Collaborative Research: Real-time Investigations of Anisotropic Nanoparticle Aggregation and Consequences for Deposition in Porous Media

纳米颗粒在自然界中普遍存在，并且以不断增加的数量以各种形状和尺寸广泛生产。这些纳米颗粒通常在水中聚集，因此它们通常以聚集体而不是单个纳米颗粒的形式在环境介质中运输和存款。然而，纳米颗粒聚集体的结构如何影响纳米颗粒在环境中的运动还没有很好地理解。该项目的总体目标是更好地了解纳米颗粒聚集体与环境介质的相互作用，以及这些相互作用如何受到单个纳米颗粒的形状和大小的影响。这项工作的结果可以有利于设计和优化广泛的工程过程，如基于过滤器的水处理，地下水修复和药物输送。该项目还将通过涉及纳米材料视频和图片的外联活动，使K-12教育受益。其他推广计划包括1）夏季编码营，在俄亥俄州大学介绍中学女生STEM领域，和2）内布拉斯加州材料和纳米科学中心在内布拉斯加州林肯大学提供的各种科学活动，以扩大K-12学生接触材料科学和工程，纳米科学和纳米技术。此外，PI将利用内布拉斯加大学林肯分校现有的REU项目，在夏季培训俄亥俄州大学的本科生。在过去，纳米颗粒聚集和沉积通常被单独研究，将纳米颗粒在环境介质中的移动性与纳米颗粒聚集体的结构联系起来的研究有限。然而，新的证据表明，各向异性纳米粒子，环境中最常见的纳米粒子形式，往往形成非紧凑的聚集体。这些非紧密聚集体的形成不能用经典的胶体聚集理论来解释。此外，非致密聚集体经历不寻常的沉积和修改环境多孔介质中的流体力学，这是经典的过滤理论没有描述。从纳米颗粒聚集和沉积的所有步骤中获取和整合定量数据是非常必要的。本项目的研究目标包括：1）量化不同长宽比的纳米颗粒在水中的各向异性扩散动力学; 2）阐明初级纳米颗粒形状对聚集体形成动力学和形态结构的作用; 3）评估聚集体结构对聚集体在环境多孔介质中传输和沉积的影响。具有不同长径比的赤铁矿纳米颗粒（即，纳米球、纳米棒、纳米盘）将在研究中合成。先进的技术将被用来可视化和量化纳米粒子的扩散，聚集，运输和沉积在环境中的矩阵。此外，实验数据将被用来更新经典的过滤理论，预测纳米颗粒在多孔介质中的行为。这项工作的预期智力成果将包括发展一系列的定量指标，从测量各向异性扩散，聚集体形成，聚集体沉积和多孔介质中的流动动力学。这些定量表征将使我们能够阐明控制各向异性纳米颗粒聚集和沉积在环境多孔介质中的机制。这将反过来提高胶体科学原理在理解和预测纳米颗粒行为方面的实用性，如胶体布朗运动理论，胶体聚集理论和经典过滤理论。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nanoparticles are prevalent in nature and widely produced in a variety of shapes and sizes in ever-increasing quantities. These nanoparticles often aggregate in water, and thus they typically transport and deposit in environmental media in the form of aggregates instead of individual nanoparticles. However, how the structure of nanoparticle aggregates influence nanoparticles' movement in the environment is not well understood. The overall objective of this project is to better understand the interactions of nanoparticulate aggregates with environmental media and how these interactions can be governed by the shape and size of the individual nanoparticles. Findings from this work can benefit the design and optimization of a broad range of engineered processes, such as filter-based water treatment, groundwater remediation, and drug delivery. This project will also benefit K-12 education through outreach activities involving videos and pictures of nanomaterials. Additional outreach programs include 1) the Summer Coding Camp, at Ohio University to introduce middle school girls to the STEM fields, and 2) various science activities offered by Nebraska Center for Materials and Nanosciences at the University of Nebraska-Lincoln to broaden the exposure of K-12 students to materials science and engineering, nanoscience, and nanotechnology. In addition, the PIs will leverage the existing REU programs at the University of Nebraska-Lincoln to train Ohio university undergraduate students during summers. In the past, nanoparticle aggregation and deposition were often studied separately, with limited research linking mobility of nanoparticles in environmental media to the structure of nanoparticle aggregates. However, new evidence suggests that anisotropic nanoparticles, the most common form of nanoparticles in the environment, often form non-compact aggregates. The formation of these non-compact aggregates cannot be explained by classic colloidal aggregation theories. Moreover, non-compact aggregates undergo unusual deposition and modify hydrodynamics in environmental porous media, which is not described by the classical filtration theory. Acquisition and integration of quantitative data from all steps involved in nanoparticle aggregation and deposition is critically needed. The research objectives of this project include: 1) Quantifying the anisotropic diffusion dynamics of nanoparticles with various aspect ratios in water; 2) Elucidating the role of the shape of primary nanoparticles on the formation kinetics and morphological structure of aggregates; and 3) Evaluating the impact of aggregate structure on the transport and deposition of aggregates in environmental porous media. Hematite nanoparticles with different aspect ratios (i.e., nanosphere, nanorod, nanodisk) will be synthesized in the study. Advanced techniques will be employed to visualize and quantify nanoparticle diffusion, aggregation, transport, and deposition in environmental matrices. Furthermore, the experimental data will be used to update classical filtration theory for predicting nanoparticle behaviors in porous media. The expected intellectual outcomes from this work will include development of a series of quantitative metrics from measurements of anisotropic diffusion, aggregate formation, and aggregate deposition and flow dynamics in porous media. These quantitative characterizations will allow us to elucidate the mechanisms which control anisotropic nanoparticle aggregation and deposition in environmental porous media. This will, in turn, improve the utility of colloidal science principles in understanding and predicting nanoparticle behaviors, such as colloid Brownian motion theory, colloid aggregation theory, and the classical filtration theory.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.