Cotransport of fullerene nanoparticles and clay colloids in porous media: the relation between aggregation and transport

In the study, cotransport of fullerene nanoparticles (nC₆₀) and mobile clay colloids (illite (ILL), kaolinite (KL), montmorillonite (ML)) in aquifer porous media and its relation to the aggregative interaction between these two types of particles was investigated. Minimal interaction occurred between nC₆₀ and ILL, resulting in unaffected transport. Strong heteroaggregation between ML and nC₆₀ resulted in not only significant retention of both particles during their cotransport but also the retention of nC₆₀ in the media pre-injected with ML. Strong homoaggregation of KL caused strong straining effect and consequently retention of both KL and nC₆₀ during their cotransport, however, did not cause retention of nC₆₀ during the sequential injection of KL and nC₆₀. Such aggregation behaviors were well demonstrated by the adsorption-sedimentation experiment, microscopic observation, the size and zeta-potential test, and model simulation. Based on the surface chemistry analysis, divalent-cation bridging between ML and nC₆₀ and hydrogen bonding between KL particles were responsible for the heteroaggregation and the homoaggregation, respectively. The study demonstrated the specificity of the aggregation between the mobile clays and nC₆₀ to the chemistry of the clays and its consequent effect on the cotransport of the particles, which is critical for assessment of the environmental risk of nC₆₀.