Fluorination nanotubes

Polymer nanocomposites with medium density polyethylene were reported with a variety of fluorinated and un-fluorinated nanotubes (37). The nanocomposites consisting of 1 wt% F-SWNT-C H (fluorinated and surface treated nanotubes) nanotubes showed an increase in tensile strength by 52.4%, modulus by 15.9% and elongation by 18.9% as compared to the pure polymer. The composites with 1 wt% F-SWNT-CnH23 (fluorinated and surface treated nanotubes) had an increase of 28.3% in modulus as compared to the pure polymer. The tensile strength also increased from 4.33 MPa for the pure polymer to 5.01 Mpa for the nanocomposite, the elongation at... 

Figure 3.70 Halogenation of carbon nanotubes. The reaction at least partly takes place as 1,4-addition. Fluorinated nanotubes are good starting materials for further functionalization (bottom).

This calls for the 1,4-addition to take place at least at some positions, which prevents the fluorinated tube from being an electric conductor. Fluorinated nanotubes differ from the unmodified species not only in electric conductivity. There are rather more characteristics being changed. Fluorinated tubes dissolve, for instance, in some organic solvents Uke DMF, THF, and different alcohols. Most of aU, the solubility in 2-propanol and 2-butanol is increased. Hydrogen bonds between the protons of the hydroxy groups and the fluorine atoms of the nanotubes are assumed to cause an effective solvation. 

The Diels-Alder reaction succeeds as well with fluorinated nanotubes. Different dienes can be connected this way to the double bonds of the nanotube surface (Figure 3.75). A 5% degree of functionaUzation is achieved in doing so. The fluori-nation enhances the reactivity of the remaining double bonds of the carbon nanotube as, firstly, the tension is increased by adjacent sp -centers and, secondly, due to the electron-withdrawing effect of fluorine atoms. Once more the double bonds of the nanotube always function as dienophile. 

Gu Z, Peng H, Hauge RH, Smalley RE, Margrave JL (2002) Cutting single-wall carbon nanotubes through fluorination. Nano Lett. 2 1009-1013. 

The fluorination of carbon nanotubes was first reported by Margrave and is traditionally performed by using elemental fluorine in the presence of small amounts of HF which serves as catalyst [24]. The loading turns out to be very high, with one fluorine atom every two carbon atoms. 

Fig. 3.7 Fluorination and further substitution of pristine carbon nanotubes.

It has also been demonstrated that CNT sidewalls can be covalently fluorinated [148 150], or they can be derivatized with certain highly reactive chemicals such as dichlorocarbene [142], In this context, Chen et al. applied derivatization chemistry with thionychloride and octadecylamine in order to obtain organic soluble SWCNTs and later they performed a reaction with dichlorocarbene that led to the covalent functionalization of the nanotube walls. 

T. Nakajima, S. Kasamatsu, Y. Matsuo, Synthesis and characterization of fluorinated carbon nanotubes, European Journal of Solid State Inorganic Chemestry, vol. 33, pp. 831-840,1996. 

An XPS scan of flame annealed nanotubes revealed the presence of carbon in all samples and a summary of the carbon content and carbon state information is provided in Table 5.5 [98], Fluorine was... 

It is known from decades, particularly for Al, that porous oxide layers can be grown by anodization typically in acidic electrolytes, while anodization in neutral electrolytes typically leads to a compact oxide layer. However, Masuda et al were the first who showed that a very high degree of order can be achieved for these porous geometries. Zwilling et first reported the porous surface of titania films electrochemically formed in fluorinated electrolyte by titanium anodization, but only a decade later Grimes et al. showed that the nanostructure is constituted by uniform titania nanotube arrays. 

Usually the nanotube arrays have been made from a titanium thick film or foil, in which case the resulting nanotubes rest upon an underlying Ti substrate as separated by a barrier layer. The nanotube arrays have also been fabricated from a titanium thin film sputtered onto a variety of substrates, such as silicon and fluorine doped tin oxide (FTO) coated conductive glass. This extends the possibility for preparing technical catalysts by deposing a thin Ti layer over a substrate (a foam, for example) and then inducing the formation of the nanostructured titania film by anodic oxidation. ... 

Chemical Modification of Nanotube Inner Wall by Direct Fluorination... 

Taking into consideration that only the inner wall surface of carbon nanotubes is exposed to atmosphere in the stage of carbon-deposited alumina film, it would be possible to modify only the inner surface if the carbon-deposited alumina film is chemically treated. On the basis of this concept, Hattori et al. tried to fluorinate only the inner surface of carbon nanotubes (42). It is well known that fluorination is quite an effective way to introduce strong hydrophobicity to carbonaceous materials, and it perturbs the carbon it electron system (43,44). Thus, by the selective fluorination of nanotube s inner surface, it would be possible to produce carbon nanotubes whose inner surface is highly hydrophobic and electrically insulating while their outer... 

A carbon-deposited film was prepared from the alumina film with 30-nm channels by the CVD technique using propylene. Fluorination was carried out by direct reaction of the film with dry fluorine gas (purity 99.7%). The film was placed in a nickel reactor and was allowed to react with 0.1 MPa of fluorine gas for 5 days at a predetennined temperature in the range of 50 to 200°C. Then the fluorinated carbon nanotubes were separated by dissolving the alumina film with HF. A schematic drawing of the fluorination process is given in Fig. 10.1.15. 

Fig. 10.1.15 Schematic diagram of the fluorination process of carbon nanotube.

In Figure 10.1.17, the Cls XPS spectrum of the carbon-deposited film fluorinated at 175°C is compared with that of the corresponding fluorinated tubes after the HF washing. The former spectrum and the latter one give information on the external flat surface of the fluorinated film and the outer surface of the fluorinated tube, respectively. In spectrum (a), the most intense component is the peak assigned to covalent CF bond. On the other hand, spectrum (b) exhibits a clear peak at 284.4 eV, which corresponds to the sp2 carbon of the nanotube. These findings indicate selective fluorination of carbon tubes the covalent CF bonds were formed almost exclusively on the inner surfaces of nanotubes, but the outer surfaces retained their sp2 hybridization. 

Fig. 10.1.17 Cls XPS spectra of (a) the fluorinated carbon deposited film and (b) the carbon nanotubes from the film (fluorination temperature 175°C). (From Ref. 42.)...

Scheme 1.2 Treatment of fluorinated tubes tized alkyl- and alkoxyl-nanotubes and amino-with strong nucleophiles and replacement of functionalized nanotubes as products, the fluorine substituents, leading to deriva-...

Derivatized products such as alkyl-, aryl-, alkoxyl- and amino-nanotubes and cross-linked nanotubes are obtained (Scheme 1.2). F-SWCNTs prepared by the HiPCO process exhibited a higher degree of alkylation using alkyllithium reagents than fluorinated SWCNTs from the laser-oven method. Dealkylation occurred at 500 °C. 1-Butene and n-butane were formed during the thermolysis... 

Selective Fluorination onto Nanotube Inner Surface.91... 

In order to examine the chemical state on the carbon surface, x-ray photoelectron spectroscopy (XPS) analysis was performed for both the fluorinated carbon-coated AAO film and the liberated nanotubes from this fluorinated film. In the resulting XPS Cls spectrum of the fluorinated film (Figure 3.11a), the most intense component is the peak assigned to the covalent C-F bond (about 290eV),... 

The fluorinated carbon-coated AAO film has an interesting adsorption characteristic that has not been reported so far. Figure 3.12 shows N2 adsorption/desorption isotherms at -196°C for the pristine carbon-coated AAO film and the films fluorinated at different temperatures [119]. The isotherm of the pristine film is characterized by the presence of a sharp rise and a hysteresis in a high relative pressure range. Such a steep increase can be ascribed to the capillary condensation of N2 gas into the nanochannels of the AAO films, that is, the inner space of the nanotubes embedded in the AAO films. The amount of N2 adsorbed by the condensation into the fluorinated channels is lower than that of the pristine one. Moreover, the amount drastically decreases with an increase in the severity of fluorination. Since TEM observation revealed that the inner structure of the fluorinated CNTs was not different from that of the pristine nanotubes, the reason why the N2 isotherm was so changed as in Figure 3.12 cannot be attributed to the alteration of the pore texture upon the... 

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