Surface-coated CNTs

An alternative efficient approach to disperse CNTs relies on the use of synthetic peptides. Peptides were designed to coat and solubilise the CNTs by exploiting a noncovalent interaction between the hydrophobic face of amphiphilic helical peptides and the graphitic surface of CNTs (Dieckmann et al., 2003 Zoibas et al., 2004 Dalton et al., 2004 Arnold et al., 2005). Peptides showed also selective affinity for CNTs and therefore may provide them with specifically labelled chemical handles (Wang et al., 2003). Other biomolecules, such as Gum Arabic (GA) (Bandyopadhyaya et al., 2002), salmon sperm DNA, chondroitin sulphate sodium salt and chitosan (Zhang et al., 2004 Moulton et al., 2005), were selected as surfactants to disperse CNTs (Scheme 2.1). 

The effects of size surface area, shape, purity method of synthesis, charge, surface coating, functionalized groups, and aggregation need to be carefully considered when assessing potential risks of CNT toxicity. Toxicology studies on CNTs should be accompanied by improved control in manufacturing and improved analysis before CNTs can be successfully used for pharmaceutical applications. 

Electrostatic interactions have recently been exploited for the synthesis of gra-phene-CNT hybrids. For example, poly(ethyleneimine) (PEI) coated graphene has been mixed with acid treated CNTs in a layer-by-layer method to form high surface area electrodes for supercapacitors [90]. Furthermore, Lu et al. prepared a supercapacitor electrode by mixing PDDA coated CNT-Mn02 hybrid with RGO [91]. 

In the case of MnO/ ( it is known to reduce on the surface of CNTs and graphene spontaneously to produce Mn02 NPs [182,183]. Solvothermal assisted precipitation of metal oxides can occur in milder solutions [184]. For example, mixed metal oxide NPs of CoFe204 have been deposited on GO from metallic salt precursors via the addition of ethanolamine followed by incubation at 180 °C in a sealed vessel [185]. Mixing GO with Cd2+ in DMSO followed by solvothermal treatment has been shown to both reduce GO to RGO and coat with CdS QDs [186]. 

Fig. 12 An electronic device based on a single rolled-up sheet of carbon atoms. (From Ref. () In the figure, a CNT (red about 1 nm in diameter) bridges two closely spaced (400 nm apart) platinum electrodes (labeled source and drain) atop a silicon surface coated with an insulating silicon oxide layer. Applying an electric field to the silicon (via a gate electrode, not shown) turns on and off the fiow of current across the nanotube, by controlling the movement of charge carriers onto the nanotube. (View this art in color at www.dekker.com.)...

In overall, the use of polymer-coated CNTs produced by in situ polymerisation, whether by covalent or non-covalent methods leads to the production of polymer nanocomposites displaying much better thermomechanical, flame retardant and electrical conductive properties, even at very low nanotube loadings. As mentioned above, the covalent approach allows the formation of a strong interface between the nanotube and polymer matrix due to strong chemical bonding of polymer molecules to the CNT surface. The in situ polymerisation technique also enables the preparation of composites with very high nanotube loadings. 

Researches have decorated CNT with CHT by surface deposition and crosslinking processes. In this method, the CHT macromolecules as polymer cationic surfactants were adsorbed onto the CNT surface. In this step, a stable dispersion of CNT was formed in an acidic aqueous solution of CHT. The pH value of the system was increased by ammonia solution, and so the CHT could no longer remain in solution. Consequently, the precipitated CHT was deposited on the surface of CNT to form a CHT coating. Finally, the surface-deposited CHT was crosslinked to CNT by glutaraldehyde, for potential applications of this composite in biosensing, gene and drug delivery. 

PEM fuel cells require catalysts for both cathode as well as anode reactions. Platinum nanoparticles are the conventionally used catalysts. Conventionally, Pt-nanoparticles are dispersed on a support material such as carbon black. The support material should have properties such as high-electronic conductivity, surface area and corrosion resistance. CNTs, owing to their superior properties, can provide superior performance as catalyst support. Superior cell performance and lifetime have been reported for Pt-nanoparticles-coated CNTs catalyst layers [160-162]. In addition, the presence of CNTs in the catalyst layer provides superior connectivity and easy charge transport. The requirement of high cost catalysts (platinum and its alloys) for both cathodic and anodic reactions makes them unsuitable for commercial applications. Development of efficient catalysts with reduced cost has drawn considerable scientific elforts. Recently, defective... 

Hwang and Hwang [49] have synthesized composite rods (carbon nanotube coated with silica) by using surfactant (CTAB)-carbon nanotube co-micelles as templates. These glass rods produced by the sol-gel method were used as inclusions to reinforce ceramic matrices. A similar approach was used by Ning et al [50] to coat the surface of CNTs with silica. 

There are also a great number of studies on sol-gel processing routes to modify the surface of CNTs. The surface modified CNTs are targeted to produce final composites with increased wettability and hence optimised load transfer from the matrix to the CNTs. Ceramics that have been considered to coat carbon nanotubes by sol-gel methods include titania [60], silica [57] and alumina... 

Gleason and coworkers have demonstrated that the surface coating of carbon nanotubes (CNTs) by hot filament CVD of tetrafluoroethylene and by plasma enhanced CVD of MMA provide surface-modified CNTs having a stable/ superhydrophobic surface and good compatibility with PMMA, respectively [91, 92]. The superhydrophobic CNT indicated superior water repellency, whereby essentially spherical and micrometer-sized water droplets were suspended on top of the nanotube forest. The multiwall-CNT/PMMA nanocomposites were dispersed into PMMA via melt mixing. The orientation of CNT in the blend was achieved by melt drawing. The dispersed CNT in the blend indicated a significant effect on mechanical properties of the blend even at a 1% concentration of CNT. 

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