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 (nC(60)) 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 nC(60) 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 nC(60) suspensions dramatically increased the mobility of nC(60), as demonstrated by coincidental nanoparticle and nonreactive tracer effluent breakthrough curves (BTCs) and minimal nC(60) retention. When columns were preflushed with surfactant, nC(60) transport was significantly enhanced compared to that in the absence of a stabilizing agent. The presence of adsorbed Tween 80 resulted in nC(60) BTCs characterized by a declining plateau and retention profiles that exhibited hyperexponential decay. The observed nC(60) 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.