The aggregation and sedimentation of two different sized copper oxide nanoparticles in soil solutions: Dependence on pH and dissolved organic matter.

Copper oxide nanoparticles (CuO NPs) in soil have received considerable attention because of their potential impact on the environment. In the present study, the stability of CuO NPs (50 nm and 80 nm) in eight soil solutions as well as the major influencing factors was investigated. The results showed that hetero-aggregation between natural colloids and NPs dominated the first stage of aggregation, afterwards the two different sized CuO NPs exhibited different aggregation behaviors. The aggregation of 80 nm CuO was inconspicuous except for notable aggregation observed in JX soil solution where the zeta potential of CuO NPs is close to zero. While for 50 nm CuO NPs, the aggregate size sharply decreased and the aggregates gradually reached a stable state. Further, the sedimentation rate and residual concentration of 50 nm CuO were found to be greater than those of 80 nm CuO. The residual amount of 80 nm CuO in the JX soil solution was lower than those in other soil solutions owing to the lowest zeta potential of the NPs. The pH of the soil solution has a significant effect on the stability of CuO NPs because of the shifting of the zeta potential of the NPs. In addition, dissolved organic carbon showed a statistically significant positive correlation with the residual concentration of CuO NPs. These findings imply the properties of CuO NPs as well as environmental factors including pH and DOC play key role in determining the fate, transport, and bioavailability of CuO NPs in soils.

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Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.