The impact of natural organic matter on the aggregation, dissolution and sedimentation of cadmium telluride quantum dots and their interacting mechanism

This study investigated how natural organic matter (NOM) affected the aggregation, dissolution and sedimentation of cadmium telluride quantum dots (CdTe QDs) in artificial freshwater and seawater, with a focus on the impact of NOM species and the mechanism of CdTe QDs-NOM interactions. Results found that NOM dispersed CdTe QDs aggregates by providing electrosteric stabilization and promoted the dissolution by facilitating their contact in most cases. Among the tested NOM, fulvic acid (FA) was the most effective for releasing Cd 2+ in freshwater due to the strongest binding affinity complexing with CdTe QDs. The sedimentation rate of CdTe QDs was accelerated by humic acid (HA) or FA but was slowed by bovine serum albumin (BSA). Isothermal titration calorimetric experiments suggested that CdTe QDs interact with three species of NOM primarily through hydrophobic forces. Approximately five units of HA and three units of BSA bind to one unit of CdTe QDs with the binding affinity of 5.24 × 10 4  M −1 and 2.40 × 10 3  M −1 , respectively. While about eight units of CdTe QDs and one unit of CdTe QDs bind to one unit of FA for the two binding sites with the binding affinity of 1.62 × 10 6  M −1 and 2.16 × 10 3  M −1 . Fourier transform infrared, UV–vis adsorption and three-dimensional fluorescence spectroscopy indicated that QDs-HA interactions affecting HA structure were mainly assigned to the aromatic skeleton of HA and were dominated by the nano-form of CdTe QDs rather than Cd 2+ . This study is helpful for better understanding the fate and transport of CdTe QDs in aquatic environment.