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Stefanov, Bozhidar IORCID iD iconorcid.org/0000-0002-1017-7067
Alternative names
Publications (10 of 19) Show all publications
Österlund, L., Mattsson, A., Brischetto, M., Johansson Byberg, J., Stefanov, B. I., Ji, Y.-X. -. & Niklasson, G. (2018). Spectral Selective Solar Light Enhanced Photocatalysis: TiO2/TiAlN Bilayer Films. Topics in catalysis, 61(15-17), 1607-1614
Open this publication in new window or tab >>Spectral Selective Solar Light Enhanced Photocatalysis: TiO2/TiAlN Bilayer Films
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2018 (English)In: Topics in catalysis, ISSN 1022-5528, E-ISSN 1572-9028, Vol. 61, no 15-17, p. 1607-1614Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer Publishing Company, 2018
National Category
Materials Chemistry Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-369879 (URN)10.1007/s11244-018-1011-5 (DOI)000451216500012 ()
Funder
Swedish Research Council, 2016-05904EU, FP7, Seventh Framework Programme, 267234
Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2019-01-07Bibliographically approved
Ivanova, T., Harizanova, A., Koutzarova, T., Vertruyen, B. & Stefanov, B. (2018). Structural and morphological properties of sol-gel ZnO:Ni films. In: 20th International Summer School on Vacuum, Electron and Ion Technologies, 2017: . Paper presented at 20th International Summer School on Vacuum, Electron and Ion Technologies, SEP 25-29, 2017, Sozopol, BULGARIA. Institute of Physics Publishing (IOPP), 992, Article ID 012044.
Open this publication in new window or tab >>Structural and morphological properties of sol-gel ZnO:Ni films
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2018 (English)In: 20th International Summer School on Vacuum, Electron and Ion Technologies, 2017, Institute of Physics Publishing (IOPP), 2018, Vol. 992, article id 012044Conference paper, Published 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.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2018
Series
Journal of Physics Conference Series, ISSN 1742-6588, E-ISSN 1742-6596 ; 992
National Category
Condensed Matter Physics Materials Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-368673 (URN)10.1088/1742-6596/992/1/012044 (DOI)000445817300044 ()
Conference
20th International Summer School on Vacuum, Electron and Ion Technologies, SEP 25-29, 2017, Sozopol, BULGARIA
Available from: 2018-12-06 Created: 2018-12-06 Last updated: 2018-12-11Bibliographically approved
Ivanova, T., Harizanova, A., Koutzarova, T., Vertruyen, B. & Stefanov, B. I. (2017). Morphological Study of Sol-Gel Derived ZnO: In Thin Films. In: Proceeding of the 2017 40Th International Spring Seminar On Electronics Technology (ISSE): . Paper presented at 40th International Spring Seminar on Electronics Technology (ISSE), 10-14 May, 2017, Sofia, Bulgaria.
Open this publication in new window or tab >>Morphological Study of Sol-Gel Derived ZnO: In Thin Films
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2017 (English)In: Proceeding of the 2017 40Th International Spring Seminar On Electronics Technology (ISSE), 2017Conference paper, Published 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.

Series
International Spring Seminar on Electronics Technology (ISSE), E-ISSN 2161-2536
National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-356256 (URN)10.1109/ISSE.2017.8000965 (DOI)000426973000088 ()978-1-5386-0582-0 (ISBN)978-1-5386-0583-7 (ISBN)
Conference
40th International Spring Seminar on Electronics Technology (ISSE), 10-14 May, 2017, Sofia, Bulgaria
Available from: 2018-07-30 Created: 2018-07-30 Last updated: 2018-08-20Bibliographically approved
Stefanov, B., Niklasson, G. A., Granqvist, C.-G. & Österlund, L. (2016). Gas-phase photocatalytic activity of sputter-deposited anatase TiO2 films: Effect of <001> preferential orientation, surface temperature and humidity. Journal of Catalysis, 335, 187-196
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
Stefanov, B. I., Lebrun, D., Mattsson, A., Granqvist, C. G. & Österlund, L. (2015). Demonstrating Online Monitoring of Air Pollutant Photodegradation in a 3D Printed Gas-Phase Photocatalysis Reactor. Journal of Chemical Education, 92(4), 678-682
Open this publication in new window or tab >>Demonstrating Online Monitoring of Air Pollutant Photodegradation in a 3D Printed Gas-Phase Photocatalysis Reactor
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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: 2019-11-24
Stefanov, B. (2015). Photocatalytic TiO2 thin films for air cleaning: Effect of facet orientation, chemical functionalization, and reaction conditions. (Doctoral dissertation). Uppsala: Acta Universitatis Upsaliensis
Open this publication in new window or tab >>Photocatalytic TiO2 thin films for air cleaning: Effect of facet orientation, chemical functionalization, and reaction conditions
2015 (English)Doctoral 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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. p. 148
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1307
Keywords
titanium dioxide, photocatalysis, thin films, surface functionallization, acetaldehyde, indoor air cleaning, sputter deposition, crystallographic modifications, preferential orientation, self-cleaning surfaces
National Category
Chemical Engineering Materials Engineering Nano Technology Theoretical Chemistry Inorganic Chemistry
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-265056 (URN)978-91-554-9387-5 (ISBN)
Public defence
2015-12-11, Polhemssalen, Lägerhyddsv. 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Projects
GRINDOOR
Funder
EU, European Research Council, ERC Grant Agreement No. 267234 (“GRINDOOR”)
Available from: 2015-11-19 Created: 2015-10-21 Last updated: 2016-01-13
Stefanov, B., Gunnar, N., Granqvist, C.-G. & Österlund, L. (2015). Quantitative relation between photocatalytic activity and degree of〈001〉orientation for anatase TiO2 thin films. Journal of Materials Chemistry A, 3(33), 17369-17375
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
Stefanov, B. I., Topalian, Z., Granqvist, C.-G. & Österlund, L. (2014). Acetaldehyde Adsorption and Condensation on Anatase TiO2: Influence of Acetaldehyde Dimerization. Journal of Molecular Catalysis A: Chemical, 381, 77-88
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
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-284408 (URN)
Available from: 2016-04-18 Created: 2016-04-18 Last updated: 2017-11-30
Stefanov, B. I., Topalian, Z., Granqvist, C.-G. & Österlund, L. (2014). Acetaldehyde adsorption and condensation on anatase TiO2: Influence of acetaldehyde dimerization. Journal of Molecular Catalysis A: Chemical, 381, 77-88
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
Stefanov, B., Lebrun, D., Mattsson, A., Granqvist, C. G. & Österlund, L. (2014). Demonstration of a 3D printed gas-phase photocatalysis reactor and its use for on-line monitoring of degradation of air pollutants.. Journal of Chemical Education
Open this publication in new window or tab >>Demonstration of a 3D printed gas-phase photocatalysis reactor and its use for on-line monitoring of degradation of air pollutants.
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2014 (English)In: Journal of Chemical Education, ISSN 0021-9584, E-ISSN 1938-1328Article in journal (Refereed) Published
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-234925 (URN)
Projects
EU GRINDOOR
Funder
EU, FP7, Seventh Framework Programme, 267234
Available from: 2014-10-27 Created: 2014-10-27 Last updated: 2017-12-05
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-1017-7067

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