| 1. |
- Su, R., et al.
(författare)
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How the Anatase-to-Rutile Ratio Influences the Photoreactivity of TiO2
- 2011
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:49, s. 24287-24292
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Tidskriftsartikel (refereegranskat)abstract
- In 1991, Bickley et al. proposed a synergetic effect between anatase and rutile in Degussa P25. Since then, there has been an intensive debate about the correctness of this proposal, the origin of the synergism, and the right polymorph composition. However, a comparison of pure titanium dioxide samples with various anatase-to-rutile ratios, but otherwise identical properties, is missing. In this paper, we report about a series of utterly pure, highly porous titanium dioxide films with identical grain sizes, surface areas, and crystallinity, but varying polymorph compositions. Photocatalytic oxidation of methylene blue was utilized to investigate the influence of the anatase-to-rutile ratio on the photoreactivity. We clearly observe the synergetic effect within a well-defined range of anatase-to-rutile ratios. A film with similar to 60% anatase and similar to 40% rutile exhibits optimal performance at a 50% improved activity compared with pure anatase.
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| 2. |
- Su, R., et al.
(författare)
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Rapid Synthesis of Porous, Mixed Phase Titania Films with Tailored Orientation of Rutile for Enhanced Photocatalytic Performance
- 2013
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:51, s. 27039-27046
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Tidskriftsartikel (refereegranskat)abstract
- We report on a new, one-step electrochemical oxidation method for the rapid synthesis of mixed phase, polycrystalline TiO2 porous films with oriented rutile within a few minutes. The orientation as well as the surface chemical composition of rutile nanocrystallites can readily be tuned by adjusting the additive concentrations of HCl or HF in the electrolyte during synthesis. All TiO2 films show similar large specific surface area, which is ideal for the application of photocatalysis and photoelectrocatalysis. Compared to the random-oriented TiO2 film, films with an increasing portion of exposed rutile (101) facets were found to be characterized by enhanced photocatalytic oxidation and photoelectrochemical performances. We also observed a synergistic promotion effect of the orientation and surface F impurity. Most interesting, our tailor-oriented porous TiO2 films prepared using HF as additive show an impressive photocurrent generation at zero bias, which is similar to 50 times higher compared to that of the random-oriented TiO2 film.
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| 3. |
- Li, W X, et al.
(författare)
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Oxidation of Pt(110)
- 2004
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 93:14, s. 146104-
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Tidskriftsartikel (refereegranskat)abstract
- Using scanning tunneling microscopy and temperature programed desorption we investigate the Pt(110) surface under strongly oxidizing conditions involving either high-pressure O-2 or atomic oxygen exposure. At low temperatures, only disordered Pt oxide structures are observed. After annealing ordered surface oxide islands are observed to coexist with a highly stable reconstructed (12x2)-O chemisorption structure. From density functional theory calculations a model for the surface oxide phase is revealed. The phase is found to be metastable, and its presence is explained in terms of stabilizing defects in the chemisorption layer and reduced Pt mobility.
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| 4. |
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| 5. |
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| 6. |
- Allentoft, Morten E., et al.
(författare)
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Population genomics of post-glacial western Eurasia
- 2024
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Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 625:7994, s. 301-311
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Tidskriftsartikel (refereegranskat)abstract
- Western Eurasia witnessed several large-scale human migrations during the Holocene1–5. Here, to investigate the cross-continental effects of these migrations, we shotgun-sequenced 317 genomes—mainly from the Mesolithic and Neolithic periods—from across northern and western Eurasia. These were imputed alongside published data to obtain diploid genotypes from more than 1,600 ancient humans. Our analyses revealed a ‘great divide’ genomic boundary extending from the Black Sea to the Baltic. Mesolithic hunter-gatherers were highly genetically differentiated east and west of this zone, and the effect of the neolithization was equally disparate. Large-scale ancestry shifts occurred in the west as farming was introduced, including near-total replacement of hunter-gatherers in many areas, whereas no substantial ancestry shifts happened east of the zone during the same period. Similarly, relatedness decreased in the west from the Neolithic transition onwards, whereas, east of the Urals, relatedness remained high until around 4,000 bp, consistent with the persistence of localized groups of hunter-gatherers. The boundary dissolved when Yamnaya-related ancestry spread across western Eurasia around 5,000 bp, resulting in a second major turnover that reached most parts of Europe within a 1,000-year span. The genetic origin and fate of the Yamnaya have remained elusive, but we show that hunter-gatherers from the Middle Don region contributed ancestry to them. Yamnaya groups later admixed with individuals associated with the Globular Amphora culture before expanding into Europe. Similar turnovers occurred in western Siberia, where we report new genomic data from a ‘Neolithic steppe’ cline spanning the Siberian forest steppe to Lake Baikal. These prehistoric migrations had profound and lasting effects on the genetic diversity of Eurasian populations.
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| 7. |
- Arnbjerg, Lene M., et al.
(författare)
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Structure and Dynamics for LiBH4-LiCl Solid Solutions
- 2009
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 21:24, s. 5772-5782
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Tidskriftsartikel (refereegranskat)abstract
- A Surprisingly high degree of structural and compositional dynamics is observed in the system LiBH4-LiCl as a function of temperature and time. Rietveld refinement of synchrotron radiation powder X-ray diffraction (SR-PXD) data reveals that Cl- readily substitutes for BH4- in the Structure of LiBH4. Prolonged heating a sample of LiBH4-LiCl (1:1 molar ratio) above the phase transition temperature and below the melting point (108 < T < 275 degrees C) can produce highly chloride substituted hexagonal lithium borohydride, h-Li(BH4)(l-x)Cl-x, e.g., x similar to 0.42, after heating from room temperature (RT) to 224 degrees C at 2.5 degrees C/min. LiCl has a higher solubility in h-LiBH4 its compared to orthorhombic lithium borohydride, o-LiBH4, which is illustrated by a LiBH4-LiCl (1:1) sample equilibrated at 245 degrees C for 24 days and left at RT for another 13 months. Rietveld refinement reveals that this sample contains o-Li(BH4)(0.91)Cl-0.09 and LiCl. This illustrates a significantly faster dissolution of LiCl in h-LiBH4 its compared to a slower segregation of LiCl from o-LiBH4, which is also demonstrated by in situ SR-PXD from three cycles of heating and cooling of the same Li(BH4)(0.91)Cl-0.09 sample. The substitution of the smaller Cl- for the larger BH4- ion is clearly observed as a reduction in the unit cell volume as a function of time and temperature. A significant stabilization of h-LiBH4 is found to depend on the degree of anion substitution. Variable temperature solid-state magic-angle spinning (MAS) Li-7 and B-13 NMR experiments oil pure LiBH4 show an increase in full width at half maximum (fwhm) when approaching the phase transition from o- to h-LiBH4, which indicates an increase of the relaxation rate (i.e. T-2 decreases). A less pronounced effect is observed for ion-substituted Li(BH4)(1-x)Cl-x, 0.09 < x < 0.42. The MAS NMR experiments also demonstrate a higher degree of motion in the hexagonal phase, i.e., fwhm is reduced by more than a Factor of 10 at the o- to h-LiBH4 phase transition.
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| 10. |
- Knudsen, Jan, et al.
(författare)
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Low-Temperature CO Oxidation on Ni(111) and on a Au/Ni(111) Surface Alloy
- 2010
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 4:8, s. 4380-4387
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Tidskriftsartikel (refereegranskat)abstract
- From an interplay between scanning tunneling microscopy, temperature programmed desorption, X-ray photoelectron spectroscopy, and density functional theory calculations we have studied low-temperature CO oxidation on Au/Ni(111) surface alloys and on Ni(111). We show that an oxide is formed on both the Ni(111) and the Au/Ni(111) surfaces when oxygen is dosed at 100 K, and that CO can be oxidized at 100 K on both of these surfaces in the presence of weakly bound oxygen. We suggest that low-temperature CO oxidation can be rationalized by CO oxidation on O-2-saturated NiO(111) surfaces, and show that the main effect of Au in the Au/Ni(111) surface alloy is to block the formation of carbonate and thereby increase the low-temperature CO2 production.
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