Adsorption of V on a hematite (0 0 0 1) surface and its oxidation: Monolayer coverage

Abstract

The adsorption of a monolayer of V on idealized Fe-and oxygen-terminated hematite (0 0 0 1) surfaces and subsequent oxidation under atomic O adsorption are studied by density functional theory. Theoretical results are compared with X-ray surface standing wave and X-ray photoelectron spectroscopic measurements, and interpreted in the light of data on sub-monolayer coverages. Near-surface Fe reduction under V adsorption and accompanying structural relaxation are examined. These effects and subsequent response to oxidation, are found to be highly site specific. A full monolayer of oxygen leads to a V 5+ state and reoxidation of subsurface Fe to the trivalent state, seen in both theory and experiment.

Electronic Structure of Metal (M = Au, Pt, Pd, or Ru) Bilayer Modified α-Fe2O3(0001) Surfaces

“…Moreover, the above adsorption energies indicate that the interaction between metal bilayer and support is weak and the interface has an ionic/metallic character. Although there is no DFT data in the literature for comparison, our results display similar bonding geometries with DFT calculated results for Pb or V modified α-Fe 2 O 3 systems. That is, stable metallic atom adsorption occurs above the surface Fe atom or through the coordination with two additional O and one surface Fe atom.…”

“…[27][28][29] DFT has also been used to explore the surface chemistry at the interface between R-Fe 2 O 3 and H 2 O. 22,30,31 For R-Fe 2 O 3 (0001) systems, DFT calculations are mainly limited to the analysis of surface structure with different O or Fe terminations. Some recent work with DFT only considered Pb, 24 Cr, 32 or V 22 adatom surface structure studies.…”

“…Recent studies only consider adatom adsorption and do not address the synergistic effect in detail. [22][23][24][25] Because of this gap in knowledge, the synergistic effect and the enhanced activity observed in Rucontaining bimetallic Al 2 O 3 catalysts remain the subject of debate. There are some advanced techniques developed to study interfaces that are crucial for composites, protective coatings, thin film technology, and electronics.…”

Cation synergies affect ammonia adsorption over VOX and (V,W)OX dispersed on α-Al2O3 (0001) and α-Fe2O3 (0001)

“…All other atoms were allowed to relax using a conjugate-gradient [41] or quasi-Newtonian scheme. For hematite, a similar 1×1 supercell [42][43][44] (a = b = 5.006 Å) was employed, with 3 metal cations and 2 oxygen layers fixed; this lattice parameter is slightly contracted from the experimental value of 5.035 Å [40]. Further details on this slab, including densities of states (DOS) calculations, can be found in Ref.…”

Engineering metal (hydr)oxide sorbents for removal of arsenate and similar weak-acid oxyanion contaminants: A critical review with emphasis on factors governing sorption processes

“…Empty d orbitals in a transitional metal act as Lewis acids for the oxyanions' electron rich oxygen atoms (Kutzelnigg, 1984;Sherman, 1985;Stair, 1982Stair, , 1991. Consequently, weak-acid oxyanion contaminants sorb onto metal (hydr)oxide surfaces by creating oxygen bridges via ligand exchange with OH − or OH 2 groups located on the sorbents' surface and form stable monodentate or bidentate inner-sphere complexes, although recent evidence suggests that tridentate complexes could also be formed under specific conditions (Figure 2) (Breynaert et al, 2008;Goldberg and Johnston, 2001;Grossl et al, 1997;Ippolito et al, 2009;Jin et al, 2007;Lange et al, 1991;Manning et al, 2002;Mitsunobu et al, 2009Mitsunobu et al, , 2010Otte et al, 2013;Peak, 2006;Rakshit et al, 2011;Wang et al, 2011;Waychunas et al, 1993Waychunas et al, , 1995a.…”