Separation of fullerenes

Separation of Fullerenes by Liquid Chromatography edited by K. Jinno, Toyohashi University of Technology, Japan... 

Saito, Y., Ohta, H., and Jinno, K., Chromatographic separation of fullerenes, Anal. 

The Fullerenes form particularly strong complexes with porphyrins as exemplified by the X-ray crystal structure of the covalent Fullerene-porphyrin conjugate 15.8 (Figure 15.29).48 This property allows fullerenes and porphyrins to form extended supramolecular arrays (even when not covalently linked) and has been used to engineer host-guest complexes in which a Fullerene is sandwiched in between a pair of porphyrins, and ordered arrays involving interleaved porphyrins and Fullerenes. Applications include the use of porphyrin solid phases in the chromatographic separation of Fullerenes and potential applications in porous frameworks and photovoltaic devices.49... 

New spatial forms of carbon - fullerenes, nanotubes, nanowires and nanofibers attract significant interest since the time of their discovery due to their unique physicochemical and mechanical properties [1-3]. There are three basic methods of manufacturing of the carbon nanomaterials (CNM) - laser evaporation, electric arc process, and catalytic pyrolysis of hydrocarbons. However, the multi-stage manufacturing process is a serious disadvantage for all of them. For example, the use of organic solvents (benzol, toluene, etc.) for separation of fullerenes from graphite soot results in delay of the synthesis process and decrease in the final product quantity. Moreover, some environmental problems can arise at this. 

As in the case of hollow fullerenes (Ajie et al., 1990 Scrivens et al., 1992 Taylor et al., 1990), liquid chromatography (LC) is the main purification technique for metallofullerenes. LC has been frequently and traditionally used in separation chemistry. One of the most powerful LC techniques is HPLC which allows separation of fullerenes according to their molecular weight, size, shape or other parameters 0inno and Saito, 1996 Kikuchi et al., 1991, 1992 Klute et al., 1992 Meier and Selegue, 1992). The HPLC technique can even allow us to separate structural isomers of various matallofullerenes (Shinohara, 2000). 

Comparison of X-ray scattering data and the microhardness valnes after annealing leads to the conclusion that there is phase separation of fullerene molecnles from the PE crystals within the material. Fnllerene-PE composites exhibit an unexpectedly large microhardness increase as the temperatnre is increased above 75 °C and this has been ascribed to the hardening of fnllerene aggregates within the composite (Balta Calleja et al, 1996). 

Feature 32-2 illustrates how size-exclusion chromatography can be used in the separation of fullerenes. 

Recently, in HPLC separations of fullerenes, the octadecyl silica (ODS) bonded stationary phase has been extensively used. " Both polymeric and monomeric ODS phases have been used, and these provide a higher selectivity than other phases. Figure 32F-5 shows the preparative separation of whole soot extract and a higher fullerenes fraction on a polymeric ODS column. These were among the first separations of the individual higher fullerenes. Note the excellent resolution compared with the size-exclusion separation of Figure 32F-4. 

K. Jinno. H. Ohta, and Y. Sato. in Separation of Fullerenes by Uquid Chromatography. 

For the separation of fullerenes by HPLC the stainless steel columns with Alusorb N 200, li Bondapak 10 CIS, LiChrosorb Diol, LiChrosorb SI 60 with bonded diphenylsilyl groups were used [16]. For the semi-preparative separation of Ceo and C70 glass column (70x12 mm) packed by LiChrosorb SI 60 with deposited carbon layer prepared by modified method [15] was used [16]. 

The most convenient column for the separation of fullerenes and their oxides is the column packed by LiChrosorb Diol with eluent containing n-hexane and n-pentane. This... 

For the purification of fullerenes from the fullerene oxides the activated alumina and silica can be used. Fulllerene oxides are adsorbed strongly on such adsorbents from solution and the oxides are removed from fullerene samples. For the preparative separation of fullerenes at present activated carbons and graphite are used [11-14], For this purpose silica with the deposited carbon layer [16] can be used also. In this case it is very easily to regulate the pore diameter and specific surface area of adsorbents as well as particle diameter. Such adsorbents is very important for the decreasing of fullerenes loss. On preparative separation of fullerenes on LiChrosorb SI 60 with deposited carbon layer by modified method [15] on glass column first fractions contained quite pure Csq. 

Thus silica with different surface chemistry is very useful for analytical and preparative separation of fullerenes. Silica with properly modified surface by deposition of carbon layer is useful adsorbent for preparative separation of fullerenes. 

Figure 3. Separation of fullerenes and fuUerene oxides on n Bondapak C 18 from i-propanol-n-hexane (20 80) eluent (column 300x4 mm, w = 0.4 ml/min) (a) and on LiChro-sorb Diol from n-hexane - n-pentane (80 20) eluent (column 250x4.6 mm, w = 0.2 ml/min)...

On separation of fullerenes on Silasorb Amin with bonded fullerene Ceo the selectivity of adsorbent is comparable with selectivity of adsorbents used for separation of fullerenes. 

New stationary phases and packings continue to be developed if not to improve on existing products to cater for new demand, e.g. a number of companies now market columns designed specifically for the separation of fullerenes and fullerene derivatives. These and other new packing materials are discussed in a review by Majors [74]. 

Nonplanar situations arise in fullerenes where a description of ji electrons in three dimensions is necessary. Haddon argued that orbital orthogonality is the key to the o—n separability, and he presents a recipe on how to conserve orbital orthogonality in three dimensions. Hirsch et al. showed that a new electron counting rule, different from the Hiickel An + 2 rule, can be used to describe the spherical aromaticity of fullerenes of symmetry. This interesting work may provide a stimulus to take a closer look into the a—n separation of fullerenes. 

Wan, J.D. Feng, Y.Q. Hu, Y.L. Da, S.L. Wang, Z.H. Preparation and evaluation of 2,4,6-trinitrophenol-modified zirconia-alumina for high performance liquid chromatography and its application in the separation of fullerenes. Chem. J. Chin. Univ. 2002, 23, 1259-1263. 

Temperature affects the separation of fullerenes quite dramatically when monomeric or polymeric C g phases are used. With hexane as mobile phase (A = 312 nm), the chromatographic changes due to temperatures ranging horn 20°C down to -70 C were studied [654]. Increased resolution of C76 to Cg4 fullerenes was obtained as the temperature was decreased from 20°C down to —20°C. Below this temperature, all resolution was completely lost regardless of the monomeric or polymeric nature of the Cig phase. The authors speculate that the bonded phase becomes rigid or frozen at temperatures below —20°C, which precluded effective interaction wife the solutes. The compatibility of alkanes with very low-temperature work is rarely utilized and could be advantageous for many other separations. 

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