Surface diffraction study of the hydrated hematite surface

Tanwar, Kunaljeet S.; Lo, Cynthia S.; Eng, Peter J.; Catalano, Jeffrey G.; Walko, Donald A.; Brown, Gordon E.; Waychunas, Glenn A.; Chaka, Anne M.; Trainor, Thomas P.

doi:10.1016/j.susc.2006.10.021

Cited by 98 publications

(138 citation statements)

References 52 publications

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“…(H atoms are not included in our CTR model; the role of protons is discussed below.) The hematite surface structures are nearly identical between wet and dry conditions, and both agree well with previous measurements 20 . The presence of ordered water under dry conditions is not surprising, given that adsorbed water persists at room temperature even under ultra-high vacuum (see Figure S2 and Ref.…”

supporting

confidence: 89%

“…Hematite (-Fe2O3) is both a naturally abundant mineral and a photoactive semiconductor of interest for heterogeneous catalysis 24 . The (11 ̅ 02) ("r-cut") surface is a prominent low-index face 25,26 that exposes high electron mobility pathways in the hematite structure 27,28 and reactive iron-oxo surface functional groups 20,29 . Early studies suggest that the most stable termination at room temperature is an iron-deficient surface with hydroxyls between ridges of terminal aquo groups 20,30 , but the water structure above this surface is debated.…”

mentioning

confidence: 99%

“…The analysis of multiple crystal truncation rods (CTRs) provides a complete 3-dimensional interface model 20,21 , but this structure is averaged over seconds to hours. Disorder parameters measured using time-averaged methods provide limited insight into interface dynamics 22 .…”

mentioning

confidence: 99%

“…The (11 ̅ 02) ("r-cut") surface is a prominent low-index face 25,26 that exposes high electron mobility pathways in the hematite structure 27,28 and reactive iron-oxo surface functional groups 20,29 . Early studies suggest that the most stable termination at room temperature is an iron-deficient surface with hydroxyls between ridges of terminal aquo groups 20,30 , but the water structure above this surface is debated. Classical MD 31 and static DFT 30 calculations suggest that the first water layer localizes between the ridges of aquo groups, stabilized by hydrogen bonding.…”

mentioning

confidence: 99%

“…Classical MD 31 and static DFT 30 calculations suggest that the first water layer localizes between the ridges of aquo groups, stabilized by hydrogen bonding. However, experimental evidence indicates that the first layer of water adsorbs more closely to terminal aquo groups, leaving void spaces above the hydroxyls 20 .…”

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confidence: 99%

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Dynamic Stabilization of Metal Oxide–Water Interfaces

et al. 2017

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ABSTRACT:The interaction of water with metal oxide surfaces plays a crucial role in the catalytic and geochemical behavior of metal oxides. In a vast majority of studies, the interfacial structure is assumed to arise from a relatively static lowest energy configuration of atoms, even at room temperature. Using hematite (-Fe2O3) as a model oxide, we show through a direct comparison of in situ synchrotron X-ray scattering with density functional theorybased molecular dynamics (DFT-MD) simulations that the structure of the (11 ̅ 02) termination is dynamically stabilized by picosecond water exchange. Simulations show frequent exchanges between terminal aquo groups and adsorbed water in locations and with partial residence times consistent with experimentally determined atomic sites and fractional occupancies. Frequent water exchange occurs even for an ultrathin adsorbed water film persisting on the surface under a dry atmosphere. The resulting time-averaged interfacial structure consists of a ridged lateral arrangement of adsorbed water molecules hydrogen bonded to terminal aquo groups. Surface pKa prediction based on bond valence analysis suggests that water exchange will influence the proton transfer reactions underlying the acid/base reactivity at the interface. Our findings provide important new insights for understanding complex interfacial chemical processes at metal oxide-water interfaces.The interfaces between metal oxides and water are among the most important in nature and in emerging energy applications, with wide ranging impacts from photocatalytic water splitting [1][2][3][4] to the geochemical cycling of elements 5,6 . Key chemical processes such as adsorption, electron transfer, growth, and dissolution all depend principally on the atomic structure adopted at these interfaces. For example, dissolution and solute adsorption are regulated by the structure of interfacial water 7,8 . Surface acid/base chemistry 9,10 arises from the types and arrangement of terminal metal-coordinating aquo/hydroxyl groups 3,11-13 .At room temperature an interface is at dynamic equilibrium. In principle, the average interfacial structure depends on the interplay of relatively static atoms at the solid surface with relatively dynamic overlying water molecules. Simulations suggest that movement of overlying water molecules can play an essential role in stabilizing the interface and influencing its chemical behavior 14,15 . However, simulated [14][15][16][17] or spectroscopically probed 18 dynamics are seldom integrated with experimentally derived interface structure models to achieve comprehensive insight into interfacial structure 4 . To understand and predict chemical processes at dynamically active metal oxide-water interfaces, structure and dynamics must be considered as a unified whole.Accurate measurements of interface structure and water ordering rely on interface-sensitive synchrotron X-ray scattering methods 19 . The analysis of multiple crystal truncation rods (CTRs) provides a complete 3-dimensional interface mode...

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supporting

confidence: 89%

mentioning

confidence: 99%

mentioning

confidence: 99%