title: Assessing the aggregation behaviour of iron oxide nanoparticles under relevant environmental conditions using a multi-method approach.
abstract: Iron nanoparticles are becoming increasingly popular for the treatment of contaminated soil and groundwater; however, their mobility and reactivity in subsurface environments are significantly affected by their tendency to aggregate. Assessing their stability under environmental conditions is crucial for determining their environmental fate. A multi-method approach (including different size-measurement techniques and the DLVO theory) was used to thoroughly characterise the behaviour of iron oxide nanoparticles (Fe2O3NPs) under environmentally relevant conditions. Although recent studies have demonstrated the importance of using a multi-method approach when characterising nanoparticles, the majority of current studies continue to use a single-method approach. Under some soil conditions (i.e. pH 7, 10 mM NaCl and 2 mM CaCl2) and increasing particle concentration, Fe2O3NPs underwent extensive aggregation to form large aggregates (>1 μm). Coating the nanoparticles with dissolved organic matter (DOM) was investigated as an alternative "green" solution to overcoming the aggregation issue instead of using the more commonly proposed polyelectrolytes. At high concentrations, DOM effectively covered the surface of the Fe2O3NPs, thereby conferring negative surface charge on the particles across a wide range of pH values. This provided electrostatic stabilisation and considerably reduced the particle aggregation effect. DOM-coated Fe2O3NPs also proved to be more stable under high ionic strength conditions. The presence of CaCl2, however, even at low concentrations, induced the aggregation of DOM-coated Fe2O3NPs, mainly via charge neutralisation and bridging. This has significant implications in regards to the reactivity and fate of these materials in the environment.
authors.affiliation: School of Civil and Environmental Engineering, University of Technology, Sydney (UTS), Post Box 129, Broadway, NSW 2007, Australia.
authors.forename: Laura
authors.initials: L
authors.lastname: Chekli
authors.forename: Sherub
authors.initials: S
authors.lastname: Phuntsho
authors.forename: Maitreyee
authors.initials: M
authors.lastname: Roy
authors.forename: Enzo
authors.initials: E
authors.lastname: Lombi
authors.forename: Erica
authors.initials: E
authors.lastname: Donner
authors.forename: Ho Kyong
authors.initials: HK
authors.lastname: Shon
mesh_terms: D004777:Environment; D005290:Ferric Compounds / Q000737:chemistry*; D031521:Fractionation, Field Flow; D006812:Humic Substances / Q000032:analysis; D057446:Hydrodynamics; D006863:Hydrogen-Ion Concentration; D008027:Light; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D009994:Osmolar Concentration; D012542:Scattering, Radiation; D055672:Static Electricity
chemical_list: D005290:Ferric Compounds; D006812:Humic Substances; C000499:ferric oxide
keywords: Aggregation; DLVO theory; Flow field-flow fractionation; Iron oxide; Nanoparticles; Surface coating