Study On The Dispersion And Aggregation Behaviors Of Fullerene(C₆₀)in Water Environment

C60 and its derivatives have been largely produced and widely applied in biomedical,analytical chemistry,energy storage and other fields due to their novel and unique physicochemical properties.With the mass production and wide application of C60,it is inevitably released into the water environment.Although the solubility of C60 in water is very low,it can form a stable colloidal dispersion(aqu/nC60)through extended mixing and suspend in water for a long time.Related toxicity studies show that C60 could pose a potential threat to ecosystems and human health.However,studies about behavior and fate of C60 in environment water are insufficient at present,which affects the development of ecological risk assessment of C60.Therfore,it is necessary to further study the environmental behavior and fate of C60 in natural water system.Accordingly,the effects and mechanism of various factors on the dispersion and aggregation behavior of C60 in environment water are investigated in this paper,which is helpful to further understand the behavior and fate of C60 in typical environmental water.The main results include the following aspects:1.The effects of turbulence intensity and sunlight on the generation and dispersion of aqu/nC60 are investigated,and its potential conversion mechanism is discussed.The results indicate that sunlight could promote the production of oxygen-containing moieties on the surface of nC60(C60 aggregates),and further form aqu/nC60 solutions with more stability and higher concentrations;higher turbulence intensity promotes nC60 smaller with larger specific surface area,provides greater opportunities to contact with oxygen molecule and radicals,and then speeds up the process of monooxygenation,so as to form more hydroxyl,epoxide or ether groups and finally accelerate dispersion of nC60 in water.Therefore,nC60 with higher concentrations formed under turbulence and illumination condition can be transported over long distances,which may cause potential exposure risks to aquatic organisms.2.The effects of humic acid(HA)on formation and dispersion of aqu/nC60 under different illumination and turbulence intensity conditions are investigated.The results indicate that HA enhanced C60 dispersion due to the increased steric hindrance effect and surface hydrophilicity.The higher the turbulence intensity,the smaller the size of nC60 generated by collision and the more HA adsorbed on the surface of nC60,the higher the dispersion stability;under illumination condition,HA-C60 complex could generate reactive oxygen species(ROS)in a synergistic way,which promotes the surface oxidization and the dispersion of C60.Statistical analysis shows that the relative order of above three factors affecting dispersion of aqu/nC60 is as follow:sunlight>turbulence intensity>HA.However,HA may reduce the dispersion of aqu/nC60 due to light screening/ROS scavenging,over-coating,or chain-like bridging mechanism.Therefore,the formation and dispersion of aqu/nC60 will become more complex due to the presence of HA.3.The dispersion and stability properties of C60 in different environmental water are investigated.The results show that after extended mixing,aqu/nC60 is stable in deionized water and typical wastewater influent;while it is difficult to form stable aqu/nC60 in typical river water,wastewater effluent,nearshore seawater and estuarine water even after 70 days extended mixing.Under illumination condition,turbulence can promote the collision between nC60 and form oxygen-containing functional groups on the surface of nC60,independent of the kind of environmental water.Once the mixed system goes under quiescent condition,aggregation and sedimentation of aqu/nC60 would occur due to charge neutralization effect of ions in water.However,an extremely short-time disturbance could easily resuspend nC60 and increase the concentrations of aqu/nC60 in the overlying water column.Thus it can be seen that the contamination level of C60 in water may be underestimated without considering the resuspension factor.4.The dispersion and stability properties of aqu/nC60 in different ionic solutions and several environmental waters are investigated.The results show that ion-induced aggregation behaviors occur more easily for aqu/nC60 formed under sunlight than that formed in the dark.The electrostatic repulsion between nC60 is enhanced by extra surface oxidation induced by high agitation intensity,which remarkably increase the dispersion of aqu/nC60 in NaCl solutions.In contrast,in CaCl2 solutions,aqu/nC60 formed at high turbulence intensity had similar or even inadequate stability to that obtained at low turbulence intensity due to the charge neutralization and cross-link bridging.In several typical environmental waters,compared with river water,lake water,wastewater influent and wastewater effluent,the aggregation behavior of aqu/nC60 in seawater is the most remarkable due to its high ionic strength.The aggregation behaviors of aqu/nC60 in seawater indicate that the particle size distribution and zeta potential of nC60 have a great influence on the aggregation behavior of aqu/nC60.The aggregation of aqu/nC60 with inhomogeneous particle size distribution in seawater presents the characteristics of segmented agglomeration and sedimentation.