Crystal surfaces are reactive in a wide variety of natural and engineered systems, and crystal size, shape, and aggregation-state can evolve substantially as a function of time, extent of reaction, and solution conditions. Both oxidative mineral growth and reductive mineral dissolution leave behind relics of where the chemical process occurred. For example, when iron oxides are exposed to Fe(II) and a reducible model pollutant molecule, oxidative mineral growth can be quantified. By examining the solid state changes in iron oxide particles using electron microscopy, we can identify the active crystal facet(s) and detect dramatic changes in the relative reactivity of the different crystal facets or even surface sites. We also quantify rates of reductive dissolution or oxidative mineral growth, which enables quantitative comparisons reactivity of materials as a function of varying solution conditions like pH, ionic strength, and the presence of organic matter. Finally, aggregation state can also change dramatically with extent of reaction, and we use in situ materials characterization methods to examine how aggregation-state evolves. This enables the characterization of how aggregation-state may or may not impact reaction kinetics.

Iron oxides in reactive systems: Aggregation, growth, and dissolution

2019 Spring National Meeting

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