Agrosphere Institute, IBG-3, Forschungszentrum Jülich GmbH, Jülich, Germany.
Water Res. 2013 May 1;47(7):2572-82. doi: 10.1016/j.watres.2013.02.025. Epub 2013 Feb 26.
Saturated sand-packed column experiments were conducted to investigate the influence of physicochemical factors on the transport and retention of surfactant stabilized silver nanoparticles (AgNPs). The normalized concentration in breakthrough curves (BTCs) of AgNPs increased with a decrease in solution ionic strength (IS), and an increase in water velocity, sand grain size, and input concentration (Co). In contrast to conventional filtration theory, retention profiles (RPs) for AgNPs exhibited uniform, nonmonotonic, or hyperexponential shapes that were sensitive to physicochemical conditions. The experimental BTCs and RPs with uniform or hyperexponential shape were well described using a numerical model that considers time- and depth-dependent retention. The simulated maximum retained concentration on the solid phase (Smax) and the retention rate coefficient (k1) increased with IS and as the grain size and/or Co decreased. The RPs were more hyperexponential in finer textured sand and at lower Co because of their higher values of Smax. Conversely, RPs were nonmonotonic or uniform at higher Co and in coarser sand that had lower values of Smax, and tended to exhibit higher peak concentrations in the RPs at lower velocities and at higher solution IS. These observations indicate that uniform and nonmonotonic RPs occurred under conditions when Smax was approaching filled conditions. Nonmonotonic RPs had peak concentrations at greater distances in the presence of excess amounts of surfactant, suggesting that competition between AgNPs and surfactant diminished Smax close to the column inlet. The sensitivity of the nonmonotonic RPs to IS and velocity in coarser textured sand indicates that AgNPs were partially interacting in a secondary minimum. However, elimination of the secondary minimum only produced recovery of a small portion (<10%) of the retained AgNPs. These results imply that AgNPs were largely irreversibly interacting in a primary minimum associated with microscopic heterogeneity.
开展了饱和砂填充柱实验，以研究物理化学因素对表面活性剂稳定的银纳米颗粒（AgNPs）的迁移和滞留的影响。AgNPs 在穿透曲线（BTC）中的归一化浓度随溶液离子强度（IS）的降低而增加，随水流速度、砂粒径和输入浓度（Co）的增加而增加。与传统过滤理论相反，AgNPs 的保留分布（RP）呈均匀、非单调或超指数形状，对物理化学条件敏感。采用考虑时间和深度相关保留的数值模型，很好地描述了具有均匀或超指数形状的实验 BTC 和 RP。模拟的固相最大保留浓度（Smax）和保留速率系数（k1）随 IS 以及粒径和/或 Co 的减小而增加。在更细质地的砂和更低的 Co 下，由于 Smax 值较高，RP 更为超指数。相反，在更高的 Co 和更粗的砂中，RP 呈非单调或均匀，由于 Smax 值较低，其 RP 中的峰值浓度较高，在较低的流速和较高的溶液 IS 下，RP 中的峰值浓度较高。这些观察结果表明，在 Smax 接近充满条件的情况下，出现了均匀和非单调的 RP。在存在过量表面活性剂的情况下，非单调 RP 具有更高的峰值浓度，这表明 AgNPs 和表面活性剂之间的竞争在靠近柱入口的地方降低了 Smax。在较粗质地的砂中，非单调 RP 对 IS 和速度的敏感性表明，AgNPs 在二级最小值处部分相互作用。然而，消除二级最小值仅恢复了一小部分（<10%）被保留的 AgNPs。这些结果表明，AgNPs 主要与微观非均质性相关的初级最小值不可逆地相互作用。
