Nanotube filters

Nanotubes can also be filled with a variety of molecules to create nanometre-scale filters. These filters can be used to remove bacteria and viruses from water including the poliovirus, which is less than 30 nm in diameter [966,967]. Nanotube filters made from carbon have the disadvantage of being more brittle, but have the advantage of being much more heat-resistant (they can be autoclaved) when compared with conventional polymer or cellulose filters [966]. In addition to water purification, nanotube filters can be used to separate components from mixtures of organic compounds [966]. 

Carbon Nanotube Filter Membranes and Modulation of Enzyme Activity through Mechanical... 

Quickly remove excess detergent by filtration on a 0.2 pm filter and washing the modified nanotubes with water. 

Double-stranded RNA (dsRNA) in yeast, 26 451—452 Double-stranded RNA viruses, 3 135 Double-suction pumps, 21 60, 63 Double tipping pan vacuum filter, 11 352 Double titration method, 15 145 Double vacuum-arc remelting (VAR), in titanium sponge consolidation, 24 854 Double wall nanotubes (DWNT), 26 737 Double-wall tanks, 24 296 Doubly smart block copolymers,... 

Shen X, Sun L, Benassi E et al (2010) Spin filter effect of manganese phthalocyanine contacted with single-walled carbon nanotube electrodes. J Chem Phys 132 054703/ 1-054703/6... 

Example 7.8. Steinhart et al. [288] used the formation of a precursor film to fabricate nanotubes of polymers. For this purpose a porous alumina filter with cylindrical holes of defined size is brought into contact with a polymer melt (Fig. 7.17). This is done at a temperature, where the polymer is liquid, which is significantly above room temperature. The precursor film of the polymer wets the walls of the pores within, typically a few seconds. Before the pores are filled completely the filter is removed from the melt, the sample is cooled to room temperature, and the filter material is dissolved in potassium hydroxide. 

Figure 7.17 Nanotubes fabricated by letting a precursor film of polystyrol enter the cylindrical pores of filter [288], A schematic of the two main steps in the fabrication process (left) and a scanning electron microscope image (right) are shown. Thanks to M. Steinhard for providing us with the picture.

In addition to fluorescence, radioisotope tracing and physical methods (e.g., microscopy) are also effective techniques for the imaging of carbon nanotubes in vitro and in vivo.100 103 For example, Porter et al. directly visualized individual SWNTs in cells through a new technique called low-loss energy-filtered transmission... 

A 200-fold excess of freshly prepared and filtered (Celite) solution of the nucleophilic carbene dipyridylimidazolidene was added to a dispersion of SWCNTs in THF at -60 °C. After stirring at -60 °C for 3 h, the reaction mixture was slowly warmed to room temperature and then diluted with ethanol. The precipitated functionalized nanotubes were isolated by centrifugation and washed with ethanol [148],... 

The wrapping process is typically carried out in liquid medium a PEI chloroform solution (1.5% w/w) is mixed with the SWCNTs under intense stirring. The blend is then treated with an ultrasonic tip for 1 h at 50% oscillation amplitude and 50% cycle time. The resulting dispersion is subsequently filtered using a 0.2 pm pore size PTFE membrane and dried under vacuum at 60°C to assure total evaporation of the solvent. The wrapped SWCNTs can be characterized by different techniques, and some results are included in Table 10.1. Figure 10.5 shows TEM images of acid-treated SWCNTs dispersed in the compatibilizer. Small nanotube bundles shrouded in PEI can be visualized in the micrographs. 

Niu Z, Fang Y (2006) Surface-enhanced Raman scattering of single-walled carbon nanotubes on silver-coated and gold-coated filter paper. J Colloid Interface Sci 303 224-228... 

Multi-walled nanotubes can also be ultrasonically dispersed in a liquid and made soluble with a surface active agent (surfactant) to inhibit coalescence. The resulting suspension is drawn through a filter to remove smaller particles and the remaining material consists of reasonably purified intact nanotubes. The surfactant is then washed off [119]. 

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