Abstract
The distribution of Fe resulting from the autocatalytic interaction of aqueous Fe(II) with the hematite (α-Fe2O3) (001) surface was directly mapped in three dimensions (3D) for the first time, using Fe isotopic labeling and atom probe tomography (APT). Micrometer-sized hematite platelets were reacted with aqueous Fe(II) enriched in 57Fe and prepared for APT using conventional focused ion beam lift-out techniques. Mass spectrum analyses show that specific Fe-ionic species (i.e., Fe2+ and FeO+) accurately reproduce isotopic ratios within natural abundance in the hematite bulk, and thus were utilized to characterize the distribution of 57Fe and quantify Fe isotopic concentrations. 3D reconstructions of Fe isotopic positions along the surface normal direction showed a zone enriched in 57Fe, consistent with oxidative adsorption of Fe(II) and growth at the relict hematite surface reacted with 57Fe(II)aq. An average net adsorption of 3.2–4.3 57Fe atoms nm–2 was estimated using Gibbsian interfacial excess princip...
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