Organic matters adsorbed on goethite inhibited the heterogeneous aggregation and adsorption of CdSe quantum dots: Experiments and extended DLVO theory

The widespread use of Cd-based quantum dots (Cd-QDs) has led to their inevitable release into the environment, and the prevalent iron oxides and natural organic matter (NOM) are the key factors affecting the environmental behavior and fate of Cd-QDs. However, the impact of NOM adsorbed on iron oxides on the behavior of Cd-QDs with iron oxides and the mechanism of its interaction are not clear. In this study, two kinds of water-soluble QDs (CdSe QDs and core-shell CdSe/ZnS QDs) were selected to study the aggregation and adsorption behavior on goethite (Goe) and goethite-humic acid/fulvic acid composites (Goe-HA/FA). Aggregation kinetics and adsorption experiments between QDs and Goe(-HA/FA), characterization, and extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory calculations indicated that electrostatic interaction was the dominant force for QDs adsorption on Goe(-HA/FA). HA/FA changed the surface charge of Goe and increased the electrostatic repulsion and steric hindrance between the particles, which in turn inhibited the adsorption of QDs on Goe. Besides, unsubstituted aromatic carbons, carboxy carbons, and carbonyl carbons played an important role in the adsorption process, and chemisorption occurred between QDs and Goe(-HA/FA). Our findings are important for better assessing the transport, fate, and potential environmental impacts and risks of Cd-QDs in iron-rich environments. [Display omitted] The continuous production and use of cadmium-based quantum dots (Cd-QDs) leads to their unavoidable release into the environment, where natural organic matter (NOM) and iron oxides could affect their fate. In this study, we demonstrated that electrostatic interaction dominated the adsorption of Cd-QDs on goethite, while NOM adsorbed on the surface of goethite inhibited the adsorption of Cd-QDs by changing its surface charge and increasing the electrostatic repulsion and steric hindrance. Our findings provide a theoretical basis for understanding the interactions of Cd-QDs with iron oxides and iron oxide-organic matter adsorption composites. •There were adsorption behaviors between QDs and Goe(-HA/FA).•Electrostatic interaction dominated the adsorption of QDs on Goe(-HA/FA).•Adsorption of HA/FA transformed the Goe surface from positively to negatively charged.•HA/FA inhibited the adsorption of QDs on Goe by electrostatic repulsion and steric hindrance.