Hydroxyl-functionalized CNTs

Chemical treatments, such as strong oxidising acid mixtures of HN03/H2S04 under sonication, modify CNT surfaces with anchor groups, including carboxylic, carbonyl and hydroxyl functions, eventually used to covalently connect molecules to the tubes. The carboxylic acid groups are often the most common... 

CNTs can be processed such as purification based on oxidation, cutting, and activation by forming carboxylic acid and hydroxyl groups on the surface of CNTs, which can further be linked with other biomolecules to realize special function (Ajayan et al., 1994). As shown in Fig. 9.19, ferritin molecules attached to the surface of CNTs via covalent bond, the nanocomposites with ferritin molecules-functionalized CNTs own better mechanical, thermal, and electronic properties... 

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. 

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... 

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. 

Teixeira et al. performed the bioelectrochemical determination of the human chorionic gonadotropin which is a key diagnostic marker of pregnancy. The biosensor comprised a SPE platform modified with electrochemically oxidized CNTs, providing hydroxyl functionalization to the surface of the CNT, and subsequently silanized to produce an amine terminated CNT. Particularly, CNTs were subjected to an electrochemical treatment by cycling the electrode potential from -0.2 to -1-1.5 V in sulphuric acid. Thereafter, the electrode surface reacted chemically with (aminopropyl) triethojqrsilane (APTES) at controlled temperature. The antibody was dissolved in a buffer solution in the presence of l-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDAC) and N-hydroxysuccinimide (NHS) and then incubated for several hours. Finally, the antibody solution was dropped onto the amine modified CNTs SPE platform. 

Integration of nanostructured Si with carbon nanomaterials such as carbon paper, CNTs, or graphene in the porous electrodes is a useful approach to improve the electrochemical performance of Si. In this composite structure, the void space accommodates the volume expansion of Si, and the carbon nanomaterials compensate for the low intrinsic electronic conductivity of Si furthermore, the overall electrode structure is allowed to maintain stable SEI layers formed on the carbon surfaces. An example is shown in Figure 8.10 [13]. It is prepared by simple mixing of aqueous dispersions including Si and N-doped carbons. Due to electrostatic interactions between the N-doped sites of graphitic carbons and surface hydroxyl functionalities of Si, this composite can be prepared at room temperature for effective encapsulation by solution mixing. The interaction between N-CNTs and Si particles is very stable. As a result, the composites display superior capacity retention of 79.4% after 200 cycles, and excellent rate capability of 914 mAh/g is observed at a 10 C rate [13]. 

One good example of noncovalent functionalization for subsequent hybridization is the use of benzyl alcohol (BA) [118]. n-n interactions between the aromatic ring of BA and the CNT sidewalls result in a good dispersibility in ethanol. Furthermore, BA offers a well-ordered and well-distributed functionalization [119] of hydroxyl groups on the sidewalls of the CNTs that can be used to hybridize the material with a large number of metal oxides using conventional chemical methods [60]. 

As discussed earlier in this book (Chapter 3) there are many potential chemical routes toward functionalizing nanocarbons. The most popular is the oxidation of nanocarbons, particularly for CNTs by treatment in acidic solutions (e.g. HN03/H2S04) or the oxidation of graphene to GO. These oxidation methods produce a range of chemical functionalities on the nanocarbons including hydroxyl, epoxy and carboxylic acid. 

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