Hematite (α-Fe<sub>2</sub>O<sub>3</sub>) and goethite (α-FeOOH) are environmentally relevant minerals that are crucial to industrial and environmental applications. Of particular interest is the incorporation of transition metal cations into the minerals to i) change the electronic properties of the material, ii) determine the importance of iron oxides in the transport of critical metals in the environment, and iii) modify mineral reactivity with select species in solution. Difference in cation compatibility in the host mineral structure greatly affect the nature and extent of these properties. Besides charge compensation the host lattice also needs to accommodate cations of different sizes and electronic structures, often by formation of protonated defects. These defects impact the local hydration of the host mineral and raise the question whether cation hydration energy and cation water exchange rates further constrain the solubility of trace elements in iron (oxyhydr)oxides. In this work, we use ab initio molecular dynamics (AIMD)-guided structural analysis to model the extended X-ray absorption fine structure (EXAFS) and X-ray total scattering data of doped iron oxide nanoparticles, focusing on Cu, Zn, and Ni. Identification of specific defect–impurity associations highlights the role of local hydration in accommodating impurities and expands our understanding of dopants/impurities in unprecedented bonding environments. Further, results from this study will establish to what extent interfacial processes imprint on the local structure and coordination of cations in host mineral phases.

Resolving structural implications for cation incorporation in iron (oxyhydr)oxides

ACS Spring 2022

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