Colloidal stability and aggregation kinetics of nanocrystal CdSe/ZnS quantum dots in aqueous systems: effects of pH and
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RESEARCH PAPER
Colloidal stability and aggregation kinetics of nanocrystal CdSe/ZnS quantum dots in aqueous systems: effects of pH and organic ligands Chunyan Li & Asra Hassan & Marcell Palmai & Preston T. Snee & Philippe C. Baveye & Christophe J. G. Darnault Received: 3 March 2020 / Accepted: 4 November 2020 # Springer Nature B.V. 2020
Abstract 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 (pHPZC) 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 pHPZC and decreased with pH when pH > pHPZC 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.
C. Li : C. J. G. Darnault (*) Department of Environmental Engineering and Earth Sciences, Laboratory of Hydrogeoscience and Biological Engineering, L.G. Rich Environmental Laboratory, Clemson University, 342 Computer Court, Anderson, SC 29625, USA e-mail: [email protected]
Introduction
A. Hassan : M. Palmai : P. T. Snee Department of Chemistry, University of Illinois at Chicago, 845 W. Taylor St, Chicago, IL 60607, USA P. C. Baveye Unité ECOSYS, AgroParisTech, Université Paris-Saclay, Avenue Lucien Brétignières, 78850 Thiverval-Grignon, France
Keywords Quantum dot nanoparticles . pH . Acetate . Oxalate . Citrate . Aggregation
Elucidating the fate, transport, retention, transformation, and reactivity of nanoparticles in the environment (Batley et al. 2013; Bundschuh et al. 2019; Godinez and Darnault 2011; Godinez et al. 2013; Gogos et al. 2019; Hotze et al. 2010; Keller et al. 2010; Li et al. 2020a; Liu et al. 2018; Lowry et al. 2012; Markiewicz et al. 2018; Montaño et al. 2014; Part et al. 2016; Reddy et al. 2014; Su et al. 2019; Ubaid e
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