Structural study of Fe(II) adsorption on hematite(11¯02)

Fe(II) adsorption on hematite (0001)

“…Comparing the results of the current study with previous work on the structure of adsorbed Fe on a-Fe 2 O 3 (1 1 0 2) (Tanwar et al, 2008) highlights two similarities. First, the common observation that on both the a-Fe 2 O 3 (0 0 0 1) and (1 1 0 2) substrates Fe(II) reaction led to the adsorption of Fe at crystallographic lattice sites.…”

“…This study complements and builds upon our recent analysis of Fe(II) adsorption on the a-Fe 2 O 3 (1 1 0 2) surface (Tanwar et al, 2008). The results of this previous study indicate that the adsorbed Fe binds at crystallographic lattice sites resulting in octahedral coordination; five first neighbors being surface (hydr)oxo groups, and the sixth being a terminal Fe-O (presumably aquo or hydroxo) moiety (Tanwar et al, 2008).…”

“…In comparison, Yanina and Rosso (2008) observed growth of hematite on the aFe 2 O 3 (0 0 0 1) surface after exposure to Fe(II) for 12 h at pH 2-3 in presence of oxalate (at 348 K). The experimental conditions used in the present study are more consistent with sub-monolayer levels of Fe(II) uptake (Jeon et al, 2001;Tanwar et al, 2008), although structurally the model is consistent with incipient growth of the substrate.…”

“…The Fe(II) solutions were prepared using de-oxygenated ultrapure water (>18 MX) and ferrous chloride tetra-hydrate (FeCl 2 Á4H 2 O) purchased from VWR (>99% purity). Our previous work shows the 4 mM Fe(II) will remain stable for more than 24 h under the employed conditions (Tanwar et al, 2008). After the reaction period, the sample was washed with ultra-pure water and immediately remounted in the sample cell under a hydrated He gas for CTR data collection.…”

“…Since layers 1, 3, and 4 are fully occupied in the unreacted surface model, a decrease in their occupancies after Fe(II) exposure would indicate dissolution of Fe from the surface unit cell. However, the dissolution of hematite under the employed reaction conditions (reaction time of 2 h at pH 5) is unlikely based on previous Fe(II) adsorption studies on hematite single crystals (Tanwar et al, 2008) and colloidal hematite (Jeon et al, 2001), where uptake of Fe(II) has been observed for up to 34 days and 30 days, respectively. Therefore, we believe the observation of partial Fe occupancies at sites A, B and C (Fig.…”