Effects of the preparation method and humic-acid modification on the mobility and contaminant-mobilizing capability of fullerene nanoparticles (nC60)

Abstract

Colloidal fullerene nanoparticles (nC₆₀) in aquatic environments may significantly affect the transport and risks of hydrophobic organic contaminants by serving as a contaminant carrier. The objective of this study was to understand how the combined variables of the preparation method and natural organic matter modification of nC₆₀ might affect the mobility and contaminant-mobilizing capability of nC₆₀, by affecting the physicochemical properties of nC₆₀. We found that an nC₆₀ sample prepared by sonicating C₆₀ powder in deionized water (son_nC₆₀) was much less mobile in saturated sandy soil columns than an nC₆₀ sample prepared by solvent-exchanging from toluene to water (tol_nC₆₀), because son_nC₆₀ was considerably larger in size. However, son_nC₆₀ exhibited greater capability to bind 2,2′,5,5′-polychlorinated biphenyl (PCB), likely because its loosely packed structures rendered more pore spaces, which were favorable adsorption sites for PCB. Forming nC₆₀ samples in Suwannee River humic acid (SRHA) solution (instead of deionized water) only moderately affected the mobility of nC₆₀, but had very significant effects on the contaminant-binding capability of nC₆₀, especially when nC₆₀ was prepared using the solvent exchange method. Adding SRHA after the formation of nC₆₀ had varied effects on the mobility and contaminant-binding capability of nC₆₀, but the fundamental mechanism seems to be linked to how and to what extent SRHA had affected the aggregation/packing of C₆₀ monomers. An important environmental implication is that nC₆₀ formed under different environmental conditions might have vastly different effects on contaminant transport and risks.