Influence of aluminum substitution on the reactivity of magnetite nanoparticles

Magnetite is an iron oxide that commonly forms in soils under reducing conditions. It is an important material in natural and engineered remediation systems because it can affect the reductive degradation of environmental toxins such as halogenated hydrocarbons. To examine the influence of redox-inactive dopants and particle size on the reactivity of magnetite nanoparticles, samples with varying size and amounts of aluminum cation substitution (0-8.07 mol %) were synthesized. These materials were characterized, and their reactivity was examined using the organic molecules benzoquinone and carbon tetrachloride. Activation energies and frequency factors for the reaction of magnetite with benzoquinone were determined from a series of variable temperature kinetic studies. The ratio of products formed during the degradation of carbon tetrachloride was also studied to assess the influence of aluminum doping on the mechanism of reaction. The activation energy and frequency factor both initially decreased with increasing aluminum substitution, then increased as the aluminum content increased from 2.14% to 8.07%. Overall, the reactivity of magnetite nanoparticles decreased as a function of aluminum substitution in both systems, while the ratio of products resulting from the reaction with carbon tetrachloride seemed to be unaffected.