Sorption of Light Fullerenes (C60 and C70) on Materials Prepared by Sublimation of Graphite Rods

Abstract

Sorption of fullerenes C 60 and C 70 from o-xylene, toluene, and o-dichlorobenzene solutions under static conditions on a sorbent prepared by sublimation of graphite rods was studied. The sorption isotherms of both fullerenes at 25oC were measured.In this study, we examined sorption of fullerenes from o-xylene, toluene, and o-dichlorobenzene solutions on a sorbent prepared by sublimation of graphite rods. The research in this field is aimed at determining the conditions of chromatographic separation of fullerene mixtures [133]. This study continues our previous investigations concerned with sorption of light fullerenes on unmodified carbon materials [3]. It should be noted that the first works in this field in Russia were those by Samonin et al. [4,5], which, however, disregarded the possibility of chromatographic separation and purification of light fullerenes.We used fullerene C 60 containing 99.9 wt % main compound (0.1 wt % C 70 ) and C 70 containing 99 wt % main compound (1 wt % C 60 ) (ILIP Joint-Stock Company, St. Petersburg, Russia). o-Xylene, o-dichlorobenzene, and toluene were of analytically pure grade. The sorbent was prepared by sublimation of graphite rods [reactor graphite of ultrapure grade (>99.995 wt %)] at 2500 + 50oC and a residual pressure of 2 0 10 !3 mm Hg. The carbon vapor was condensed on a steel support water-cooled to temperatures below 70oC. The resulting carbon crust was ball-milled using steel balls. The powder was mechanically sieved into fractions. We used a fraction with the following particle size distribution: d > 70 mm less than 10 wt %, d = 40370 mm 803 85 wt %, and d < 40 mm 5310 wt %. Just before the experiment, the sorbent was heated in air at 200 + 20oC for 1.532.0 h.To study the sorption properties of the carbon, concentrated stock solutions of the fullerenes in the above solvents were prepared (taking into account their solubilities) by isothermal saturation at 25oC for 24 h. The concentration of C 60 and C 70 in o-xylene, toluene, and o-dichlorobenzene was 4.1 and 2,3, 1.3 and 0.46, and 26 and 3.3 g l !1 , respectively. Less concentrated solutions in all of these solvents were prepared by sequential dilutions.To weighed portions of the carbon (1 g), 10-ml aliquots of the fullerene solutions of different concentrations were added. The mixture was stirred on a magnetic stirrer for 24 h at 25 + 0.05oC. This time is required to attain an equilibrium in the carbon-solution system. The mixture was filtered through a Schott filter (porosity 16) to remove the sorbent, and the fullerene content in the resulting solution was determined.The content of C 60 and C 70 in the solutions before and after the sorption was determined spectrophotometrically on an SF-46 spectrophotometer from the optical density at l = 335.5 and 472.0 nm [6]. The concentrations were calculated by the following empirical equations: c(C 60 ) = 13.10(D 335 3 1.8080D 472 ), (1) c(C 70 ) = 42.51(D 472 3 1.0081D 335 ), (2)where D 335 and D 472 are the optical densities of a 1-cm layer of the solution at the indic...