Comparison of Electrokinetic Properties of Colloidal Fullerenes (n-C60) Formed Using Two Procedures

Abstract

In this study we report on the electrokinetic behavior of colloidal aggregates of C₆₀fullerenes (n-C₆₀) produced through two different techniques: solvent exchange and extended mixing with water. In the first technique, used to produce colloidal materials in several recent toxicity and transport studies, an organic solvent such as tetrahydrofuran (THF) is used to dissolve the C₆₀ before mixing with water. The second technique is more indicative of conditions that might occur in natural aquatic systems. Both types of n-C₆₀ were observed to be negatively charged under a variety of solution chemistries; however, the n-C₆₀ formed using THF was more strongly charged. We conclude that n-C₆₀ likely acquires charge through charge transfer from the organic solvent (when present) and surface hydrolysis reactions. Nevertheless, C₆₀ is capable of acquiring charge and becoming dispersed as n-C₆₀ in water without the aid of organic solvents, a pathway that may be important in determining the mobility of fullerenes in natural systems. These findings also show that n-C₆₀ made using THF retains a portion of the solvent in the cluster structure, subsequently influencing the characteristics of the n-C₆₀ and possibly requiring a re-interpretation of results from recent studies on n-C₆₀ toxicity using THF-derived materials.