Chen Kai Loon, Mylon Steven E, Elimelech Menachem
Department of Chemical Engineering, Environmental Engineering Program, Yale University, New Haven, Connecticut 06520-8286, USA.
Environ Sci Technol. 2006 Mar 1;40(5):1516-23. doi: 10.1021/es0518068.
The early stage aggregation kinetics of bare and alginate-coated hematite nanoparticles are acquired through time-resolved dynamic light scattering (DLS). Varying concentrations of monovalent (NaCl) and divalent (MgCl2 and CaCl2) electrolytes are employed to induce aggregation. In the presence of NaCl and MgCl2, the alginate-coated hematite nanoparticles undergo aggregation through electrostatic destabilization as described by the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. This is ascertained through examination of the favorable and unfavorable regimes of the stability curves depicting the attachment efficiency as a function of salt concentration. Additional evidence may be found in the aggregation kinetics of alginate-coated particles, which, under favorable aggregation conditions, are reasonably close to that of bare hematite nanoparticles. However, in the presence of CaCl2, the aggregate growth rate of alginate-coated hematite nanoparticles is much higher than that which conventional diffusive aggregation predicts. Dispersed hematite primary particles and lower-order aggregates enmeshed within extended alginate gel networks were observed under transmission electron microscope (TEM). The proposed mechanism for enhanced aggregation suggests an apparent increase in the collision radii of alginate-coated hematite nanoparticles through alginate gel network formation from the particle surface. Additionally, cross-linking between unadsorbed (suspended) alginate macromolecules may form bridges between hematite-alginate gel clusters. It is further established that the presence of background electrolyte NaCl in solution is detrimental to the calcium-induced enhanced aggregation.
通过时间分辨动态光散射（DLS）获得了裸露的和海藻酸盐包覆的赤铁矿纳米颗粒的早期聚集动力学。使用不同浓度的单价（NaCl）和二价（MgCl2和CaCl2）电解质来诱导聚集。在NaCl和MgCl2存在下，海藻酸盐包覆的赤铁矿纳米颗粒通过经典的Derjaguin-Landau-Verwey-Overbeek（DLVO）理论所描述的静电失稳作用发生聚集。这是通过检查稳定性曲线的有利和不利区域来确定的，该曲线描述了附着效率随盐浓度的变化。在海藻酸盐包覆颗粒的聚集动力学中可以找到更多证据，在有利的聚集条件下，其聚集动力学与裸露的赤铁矿纳米颗粒的聚集动力学相当接近。然而，在CaCl2存在下，海藻酸盐包覆的赤铁矿纳米颗粒的聚集体生长速率远高于传统扩散聚集所预测的速率。在透射电子显微镜（TEM）下观察到分散的赤铁矿初级颗粒和包裹在扩展的海藻酸盐凝胶网络中的低阶聚集体。提出的增强聚集机制表明，通过从颗粒表面形成海藻酸盐凝胶网络，海藻酸盐包覆的赤铁矿纳米颗粒的碰撞半径明显增加。此外，未吸附（悬浮）的海藻酸盐大分子之间的交联可能在赤铁矿-海藻酸盐凝胶簇之间形成桥梁。进一步确定，溶液中背景电解质NaCl的存在不利于钙诱导的增强聚集。
