Formation of Aqueous Suspensions of Fullerenes

Abstract

Colloidal suspensions of C60, C70, and a derivative of C60, PCBM ([6,6]-Phenyl C61-butyric acid methyl ester)were produced by extended mixing in water. We examined the contribution of background solution chemistry (pH, ionic strength) on the formation of colloidal suspensions in terms of mass, aggregate size, and zeta potential. These parameters were also compared between free-settling and filtered treatments. Results indicated that all three fullerenes were highly negatively charged in aqueous systems, that it took a finite time to reach kinetically stable suspensions, and that suspension formation was pH and ionic strength dependent. With isoelectric points approaching zero, the suspensions were generally stable at pH > 3. The results indicate that it is critical to state the condition under which the formation of aqueous fullerene suspensions occurs when employing such suspensions to evaluate environmental toxicity or fate and transport of fullerenes.

Characterisation and determination of fullerenes: A critical review

“…The results show that the presence of divalent cations and NOM in the water stabilizes the aqu/nC 60 nanoparticles leading to sizes lower than the ones observed in deionised water (average sizes of 150-175 nm and 210-230 nm, respectively). Moreover, a decrease in the ζ potential of aqu/nC 60 with time has been reported under laboratory lighting conditions [84] and under natural sunlight [99] . Thus, the sunlight and the presence of NOM lead to a decrease in the size and zeta potential of aqu/nC 60 aggregates making them more stable and more available for transport and organism uptake.…”

“…Microscopy provides a basis for comparison and is suitable for elucidating particle shape and to some degree aggregate structures but cannot provide information about the size distribution of the aggregates. Hence, for the accurate knowledge of the morphology, aggregation state and size distribution of fullerenes in aqueous solutions, other techniques and mostly light scattering (LS) must be also used [6,7,10,11,15,63,[83][84][85][86] . For instance, Brant et al [6] investigated the characteristics of nC 60 obtained using four different preparation procedures by TEM, DLS and SLS (Table 3).…”

“…Knowledge of the stability, mobility and aggregation behaviour of fullerenes as a function of matrix composition, pH and ionic strength will allow us to gain an insight into their potential behaviour when released into the environment. Several studies have been carried out for this purpose for aqu/nC 60 [6,7,10,15,68,84,85,93] , aqu/nC 70 [84] and also for some functionalised fullerenes [80,84] .…”

“…Moreover, several authors studied the effect of the ionic strength and pH on the degree of aggregation of fullerene in aqueous solutions [7,10,15,80,84,101] . For example, Fortner et al [15] reported that C 60 heteroaggregates stay stable for months at low ionic strengths similar to those of most surface waters but the average particle size increased up to 360 nm at an ionic strength of 0.05 and values above 0.1 are high enough to precipitate the particles after 48-72 h. Moreover, the average particle sizes also depend on the pH, decreasing at high pH values from 120 nm (pH 3.7) to 60 nm (pH 10).…”

“…Due to the increase in the production and use of functionalised fullerenes their behaviour in aqueous solutions has also been recently evaluated [80,84,94,101] . The studies show that their aggregation is also promoted by the increase of the ionic strength as observed for aqu/nC 60 , but the aggregates present smaller sizes.…”