Phenrat Tanapon, Saleh Navid, Sirk Kevin, Tilton Robert D, Lowry Gregory V
Departments of Biomedical Engineering, Chemical Engineering, Carnegie Institute of Technology, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213-3890, USA.
Environ Sci Technol. 2007 Jan 1;41(1):284-90. doi: 10.1021/es061349a.
Nanoscale zerovalent iron (NZVI) rapidly transforms many environmental contaminants to benign products and is a promising in-situ remediation agent. To be effective, NZVI should form stable dispersions in water such that it can be delivered in water-saturated porous media to the contaminated area. Limited mobility of NZVI has been reported, however, attributed to its rapid aggregation. This study uses dynamic light scattering to investigate the rapid aggregation of NZVI from single nanoparticles to micrometer size aggregates, and optical microscopy and sedimentation measurements to estimate the size of interconnected fractal aggregates formed. The rate of aggregation increased with increasing particle concentration and increasing saturation magnetization (i.e., the maximum intrinsic magnet moment) of the particles. During diffusion limited aggregation the primary particles (average radius = 20 nm) aggregate to micrometer-size aggregates in only 10 min, with average hydrodynamic radii ranging from 125 nm to 1.2 microm at a particle concentration of 2 mg/L (volume fraction(phi= 3.2 x 10(-7)) and 60 mg/L (phi = 9.5 x 10(-6)), respectively. Subsequently, these aggregates assemble themselves into fractal, chain-like clusters. At an initial concentration of just 60 mg/L, cluster sizes reach 20-70 microm in 30 min and rapidly sedimented from solution. Parallel experiments conducted with magnetite and hematite, coupled with extended DLVO theory and multiple regression analysis confirm that magnetic attractive forces between particles increase the rate of NZVI aggregation as compared to nonmagnetic particles.
纳米零价铁（NZVI）能迅速将许多环境污染物转化为无害产物，是一种很有前景的原位修复剂。为了发挥有效作用，NZVI应在水中形成稳定的分散体，以便能够输送到水饱和多孔介质中的污染区域。然而，据报道NZVI的迁移率有限，这归因于其快速聚集。本研究使用动态光散射来研究NZVI从单个纳米颗粒快速聚集为微米级聚集体的过程，并通过光学显微镜和沉降测量来估计形成的相互连接的分形聚集体的大小。聚集速率随颗粒浓度的增加以及颗粒饱和磁化强度（即最大固有磁矩）的增加而提高。在扩散限制聚集过程中，初级颗粒（平均半径 = 20 nm）在仅10分钟内就聚集为微米级聚集体，在颗粒浓度为2 mg/L（体积分数(phi = 3.2 x 10(-7))）和60 mg/L（phi = 9.5 x 10(-6)）时，平均流体动力学半径分别为125 nm至1.2微米。随后，这些聚集体自行组装成分形的链状簇。在初始浓度仅为60 mg/L时，簇尺寸在30分钟内达到20 - 70微米，并迅速从溶液中沉淀出来。用磁铁矿和赤铁矿进行的平行实验，结合扩展的DLVO理论和多元回归分析证实，与非磁性颗粒相比，颗粒之间的磁性吸引力增加了NZVI的聚集速率。
