University of Geneva, Institute of Environmental Science, Department F.-A. Forel for Environmental and Aquatic Sciences, Group of Environmental Physical Chemistry, Uni Carl Vogt, 66, boulevard Carl-Vogt, CH-1211 Geneva 4, Switzerland.
University of Vienna, Department of Environmental Geosciences and Environmental Science Research Network, Althanstr. 14 UZA2, 1090 Vienna, Austria.
Sci Total Environ. 2019 Feb 10;650(Pt 1):530-540. doi: 10.1016/j.scitotenv.2018.09.017. Epub 2018 Sep 4.
Understanding the transformation and transport of manufactured nanoparticles (NPs) in aquatic systems remains an important issue due to their potential hazard. Once released in aquatic systems, NPs will interact with natural compounds such as suspended inorganic particles and/or natural organic matter (NOM) and heteroaggregation will control their ultimate fate. Unfortunately, systematic experimental methods to study heteroaggregation are not straightforward and still scarce. In addition, the description of heteroaggregation rate constants and attachment efficiencies is still a matter of debate since no clear definition exists. In this work, an original cluster-cluster Monte Carlo model is developed to get an insight into heteroaggregation process descriptions. A two-component system composed of NPs and NOM fulvic acid monomers is investigated by considering several water models to cover a range of (relevant) conditions from fresh to marine waters. For that purpose, homo- and hetero- individual attachment efficiencies between NPs and NOM units are adjusted (NP-NP, NOM-NOM and NP-NOM). The influence of NP/NOM ratio, NOM-NOM homoaggregation versus heteroaggregation, and surface coating effects is studied systematically. From a quantitative point of view, aggregation rate constants as well as attachment efficiencies are calculated as a function of physical time so as to characterize the individual influence of each parameter and to allow future comparison with experimental data. Heteroaggregation processes and global attachment efficiencies corresponding to several mechanisms and depending on the evolution of heteroaggregate structures all along the simulations are defined. The calculation of attachment efficiency values is found dependent on NP/NOM concentration ratios via coating effects, by the initial set of elementary attachment efficiencies and influence of homoaggregation. Marine water represents a specific case of aggregation where all particle contacts are effective. On the other hand, in "ultrapure" and "fresh waters", a competition between homo- and heteroaggregation occurs depending on the initial attachment efficiencies therefore indicating that a subtle change in the NP surface properties as well as in the water chemistry have a significant impact on heteroaggregation processes.
由于制造的纳米颗粒（NPs）的潜在危害，了解它们在水生系统中的转化和传输仍然是一个重要问题。一旦在水生系统中释放，NPs 将与悬浮无机颗粒和/或天然有机物（NOM）等天然化合物相互作用，并且异质聚集将控制它们的最终命运。不幸的是，研究异质聚集的系统实验方法并不简单，而且仍然很少。此外，由于没有明确的定义，异质聚集速率常数和附着效率的描述仍然存在争议。在这项工作中，开发了一种原始的簇-簇蒙特卡罗模型，以深入了解异质聚集过程的描述。通过考虑几种水模型来考察由 NPs 和 NOM 富里酸单体组成的两组件系统，以涵盖从淡水到海水的一系列（相关）条件。为此，调整了 NPs 和 NOM 单元之间的同-异质个体附着效率（NP-NP、NOM-NOM 和 NP-NOM）。系统研究了 NP/NOM 比、NOM-NOM 同聚与异聚以及表面涂层效应的影响。从定量的角度来看，将聚集速率常数以及附着效率作为物理时间的函数进行计算，以表征每个参数的个体影响，并允许将来与实验数据进行比较。根据几种机制和异质聚集体结构的演变，定义了异质聚集过程和相应的整体附着效率。附着效率值的计算发现依赖于 NP/NOM 浓度比，通过涂层效应、初始基本附着效率以及同聚的影响。海水代表了一种特殊的聚集情况，其中所有颗粒接触都是有效的。另一方面，在“超纯”和“淡水”中，根据初始附着效率，同聚和异聚之间会发生竞争，这表明 NP 表面性质以及水化学的细微变化对异质聚集过程有重大影响。
