Chemically modified CNTs

In recent years, CNTs have been receiving considerable attention because of their potential use in biomedical applications. Solubility of CNTs in aqueous media is a fundamental prerequisite to increase their biocompatibility. For this purpose several methods of dispersion and solubilisation have been developed leading to chemically modified CNTs (see Paragraph 2). The modification of carbon nanotubes also provides multiple sites for the attachment of several kinds of molecules, making functionalised CNTs a promising alternative for the delivery of therapeutic compounds. 

The transition from fundamental research to materials engineering and applications involves good knowledge of the physico-chemical properties of the investigated materials, and their electronic and vibrational features provide primary information. In the following, via the presentation of some specific cases, we demonstrate the ability of Raman scattering to characterize, in detail, chemically modified CNT-polymers hybrid materials. 

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... 

Gas phase approaches have the advantage that the nanocarbons do not need to be filtered or washed after hybridization making them ideal for nanocarbons produced on substrates such as CVD grown graphene films or CNT forests which tend to lose their structure upon immersion and/or drying. Consequently they are not ideal for chemically modified GO or CNTs. 

Fig. 15.11 (a),(b) Fraction of CNT catalysts combusted after 24 h time on stream in a 02/He gas mixture (a) CNTs, (b) 5 wt% P205/CNTs. (a),(b) Reprinted with permission from [25]. Copyright (2011) American Chemical Society, (c) Catalytic performance of B203-modified CNT catalysts in the ODH of propane. Propene selectivity at 5 % propane conversion ( ) and reaction rate (o) as a function of B203 loading, (d) Reaction scheme of CNT-cataiyzed ODH. (c),(d) Reprinted with permission from [61]. Copyright (2009) Wiley VCH. 

Gabay et al. [27] MW CNT, purified and chemically modified Neurons - inoculation on CNT, observation - 4 days Localization on CNT, proliferation of aksons. Cytotoxicity is absent... 

XPS and FT-IR were used to characterize the modified CNT surfaces. The combined results provided quantitative information on the chemical composition and structure of CNTs. For XPS, when an X-ray beam is directed at the SWNT surface, the energy of the X-ray photon is absorbed by a carbon core electron. The core electron escapes from the atom if the photon energy is sufficiently large. Since CNTs are made up of a hexagonal lattice of carbon atoms analogous to die atomic planes of graphite, one can easily obtain the main peak at 285 eV from Cls. However, die raw material usually contains amorphous carbon and various... 

Pillai et al. described a comparison between two chemical functionalization strategies for the amine functionalization of multiwalled CNTs. The modified CNTs with optimum amine content were used to prepare PLA/CNT nanocomposites through solution casting method. The polymer nanocomposite thus prepared showed improved thermal properties when compared to the neat PLA [65]. 

Covalent functionalisation and the surface chemistry of CNTs have been envisaged as very important factors for the processing and applications of nanotubes. Recently, many efforts on polymer composite reinforcement have been focused on an integration of chemically modified nanotubes containing different functional groups into the polymer matrix. Covalent functionalisation of CNTs can be achieved by either direct addition reactions of reagents to the sidewalls of nanotubes or the modification of appropriate surface-bound functional e.g. carboxylic acid) groups on to the nanotubes. " ... 

The functionalization of CNTs through plasma treatment represents a novel and easy approach to scale up towards industrial applications. In more recent works, there were many attempts to fluorinate CNT sidewalls in such manner. The CF4 plasma treatment of SWNT sidewalls was demonstrated to enhance the reactivity of tubes with aliphatic amines.The cure reaction of diglycidyl ether of bisphenol A-based epoxy resin (DGEBA), when reacted with butylamine molecules (BAMs) anchored on to the plasma treated fluorinated SWNTs, was reported. The advantage of this method was that the functionalization could be achieved through a simple approach, which is widely used in thin film technologies. As covalently modified CNTs with fluorine groups offer the opportunity for chemical interactions with the amine systems, it was recently demonstrated that this... 

The CNTs can be chemically modified with fimctional groups such as -COOH, -CHO, -NH2, and -OH on the walls or at the end portions after the add treatment. These functional groups can cause the CNTs to become soluble and dispersible in the solvent. 

Therefore, the key step for the in-situ polymerization of PUCNs is the dispersion of CNTs in macromolecular polyols. In order to reduce the aggregations, it is necessary to physically or chemically modify the surface of CNTs to reduce the van der Waals force among the nanotubes. Strong mechanical tools such as ball milling and ultrasonic treatment can be used to help break down the aggregation of CNTs. The kinetics of PU chain growth should be taken into account although it is rarely reported in up-to-date publicahons. 

In order to manipulate the ability of CNTs to pierce cells, Cai et al reported the use of iron tipped MWCNTs s)mthesized by plasma-enhanced chemical deposition (PECVD) method, in the presence of a ferromagnetic catalyst. The MWCNTs were covalently linked to DNA (Fig. 18.9) and the conjugates were added to cells. A magnetic field was applied below the cells in order to direct thee DNA-modified CNTs across the cell membrane. 

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