Surface-Modified Carbon Nanotubes Approaches

To take advantages of the unique properties of CNTs, a general approach is the immobilization of DNA on CNTs and the further immobilization of the DNA-modified CNTs on an easier-to-handle pure conductor, e.g., GC [26], Ft [121], Au [ 122]. Another approach consists of the prior modification of the pure conductor (GC) with the CNTs through dry-adsorption and the further DNA or DNA derivatives adsorption on the CNT-modified surface [123-125]. 

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Finally, the possibility of involving y-irradiation in reduction of Fe and Pd ions was demonstrated for the preparation of nanocopmposite materials containing sulfonated PANI, multiwall carbon nanotubes, and Fe, Pd, or Fe-Pd alloy NPs [265]. Recently, UV-induced photoreduction was used for the formation of Pt particle-modified PANI and TiOa-PANI composite layers [266]. This turned out to be an effective approach for achieving a homogeneous distribution of small enough metal particles on the CP surface. 

One of the first examples of the grafting to approach was published by Sun et al. in 2001 [32]. In this work carboxylic acid groups on the nanotube surface were converted into acyl chlorides by refluxing the samples in thionyl chloride. Then the acid chloride functionalized carbon nanotubes were reacted with hydroxyl groups of dendritic PEG polymers via esterification reactions. Similarly, many polymers terminated with amino or hydroxyl moieties have been used in amidation and esterification reactions with acid chloride modified NTs poly(propionylethylenimine-co-ethylenimine) (PPEI-EI) [33], poly(styrene-co-aminomethylstyrene) (PSN) [34], poly-(amic acid) containing bithiazole rings [35], monoamine-terminated poly(ethylene oxide) (PEO) [36], poly(styrene-co-hydroxymethylstyrene) (PSA) [37], poly(styrene-co-p-[4-(4 -vinylphenyl)-3-oxabutanol]) (PSV) [38], poly(vinyl alcohol) (PVA) [39], poly(vinyl acetate-co-vinyl alcohol) (PVA-VA) [40] or poly[3-(2-hydroxyethyl)-2,5-thienylene] (PHET) [41]. 

Irrespective of the method of preparation there are two fundamental and critical issues associated with translating or transferring the unique properties of carbon nanotubes to a polymer matrix. Firstly, the nanotubes must be uniformly distributed and dispersed throughout the polymer matrix, and secondly, there must be enhanced interfacial interaction/wetting between the polymer and the nanotubes. For example, any load applied to the polymer matrix should be transferred to the nanotube. This load relies on the effective interfacial stress transfer at the polymer-nanotube interface, which tends to be polymer dependent (7). Three general approaches have been adopted in attempts to modify the surface of CNTs to promote such interfacial interactions chemical, electrochemical and plasma treatment. For example, Castafio et al. (8) placed different organofunctional groups... 

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