Solution conditions can enhance or inhibit iron oxide nanoparticle aggregation and modify surface chemistry substantially, resulting in large changes in redox reactivity. For example, at low concentrations of natural organic matter, goethite nanoparticles substantially aggregate, while at higher concentrations, goethite aggregation is strongly inhibited. Here, results tracking reactivity and the degree of aggregation, using the rate of reductive degradation of 4-chloronitrobenzene or oxidation of hydroquinone as assays of reactivity and dynamic light scattering and cryogenic transmission electron microscopy to quantify aggregation state, as a function of solution conditions are presented. In general, reactivity drops with increasing aggregation state. However, with the addition of natural organic matter, trends changed substantially. For example, increased aggregation was observed with trace concentrations of natural organic matter but without a substantial drop in reactivity. At higher concentrations of natural organic matter, aggregation and reactivity were suppressed, which is consistent with the natural organic matter blocking surface sites. Results from experiments with different iron oxide minerals and varied solution conditions (e.g., ionic strength, buffer identity and concentration, NOM identity and concentration, and more) will be presented.

Characterizing the dynamics of iron oxide aggregation and reactivity in aqueous systems

249th National Meeting (2015)

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