Cotransport of Titanium Dioxide and Fullerene Nanoparticles in Saturated Porous Media

This study investigated the cotransport of titanium dioxide nanoparticles (<i>n</i>TiO₂) and fullerene nanoparticles (<i>n</i>C₆₀), two of the most widely utilized nanoparticles, in saturated quartz sand under a series of ionic strengths in NaCl solutions (0.1–10 mM) at both pH 5 and 7. Under all examined ionic strengths at pH 5, both breakthrough curves and retained profiles of <i>n</i>TiO₂ in the copresence of <i>n</i>C₆₀ were similar to those without <i>n</i>C₆₀, indicating that <i>n</i>C₆₀ nanoparticles copresent in suspensions did not significantly affect the transport and retention of <i>n</i>TiO₂ in quartz sand at pH 5. In contrast, under all examined ionic strengths at pH 7, the breakthrough curves of <i>n</i>TiO₂ in the copresence of <i>n</i>C₆₀ in suspensions were higher and the retained profiles were lower than those without <i>n</i>C₆₀, which demonstrated that the presence of <i>n</i>C₆₀ in suspensions increased the rate of transport (decreased retention) of <i>n</i>TiO₂ in quartz sand at pH 7. Competition of deposition sites on quartz sand surfaces by the copresence of <i>n</i>C₆₀ was found to contribute to the increased <i>n</i>TiO₂ transport at pH 7. Under all examined ionic strength conditions at both pH 5 and 7, the breakthrough curves of <i>n</i>C₆₀ were reduced in the copresence of <i>n</i>TiO₂, and the corresponding retained profiles were higher than those without <i>n</i>TiO₂, indicating that the presence of <i>n</i>TiO₂ decreased the transport of <i>n</i>C₆₀ in quartz sand. Co-deposition of <i>n</i>C₆₀ with <i>n</i>TiO₂ in the form of <i>n</i>TiO₂-<i>n</i>C₆₀ clusters as well as the deposition of <i>n</i>C₆₀ onto previously deposited <i>n</i>TiO₂ were responsible for the increased <i>n</i>C₆₀ deposition in the presence of <i>n</i>TiO₂ at pH 5, whereas deposition of <i>n</i>C₆₀ onto surfaces of predeposited <i>n</i>TiO₂ was found to be responsible for the increased <i>n</i>C₆₀ deposition at pH 7