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    Iron oxide surface

    時間:2018-05-31 瀏覽:476次

      The present knowledge about iron oxide, magnetite (Fe3O4), hematite (-Fe2O3), hematite (alpha -Fe2O3) and wolfram iron (Fe1-xO) is reviewed. This paper first introduces the applications of iron oxide surface, including corrosion, catalysis, spintronics, magnetic nanoparticles (MNPs), biomedicine, photochemical water decomposition and groundwater remediation. Then the bulk structure and properties are briefly introduced. Each compound is based on the tightly packed anionic lattice, and the distribution and oxidation state of Fe cations in the gap position are different. Bulk defect chemistry is dominated by cation vacancies and gaps (rather than oxygen vacancies), which provides a background to understand the surface of iron oxide, and the surface of iron oxide represents the front of the reduction and oxidation process. Fe responds to O2 chemical potential and diffuses into and away from the body, forming sometimes complex mesophase on the surface. For example, the surface of alpha -Fe2O3 is Fe3O4 like, and Fe3O4 also adopts Fe1-xO like structure under reducing conditions. Some people think that the known volume defect structure is the starting point for constructing the surface model of iron oxide.

      The atomic scale structure of iron oxide with low refractive index surface is the focus of this review. Fe3O4 is the most studied iron oxide in surface science, mainly because its stability range corresponds well to ultra high vacuum environment. It is also an electrical conductor, which makes direct research on the most commonly used surface science methods, such as XPS (UPS) and scanning tunneling microscope (STM). The influence of the surface on the measurement of magnetic properties, Verwey transition and (predicted) half metallic degree isometric properties is discussed.

      At present, the most familiar surface of iron oxide may be Fe3O4 (100). The structure is known with high accuracy, and its main defects and properties are well characterized. One major factor is that the terminals on the Feoct-O plane can be repeated in a variety of ways, as long as the surface is annealed at the final stage of preparation in the 10-7-10-5 MBA O2. This simple preparation of single-phase termination is usually not the case of iron oxide. All existing evidence shows that the rearrangement of the cationic lattice in the outermost cell battery has been studied (2 * * 2) R45 degree reconstruction, of which two eight - hedral cations are replaced by a tetrahedral gap and a known Koch-Cohen defect in Fe1-xO. The cation defect leads to Fe11O16 stoichiometry, which is consistent with the chemical potential in ultra high vacuum (UHV), which is close to the boundary between Fe 3 O 4 and Fe 2 O 3 phase.

      The Fe3O4 (111) surface is also subject to a lot of research, but two different surface terminals exist in energy proximity and can coexist, which makes the sample preparation and data interpretation a bit tricky. When the edge of the sample changes, the surface of Fe3O4 (100) and Fe3O4 (111) exhibits iron rich termination. The one dimensional (1 * 3) reconstruction of the Fe3O4 (110) surface is connected to the nanopore, which exposes a more stable Fe 3 O 4 (111) surface. Alpha -Fe2O3 (0001) is the most studied hematite surface, but the difficulty of preparing stoichiometric surfaces under UHV conditions hinders the structural certainty. There is evidence that there are at least three terminals: block termination on the oxygen plane, half of the cation layer and termination of iron base. When the surface is reduced, the so-called "dual phase" structure is formed, and finally transformed to Fe 3 O 4 (111). The structure of biphasic surfaces is controversial; recently, a widely accepted model of Fe1-xO and alpha -Fe2O3 (0001) island coexistence has been challenged, and a new structure of Fe3O4 (111) thin films based on alpha -Fe2O3 (0001) is proposed. Discuss the advantages of the competition model. It is recommended to use the surface of alpha -Fe2O3 (11 * 02) "R cut" as a good prospect for future research, because it is easy to prepare and its popularity in nanomaterials.

      In the latter part, the literature on iron oxide adsorption is reviewed. First, we discuss the adsorption of molecules (H 2, H 2 O, CO, CO 2, O 2, HCOOH, CH 3 OH, CCl 4, CH 3 I, 2, 2, 2, 2, 2, 2, ethylbenzene, styrene, and 3), using ferric oxide as a catalyst (water gas conversion, Fischer to styrene dehydrogenation to styrene) or catalyst carrier (oxidation). The known interaction between iron oxide surface and metal is described, and it is shown that behavior is determined by a stable three element phase formed between metal and iron oxide. (Ni, Co, Mn, Cr, V, Cu, Ti, Zr, Sn, Li, K, Na) are preferred to form three dimensional particles into the oxide lattice. The mixing temperature changes with the heat formed by the most stable metal oxides. Special efforts are made to emphasize the mechanism of the separation of metal adsorbed on the Fe3O4 surface, and the potential applications of the model system to understand the single atom catalysis and subnanocluster catalysis are also discussed. The review ends with a brief summary and provides a perspective, including the exciting lines for future research.

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