Department of Geography and Environmental Engineering, Johns Hopkins University, Baltimore, Maryland 21218-2686, United States.
Environ Sci Technol. 2011 Jul 1;45(13):5564-71. doi: 10.1021/es200157h. Epub 2011 Jun 1.
The aggregation kinetics of silver nanoparticles (AgNPs) that were coated with two commonly used capping agents-citrate and polyvinylpyrrolidone (PVP)--were investigated. Time-resolved dynamic light scattering (DLS) was employed to measure the aggregation kinetics of the AgNPs over a range of monovalent and divalent electrolyte concentrations. The aggregation behavior of citrate-coated AgNPs in NaCl was in excellent agreement with the predictions based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, and the Hamaker constant of citrate-coated AgNPs in aqueous solutions was derived to be 3.7 × 10(-20) J. Divalent electrolytes were more efficient in destabilizing the citrate-coated AgNPs, as indicated by the considerably lower critical coagulation concentrations (2.1 mM CaCl(2) and 2.7 mM MgCl(2) vs 47.6 mM NaCl). The PVP-coated AgNPs were significantly more stable than citrate-coated AgNPs in both NaCl and CaCl(2), which is likely due to steric repulsion imparted by the large, noncharged polymers. The addition of humic acid resulted in the adsorption of the macromolecules on both citrate- and PVP-coated AgNPs. The adsorption of humic acid induced additional electrosteric repulsion that elevated the stability of both nanoparticles in suspensions containing NaCl or low concentrations of CaCl(2). Conversely, enhanced aggregation occurred for both nanoparticles at high CaCl(2) concentrations due to interparticle bridging by humic acid aggregates.
研究了两种常用稳定剂（柠檬酸盐和聚乙烯吡咯烷酮（PVP））包覆的银纳米颗粒（AgNPs）的聚集动力学。采用时间分辨动态光散射（DLS）测量了在一系列单价和二价电解质浓度范围内AgNPs 的聚集动力学。柠檬酸盐包覆的AgNPs 在 NaCl 中的聚集行为与基于德加古林-兰德维韦-奥弗贝克（DLVO）理论的预测非常吻合，并推导出柠檬酸盐包覆的AgNPs 在水溶液中的哈马克常数为 3.7×10(-20) J。二价电解质更有效地使柠檬酸盐包覆的 AgNPs 不稳定，这表明其临界聚沉浓度明显较低（2.1 mM CaCl2 和 2.7 mM MgCl2 与 47.6 mM NaCl 相比）。在 NaCl 和 CaCl2 中，PVP 包覆的 AgNPs 比柠檬酸盐包覆的 AgNPs 稳定得多，这可能是由于大的非带电聚合物赋予的空间排斥作用。腐殖酸的加入导致大分子在柠檬酸盐和 PVP 包覆的 AgNPs 上的吸附。腐殖酸的吸附诱导了额外的电动排斥，从而提高了这两种纳米颗粒在含有 NaCl 或低浓度 CaCl2 的悬浮液中的稳定性。相反，由于腐殖酸聚集体的颗粒间桥接，在高浓度 CaCl2 下，两种纳米颗粒的聚集都增强了。
