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Photoinduced reduction of surface states in Fe:ZnO
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
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2015 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 142, no 20, 204703Article in journal (Refereed) Published
Abstract [en]

We report on the electronic structure of nano-crystalline Fe:ZnO, which has recently been found to be an efficient photocatalyst. Using resonant photoemission spectroscopy, we determine the binding energy of Fe 3d states corresponding to different valencies and coordination of the Fe atoms. The photo-activity of ZnO reduces Fe from 3+ to 2+ in the surface region of the nano-crystalline material due to the formation of oxygen vacancies. Electronic states corresponding to low-spin Fe2+ are observed and attributed to crystal field modification at the surface. These states are potentially important for the photocatalytic sensitivity to visible light due to their location deep in the ZnO bandgap. X-ray absorption and x-ray photoemission spectroscopy suggest that Fe is only homogeneously distributed for concentrations up to 3%. Increased concentrations does not result in a higher concentration of Fe ions in the surface region. This is limiting the photocatalytic functionality of ZnO, where the most efficient Fe doping concentration has been shown to be 1%-4%.

Place, publisher, year, edition, pages
2015. Vol. 142, no 20, 204703
National Category
Physical Sciences Engineering and Technology
URN: urn:nbn:se:uu:diva-258046DOI: 10.1063/1.4921570ISI: 000355919300030PubMedID: 26026457OAI: oai:DiVA.org:uu-258046DiVA: diva2:841406
Available from: 2015-07-13 Created: 2015-07-10 Last updated: 2016-06-01
In thesis
1. Solution-Chemical Synthesis of Cobalt and Iron:Zinc Oxide Nanocomposite Films
Open this publication in new window or tab >>Solution-Chemical Synthesis of Cobalt and Iron:Zinc Oxide Nanocomposite Films
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The potentially most important challenges today are related to energy and the environment. New materials and methods are needed in order to, in a sustainable way, convert and store energy, reduce pollution, and clean the air and water from contaminations. In this, nanomaterials and nanocomposites play a key role, and hence knowledge about the relation between synthesis, structure, and properties of nanosystems is paramount.

This thesis demonstrates that solution-chemical synthesis, using amine-modified acetates and nitrates, can be used to prepare widely different nanostructured films. By adjusting the synthesis parameters, metals, oxides, and metal–oxide or oxide–oxide nanocomposites were prepared for two systems based on Co and Zn:Fe, respectively, and the films were characterised using diffraction, spectroscopy, and microscopy techniques, and SQUID magnetometry.

A variety of crystalline cobalt films—Co metal, CoO, Co3O4, and composites with different metal:oxide ratios—were synthesised. Heat-treatment parameters and control of the film thickness enabled tuning of the phase ratios. Random and layered Co–CoO composites were prepared by utilising different heating rates and gas flow rates together with a morphology effect associated with the furnace tube. The Co–CoO films exhibited exchange bias due to the ferromagnetic–antiferromagnetic interaction between the Co and CoO, whereas variations in e.g. coercivity and exchange bias field were attributed to differences in the structure and phase distribution.

Ordered structures of wurtzite ZnO surrounded by amorphous ZnxFeyO were prepared through controlled phase segregation during the heating, which after multiple coating and heating cycles yielded ZnO–ZnxFeyO superlattices. The amorphous ZnxFeyO was a prerequisite for superlattice formation, and it profoundly affected the ZnO phase, inhibiting grain growth and texture, already from 1% Fe. In addition, ZnO–ZnxFeyO exhibited a photocatalytic activity for the oxidation of water that was higher than results reported for pure ZnO, and comparable to recent results reported for graphene-modified ZnO.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 85 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1356
Fe:Zn oxide, Co-CoO, Solution-chemical synthesis, Heat treatment parameters, Nanocomposite, Film, Multilayer, Phase ratio, Phase distribution, Exchange bias, Magnetism, Photocatalysis
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
urn:nbn:se:uu:diva-280619 (URN)978-91-554-9520-6 (ISBN)
Public defence
2016-06-09, Å 2005, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Available from: 2016-05-17 Created: 2016-03-11 Last updated: 2016-06-01

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Knut, RonnySvedlindh, PeterPohl, AnnikaKaris, Olof
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