Development of Standard Reference Samples of Aqueous Fullerene Dispersions

Abstract

The work considers a possibility of creating standard reference samples of aqueous dispersions of unmodified fullerenes and endohedral fullerenes. Procedures for preparing highly concentrated dispersions and methods for determining the concentration of the main component, elemental impurity composition, organic composition, and dimensional characteristics are discussed. Commercially available fullerenes C60 and C70 and endohedral fullerene Y@C82 (C2v isomer) synthesized by the electric arc method were used as the starting materials. Aqueous fullerene dispersions (AFDs) were prepared by replacing the organic solvent (toluene) under additional ultrasonic treatment. The maximum concentrations of fullerenes C60, C70, and Y@C82 were 150 ± 3, 55 ± 2, and 2.8 ± 0.1 mg/L, respectively. The long-term stability of solutions (more than 5 years) on storage was found. A set of methods and procedures that enable the determination of the main components of AFDs (fullerenes) and accompanying components (impurities of organic solvents and metals at the level of trace concentrations) is discussed. The sizes of fullerene clusters in solutions (from 100 to 120 nm for all solutions) are characterized; the stability of dispersions is estimated based on the electrokinetic potential (ca. –40 mV). The combined use of spectrophotometry, determination of total organic carbon, inductively coupled plasma atomic emission spectrometry, headspace gas chromatographic analysis, and HPLC offers a complete description of the physicochemical properties of AFDs, which further ensures the validation of AFDs as standard reference samples.