Natural Organic Matter-Mediated Phase Transfer of Quantum Dots in the Aquatic Environment

Abstract

Imminent commercialization of semiconductor quantum dots (QDs) has raised concerns regarding the potential environmental impact of these materials. Understanding the partitioning behavior and obtaining information on the mobility and persistence of QDs in water is key to evaluating potential ecological hazards posed by QDs in the environment The role of natural organic matter (NOM) in the phase transfer of trioctylphosphine oxide-capped CdSe QDs from an organic solvent to water has been investigated. Results show that humic and fulvic acids, which have been used as model NOM, facilitate the stabilization of organic-capped QDs in water in less than 24 h. Spectroscopic studies indicate that some or all of the organic ligands of QDs are conserved during the phase transfer. The displacement of organic ligands by NOM also appears to play a role in phase transfer. This NOM-mediated phase transfer has also been demonstrated using two natural surface water samples. This study presents the first evidence of the stabilization of QDs in water by humic substances in real environmental samples, illustrating that interactions with NOM will play a significant role in the fate and transport of QDs in natural aquatic systems.

Partitioning of hydrophobic CdSe quantum dots into aqueous dispersions of humic substances: Influence of capping-group functionality on the phase-transfer mechanism

“…Nonetheless, the raw correlation curves indicate that the average dimensions of QD-HA agglomerates were greater than those of QDs or HA alone. We previously reported similar data for TOPO-capped QDs after phase transfer into aqueous solutions of FA [46].…”

“…We recently reported that CdSe QDs capped with TOPO were transferred efficiently from hexane into aqueous solutions of humic acid (HA) or fulvic acid (FA) [46]. After phase transfer, QDs were present within agglomerates of HA or FA.…”

Degradation Products from Consumer Nanocomposites: A Case Study on Quantum Dot Lighting

“…Possibilities (i) and (ii) could arise if the polymer degrades to produce hydrophobic debris that adheres to the bulk optic, and the debris transports to the filtrate only in the presence of NOM that acts as a surfactant. In a related observation, Navarro et al 30 reported that NOM facilitated phase transfer of organic ligand capped CdSe QDs from organic solvent to the water phase. Here we used UV-vis and fluorescence spectrometry to look for suspended QDs in the filtrates but could not detect any spectral features characteristic of QDs.…”

PEI-conjugated AuNPs as a sensing platform for arsenic (AS-III)

“…Steric repulsive forces result from adsorbed polymers or surfactants used to modify NP surfaces or the adsorption of NOM in aquatic environments and prevent particles from coming into the close contact required for aggregation. When sterically stabilised particles approach each other, the interactions between the large chain-like adsorbed molecules cause repulsion due to an increasing number of chain-chain interactions at the expense of more favourable chain-solvent interactions [51]. Hydration forces arise in the case of nanoparticles modified with hydrophilic molecules which may have significant amounts of bound water; an additional repulsive force occurs hindering the approach of the two hydrated surfaces as those water molecules must be displaced for the particles to come into contact [52].…”