Peapods

A detailed study of the C60/CNT system (named peapod , Fig. 3.15) was conducted, highlighting how the fullerene appears to be the perfect candidate for encapsulation, as a consequence of the similar graphitic scaffold, an ideal structural match between the C60 spherical shape and the internal CNT channels and strong van der Waals interactions [79]. 

Fig. 3.15 Schematic representation (top) and microscopy image (bottom) of the peapod system where fullerene molecules are encapsulated inside CNTs. Adapted with permission from [90], 2005, American Chemical Society.

Very recently author of this review successfully hydrogenated fullerenes inside of single walled carbon nanotubes (so called peapods). Evidence of hydrogenation was provided by NMR studies and Raman spectroscopy (Abou-Hamad et al. 2009). 

So far, direct evidence of C60 hydrogenation inside of nanotubes from HRTEM imaging is absent. It is required as a decisive demonstration of possibility for hydrogen to penetrate inside of peapods but could possibly be challenging experimentally. Chemical reaction within nanospace of carbon nanotubes is possibly only first example of interesting nanoscale chemistry and fullerene hydrogenation in other exotic environments will possibly be successfully demonstrated in future. It is quite likely that hydrogenation in confined space results in formation of fulleranes with different molecular structures. 

Abou-Hamad E, Kim Y, Talyzin AV, Goze-Bac C, Luzzi DE, Rubio A, Wagberg T (2009) Hydrogenation of C60 in Peapods physical chemistry in nano vessels. J Phys Chem C 113 8583-8587... 

Synthesis of nanotube peapods in which a nanotube includes a row of C60 molecules 2000 Thermal conductivity of nanotubes... 

From the structural studies given in this article, it is evident that the charge density study by the MEM/Rietveld method using SR powder diffraction data is powerful for determination of the endohedral nature of metallofullerenes. There is no doubt the structural information provided greatly contributes to progress in research of endofullerenes as well as endofullerene peapod, which is the met-allofullerene-encapsulating carbon nanotube. 

In the class of metallofullerene peapods, in addition to Gd Cg2-containing peapods (Fig. 1.22) [267], also Dy C82-, La Cg2- and Sm Cg2-containing peapods and dimetallofullerene-containing peapods with peas of the kind of Ti2 Cgo, La2 Cg0 and Gd2 C92 have been synthesized (see the references in [254]). 

NEW ALLOTROPES OF CARBON GRAPHITE INTERCALATION COMPOUNDS, FULLERENES, FULLEROIDS, CARBON NANOTUBES, PEAPODS, AND GRAPHENE... 

Intercalation of fullerenes into nanotubes ("peapods") was discovered [93], and even endohedral fullerenes (e.g., Gd C82 inside SWCNT) [94,95]. A very rich chemistry was soon explored to bond C(,o covalently to disparate organic ligands (an early smorgasbord is shown in Fig. 12.13) [96]. 

Inner tubes of DWCNTs Catalyst free growth from peapods by coalescence of C bU molecules 0.7 (0.55-1) Well shielded, best quality CNTs. Separation from outer tubes is very challenging... 

EMFs Inside Carbon Nanotubes - Nano Peapods ... 

Incorporation of small molecules into the hollow cavities of carbon nanotubes (CNTs) generates a new class of hybrid materials, which show potential applications ranging from nano-size containers for chemical reactions or for drug delivery to data storage and possibly high-temperature superconductors [181]. Because of their unique structure, such materials are called nano peapods [182]. 

Vostrowsky, O. and Hirsch, A. (2004) Molecular peapods as supramolecular carbon allotropes. Angewandte Chemie International Edition, 43, 2326-2329. 

Debarre, A., Jaffiol, R., Mien, C. et al. (2003) Specific Raman signatures of a dimetallofullerene peapod. Physical Review Letters, 91, 085501. 

The Raman spectra of C6o SWCNT peapods included features due to coupling of C60 totally symmetric modes with fullerene translational mobility within the tube.204 Raman data were reported for fullerene peapod species C60.C70 SWCNT.205 Raman spectra were also reported for the charge-transfer species C60 SWCNT and C70 SWCNT.206 207 High pressure resonance Raman spectra were reported for C60 and C70 peapods in SWCNT, at pressures of up to 9 GPa.208 Raman spectroscopy was used to follow the transformation of C60 peapods into SWCNT,209 and of C6o-SWCNT peapods into DWCNT.210... 

Resonance Raman excitation profiles were measured for individually dispersed SWCNT in aqueous solution (excitation 695-985 nm.).218 The IR and Raman spectra of SWCNT functionalised by long-chain hydrophobic groups show that the fundamental structure is unchanged on modification.219 A review has appeared of Raman data for SWCNT and DWCNT, especially the conversion of C60/SWCNT peapods into DWCNT at high temperatures.220... 

The Raman spectra of DWCNT s were analysed in terms of chiral, (n,m) assignments for these tubes.266 The Raman spectrum of I2-doped DWCNT gave assignments to radial breathing and tangential modes.267 Resonance Raman spectra of DWCNT were analysed to probe diameters and chiralities.268 The Raman spectra of DWCNT (from fullerene peapods annealed at high temperatures) show that the inner tubes are remarkably defect-free.269 Very low levels of defects were also observed from the Raman spectra of DWCNT produced by the catalytic decomposition of benzene over Fe-Mo/ A1203 catalysts at 900°C (i.e. very weak D-band at 1265.5 cm-1).270... 

Kavan, L. Dunsch, L. Kataura, H. Electrochemical tuning of electronic structure of carbon nanotubes and fullerene peapods. Carbon 2004, 42, 1011-1019. 

This section deals with adsorption inside the nanotubes. Access of molecules to this region requires a sample preparation technique that leaves open the ends or the walls of the tubes, because molecules cannot tunnel through the close-packed, graphene-like tube wall (interatomic spacing 0.14 nm). The other possibility is that the tube forms around the molecules, as is likely to be the case for endohedral Cgg (the system nicknamed peapods [21]). 

Girifalco, L.A. and Hodak, M. (2003). One-dimensional statistical mechanics models with applications to peapods. Appl. Phys. A, 76, 487-98. 

LABURNUM Laburnum anagyroides, Medikus and Laburnum alpinum (Miller) Bercht et J.Presl., Family Fabaceae, are well-known ornamental trees in the garden. In spring they produce yellow flowers in large hanging racemes and the fruit is a capsule similar to a peapod. 

A special host- est geometry is realized in the so-caUed peapods. These are single-waUed carbon nanotubes with fuUerenes enclosed in their irmer void so they are arranged tike peas in their pod (also refer to Section 3.5.6). The embedded fuUerenes can be > as well as higher homologs. These may themselves contain endohedral guests, which turns peapod-formation reaUy into a super-supramo-... 

Similar arguments like for the peapods hold for C ) surrounded by a belt-hke aromatic compounds (Figure 2.72a). Depending on their side chains the latter may confer some solubility in polar solvents. The interactions between belt and central fullerene are mainly of the ir-ji-type. They are exceptionally favorable due to the bent surface of both bonding partners. Inherently curved compounds tike perchlo-rotriquinacene can as well coordinate to by n-n interactions. 

Figure 3.98 Generation of peapods by the diffusion of flillerene molecules into an SWNT. Upon electron bombardment and heating DWNTs are formed (top). Endofliller-enes are incorporated, too. Upon coales-...

A direct attack of oxygen on the included fuUerenes, on the other hand, is much more complicated as it would have to happen through the tube s wall. Thermo-gravimetric measurements did show that the oxidation only sets in once the outer tube is oxidatively destroyed as well. Normally Cgo is oxidized at lower temperatures, but in case of the peapods the reaction is suppressed by the impossibility of oxygen molecules entering into the filled tube. 

Besides the substances mentioned so far, functionalized fuUerenes like the simple Bingel adduct can be intercalated into nanotubes as well (Section 2.5.5.2). The formation of peapods has further been described for metallocenes (e.g., ferrocene), porphyrines (e.g., erbium phthalocyanine complex) and small fragments of nanotubes. The most important prerequisite for the feasibility of inclusion is always a suitable proportion of sizes of both the tube and the structure to be embedded. For example, this effect can be observed for the intercalation of different cobaltocene derivatives into SWNT. The endohedral functionalization only takes place at an internal diameter of 0.92nm or above (Figure 3.100). But there is also an upper limit to successful incorporation. When the diameter of the nanotube is too large, the embedded species can easily diffuse away again from the host. Only few molecules are consequently found inside such a wide tube. 

Endohedral peapod formation, intercalation of metal atoms, storage of hydrogen... 

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