Importance of heteroaggregation in aquatic systems

Article about Heteroaggregation of CeO₂ nanoparticles in presence of alginate and iron (III) oxide published in Science of The Total Environment.

When manufactured nanoparticles are released to natural waters, heteroaggregation between nanoparticles and water compounds is expected to occur and play a key role in nanoparticle fate, transport and transformation. In this work, the heteroaggregation between CeO₂ nanoparticles and Fe₂O₃ inorganic colloids, which represent the main inorganic fraction from Lake Geneva water, is studied. The heteroaggregation processes between CeO₂, Fe₂O₃ and alginate in multiple water samples are investigated using zeta potential and z-average diameter measurements. The kinetics of heteroaggregation of individual components as well as mixtures of CeO₂ nanoparticles and Fe₂O₃ colloids and alginate are studied using time resolved dynamic light scattering. The global attachment efficiency (α_global) is calculated using data from kinetic experiments. α_global for pristine CeO₂ nanoparticles varied from 0.5 to 0.7 in lake and synthetic waters and is found around 1 for pristine Fe₂O₃ and mixture CeO₂ and Fe₂O₃. Our findings demonstrate that heteroaggregation is highly dependent on environmental conditions and resulting electrostatic scenarios. No heteroaggregation at pH 8 between CeO₂, Fe₂O₃ and alginate is observed in ultrapure water, because of electrostatic repulsions between negatively charged compounds. In synthetic and lake waters, the situation is opposite. Indeed, specific adsorption of divalent cations and presence of salt are found to promote heteroaggregation via cation bridging and screening effects. The kinetic experiments indicate that aggregation rate of pristine Fe₂O₃ is higher (89 nm/min in lake water) compared to pristine CeO₂ nanoparticles (50 nm/min) and on the same level as mixture of CeO₂ and Fe₂O₃ (96 nm/min). Low alginate concentration, 0.25 mg/L, has no effect on heteroaggregation in mixture of CeO₂ and Fe₂O₃ in lake and synthetic waters. On the other hand, in natural water, the presence of higher alginate concentration, 2 mg/L, is found to reduce the heteroaggregation rate.

Oriekhova, Olena, and Serge Stoll. 2019. ‘Heteroaggregation of CeO2 Nanoparticles in Presence of Alginate and Iron (III) Oxide’. Science of The Total Environment 648 (January): 1171–78. https://doi.org/10.1016/j.scitotenv.2018.08.176.

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