Zachary Wiethorn

Ferrihydrite is a naturally occurring iron oxide that has variations in structure and composition. Due to this lack of crystallinity, ferrihydrite acts as a precursor to the formation of more thermodynamically stable iron oxides such as goethite and hematite. Aluminum substitution in ferrihydrite is notable in natural systems. This study focuses on testing how varying levels of aluminum substitution along with pH may influence the phase transformations of ferrihydrite in the environment as well as how potential end phases, goethite and hematite will react with environmental contaminants. Multiple samples of ferrihydrite nanoparticles were synthesized in triplicate with varying molar percentages of aluminum. To determine the influence of pH, each triplicate sample was adjusted to pH 2, 7, or 12. Additionally, previously synthesized goethite and hematite nanoparticles with 3.7 and 6.1 molar percentages of aluminum were reacted with varying concentrations of 4-chloronitrobenzene. Successful synthesis of all iron oxides was determined by transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). Inductively coupled plasma optical emission spectrometry (ICP-OES) and energy-dispersive X-ray spectroscopy (EDS) were used to determine the relative molar ratios of aluminum to iron. Over the past 16 months new phase formations in ferrihydrite samples have been identified by TEM and XRD. At the lower aluminum concentrations, goethite formation has been favored at higher pH. Whereas, at higher aluminum concentrations, goethite formation in acidic conditions preceded that in basic conditions where hematite formation has been observed. Despite other trends, ferrihydrite has remained relatively stable for all aluminum concentrations at pH 7.