Enhanced mobility of fullerene (C₆₀) nanoparticles in the presence of stabilizing agents

Experimental and mathematical modeling studies were performed to examine the effects of stabilizing agents on the transport and retention of fullerene nanoparticles (nC₆₀) in water-saturated quartz sand. Three stabilizing systems were considered: naturally occurring compounds known to stabilize nanoparticles (Suwannee river humic acid (SRHA) and fulvic acid (SRFA)), synthetic additives used to enhance nanoparticle stability (Tween 80, a nonionic surfactant), and residual contaminants resulting from the manufacturing process (tetrahydrofuran (THF)). The results of column experiments demonstrated that the presence of THF, at concentrations up to 44.5 mg/L, did not alter nC₆₀ transport and retention behavior, whereas addition of SRHA (20 mg C/L), SRFA (20 mg C/L), or Tween 80 (1000 mg/L) to the influent nC₆₀ suspensions dramatically increased the mobility of nC ₆₀, as demonstrated by coincidental nanoparticle and nonreactive tracer effluent breakthrough curves (BTCs) and minimal nC₆₀ retention. When columns were preflushed with surfactant, nC₆₀ transport was significantly enhanced compared to that in the absence of a stabilizing agent. The presence of adsorbed Tween 80 resulted in nC₆₀ BTCs characterized by a declining plateau and retention profiles that exhibited hyperexponential decay. The observed nC₆₀ transport and retention behavior was accurately captured by a mathematical model that accounted for coupled surfactant adsorption-desorption dynamics, surfactant-nanoparticle interactions, and particle attachment kinetics.