Adsorption Properties of Carbon Nanotubes

The most unexpected and potentially most important adsorption property of carbon nanotubes is hydrogen storage. While controversy remains, intensive research efforts on this subject are on-going worldwide. This subject will be discussed separately in Chapter 10. 

Since the first study on adsorption in carbon nanotubes by Pederson and Broughton (1992), most have been simulations. Few experimental studies have appeared, however. The observations from both simulations and experiments are discussed below. 

CARBON NANOTUBES, PILLARED CLAYS, AND POLYMERIC RESINS 

The results given in Table 9.3 indicate that for the same level of purification, much less sorbent is needed if the activated carbon is replaced by carbon nanotubes. Alternatively, if the same size adsorber is used, a much higher level of purification can be accomplished. 

In the commercial operation of incinerators, activated carbon is used to adsorb both dioxins and Hg. The temperature of adsorption is near 150 °C. Adsorption at higher temperatures would be more economical however, the temperature is limited by the sorbent capacity. By replacing activated carbon with carbon nanotubes, operation at higher temperatures would be possible. 

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The history, syntheses, and general adsorption properties of carbon nanotubes that have been reported are given in Chapter 9. A number of reviews on hydrogen storage in carbon nanotubes have appeared (Dresselhaus et al., 1999 Cheng et al., 2001 Ding et al., 2001 Dillon and Heben, 2001 Darkrim et al., 2002 Simonyan and Johnson, 2002). 

Recently, the influence of gas adsorption on physical properties of carbon nanotubes has attracted a considerable interest. It is caused by a possibility to create gas nanosensors [1,2]. The analysis of calorimetric data has shown that the gas adsorption in space between nanotubes gives the main effect on physical properties [3]. The measurement of the conductivity is simple and convenient method to detect a response of multiwalled nanotubes with respect to an external influence. This response can be used to construct a resistive sensor. 

In mesopores the sorption mass transport is less influenced by the structure and size of the alkane adsorptives than in micropores where the transport can be controlled also by geometric factors. The dynamic sorption properties of carbon nanotubes were shown to be strongly affected by the presence or absence of surface functional groups. 

JogiBF, Sawant M, Kulkarni M, BrahamkarPK. Dispersion and performance properties of carbon nanotubes (CNTs) based polymer composites areview. J Encapsul Adsorption Sci 2012 2 69-78. 

S.S. Han, H.M. Lee, Adsorption properties of hydrogen on (10, 0) single-walled carbon nanotube through density functional theory. Carbon 42, 2169 (2004)... 

Rekoske and Barteau (68) used TEOM in scaling-up to higher pressure surface-science results dealing with solid reactions related to redox cycles. These authors investigated reduction kinetics and reaction on titanium oxide (69,70). Recent applications also include the investigation of carbon nanofibers (9) and hydrogen adsorption properties of single-walled carbon nanotubes (71). 

Davydov, V.Y., Kalashnikova, E.V., Kamatsevich, V.L., and Kirillow, A.L. (2004). Adsorption properties of multi-wall carbon nanotubes. Fullerenes Nanotubes Carbon Nanostruct., 12, 513-18. 

Darkrim, F. and Levesque, D. (2000). High adsorptive property of opened carbon nanotubes at 17K.J. Phys. Chem. B, 104, 6773—6. 

Carbon nanotubes are a new allotropic form of caibon and possess interesting physicochemical properties. Their chance discovery was a result of an enormous interest in fullerenes. Carbon nanotubes are built of graphene layers and can assume single- or multi-wallet structures [23,25,35]. Chemical modifications of nanotubes in both open terminated areas and on outer and inner walls create many possibilities. Prospective and present applications of nanotubes depend on their physicochemical properties, such as density, resistance to stretching and bending, thermal and electrical conductivity, field emission, as well as resistance to temperature. Good adsorption properties of nanocarbon materials contribute to their extensive practical application. 

Under normal conditions, any solid surfaces coated with filnrs of atonrs or molecules adsorbed from the environment, or left on the surface in the diffusion process [3], The most of elements adsorption on metals forms a chentical bond. The high reactivity of the surface of carbon nanotubes nrakes them an exception. Therefore, current interest is the study of the influence of the adsorption of atonrs and various chemical elements and molecules on the electrical properties of carbon nanostmc-tures. 

Krypton is a subcritical vapour at the nitrogen boiling temperature. As such, its adsorption on crystalline surfaces leads to eondensation steps, typical of type VI isotherms according to lUPAC, while its adsorption on rough surfaces is BET-like. Based on this property of krypton adsorption at 77 K, a methodology is proposed to determine the purity of carbon nanotubes samples. The method is tested on model samples obtained by mixing mechanically purified multi-walled carbon nanotubes with various amounts of the same catalyst as used for their synthesis. 

Adsorption significant adsorption and interaction phenomena occur between carbon nanotubes and gases. There are two possible applications for this sector. The first is characterized by the molecular adsorption, which is related to carbon nanotube electrical properties and, then, with the possibility of developing chemical sensors. The second includes gas storage and separation due to the high surface area of carbon nanotubes. 

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