Aggregation behavior of aqu/nC₆₀ produced via extended mixing: Influence of sunlight and agitation intensity

Aggregation of C₆₀, as an important process governing its mobility and toxicity, has been quantitatively investigated. However, effects of sunlight and agitation intensity on the aggregation behavior of aqu/nC₆₀ produced via extended mixing, have not been clarified. Therefore, in the present study, the aggregation behavior of aqu/nC₆₀ produced at 500 and 800 rpm in the absence and presence of sunlight was investigated. Aggregation with increasing concentrations could be accelerated, while changes of Z_ave and zeta potential were not obvious. Critical coagulation concentrations (CCCs) of aqu/nC₆₀ obtained at 800 rpm in the absence/presence of sunlight and that at 500 rpm under sunlight were 330, 205 and 170 mM NaCl, and 10.0, 2.6 and 3.1 mM CaCl₂, respectively. These CCCs indicated that the aqu/nC₆₀ prepared by the extended mixing were more stable than those produced by other methods. Salt-induced aggregation occurred more easily for aqu/nC₆₀ formed under sunlight than that formed in the dark. Extra surface oxidation induced by high agitation intensity remarkably increased the stability of aqu/nC₆₀ in NaCl solutions. In contrast, in CaCl₂ solutions, aqu/nC₆₀ formed at high agitation intensity had similar stability or even inadequate stability to that obtained at low agitation intensity due to the charge neutralization and cross-link bridging.