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  • 1.
    Arvizu, Miguel A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Triana, Carlos A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Stefanov, Bozhidar I
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Electrochromism in sputter-deposited W-Ti oxide films: Durability enhancement due to Ti2014In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 125, p. 184-189Article in journal (Refereed)
    Abstract [en]

    Thin films of W-Ti oxide were prepared by reactive DC magnetron sputtering and were characterized by Rutherford bathcattering spectrometry, X-ray diffraction, scanning electron microscopy and atomic force microscopy. The electrochromic properties were studied by cyclic voltammetry in an electrolyte of lithium perchlorate in propylene carbonate and by optical transmittance measurements. The addition of Ti significantly promoted the amorphous nature of the films and stabilized their electrochemical cycling performance and dynamic range for electrochromism. (C) 2014 Elsevier B.V. All rights reserved.

  • 2.
    Ivanova, T.
    et al.
    Bulgarian Acad Sci, Cent Lab Solar Energy & New Energy Sources, 72 Tzarigradsko Chaussee, BU-1784 Sofia, Bulgaria.
    Harizanova, A.
    Bulgarian Acad Sci, Cent Lab Solar Energy & New Energy Sources, 72 Tzarigradsko Chaussee, BU-1784 Sofia, Bulgaria.
    Koutzarova, T.
    Bulgarian Acad Sci, E Djakov Inst Elect, 72 Tzarigradsko Chaussee, BU-1784 Sofia, Bulgaria.
    Vertruyen, B.
    Univ Liege, LCIS SUPRATECS, Inst Chem B6, B-4000 Liege, Belgium.
    Stefanov, Bozhidar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Structural and morphological properties of sol-gel ZnO:Ni films2018In: 20th International Summer School on Vacuum, Electron and Ion Technologies, 2017, Institute of Physics Publishing (IOPP), 2018, Vol. 992, article id 012044Conference paper (Refereed)
    Abstract [en]

    Ni doping induces modifications and considerable changes in the optical, electrical and magnetic properties of ZnO films. In this work, the influence is discussed of Ni-doping (two nickel concentrations) and annealing temperature (ranging from 300 degrees C to 800 degrees C) on the structural and optical properties of sol-gel derived ZnO: Ni films. Uniform and smooth films were obtained by spin-coating on quartz and Si substrates. The ZnO: Ni films were crystallized in wurtzite phase with no impurity phases found for annealing temperatures up to 600 degrees C. The size of the crystallites was strongly affected by the Ni content and the heat treatment. Furthermore, the Ni doping improved the optical transparency of the sol-gel films, while the AFM studies showed that the film morphology and the roughness were influenced by the nickel doping.

  • 3.
    Ivanova, Tatyana
    et al.
    Bulgarian Acad Sci, Cent Lab Solar Energy & New Energy Sources, Sofia, Bulgaria.
    Harizanova, Antoaneta
    Bulgarian Acad Sci, Cent Lab Solar Energy & New Energy Sources, Sofia, Bulgaria.
    Koutzarova, Tatyana
    Bulgarian Acad Sci, Inst Elect, Sofia, Bulgaria.
    Vertruyen, Benedicte
    Univ Liege, LCIS SUPRATECS, Inst Chem B6, Liege, Belgium.
    Stefanov, Bozhidar I
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Morphological Study of Sol-Gel Derived ZnO: In Thin Films2017In: Proceeding of the 2017 40Th International Spring Seminar On Electronics Technology (ISSE), 2017Conference paper (Refereed)
    Abstract [en]

    This work presents morphological, structural and optical studies of ZnO and ZnO:In nanostructured thin films depending on In doping (four different concentrations). XRD study of 600°C annealed ZnO:In films reveals that crystallization strongly depends on indium concentration. The films are crystallized in wurtzite structure and only for the films with highest In addition, two crystal phases are detected wurtzite ZnO and cubic In 2 O 3 . The AFM investigation reveals that the lowest Root Mean Squared Roughness(RMS) is revealed for ZnO:In 0.5 film (15.96 nm) and the roughness increases up to 64.52 nm for ZnO:In 1. Columnar type structures can be observed in the AFM micrographs of the other two films - ZnO:In 2 and ZnO:In 3, as the columns vary in height and size. The effect of the indium doping into ZnO reveals changing of optical transmittance compared to ZnO film. The optical band gap of ZnO:In films, annealed at 600°C is in the range of 3.06-3.27 eV.

  • 4.
    Stefanov, B. I.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Enhancing the Photocatalytic Activity of Nanocrystalline Anatase TiO2 Thin Films by Fine-Tuning the <001> Orientation2014Conference paper (Refereed)
  • 5.
    Stefanov, B. I.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Fine Control of the Amount of  Preferential <001> Orientation in DC Magnetron Sputtered Nanocrystalline TiO2 Films2014In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 559, no 012011, p. 012011/1-012011/5Article in journal (Refereed)
    Abstract [en]

    ABSTRACT: Different crystal facets of anatase TiO2 are known to have different chemical reactivity; in particular the {001} facets which truncates the bi-tetrahedral anatase morphology are reported to be more reactive than the usually dominant {101} facets. Anatase TiO2 thin films were deposited by reactive DC magnetron sputtering in Ar/O2 atmosphere and were characterized using Rietveld refined grazing incidence X-ray diffraction, atomic force microscopy and UV/Vis spectroscopy. By varying the partial O2 pressure in the deposition chamber, the degree of orientation of the grains in the film could be systematically varied with preferred <001> orientation changing from random upto 39% as determined by March-Dollase method. The orientation of the films is shown to correlate with their reactivity, as measured by photo-degradation of methylene blue in water solutions. The results have implications for fabrication of purposefully chemically reactive thin TiO2 films prepared by sputtering methods.

    Full-text · Article · Nov 2014 · Journal of Physics Conference Series

  • 6.
    Stefanov, B. I.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Topalian, Z.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Acetaldehyde Adsorption and Condensation on Anatase TiO2: Influence of Acetaldehyde Dimerization2014In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 381, p. 77-88Article in journal (Refereed)
  • 7.
    Stefanov, Bozhidar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Photocatalysis for Indoor Air Cleaning: In situ FTIR and DFT Study of Acetaldehyde Photo-Oxidation on TiO2 and Sulfate-Modified TiO22013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Acetaldehyde is among the group of VOC’s causing the so-called "sick building" syndrome. WHO has estimated that this problem, related to the indoor air-quality, affects one third of all buildings worldwide. TiO2 is an attractive material for the photocatalytic removal of VOC’s in the indoor environment. Deactivation of the photocatalyst is, however, commonly deteriorating its performance over usage time, and ways to mitigate this problem must be invented. Thus modification of TiO2 surface properties is an area of considerable interest. It is possible to enhance the surface acidity of TiO2 through sulfation which effectively lowers the affinity of acidic intermediates. In addition, surface modification of photocatalysts may be used to control adsorption and wetting properties, as well as providing scavengers for photo-excited electrons and holes to suppress unwanted recombination and increase the quantum yield.

    In this work the interaction of gaseous acetaldehyde with TiO2 and SO4-modified anatase TiO2 is investigated. Films were prepared by doctor-blading of commercial TiO2 nanoparticle suspensions and characterized by means of XRD and TEM. The adsorption and photo-oxidation of acetaldehyde were studied with in situ FTIR spectroscopy and DFT calculations.

    On TiO2 nanoparticles, which exhibit predominantly (101) facets, in situ FTIR shows that acetaldehyde adsorption is accompanied by the appearance of a hitherto non-assigned absorption band at 1643 cm−1, shown to be due to acetaldehyde dimers. The results are supported by DFT calculations performed at the M06/6-31++G** level. Vibrational frequencies calculated within a partially relaxed cluster model for molecular acetaldehyde and its dimer, and for the corresponding adsorbed species on the anatase (101) surface, were in good agreement with the experimental results. Inclusion of dimer formation is shown to give an improved description of the reaction kinetics on TiO2.

    Based on mode-resolved in situ FTIR, kinetic models were constructed, which describe the observed photo-oxidation surface products on both TiO2 and SO4-modified TiO2. The surface concentration of main surface products and corresponding reaction rates were determined. It was observed that formate is the major reaction product, whose further oxidation limits the complete oxidation to gaseous species. Formate thus acts as an inhibitor, blocking adsorption sites, and is responsible for photocatalyst deactivation. The oxidation reaction is characterized by two reaction pathways, one fast and one slow, associated with two types of surface reaction sites. On the SO4-modified TiO2 fewer intermediates are accumulated, and it resists deactivation much better compared with the pure TiO2 photocatalyst, which is attributed to the acidic character of the modified surface. The results presented here are of interest for applications to photocatalytic air purification, and surfaces with controlled wettability.

    List of papers
    1. Acetaldehyde adsorption and condensation on anatase TiO2: Influence of acetaldehyde dimerization
    Open this publication in new window or tab >>Acetaldehyde adsorption and condensation on anatase TiO2: Influence of acetaldehyde dimerization
    2014 (English)In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 381, p. 77-88Article in journal (Refereed) Published
    Abstract [en]

    Conversion of acetaldehyde to crotonaldehyde on anatase TiO2 films was studied by in situ Fourier transform infrared spectroscopy (FTIR) and by density functional theory (DFT) calculations. In situ FTIR showed that acetaldehyde adsorption is accompanied by the appearance of a hitherto non-assigned absorption band at 1643 cm−1, which is shown to be due to acetaldehyde dimers. The results were supported by DFT calculations. Vibrational frequencies calculated within a partially relaxed cluster model for molecular acetaldehyde and its dimer, and for the corresponding adsorbed species on the anatase (101) surface, were in good agreement with experimental results. A kinetic model was constructed based on the combined FTIR and DFT results, and was shown to explain the essential features of the acetaldehyde condensation reaction.

    Place, publisher, year, edition, pages
    Elsevier, 2014
    Keywords
    TiO2, acetaldehyde, Crotonaldehyde, Dimer, Adsorption, DFT, FTIR
    National Category
    Chemical Process Engineering Nano Technology Inorganic Chemistry Theoretical Chemistry
    Research subject
    Chemistry with specialization in Materials Chemistry; Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-209695 (URN)10.1016/j.molcata.2013.10.005 (DOI)000329384300011 ()
    Projects
    EU GRINDOOR
    Funder
    EU, FP7, Seventh Framework Programme, 267234Swedish Research Council, VR 2010-3514
    Available from: 2013-10-26 Created: 2013-10-24 Last updated: 2017-12-06Bibliographically approved
    2. Adsorption and photo-oxidation of acetaldehyde on TiO2 and sulfate-modified TiO2: Studies by in situ FTIR spectroscopy and micro-kinetic modeling
    Open this publication in new window or tab >>Adsorption and photo-oxidation of acetaldehyde on TiO2 and sulfate-modified TiO2: Studies by in situ FTIR spectroscopy and micro-kinetic modeling
    2013 (English)In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 307, p. 265-274Article in journal (Refereed) Published
    Abstract [en]

    Adsorption and photocatalytic oxidation of acetaldehyde have been investigated on TiO2 and sulfate-modified TiO2 films (denoted SO4TiO2). In situ Fourier transform infrared spectroscopy was used to study surface reactions as a function of time and number of experimental cycles. Spectral analysis and micro-kinetic modeling show that crotonaldehyde formation occurs spontaneously on TiO2 but is impeded on SO4TiO2, where instead acetaldehyde desorption is significant. Photo-oxidation yields significant amounts of formate on TiO2 and was identified as the rate-determining step and associated with site blocking. Significantly smaller amounts of formate were observed on SO4TiO2, which is due to the acidity of this surface resulting in weaker bonding of aldehyde and carboxylate intermediate species. Our results are of considerable interest for applications to photocatalytic air purification and to surfaces with controlled wettability.

    Place, publisher, year, edition, pages
    Elsevier, 2013
    Keywords
    Acetaldehyde, TiO2, Photocatalysis, In situ Fourier transform infrared spectroscopy, Micro-kinetic modeling, Acid–base properties, Surface functionalization
    National Category
    Inorganic Chemistry Chemical Process Engineering Nano Technology
    Research subject
    Engineering Science with specialization in Nanotechnology and Functional Materials; Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-209690 (URN)10.1016/j.jcat.2013.08.004 (DOI)000327903900029 ()
    Funder
    EU, European Research Council, ERC Advanced Grant 267234Swedish Research Council, VR 2010-3514
    Available from: 2013-10-26 Created: 2013-10-24 Last updated: 2017-12-06Bibliographically approved
  • 8.
    Stefanov, Bozhidar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Photocatalytic TiO2 thin films for air cleaning: Effect of facet orientation, chemical functionalization, and reaction conditions2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Poor indoor air quality is a source of adverse health effects. TiO2 coatings deposited on well-illuminated surfaces, such as window panes, can be used to fully mineralize indoor air pollutants by photocatalysis. In such applications it is important to ensure stable photocatalytic activity for a wide range of operating conditions, such as relative humidity and temperature, and to avoid deactivation of the catalyst.

    In this thesis photocatalytic removal of the indoor-pollutant acetaldehyde (CH3CHO) on nanostructured TiO2 films is investigated, and in particular it is proposed how such films can be modified and operated for maximum performance. Catalyst deactivation can be reduced by purposefully changing the surface acidity of TiO2 by covalently attaching SO4 to the surface. Moreover, the overall photocatalytic activity on anatase TiO2 films can be improved by increasing the fraction of exposed reactive {001} surfaces, which otherwise are dominated by {101} surfaces.

    In the first part of the thesis mode-resolved in-situ FTIR is used to elucidate the reaction kinetics of CH3CHO adsorption and photo-oxidation on the TiO2 and SO4 – modified TiO2 surfaces. Surface concentrations of main products and corresponding reaction rates were determined. Formate is the major reaction product, whose further oxidation limits the complete oxidation to gaseous species, and is responsible for photocatalyst deactivation by site inhibition. The oxidation reaction is characterized by two reaction pathways, which are associated with two types of surface reaction sites. On the sulfate modified TiO2 catalyst fewer intermediates are accumulated, and this catalyst resists deactivation much better than pure TiO2. A hitherto unknown intermediate – surface-bound acetaldehyde dimer with an adsorption band at 1643 cm−1 was discovered, using interplay between FTIR spectroscopy and DFT calculations.

    The second part of the thesis treats the effect of increasing the relative abundance of exposed {001} facets on the photocatalytic activity of anatase TiO2 films prepared by DC magnetron sputtering. A positive effect was observed both for liquid-phase photo-oxidation of methylene blue, and for gas-phase photocatalytic removal of CH3CHO. In both cases it was found that the exposed {001} surfaces were an order of magnitude more reactive, compared to the {101} ones. Furthermore, it was found that the reactive films were more resilient towards deactivation, and exhibited almost unchanged activity under varying reaction conditions. Finally, a synergetic effect of SO4 – modification and high fraction of exposed {001} surfaces was found, yielding photocatalysts with sustained high activity.

    The results presented here for facet controlled and chemically modified TiO2 films are of interest for applications in the built environment for indoor air purification and as self-cleaning surfaces.

    List of papers
    1. Acetaldehyde adsorption and condensation on anatase TiO2: Influence of acetaldehyde dimerization
    Open this publication in new window or tab >>Acetaldehyde adsorption and condensation on anatase TiO2: Influence of acetaldehyde dimerization
    2014 (English)In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 381, p. 77-88Article in journal (Refereed) Published
    Abstract [en]

    Conversion of acetaldehyde to crotonaldehyde on anatase TiO2 films was studied by in situ Fourier transform infrared spectroscopy (FTIR) and by density functional theory (DFT) calculations. In situ FTIR showed that acetaldehyde adsorption is accompanied by the appearance of a hitherto non-assigned absorption band at 1643 cm−1, which is shown to be due to acetaldehyde dimers. The results were supported by DFT calculations. Vibrational frequencies calculated within a partially relaxed cluster model for molecular acetaldehyde and its dimer, and for the corresponding adsorbed species on the anatase (101) surface, were in good agreement with experimental results. A kinetic model was constructed based on the combined FTIR and DFT results, and was shown to explain the essential features of the acetaldehyde condensation reaction.

    Place, publisher, year, edition, pages
    Elsevier, 2014
    Keywords
    TiO2, acetaldehyde, Crotonaldehyde, Dimer, Adsorption, DFT, FTIR
    National Category
    Chemical Process Engineering Nano Technology Inorganic Chemistry Theoretical Chemistry
    Research subject
    Chemistry with specialization in Materials Chemistry; Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-209695 (URN)10.1016/j.molcata.2013.10.005 (DOI)000329384300011 ()
    Projects
    EU GRINDOOR
    Funder
    EU, FP7, Seventh Framework Programme, 267234Swedish Research Council, VR 2010-3514
    Available from: 2013-10-26 Created: 2013-10-24 Last updated: 2017-12-06Bibliographically approved
    2. Adsorption and photo-oxidation of acetaldehyde on TiO2 and sulfate-modified TiO2: Studies by in situ FTIR spectroscopy and micro-kinetic modeling
    Open this publication in new window or tab >>Adsorption and photo-oxidation of acetaldehyde on TiO2 and sulfate-modified TiO2: Studies by in situ FTIR spectroscopy and micro-kinetic modeling
    2013 (English)In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 307, p. 265-274Article in journal (Refereed) Published
    Abstract [en]

    Adsorption and photocatalytic oxidation of acetaldehyde have been investigated on TiO2 and sulfate-modified TiO2 films (denoted SO4TiO2). In situ Fourier transform infrared spectroscopy was used to study surface reactions as a function of time and number of experimental cycles. Spectral analysis and micro-kinetic modeling show that crotonaldehyde formation occurs spontaneously on TiO2 but is impeded on SO4TiO2, where instead acetaldehyde desorption is significant. Photo-oxidation yields significant amounts of formate on TiO2 and was identified as the rate-determining step and associated with site blocking. Significantly smaller amounts of formate were observed on SO4TiO2, which is due to the acidity of this surface resulting in weaker bonding of aldehyde and carboxylate intermediate species. Our results are of considerable interest for applications to photocatalytic air purification and to surfaces with controlled wettability.

    Place, publisher, year, edition, pages
    Elsevier, 2013
    Keywords
    Acetaldehyde, TiO2, Photocatalysis, In situ Fourier transform infrared spectroscopy, Micro-kinetic modeling, Acid–base properties, Surface functionalization
    National Category
    Inorganic Chemistry Chemical Process Engineering Nano Technology
    Research subject
    Engineering Science with specialization in Nanotechnology and Functional Materials; Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-209690 (URN)10.1016/j.jcat.2013.08.004 (DOI)000327903900029 ()
    Funder
    EU, European Research Council, ERC Advanced Grant 267234Swedish Research Council, VR 2010-3514
    Available from: 2013-10-26 Created: 2013-10-24 Last updated: 2017-12-06Bibliographically approved
    3. Fine control of the amount of preferential <001> orientation in DC magnetron sputtered nanocrystalline TiO2 film
    Open this publication in new window or tab >>Fine control of the amount of preferential <001> orientation in DC magnetron sputtered nanocrystalline TiO2 film
    2014 (English)In: INERA Workshop: Transition Metal Oxide Thin Films-functional Layers in "Smart windows" and Water Splitting Devices. Parallel session of the 18th International School on Condensed Matter Physics / [ed] Prof. DSc Kostadinka Gesheva, Institute of Physics (IOP), 2014, p. UNSP 012011-Conference paper, Published paper (Refereed)
    Abstract [en]

    Different crystal facets of anatase TiO2 are known to have different chemical reactivity; in particular the {001} facets which truncates the bi-tetrahedral anatase morphology are reported to be more reactive than the usually dominant {101} facets. Anatase TiO2 thin films were deposited by reactive DC magnetron sputtering in Ar/O2 atmosphere and were characterized using Rietveld refined grazing incidence X-ray diffraction, atomic force microscopy and UV/Vis spectroscopy. By varying the partial O2 pressure in the deposition chamber, the degree of orientation of the grains in the film could be systematically varied with preferred <001> orientation changing from random upto 39% as determined by March-Dollase method. The orientation of the films is shown to correlate with their reactivity, as measured by photo-degradation of methylene blue in water solutions. The results have implications for fabrication of purposefully chemically reactive thin TiO2 films prepared by sputtering methods.

    Place, publisher, year, edition, pages
    Institute of Physics (IOP), 2014
    Series
    Journal of Physics Conference Series, ISSN 1742-6588 ; 559
    Keywords
    anatase, photocatalysis, preferential, orientation, sputtering
    National Category
    Nano Technology Chemical Process Engineering Inorganic Chemistry Condensed Matter Physics
    Research subject
    Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-236977 (URN)10.1088/1742-6596/559/1/012011 (DOI)000346420600011 ()
    Conference
    INERA Workshop: Transition Metal Oxide Thin Films-functional Layers in "Smart windows" and Water Splitting Devices. Parallel session of the 18th International School on Condensed Matter Physics, 4–6 September 2014, Varna, Bulgaria
    Funder
    EU, European Research Council, 267234
    Available from: 2014-11-25 Created: 2014-11-25 Last updated: 2016-01-13Bibliographically approved
    4. Tuning the Photocatalytic Activity of Anatase TiO2 Thin Films by Modifying the Preferred <001> Grain Orientation with Reactive DC Magnetron Sputtering
    Open this publication in new window or tab >>Tuning the Photocatalytic Activity of Anatase TiO2 Thin Films by Modifying the Preferred <001> Grain Orientation with Reactive DC Magnetron Sputtering
    2014 (English)In: Coatings, ISSN 2079-6412, Vol. 4, no 3, p. 587-601Article in journal (Refereed) Published
    Abstract [en]

    Anatase TiO2 thin films were deposited by DC reactive magnetron sputtering on glass substrates at 20 mTorr pressure in a flow of an Ar and O2 gas mixture. The O2 partial pressure (PO2) was varied from 0.65 mTorr to 1.3 mTorr to obtain two sets of films with different stoichiometry. The structure and morphology of the films were characterized by secondary electron microscopy, atomic force microscopy, and grazing-angle X-ray diffraction complemented by Rietveld refinement. The as-deposited films were amorphous. Post-annealing in air for 1 h at 500 °C resulted in polycrystalline anatase film structures with mean grain size of 24.2 nm (PO2 = 0.65 mTorr) and 22.1 nm (PO2 = 1.3 mTorr), respectively. The films sputtered at higher O2 pressure showed a preferential orientation in the <001> direction, which was associated with particle surfaces exposing highly reactive {001} facets. Films sputtered at lower O2 pressure exhibited no, or very little, preferential grain orientation, and were associated with random distribution of particles exposing mainly the thermodynamically favorable {101} surfaces. Photocatalytic degradation measurements using methylene blue dye showed that <001> oriented films exhibited approximately 30% higher reactivity. The measured intensity dependence of the degradation rate revealed that the UV-independent rate constant was 64% higher for the <001> oriented film compared to randomly oriented films. The reaction order was also found to be higher for <001> films compared to randomly oriented films, suggesting that the <001> oriented film exposes more reactive surface sites.

    Keywords
    TiO2, photocatalysis, DC magnetron sputtering, preferred orientation, (001) facets
    National Category
    Materials Chemistry Inorganic Chemistry Nano Technology
    Research subject
    Chemistry with specialization in Materials Chemistry; Chemistry with specialization in Physical Chemistry; Chemistry with specialization in Inorganic Chemistry; Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-229598 (URN)10.3390/coatings4030587 (DOI)000209733700011 ()
    Projects
    ERC Grant Agreement No. 267234 (“GRINDOOR”)
    Funder
    EU, FP7, Seventh Framework Programme, 267234 ("GRINDOOR")
    Available from: 2014-08-11 Created: 2014-08-11 Last updated: 2017-12-05Bibliographically approved
    5. Quantitative relation between photocatalytic activity and degree of〈001〉orientation for anatase TiO2 thin films
    Open this publication in new window or tab >>Quantitative relation between photocatalytic activity and degree of〈001〉orientation for anatase TiO2 thin films
    2015 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, no 33, p. 17369-17375Article in journal (Refereed) Published
    Abstract [en]

    We demonstrate a quantitative relation between exposed crystal surfaces and photocatalytic activity of nanocrystalline anatase TiO2. Thin films with controlled amount of 〈001〉 preferential orientation were prepared by reactive DC magnetron sputtering in Ar/O2 atmosphere with the partial O2 pressure as control parameter. The samples were characterized with X-ray diffraction, transmission electron microscopy and atomic force microscopy, from which the degree of preferential 〈001〉 orientation and exposed facets were determined by an extension of the March–Dollase model. Photocatalytic degradation of methylene blue dye shows that the photocatalytic reaction rate increases approximately with the square of the fraction of 〈001〉 oriented surfaces, with about eight times higher rate on the {001} surfaces, than on {101}, thus quantifying the effect of crystal facet abundancy on the photocatalytic activity of anatase TiO2.

    Place, publisher, year, edition, pages
    Royal Society of Chemistry, 2015
    Keywords
    tio2, anatase, preferred orientation, 001, sputtering
    National Category
    Materials Engineering Inorganic Chemistry Materials Chemistry Nano Technology
    Research subject
    Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-259523 (URN)10.1039/C5TA04362J (DOI)000359459900051 ()
    Funder
    EU, European Research Council, 267234
    Available from: 2015-08-06 Created: 2015-08-06 Last updated: 2018-08-30Bibliographically approved
    6. Gas-phase photocatalytic activity of sputter-deposited anatase TiO2 films: Effect of <001> preferential orientation, surface temperature and humidity
    Open this publication in new window or tab >>Gas-phase photocatalytic activity of sputter-deposited anatase TiO2 films: Effect of <001> preferential orientation, surface temperature and humidity
    2016 (English)In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 335, p. 187-196Article in journal (Refereed) Published
    Abstract [en]

    We present a systematic in situ study of the environmental reaction conditions on the photocatalytic activity of sputter deposited anatase TiO2 films with controlled amounts of preferential <001> orientation. In particular, the effects of relative humidity (RH) and substrate temperature ( ) are investigated. It is found that {001} facets, which are present in higher abundance on highly oriented samples, exhibit an order of magnitude higher reactivity for gas-phase photocatalytic oxidation of the indoor air pollutant acetaldehyde (CH3CHO) than {101} facets do, and a functional dependence of the reaction rate on facet orientation is determined. It is proposed that water adsorbed on the film contributes with two counteracting effects on the photocatalytic activity: (i) It provides hole acceptors to complete the photo-induced redox cycle and subsequent OH– radical formation for pollutant degradation, and (ii) it creates a diffusion barrier between the catalyst interface and pollutant molecules adsorbed in the water layer. As a consequence, increasing  at high RH has the beneficial effect of removing excess water and reducing the diffusion barrier, thereby improving the photocatalytic activity. A comparison is also made with a commercial anatase TiO2 film, with less developed surface crystallinity and random facet distribution, where the improvement is even more pronounced. Films with a higher degree of orientation exhibit much more stable performance over a range of operating conditions, which suggests that it is possible to tune the effects of water and exposed facet orientation to achieve optimum activity and making TiO2 films amenable to a larger (RH, ) parameter space for practical applications.

    National Category
    Inorganic Chemistry Condensed Matter Physics Chemical Engineering Nano Technology
    Research subject
    Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-265055 (URN)10.1016/j.jcat.2015.12.002 (DOI)000371098200018 ()
    External cooperation:
    Projects
    GRINDOOR
    Funder
    EU, FP7, Seventh Framework Programme, FP7/2007-2013
    Available from: 2015-10-21 Created: 2015-10-21 Last updated: 2018-08-30Bibliographically approved
    7. Demonstrating Online Monitoring of Air Pollutant Photodegradation in a 3D Printed Gas-Phase Photocatalysis Reactor
    Open this publication in new window or tab >>Demonstrating Online Monitoring of Air Pollutant Photodegradation in a 3D Printed Gas-Phase Photocatalysis Reactor
    Show others...
    2015 (English)In: Journal of Chemical Education, ISSN 0021-9584, E-ISSN 1938-1328, Vol. 92, no 4, p. 678-682Article in journal (Refereed) Published
    Abstract [en]

    We present a demonstration of online monitoring of gas-phase photocatalytic reactions. A cotton cloth impregnated with commercial titanium dioxide nanoparticles is used as a photocatalytic filter to clean air contaminated with a model pollutant. A fan forces air through the filter while it is irradiated by UV diodes. The concentration of the air pollutant is measured online by an inexpensive, commercially available semiconductor air quality sensor. The structural parts of the reactor were 3D printed in polylactide bioplastic. We provide all schematics, 3D printed model parts, hardware, firmware, and computer code of the reactor and control units. The device can be used for interactive learning of both gas phase photocatalysis and gas sensing, as well as in student laboratory classes for measuring air pollutants and their photodegradation. The experimental setup can also form the basis for a project work for chemical engineering university students, and it can be employed as a building block for development of other gas phase chemical reaction demonstrations.

    Keywords
    Chemical Engineering, General Public, Photocatalysis, Gases, Photochemistry, Reactions, Nanotechnology, Laboratory Equipment/Apparatus
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Solid State Physics
    Identifiers
    urn:nbn:se:uu:diva-253071 (URN)10.1021/ed500604e (DOI)000353368000017 ()
    Available from: 2015-06-11 Created: 2015-05-20 Last updated: 2020-02-18Bibliographically approved
  • 9.
    Stefanov, Bozhidar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, C.-G.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Enhancing the Photocatalytic Activity of Nanocrystalline Anatase TiO2 Thin Films by Fine-Tuning the <001> Orientation2014Conference paper (Refereed)
  • 10.
    Stefanov, Bozhidar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Fine control of the amount of preferential <001> orientation in DC magnetron sputtered nanocrystalline TiO2 film2014In: INERA Workshop: Transition Metal Oxide Thin Films-functional Layers in "Smart windows" and Water Splitting Devices. Parallel session of the 18th International School on Condensed Matter Physics / [ed] Prof. DSc Kostadinka Gesheva, Institute of Physics (IOP), 2014, p. UNSP 012011-Conference paper (Refereed)
    Abstract [en]

    Different crystal facets of anatase TiO2 are known to have different chemical reactivity; in particular the {001} facets which truncates the bi-tetrahedral anatase morphology are reported to be more reactive than the usually dominant {101} facets. Anatase TiO2 thin films were deposited by reactive DC magnetron sputtering in Ar/O2 atmosphere and were characterized using Rietveld refined grazing incidence X-ray diffraction, atomic force microscopy and UV/Vis spectroscopy. By varying the partial O2 pressure in the deposition chamber, the degree of orientation of the grains in the film could be systematically varied with preferred <001> orientation changing from random upto 39% as determined by March-Dollase method. The orientation of the films is shown to correlate with their reactivity, as measured by photo-degradation of methylene blue in water solutions. The results have implications for fabrication of purposefully chemically reactive thin TiO2 films prepared by sputtering methods.

  • 11.
    Stefanov, Bozhidar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnar, Niklasson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Quantitative relation between photocatalytic activity and degree of〈001〉orientation for anatase TiO2 thin films2015In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, no 33, p. 17369-17375Article in journal (Refereed)
    Abstract [en]

    We demonstrate a quantitative relation between exposed crystal surfaces and photocatalytic activity of nanocrystalline anatase TiO2. Thin films with controlled amount of 〈001〉 preferential orientation were prepared by reactive DC magnetron sputtering in Ar/O2 atmosphere with the partial O2 pressure as control parameter. The samples were characterized with X-ray diffraction, transmission electron microscopy and atomic force microscopy, from which the degree of preferential 〈001〉 orientation and exposed facets were determined by an extension of the March–Dollase model. Photocatalytic degradation of methylene blue dye shows that the photocatalytic reaction rate increases approximately with the square of the fraction of 〈001〉 oriented surfaces, with about eight times higher rate on the {001} surfaces, than on {101}, thus quantifying the effect of crystal facet abundancy on the photocatalytic activity of anatase TiO2.

  • 12.
    Stefanov, Bozhidar I.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lebrun, Delphine
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mattsson, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Demonstrating Online Monitoring of Air Pollutant Photodegradation in a 3D Printed Gas-Phase Photocatalysis Reactor2015In: Journal of Chemical Education, ISSN 0021-9584, E-ISSN 1938-1328, Vol. 92, no 4, p. 678-682Article in journal (Refereed)
    Abstract [en]

    We present a demonstration of online monitoring of gas-phase photocatalytic reactions. A cotton cloth impregnated with commercial titanium dioxide nanoparticles is used as a photocatalytic filter to clean air contaminated with a model pollutant. A fan forces air through the filter while it is irradiated by UV diodes. The concentration of the air pollutant is measured online by an inexpensive, commercially available semiconductor air quality sensor. The structural parts of the reactor were 3D printed in polylactide bioplastic. We provide all schematics, 3D printed model parts, hardware, firmware, and computer code of the reactor and control units. The device can be used for interactive learning of both gas phase photocatalysis and gas sensing, as well as in student laboratory classes for measuring air pollutants and their photodegradation. The experimental setup can also form the basis for a project work for chemical engineering university students, and it can be employed as a building block for development of other gas phase chemical reaction demonstrations.

  • 13.
    Stefanov, Bozhidar I
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Acetaldehyde adsorption and condensation on anatase TiO2: Influence of acetaldehyde dimerization2014In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 381, p. 77-88Article in journal (Refereed)
    Abstract [en]

    Conversion of acetaldehyde to crotonaldehyde on anatase TiO2 films was studied by in situ Fourier transform infrared spectroscopy (FTIR) and by density functional theory (DFT) calculations. In situ FTIR showed that acetaldehyde adsorption is accompanied by the appearance of a hitherto non-assigned absorption band at 1643 cm−1, which is shown to be due to acetaldehyde dimers. The results were supported by DFT calculations. Vibrational frequencies calculated within a partially relaxed cluster model for molecular acetaldehyde and its dimer, and for the corresponding adsorbed species on the anatase (101) surface, were in good agreement with experimental results. A kinetic model was constructed based on the combined FTIR and DFT results, and was shown to explain the essential features of the acetaldehyde condensation reaction.

  • 14.
    Stefanov, Bozhidar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Lebrun, Delphine
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mattsson, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Demonstration of a 3D printed gas-phase photocatalysis reactor and its use for on-line monitoring of degradation of air pollutants.2014In: Journal of Chemical Education, ISSN 0021-9584, E-ISSN 1938-1328Article in journal (Refereed)
  • 15.
    Stefanov, Bozhidar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar A
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gas-phase photocatalytic activity of sputter-deposited anatase TiO2 films: Effect of <001> preferential orientation, surface temperature and humidity2016In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 335, p. 187-196Article in journal (Refereed)
    Abstract [en]

    We present a systematic in situ study of the environmental reaction conditions on the photocatalytic activity of sputter deposited anatase TiO2 films with controlled amounts of preferential <001> orientation. In particular, the effects of relative humidity (RH) and substrate temperature ( ) are investigated. It is found that {001} facets, which are present in higher abundance on highly oriented samples, exhibit an order of magnitude higher reactivity for gas-phase photocatalytic oxidation of the indoor air pollutant acetaldehyde (CH3CHO) than {101} facets do, and a functional dependence of the reaction rate on facet orientation is determined. It is proposed that water adsorbed on the film contributes with two counteracting effects on the photocatalytic activity: (i) It provides hole acceptors to complete the photo-induced redox cycle and subsequent OH– radical formation for pollutant degradation, and (ii) it creates a diffusion barrier between the catalyst interface and pollutant molecules adsorbed in the water layer. As a consequence, increasing  at high RH has the beneficial effect of removing excess water and reducing the diffusion barrier, thereby improving the photocatalytic activity. A comparison is also made with a commercial anatase TiO2 film, with less developed surface crystallinity and random facet distribution, where the improvement is even more pronounced. Films with a higher degree of orientation exhibit much more stable performance over a range of operating conditions, which suggests that it is possible to tune the effects of water and exposed facet orientation to achieve optimum activity and making TiO2 films amenable to a larger (RH, ) parameter space for practical applications.

  • 16.
    Stefanov, Bozhidar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Adsorbtion and reaction of acetaldehyde on pristine and SO2 modified anatase TiO22013Conference paper (Refereed)
  • 17.
    Stefanov, Bozhidar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Tuning the Photocatalytic Activity of Anatase TiO2 Thin Films by Modifying the Preferred <001> Grain Orientation with Reactive DC Magnetron Sputtering2014In: Coatings, ISSN 2079-6412, Vol. 4, no 3, p. 587-601Article in journal (Refereed)
    Abstract [en]

    Anatase TiO2 thin films were deposited by DC reactive magnetron sputtering on glass substrates at 20 mTorr pressure in a flow of an Ar and O2 gas mixture. The O2 partial pressure (PO2) was varied from 0.65 mTorr to 1.3 mTorr to obtain two sets of films with different stoichiometry. The structure and morphology of the films were characterized by secondary electron microscopy, atomic force microscopy, and grazing-angle X-ray diffraction complemented by Rietveld refinement. The as-deposited films were amorphous. Post-annealing in air for 1 h at 500 °C resulted in polycrystalline anatase film structures with mean grain size of 24.2 nm (PO2 = 0.65 mTorr) and 22.1 nm (PO2 = 1.3 mTorr), respectively. The films sputtered at higher O2 pressure showed a preferential orientation in the <001> direction, which was associated with particle surfaces exposing highly reactive {001} facets. Films sputtered at lower O2 pressure exhibited no, or very little, preferential grain orientation, and were associated with random distribution of particles exposing mainly the thermodynamically favorable {101} surfaces. Photocatalytic degradation measurements using methylene blue dye showed that <001> oriented films exhibited approximately 30% higher reactivity. The measured intensity dependence of the degradation rate revealed that the UV-independent rate constant was 64% higher for the <001> oriented film compared to randomly oriented films. The reaction order was also found to be higher for <001> films compared to randomly oriented films, suggesting that the <001> oriented film exposes more reactive surface sites.

  • 18.
    Topalian, Zareh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Stefanov, Bozhidar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Granqvist, Claes-Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Adsorption and photo-oxidation of acetaldehyde on TiO2 and sulfate-modified TiO2: Studies by in situ FTIR spectroscopy and micro-kinetic modeling2013In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 307, p. 265-274Article in journal (Refereed)
    Abstract [en]

    Adsorption and photocatalytic oxidation of acetaldehyde have been investigated on TiO2 and sulfate-modified TiO2 films (denoted SO4TiO2). In situ Fourier transform infrared spectroscopy was used to study surface reactions as a function of time and number of experimental cycles. Spectral analysis and micro-kinetic modeling show that crotonaldehyde formation occurs spontaneously on TiO2 but is impeded on SO4TiO2, where instead acetaldehyde desorption is significant. Photo-oxidation yields significant amounts of formate on TiO2 and was identified as the rate-determining step and associated with site blocking. Significantly smaller amounts of formate were observed on SO4TiO2, which is due to the acidity of this surface resulting in weaker bonding of aldehyde and carboxylate intermediate species. Our results are of considerable interest for applications to photocatalytic air purification and to surfaces with controlled wettability.

  • 19.
    Österlund, Lars
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mattsson, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Brischetto, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Johansson Byberg, Joel
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Stefanov, Bozhidar I
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ji, Yu -Xia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Niklasson, Gunnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Spectral Selective Solar Light Enhanced Photocatalysis: TiO2/TiAlN Bilayer Films2018In: Topics in catalysis, ISSN 1022-5528, E-ISSN 1572-9028, Vol. 61, no 15-17, p. 1607-1614Article in journal (Refereed)
    Abstract [en]

    We demonstrate that spectral selective photocatalytic multilayer films can be tailored such that they can harness the full solar spectrum for enhanced photocatalytic gas-phase oxidation of acetaldehyde. Thin films of anatase TiO2 were deposited on a thin solar absorber TiAlN film to fabricate bilayer TiO2/TiAlN films by dc magnetron sputtering on aluminium substrates. The structural and optical properties of the films were characterized by X-ray diffraction and Raman spectroscopy. The reaction rate and quantum yield for acetaldehyde removal was measured and an almost tenfold enhancement of the quantum yield was observed for the TiO2/TiAlN films compared with the single TiO2 film, on par with enhancements achieved with new heterojunction photocatalysts. The results were interpreted by a temperature-induced change of the reaction kinetics. Absorption of simulated solar light illumination resulted in a temperature increase of the TIAlN film that was estimated to be at most 126 K. We show that a concomitant temperature increase of the top layer TiO2 by 100 K shifts the water gas surface equilibrium from multilayer to submonolayer coverage. We propose that this is the main reason for the observed enhancement of the photocatalytic activity, whereby gas phase molecules may come in direct contact with free surface sites instead of having to diffuse through a thin water film. The implications of the results for judicious control of temperature and relative humidity for efficient gas-phase photocatalysis and exploitation of selective solar absorbing films are discussed.

1 - 19 of 19
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