Abstract
Significant advances have been made on our understanding of the fate and transport of engineered nanomaterials. One unexplored aspect of nanoparticle aggregation is how environmental stimuli such as light exposure and temperature variations affect the mobility of engineered nanoparticles. In this study, TiO2, ZnO, and CeO2 were chosen as model materials for investigating the mobility of nanoparticles under three external stimuli: heat, light and sonication. Sunlight and high power sonication were able to partially disagglomerate metal oxide clusters, but primary particles bonded by solid state necks were left intact. A cycle of temperature increase from 25°C to 65°C and then decrease back was found to disagglomerate the compact clusters in the heating phase and reagglomerate them as more open fractal structures during the cooling phase. A fractal model summing the pair-wise DLVO interactions between primary particles within two fractal agglomerates predicts weak attractions on the order of a few kT. Our study shows that common environmental stimuli such as light exposure or temperature variation can disagglomerate nanoparticle clusters and enhance their mobility in open waters. This phenomenon warrants attention since it is likely that metal oxide nanoparticles will experience these natural stimuli during their transport in the environment.
Highlights
A great amount of effort has been devoted to evaluating the potential environmental impacts of nanotechnology [1,2,3,4] due to the increasing applications of nanomaterials
Studies conducted in different aqueous media, including synthetic matrices [6,7,8,9,10,11,12,13,14,15,16], natural waters [17,18], and culture media [19,20] have indicate that pH, ionic strength [7, 9,10,11], nanoparticle concentration [10], and natural organic matter [6,8] affect nanoparticle aggregation
The bonding attractions between primary particles range from strong chemical bonds, established during the cooling phase of their synthesis, that form essentially unbreakable aggregates to weak physical interactions such as van der Waals forces which form agglomerates that are readily disrupted by sample preparation methods [21,22,23]
Summary
A great amount of effort has been devoted to evaluating the potential environmental impacts of nanotechnology [1,2,3,4] due to the increasing applications of nanomaterials. Studies conducted in different aqueous media, including synthetic matrices [6,7,8,9,10,11,12,13,14,15,16], natural waters [17,18], and culture media [19,20] have indicate that pH, ionic strength [7, 9,10,11], nanoparticle concentration [10], and natural organic matter [6,8] affect nanoparticle aggregation Questions such as how the sintered structure and the presence of clay minerals affect the aggregation process remain to be answered. This structural conformation and its effects on the stability and mobility of nanoparticles have not been addressed to any significant extent in the environmental context
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