Effect of surface temperature on the concentration of C60/C70 molecules in dc arc discharge fullerene generator

Synthesis of C60, C70 and higher fullerenes was carried out at Pakistan Institute of Nuclear Science and Technology (PINSTECH) using dc arc discharge technique. High-performance liquid chromatography (HPLC) and UV-vis spectroscopy are employed to characterize the fullerenes. The toluene extracted fullerene solutions of the raw soot collected from four different regions (A-D) of dc arc discharge fullerene generator were compared with pure C60 toluene solution. Due to poor solubility of C60 in HPLC grade methanol, different fractions of methanol as a mobile phase with toluene were tried. The mobile phase composition of 80:20 methanol:toluene was found an optimal ratio to achieve the best separation factor of 1.246 between C60 and C70 fullerenes. Quantitative concentration is calculated from the HPLC and UV-vis spectra. The molarity of C60 carbon molecules for all the regions is calculated from the HPLC spectra by comparing the spectra of known molar solution of C60. The maximum concentration of C70 is found to be 21% in the region B that is nearer the arc zone and at a higher temperature than other regions. Both the techniques confirm the presence of C60, C70 and higher fullerenes in all the four regions with variation in concentration of C60 and C70. UV-vis spectra of the region C show the additional absorption bands at 285 and 305 nm