OH-MWCNTs

A novel chemical functionalization method for MWCNTs through an oxidation and silylation process was reported in 2002. Purified and oxidatively functionalized MWCNTs were reacted with 3-mercaptopropyltrimethoxysilane, the CNT surface being joined to the organosilane moieties through OH groups [143], Similarly, MWCNTs were functionalized by KMn04 oxidation under PTC catalysis and subsequent reaction with the hydrolysis product of 3-methacryloxypropyltri-methoxysilane (3-MPTS) (Scheme 1.13). The O-silyl-functionalized MWCNTs were characterized by FT-IR spectroscopy and energy-dispersive spectroscopy... 

The role played by MWCNTs is to provide electrons into the Ti02 condnction band under visible light irradiation and to trigger the formation of very reactive radicals snch as the snperoxide radical ion 0 . Back electron transfer from adsorbed OH closes the electrocatalytic cycle and provides a sonrce for the hydroxyl radical HO, which is responsible for the degradation of the organic molecnles (Fignre 13.2). 

Nitrene chemistry approach to functionalize CNTs (top), and representative TEM images (bottom) of pristine (p-) MWCNTs (a) and hydroxyl-functionalized MWCNTs (MWCNT-OH) (b ). Other functionalized CNTs (f-CNTs) showed similar TEM images to the MWCNT-OH. Reprinted with permission from Gao et al... 

Alternatively, hydrophilic multi-hydroxyl poly(GMA-OH)-grafted MWCNTs could be converted into multicarboxyl polymer-functionalized CNTs by reaction with succinic anhydride and then used as templates to efficiently sequestrate metal ions such as Ag", Co ", Ni , Au , La and (Scheme 5.3), generating MWCNT-polymer/metal hybrid nanocomposites, nanowires or necklace-like nanostructures, depending on the grafted polymer content and the nature of the captured metals. The combination of SEM, TEM and energy dispersive spectroscopy (EDS) characterizations demonstrated the structure and elements of the hybrid nano-objects. 

Scheme 5.3 Functionalization of MWCNTs with poly(GMA-OH) by ATRP, conversion of the hydroxyl groups of poly(GMA-OH) into carboxylic groups, and metal sequestration/reduction by the grafted polyacid chains. ...

Alternatively, hydrophilic multi-hydroxyl poly(GMA-OH)-grafted MWCNTs could be converted into multicarboxyl polymer-functionalized CNTs by reaction with succinic anhydride and then used as templates to... 

Scheme 5.3 Functionalization of MWCNTs with poly(GMA-OH) by ATRP...

The main functional group attached to oxidized carbon nanotubes was carboxylic. Comparison between spectra of pristine nanotubes and oxidized N-MWCNTs showed that the bands at 1444 cm-i, 1373 cm-i and 1251 cm-i, attributed to vibration of MWCNTs and C-N bonding in N-MWCNTs, were overcome by several vibrations in carbonyl and carboxyhc functionalities in the range of 1720 to 1250 cm-i (Choi et al., 2004 Misra et al., 2007). A strong band appeared from 3600 cnri to 3300 cnri by the stretching of the bonding -OH of carboxylic group in oxidized nanotubes (Zawadski, 1980 Chen and Wu, 2004). 

Fig ure 11.4 Schematic representation of the immobilisation of [M((OH)2sa/e/2)] complexes onto MWCNTs functionalised with acyl groups. Adapted from ref. 33. 

After the discovery of carbon nanotube (CNT) by Ijima (1991), extensive works have been devoted in extracting the optimum properties of the CNTs. Wu (2009) studied PTT/MWCNT composites. The hydroxyl functionalized (MW-CNT-OH) behaves as anchoring sites for the PTT grafted with acrylic acid (PTT-g-AA) (compare to Scheme 1). The functionalization of MWCNT improves the compatibility and dispersibility of the MWCNT in the matrix of PTT. The thermal and mechanical properties (compare to Tables 14 and 15) show a dramatic increase leading to the conclusion that functionalized MWCNT can be used for preparing high performance PTT nanocomposites. 

TABLE 14 Thermal properties of PTT/MWCNT and PTT-g-AA/MWCNT-OH as proposed by Wu (2009) (Adapted from Wu (2009)... 

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