Determination of the Three-Dimensional Structure of Ferrihydrite Nanoparticle Aggregates
Determination of the Three-Dimensional Structure of Ferrihydrite Nanoparticle Aggregates
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DOI：
10.1021/la502128d
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发表时间：
2014-08-26
期刊：
影响因子：
3.9
通讯作者：
Banfield, Jillian F.
中科院分区：
文献类型：
--
作者：
Legg, Benjamin A.;Zhu, Mengqiang;Banfield, Jillian F.
聚集体影响纳米材料的反应性、胶体稳定性和传输行为，但表征聚集体基本结构特征的方法有限。在这里，低温透射电子显微镜（cryo-TEM）为基础的断层扫描是利用作为一种方法，用于直接成像的纳米颗粒在水悬浮液中的脆弱的聚集体，并从所得的三维结构模型中提取定量分形维数的方法被引入。结构定量方法是基于质量自相关函数，并直接与小角X射线散射（SAXS）模型。这使得能够准确表征聚集体结构，即使在聚集体簇尺寸高度多分散且传统SAXS建模不可靠的悬浮液中。该技术被应用于研究真实的水铁矿纳米颗粒悬浮液。通过比较层析测量与SAXS为基础的测量，我们推断，某些悬浮液中含有多分散聚集体的尺寸分布。在其他悬浮液中，分形类型的结构被识别为具有低的内在分形维数。分形维数低于预测的简单模型的颗粒聚集，这种低维使大，低密度的聚集体存在于稳定的胶体悬浮液。
Aggregation impacts the reactivity, colloidal stability, and transport behavior of nanomaterials, yet methods to characterize basic structural features of aggregates are limited. Here, cryo-transmission electron microscope (cryo-TEM) based tomography is utilized as a method for directly imaging fragile aggregates of nanoparticles in aqueous suspension and an approach for extracting quantitative fractal dimensions from the resulting three-dimensional structural models is introduced. The structural quantification approach is based upon the mass autocorrelation function, and is directly comparable with small-angle X-ray scattering (SAXS) models. This enables accurate characterization of aggregate structure, even in suspensions where the aggregate cluster size is highly polydisperse and traditional SAXS modeling is not reliable. This technique is applied to study real suspensions of ferrihydrite nanoparticles. By comparing tomographic measurements with SAXS-based measurements, we infer that certain suspensions contain polydisperse aggregate size distributions. In other suspensions, fractal-type structures are identified with low intrinsic fractal dimensions. The fractal dimensions are lower than would be predicted by simple models of particle aggregation, and this low dimensionality enables large, low-density aggregates to exist in stable colloidal suspension.