. Normally, these vertically aligned CNTs are highly porous because of the interstitial
space between individual CNTs and their lumina. Interstitial spaces between CNT arrays are commonly filled with an imper-
meable material by infiltration or spin coating that forms a continuous matrix. Subsequently, the excess matrix material and
substrate are removed, and the CNT tips are uncapped through plasma chemistry [112]. The resultant CNT-based membrane
has a near-unity tortuosity factor, which suggests the presence of straight pores [119]. The procedure of producing vertically
aligned CNT membranes is illustrated in FigureĀ 8.5.
Since the introduction of the first prototype of vertically aligned CNT membranes by Hind et al. [120], a number of
researchers have envisioned their potential in water technology development. The measured water flow rates across vertically
Step 1
Step 2
Step 3
fiGure 8.5 Schematic of the general approach to producing vertically aligned carbon nanotube (CNT) membranes [112]. Step 1: Forest
vertical arrays of CNTs are grown on a substrate. Step 2: The interstitial spaces between CNTs are filled matrix material. Step 3: The substrate
is removed and the CNT termini are uncapped.
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