Solubility and Size Separation of Large Fullerenes in Concentrated Sulfuric Acids†
journal contributionposted on 06.12.2007, 00:00 by Pradeep K. Rai, A. Nicholas G. Parra-Vasquez, Haiqing Peng, Robert H. Hauge, Matteo Pasquali
We show that large fullerenes (LFs) are soluble in concentrated sulfuric acids. We employ a centrifugation technique in conjunction with ultraviolet−visible and near-infrared (UV−vis−nIR) spectroscopy to quantify solubility. The Beer's Law dependence of UV−vis−nIR absorbance of LFs in concentrated sulfuric acids between 400 and 1400 nm facilitates the construction of linear calibration curves for measuring LF concentration in acids. Centrifugation of concentrated dispersions of LFs in concentrated sulfuric acids results in a clear phase separation. UV−vis-nIR absorbance measurements on the less concentrated phase yield the solubility of LFs. Large fullerenes exhibit an unusually high solubility in sulfuric acids concentrated in the range of 88−96%. The solubility of LFs in 96% sulfuric acid is higher than the solubility of the smallest fullerene (C60) in many organic solvents. We find that the solubility of LFs grows with acid strength, as is expected for solubilization by a protonation mechanism. Moreover, the average size of LFs solubilized in sulfuric acid increases with the strength of the acid.