Aggregation and deposition characteristics of fullerene nanoparticles in aqueous systems

The propensity of n-C-60 to aggregate and deposit will play a key role in determining its longevity in aquatic systems, and therefore the potential exposure and risk presented by these colloids. We consider the origin of n-C-60 stability and compare the aggregation and deposition characteristics of n-C-60 under conditions of variable ionic strength using an indifferent electrolyte. Relatively weak electrolyte solutions (0.001 M) were observed to destabilize suspensions of n-C-60 resulting in the formation of settleable aggregates. This behavior supports the hypothesis that the stabilizing mechanism for n-C-60 clusters is electrostatic in origin. Similarly, the deposition of n-C-60 in porous media increased as ionic strength increased. These observations suggest that under some conditions present in natural aquatic systems, these materials may have limited mobility as they form large aggregates that may settle out of suspension or deposit on surfaces. These phenomena may, at least partially, offset any risk presented by n-C-60 toxicity due to a reduced potential for exposure.