Studies on fate and transport of engineered nanomaterials are invaluable in predicting their environmental impact. The partitioning, mobility, and persistence of quantum dots (QDs) in the environment may dramatically influence their toxicity. We report the influence of humic acids (HA) on the phase transfer of hydrophobically capped QDs from hexane to water. QDs capped with various capping agents, such as tri-n octylphosphine oxide, tetradecylphosphonic acid, and oleic acid, together with model ligands (syringic acid and cetyltrimethylammonium bromide) were used to elucidate mechanisms of interactions between HA and QDs. Results showed that phase-transferred QDs were intact and stabilized by humic substances, but on longer timescales, Cd2+ leached into the aqueous solution.  Our data suggest that two mechanisms act in concert to promote phase transfer of QD-HA agglomerates: (1) hydrophobic interactions between hydrocarbon moieties of HA and alkyl chains of capping agents, and (2) displacement of capping groups by Lewis basic groups of HA.

Mechanisms of interaction between humic acid and hydrophobic CdSe quantum dots facilitating the partitioning into aqueous phase

240th National Meeting (2010)

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