Colloidal stability and aggregation kinetics of nanocrystal CdSe/ZnS quantum dots in aqueous systems: effects of pH and organic ligands

• Published in: Journal of nanoparticle research : an interdisciplinary forum for nanoscale science and technology 2020-11, Vol.22 (11), Article 349
• Main Authors: Li, Chunyan, Hassan, Asra, Palmai, Marcell, Snee, Preston T., Baveye, Philippe C., Darnault, Christophe J. G.
• Format: Article
• Language: English
• Subjects: Acetic acid; Agglomeration; Aggregation behavior; Aqueous environments; Bioavailability; Cadmium selenides; Characterization and Evaluation of Materials; Chemical Sciences; Chemistry and Materials Science; Citric acid; Coordination compounds; Environmental Sciences; Inorganic Chemistry; Kinetics; Lasers; Ligands; Materials Science; Nanocrystals; Nanoparticles; Nanotechnology; Optical Devices; Optics; Oxalic acid; pH effects; Photonics; Physical Chemistry; Public health; Quantum dots; Research Paper; Risk assessment; Stability; Toxicity; Zeta potential; Zinc sulfide
• ISSN: 1388-0764; 1572-896X
• DOI: 10.1007/s11051-020-05080-6

Advancing the understanding of stability behavior and aggregation mechanisms of quantum dot (QD) nanoparticles in natural systems is fundamental to elucidate their fate and transport, bioavailability, environmental toxicity, and subsequent risks to environmental and public health. This study investigates the aggregation kinetics and colloidal stability of QDs as a function of pH and organic ligands—acetate, oxalate, and citrate. Results indicated an influence of solution chemistry upon both the aggregation kinetics and colloidal stability of QDs. The zeta potential of QDs, with a point of zero charge (pH PZC ) between pH 1.5 and 3.5, decreased (from positive to negative) with increasing solution pH. The diameter of QD aggregates was ~500 nm in the region of pH PZC and decreased with pH when pH > pH PZC to 40–50 nm. Organic ligands enhanced the negative zeta potentials of QDs at pH = 1.5 and pH = 3.5. The impact of ligands on the levels and rates of aggregation was pH dependent; furthermore, the presence of ligands increased the diameters of all QD nanoaggregates at pH 3.5 (e.g., 817 nm for 0.001 M citrate). QDs and organic ligand-QD nanoparticle complexes remained stable across pH values 5–9. In terms of environmental and toxicological risk assessments, results revealed that QDs and organic ligand-QD nanoparticle complexes remain stable across a significant range of pH values (5–9), indicating that this stability behavior could enhance the mobility, transport, and residence time of QDs in terrestrial and aqueous environments, and facilitate the bioavailability of QDs, therefore augmenting the adverse effects of QDs in the environment.