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Environmental Engineering Research 2022;27(6): 210470 DOI: https://doi.org/10.4491/eer.2021.470
The effect of ionic strength, pH and natural organic matter on heteroaggregation of CeO2 nanoparticles with montmorillonite clay minerals
Sujin Bae1, John J. Lenhart2, and Yu Sik Hwang1,3 
1Environmental Fate & Exposure Research Group, Korea Institute of Toxicology, Jinju, 52834, Republic of Korea
2Department of Civil, Environmental and Geodetic Engineering, The Ohio State University, Columbus, Ohio 43210, United States
3Department of Human and Environmental Toxicology, University of Science & Technology, Daejeon 34113, Republic of Korea
Corresponding Author: Yu Sik Hwang ,Tel: +82-55-750-3834, Fax: +82-55-750-3824, Email: yshwang@kitox.re.kr
Received: September 27, 2021;  Accepted: December 10, 2021.
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An accurate assessment of the fate and transport of engineered nanoparticles (ENPs) in aquatic environments hinges on developing an understanding of interaction between ENPs and natural colloids. In this study, we investigated the effects of pH and natural organic matter (NOM) on homoaggregation of CeO2 nanoparticles and their heteroaggregation with montmorillonite clay minerals. Time-resolved dynamic light scattering (TR-DLS) was employed to investigate the aggregation kinetics as function of electrolyte concentration in both homo- and heteroaggregation scenarios. The surface charge of CeO2 nanoparticles changed from positive to negative with pH increase while montmorillonite was negatively charged over the range of pH 4−11. At low pH, the critical coagulation concentration (CCC) of the montmorillonite-CeO2 mixtures shifted to a lower electrolyte concentration when compared to the homogenous system, indicating the negatively charged montmorillonite reduced the stability of positively charged CeO2 via heteroaggregation. In contrast, at high pH, the mixtures were stable because both montmorillonite and CeO2 nanoparticles were negatively charged. The presence of humic acid stabilized the systems against homo- and heteroaggregation. Our results suggest that the complex interactions between ENPs, natural colloids, and NOM should be considered to better understand the fate and transport of ENPs in realistic aquatic environments.
Keywords: CeO2 nanoparticle | Heteroaggregation | Homoaggregation | Montmorillonite | Natural organic matter
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