Carbon nanotubes adsorption

Striolo, A., Chialvo, A.A., Gubbins, K.E., and Cummings, P.T. (2005). Water in carbon nanotubes adsorption isotherms and thermodynamic properties from molecular simulation. J. Chem. Phys. 122, 234712. 

Multiwall carbon nanotubes (MWCNTs) have been synthesized by catalytic chemical vapor deposition (CCVD) of ethylene on several mesoporous aluminosilicates impregnated with iron. The aluminosilicates were synthesized by sol-gel method optimizing the Si/Al ratios from 6 to 80. The catalysts are characterized by nitrogen adsorption, X-ray diffraction, 27A1 NMR, thermogravimetric analysis (TGA) and infrared. The MWCNTs are characterized by TGA and transmission and scanning electron microscope. 

Figure 15.12 Detergent molecules can be used to solubilize carbon nanotubes by adsorption onto the surface through hydrophobic interactions and create half-micelle structures with the hydrophilic head groups facing outward into the aqueous environment.

Figure 15.14 The NHS ester of a pyrene butyric acid derivative can be used to modify a carbon nanotube by adsorption of its rings onto the surface of the tube. The NHS ester groups then can be used to couple amine-containing molecules to form amide bonds.

Maehashi et al. (2007) used pyrene adsorption to make carbon nanotubes labeled with DNA aptamers and incorporated them into a field effect transistor constructed to produce a label-free biosensor. The biosensor could measure the concentration of IgE in samples down to 250 pM, as the antibody molecules bound to the aptamers on the nanotubes. Felekis and Tagmatarchis (2005) used a positively charged pyrene compound to prepare water-soluble SWNTs and then electrostatically adsorb porphyrin rings to study electron transfer interactions. Pyrene derivatives also have been used successfully to add a chromophore to carbon nanotubes using covalent coupling to an oxidized SWNT (Alvaro et al., 2004). In this case, the pyrene ring structure was not used to adsorb directly to the nanotube surface, but a side-chain functional group was used to link it covalently to modified SWNTs. 

Figure 15.15 An aldehyde derivative of pyrene can be used to couple a hydrophilic amino-PEG-carboxylate spacer by reductive amination. The resultant derivative then can be used to coat a carbon nanotube through pyrene ring adsorption and result in a water-soluble derivative containing terminal carboxylates for coupling amine-containing ligands.

In view of the conductive and electrocatalytic features of carbon nanotubes (CNTs), AChE and choline oxidases (COx) have been covalently coimmobilized on multiwall carbon nanotubes (MWNTs) for the preparation of an organophosphorus pesticide (OP) biosensor [40, 41], Another OP biosensor has also been constructed by adsorption of AChE on MWNTs modified thick film [8], More recently AChE has been covalently linked with MWNTs doped glutaraldehyde cross-linked chitosan composite film [11], in which biopolymer chitosan provides biocompatible nature to the enzyme and MWNTs improve the conductive nature of chitosan. Even though these enzyme immobilization techniques have been reported in the last three decades, no method can be commonly used for all the enzymes by retaining their complete activity. 

One interesting development in the carbon nanotube-based electrochemical sensor is the ability to self-assemble the CNT to other types of nano materials such as gold and silver nanoparticles or to a polymer surface. The enhancement of Raman signals of carbon nanotubes through the adsorption on gold or silver substrate has been also reported [142-146],... 

H. Tang, J. Chen, S. Yao, L. Nie, G. Deng, and Y. Kuang, Amperometric glucose biosensor based on adsorption of glucose oxidase at platinum nanoparticle-modified carbon nanotube electrode. Anal. Biochem. 331, 89-97 (2004). 

Chahine, R., T.K. Bose, Hydrogen adsorption and cohesive energy of single-walled carbon nanotubes. Int.. Hydrogen Energ. 19,161,1994. 

Poirier, E., R. Chahine, P. Benard, G. Dorval-Douville, L. Lafi, P.A. Chandonia, Hydrogen adsorption measurements and modeling on metal-organic frameworks and single-walled carbon nanotubes. Langmuir 22(21), 8784-8789, 2006. 

Hou, P.X., S.T. Xu, Z. Ying, Q.H. Yang, C. Liu, H.M. Cheng, Hydrogen adsorption/desorption behavior of multi-walled carbon nanotubes with different diameters. Carbon 41,2471-2476,2003. 

Valenti LE, Fiorito PA, Garcia CD, Giacomelli CE (2007) The adsorption-desorption process of bovine serum albumin on carbon nanotubes. J. Colloid Interface Sci. 307 349-356. 

Q. Y. Wang and J. K. Johnson, Molecular simulation of hydrogen adsorption in single-walled carbon nanotubes and idealized carbon slit pores,./ Chem. Phys., 110, 577-586 (1999). 

The vast majority of functionalization methods of carbon nanotubes belong to two broad categories (a) covalent and (b) noncovalent functionalization of the external CNT surface. The former is achieved by covalent attachment of functional groups to the C-C double bond of the n-conjugated framework. The latter is based on the adsorption through van der Waals type bonds of various functional entities. 

Velickovic, Z., et ah, Adsorption of arsenate on iron(lll) oxide coated ethylenediamine functionalized multiwall carbon nanotubes. Chemical Engineering Journal, 2012.181-182(0) p. 174-181. 

To summarize, one can say that the electrochemical performance of CNT electrodes is correlated to the DOS of the CNT electrode with energies close to the redox formal potential of the solution species. The electron transfer and adsorption reactivity of CNT electrodes is remarkably dependent on the density of edge sites/defects that are the more reactive sites for that process, increasing considerably the electron-transfer rate. Additionally, surface oxygen functionalities can exert a big influence on the electrode kinetics. However, not all redox systems respond in the same way to the surface characteristics or can have electrocatalytical activity. This is very dependent on their own redox mechanism. Moreover, the high surface area and the nanometer size are the key factors in the electrochemical performance of the carbon nanotubes. 

J. Miyamato, Y. Hattoii, D. Noguchi, H. Tanaka, T. Ohba, S. Utsumi, H. Kanoh, Y.A. Kim, H. Muramatsu, T. Hayashi, M. Endo, K. Kaneko, Efficient H adsorption by nanopores of high-puiity double-walled carbon nanotubes. J. Am. Chem. Soc., 128 (2006) 12636-12637. 

Y. Ren, D.L. Price, Neuton scattering study of H adsorption in single-walled carbon nanotubes. App/. Phys. Lett, 79(22) (2001) 3684-3487. 

Q. Wang, J.K. Johnson, Optimization of carbon nanotube arrays for hydrogen adsorption. J. Phys. Chem. B, 103 (1999) 4809-4813. 

Similarly to SPE, for the SPME technique CNTs with high porosity and large adsorption area seems to be a good candidate for SPME coating. In addition, the more thermal and physical resistance of carbon nanotubes in comparison with commercial SPME coatings, are the other important characteristics from the practical point of view. However, this technique has been just applied in environmental analysis till now. 

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