The initial stages of water adsorption on magnetite Fe O (111) surface and the atomic structure of the water/oxide interface remain controversial. Herein, we provide experimental results obtained by infrared reflection-absorption spectroscopy (IRAS) and temperature-programmed desorption (TPD), corroborated by density functional theory (DFT) calculations showing that water readily dissociates on Fe sites to form two hydroxo species. These act as an anchor for water molecules to form a dimer complex which self-assembles into an ordered (2×2) structure. Water ad-layer ordering is rationalized in terms of a cooperative effect induced by a hydrogen-bonding network.

Although the (111) surface of FeO (magnetite) has been investigated for more than 20 years, substantial controversy remains in the literature regarding the surface termination proposed based on structural and adsorption studies. The present article provides density functional theory results that allow to rationalize experimental results of infrared reflection-absorption spectroscopy and temperature-programmed desorption studies on CO adsorption, thus leading to a unified picture in which the FeO(111) surface is terminated by a / monolayer of tetrahedrally coordinated Fe ions on top of a close-packed oxygen layer as previously determined by low energy electron diffraction. However, surface defects play a crucial role in adsorption properties and may dominate chemical reactions on FeO(111) when exposed to the ambient.

We monitored adsorption of water on a well-defined Fe3O4(111) film surface at different temperatures as a function of coverage using infrared reflection-absorption spectroscopy, temperature programmed desorption, and single crystal adsorption calorimetry. Additionally, density functional theory was employed using a Fe3O4(111)-(2 × 2) slab model to generate 15 energy minimum structures for various coverages. Corresponding vibrational properties of the adsorbed water species were also computed. The results show that water molecules readily dissociate on regular surface Fetet1-O ion pairs to form "monomers", i.e., terminal Fe-OH and surface OH groups. Further water molecules adsorb on the hydroxyl covered surface non-dissociatively and form "dimers" and larger oligomers, which ultimately assemble into an ordered (2 × 2) hydrogen-bonded network structure with increasing coverage prior to the formation of a solid water film.

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We monitored the adsorption of carbon dioxide (CO 2 ) on well-ordered Fe 3 O 4 (111) films using infrared reflection-adsorption spectroscopy (IRAS) and temperature-programmed desorption (TPD). The results show that CO 2 weakly interacts with the regular Fe 3 O 4 (111) surface and almost fully desorbs at temperatures above ∼140 K. Accordingly, IRA spectra show mainly physisorbed CO 2 species. However, TPD and IRAS features corresponding to a more strongly bound, chemisorbed species were also observed. Their formation required relatively long CO 2 exposure times, which we associated with adventitious coadsorption of residual water from the vacuum background. Since the Fe 3 O 4 (111) surface is known to be very sensitive toward water, we additionally investigated the correlation between water and CO 2 adsorption process and found that the degree of surface hydroxylation plays a crucial role in CO 2 binding to the Fe 3 O 4 (111) surface, ultimately leading to the formation of bicarbonate species.