State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P. O. Box 2871, Beijing 100085, China.
State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P. O. Box 2871, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Sci Total Environ. 2021 Aug 25;784:147190. doi: 10.1016/j.scitotenv.2021.147190. Epub 2021 Apr 19.
This study investigated heteroaggregation of three surface-functionalized polystyrene nanoparticles (PSNPs), i.e. negatively charged unfunctionalized nanoparticles (Bare-PS) and carboxylated nanoparticles (COOH-PS), and positively charged amino-functionalized nanoparticles (NH-PS), with two model natural colloids, positively charged hematite and negatively charged kaolin, respectively. Heteroaggregation was conducted at a constant natural colloid concentration and variable NP/colloid concentration ratios. Electrostatic interaction was the main mechanism driving the formation of heteroaggregates. In binary systems containing hematite and Bare-PS/COOH-PS, a charge neutralization - charge inverse mechanism was observed with the increase of PSNP concentration. At NP/hemetite concentration ratios much smaller or larger than the full charge neutralization point, the primary heteroaggregates were stable, while full charge neutralization induced the formation of large secondary heteroaggregates. Large aggregates were not observed in suspensions containing kaolin and NH-PS, as highly positively charged NH-PS reversed surface charges of kaolin at extremely low concentrations. Heteroaggregation between PSNPs and natural colloids with the same charge is unfavorable due to strong electrostatic repulsion. In the presence of electrolytes, homoaggregation and heteroaggregation both occurred, and homoaggregation of hematite played a key role when the concentration of PSNPs was low. The presence of Suwannee River natural organic matter (SRNOM) could modify surface charges of nanoparticles, and thus affect heteroaggregation behaviors of the binary suspension. When SRNOM and electrolytes were both present, whether SRNOM inducing or hindering the stability of the binary system was a combined effect of NP/colloid concentration ratios, SRNOM concentrations, electrolyte types and ionic strength. Mechanisms extensively reported in homoaggregation such as steric hindrance and cation bridging effects between SRNOM and Ca also stand for heteroaggregation. These results highlight the critical role of surface modification on the environmental behaviors of NPs, and will underpin our understanding of the fate and transport of NPs in the aquatic environment.
本研究考察了三种表面功能化聚苯乙烯纳米颗粒（PSNP），即不带电的未功能化纳米颗粒（Bare-PS）和羧基化纳米颗粒（COOH-PS），以及带正电的氨基功能化纳米颗粒（NH-PS）与两种模型天然胶体，即带正电的赤铁矿和带负电的高岭土之间的异质聚集。在恒定的天然胶体浓度和可变的 NP/胶体浓度比下进行异质聚集。静电相互作用是驱动异质聚集形成的主要机制。在含有赤铁矿和 Bare-PS/COOH-PS 的二元体系中，随着 PSNP 浓度的增加，观察到电荷中和-电荷反转机制。在 NP/赤铁矿浓度比远小于或大于完全电荷中和点时，主要的异质聚集体是稳定的，而完全电荷中和导致大的二次异质聚集体的形成。在含有高岭土和 NH-PS 的悬浮液中未观察到大的聚集体，因为高度带正电的 NH-PS 在极低浓度下反转了高岭土的表面电荷。带相同电荷的 PSNP 和天然胶体之间的异质聚集是不利的，因为强静电排斥。在电解质存在的情况下，均相聚集和异质聚集都发生，并且当 PSNP 浓度较低时，赤铁矿的均相聚集起着关键作用。苏万尼河天然有机物（SRNOM）的存在可以改变纳米颗粒的表面电荷，从而影响二元悬浮液的异质聚集行为。当 SRNOM 和电解质都存在时，SRNOM 是否诱导或阻碍二元体系的稳定性是 NP/胶体浓度比、SRNOM 浓度、电解质类型和离子强度的综合效应。在均相聚集中广泛报道的机制，如空间位阻和 SRNOM 与 Ca 之间的阳离子桥接效应，也适用于异质聚集。这些结果强调了表面修饰对纳米颗粒环境行为的关键作用，并将支持我们对纳米颗粒在水环境中归宿和传输的理解。
