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.

Analysis of Wear Particles Formed in Boundary-Lubricated Sliding Contacts

“…In order to get a simple equation, it was assumed that the interaction between the particles is negligible. It should be noticed that the interaction of particles may lead to agglomeration [33,34] and increased mass of the formed agglomerate. This would lead to higher centrifugal force and decrease the centrifuging time.…”

Stability of Fe-oxide nanoparticles coated with natural organic matter under relevant environmental conditions

“…The methodology for sample preparation of NOM-coated Fe-oxide NPs can be found in our previous study (Chekli et al, 2013a). In brief, 10 mL of concentrated Fe-oxide NPs (i.e.…”

“…different pH and ionic strength). Results from this study were also compared with our previous study (Chekli et al, 2013a) where HA were used as a NOM source instead of SRNOM.…”

“…In this study, we investigated the effect of NOM concentration on the stabilisation of manufactured Fe-oxide nanoparticles. While many studies employed humic acid (HA) as surrogate for NOM Chekli et al, 2013a), aquatic natural organic matter extracted from the Suwannee River NOM (SRNOM, Florida, USA) was utilised to better mimic environmental sample complexity. In fact, one of our previous studies (Chekli et al, 2013b) showed that SRNOM composition is quite complex and consists of humic substances as well as high molecular weight compounds (i.e.…”

Agglomeration behaviour of titanium dioxide nanoparticles in river waters: A multi-method approach combining light scattering and field-flow fractionation techniques

“…The benefit of using a multi-method approach to characterise ENPs in complex environmental samples has already been demonstrated (Domingos et al, 2009;Chekli et al, 2013a) but has not been systematically applied in aggregation studies using natural waters; b) to assess the strength and recovery factors and the structure of the aggregates formed in the river waters.…”