| 1. |
- Walle, L. E., et al.
(författare)
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High resolution photoemission and x-ray absorption spectroscopy of a lepidocrocite-like TiO(2) nanosheet on Pt(110) (1 x 2)
- 2011
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 135:5, s. 054706-
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of TiO(2) nanosheets on the Pt(110)-(1 x 2) surface has been investigated by using high resolution photoemission spectroscopy and x-ray absorption spectroscopy (XAS). The Ti 2p XAS spectra of the deposited TiO(2) films have been theoretically evaluated and, from the comparison with the experimental data, the assignment to a lepidocrocite-like structure is confirmed. Coexistence of TiO(2) islands with PtO(2) stripes for incomplete nanosheets is confirmed by high resolution photoemission data. The location of the valence and conduction band edges of the nanosheet has been experimentally determined allowing us to describe in details subtle electronic effects due to the interface with the substrate. The locations of the valence band maximum and the leading peak in the O 1s XAS spectrum indicate a band gap similar to anatase but with the Fermi level closer to mid-gap than found for bulk, n-type TiO(2).
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| 2. |
- Bartels-Rausch, T., et al.
(författare)
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Interfacial supercooling and the precipitation of hydrohalite in frozen NaCl solutions as seen by X-ray absorption spectroscopy
- 2021
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Ingår i: Cryosphere. - : Copernicus GmbH. - 1994-0416. ; 15:4, s. 2001-2020
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Tidskriftsartikel (refereegranskat)abstract
- Laboratory experiments are presented on the phase change at the surface of sodium chloride-water mixtures at temperatures between 259 and 241 K. Chloride is a ubiquitous component of polar coastal surface snow. The chloride embedded in snow is involved in reactions that modify the chemical composition of snow as well as ultimately impact the budget of trace gases and the oxidative capacity of the overlying atmosphere. Multiphase reactions at the snow-air interface have been of particular interest in atmospheric science. Undoubtedly, chemical reactions proceed faster in liquids than in solids; but it is currently unclear when such phase changes occur at the interface of snow with air. In the experiments reported here, a high selectivity to the upper few nanometres of the frozen solution-air interface is achieved by using electron yield near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy. We find that sodium chloride at the interface of frozen solutions, which mimic sea-salt deposits in snow, remains as supercooled liquid down to 241 K. At this temperature, hydrohalite exclusively precipitates and anhydrous sodium chloride is not detected. In this work, we present the first NEXAFS spectrum of hydrohalite. The hydrohalite is found to be stable while increasing the temperature towards the eutectic temperature of 252 K. Taken together, this study reveals no differences in the phase changes of sodium chloride at the interface as compared to the bulk. That sodium chloride remains liquid at the interface upon cooling down to 241 K, which spans the most common temperature range in Arctic marine environments, has consequences for interfacial chemistry involving chlorine as well as for any other reactant for which the sodium chloride provides a liquid reservoir at the interface of environmental snow. Implications for the role of surface snow in atmospheric chemistry are discussed. © 2021 BMJ Publishing Group. All rights reserved.
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| 3. |
- Kong, Xiangrui, et al.
(författare)
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A surface-promoted redox reaction occurs spontaneously on solvating inorganic aerosol surfaces
- 2021
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 374:6568
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Tidskriftsartikel (refereegranskat)abstract
- A surface-promoted sulfate-reducing ammonium oxidation reaction was discovered to spontaneously take place on common inorganic aerosol surfaces undergoing solvation. Several key intermediate species-including elemental sulfur (S-0), bisulfide (HS-), nitrous acid (HONO), and aqueous ammonia [NH3(aq)]-were identified as reaction components associated with the solvation process. Depth profiles of relative species abundance showed the surface propensity of key species. The species assignments and depth profile features were supported by classical and first-principles molecular dynamics calculations, and a detailed mechanism was proposed to describe the processes that led to unexpected products during salt solvation. This discovery revealed chemistry that is distinctly linked to a solvating surface and has great potential to illuminate current puzzles within heterogeneous chemistry.
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| 4. |
- Kong, Xiangrui, et al.
(författare)
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Adsorbed Water Promotes Chemically Active Environments on the Surface of Sodium Chloride
- 2023
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Ingår i: Journal of Physical Chemistry Letters. - 1948-7185. ; 14:26, s. 6151-6156
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Tidskriftsartikel (refereegranskat)abstract
- Gas-particleinterfaces are chemically active environments.This study investigates the reactivity of SO2 on NaCl surfacesusing advanced experimental and theoretical methods with a NH4Cl substrate also examined for cation effects. Results showthat NaCl surfaces rapidly convert to Na2SO4 with a new chlorine component when exposed to SO2 underlow humidity. In contrast, NH4Cl surfaces have limitedSO(2) uptake and do not change significantly. Depth profilesreveal transformed layers and elemental ratios at the crystal surfaces.The chlorine species detected originates from Cl- expelled from the NaCl crystal structure, as determined by atomisticdensity functional theory calculations. Molecular dynamics simulationshighlight the chemically active NaCl surface environment, driven bya strong interfacial electric field and the presence of sub-monolayerwater coverage. These findings underscore the chemical activity ofsalt surfaces and the unexpected chemistry that arises from theirinteraction with interfacial water, even under very dry conditions.
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| 5. |
- Kong, Xiangrui, et al.
(författare)
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Coexistence of Physisorbed and Solvated HCI at Warm Ice Surfaces
- 2017
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Ingår i: Journal of Physical Chemistry Letters. - 1948-7185. ; 8:19, s. 4757-4762
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Tidskriftsartikel (refereegranskat)abstract
- The interfacial ionization of strong acids is an essential factor of multiphase and heterogeneous chemistry in environmental science, cryospheric science, catalysis research and material science. Using near ambient pressure core level X-ray photoelectron spectroscopy, we directly detected a low surface coverage of adsorbed HCl at 253 K in both molecular and dissociated states. Depth profiles derived from XPS data indicate the results as physisorbed molecular HCl at the outermost ice surface and dissociation occurring upon solvation deeper in the interfacial region. Complementary X-ray absorption measurements confirm that the presence of ions induces significant changes to the hydrogen bonding network in the interfacial region. This study gives clear evidence for nonuniformity across the air ice interface and questions the use of acid base concepts in interfacial processes.
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| 6. |
- Orlando, F., et al.
(författare)
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Disordered Adsorbed Water Layers on TiO2 Nanoparticles under Subsaturated Humidity Conditions at 235 K
- 2019
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 10:23, s. 7433-7438
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of water with TiO2 is of substantial scientific and technological interest as it determines the activity of TiO2 in photocatalytic and environmental applications in nanoparticle suspensions in water, in complex appliances, or in pure form interacting with water vapor. The influence of TiO2 nanoparticles on the hydrogen bonding structure of water molecules is an important factor that controls hydration of other species, reactions, or nucleation processes. We use a combination of ambient-pressure X-ray photoelectron spectroscopy and electron yield near-edge X-ray absorption fine structure (NEXAFS) spectroscopy at the oxygen K-edge to investigate the hydrogen bonding structure of adsorbed water on titania nanoparticles in equilibrium with nearly saturated water vapor at 235 K. The results clearly show that the net NEXAFS spectrum of adsorbed water resembles that of liquid, disordered water at 235 K, a temperature at which both homogeneous and heterogeneous freezing of bulk water is anticipated.
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