The role of continuous contaminant exposure and natural organic matter on the evolving reactivity of iron oxide nanoparticles

Abstract

The global water crisis is a critical issue that the world is facing, and the lack of access to clean water not only leads to health-related problems, but also causes social injustice. Groundwater is an important source for high quality water but is highly prone to contamination. Developing new remediation methods and improving traditional ones are critical to restoring groundwater resources. Iron oxide particles are promising materials for the remediation of different classes of groundwater contaminants, such as nitroaromatic compounds and heavy metals, because the minerals can facilitate contaminant destruction or immobilization. Because of the complexity of subsurface environments in terms of mineralogy, geochemistry, and hydrology, understanding the interaction of iron oxide particles and their reactivity in presence different subsurface constituents is necessary. In this thesis, iron oxide nanoparticle reactivity was investigated under more realistic, environmentally relevant conditions including continuous exposure to reactants, attachment to other minerals, and the presence of natural organic matter. In this work, kinetic studies in combination with solid-state characterization were used to elucidate the evolving reactivity and mineralogy of iron oxide particles (goethite and hematite) during reaction with a nitroaromatic probe compound and chromate. The kinetics of model pollutants were quantified and used to evaluate the effect of evolving mineralogy and the presence of natural organic matter on reactivity. Materials characterization techniques, including X-ray diffraction and electron microscopy, were used to quantify changes in the minerals present and mineral growth. Spectroscopy and chromatography techniques provided information about which fractions of natural organic matter associated with minerals and how strong these associations were. The findings of this research demonstrated that the reactivity of iron oxide particles evolved during exposure to contaminants and depends on the iron oxide phase, hydrodynamics of water flow, and the presence of other environmentally relevant components like natural organic matter. By advancing our understanding of iron oxide reactivity in the subsurface environments, better prediction of the efficacy and optimization of remediation methods are possible.