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Quantitative relation between photocatalytic activity and degree of〈001〉orientation for anatase TiO2 thin films
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
2015 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 3, no 33, 17369-17375 p.Article 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. Vol. 3, no 33, 17369-17375 p.
Keyword [en]
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: urn:nbn:se:uu:diva-259523DOI: 10.1039/C5TA04362JISI: 000359459900051OAI: oai:DiVA.org:uu-259523DiVA: diva2:844589
Funder
EU, European Research Council, 267234
Available from: 2015-08-06 Created: 2015-08-06 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Photocatalytic TiO2 thin films for air cleaning: Effect of facet orientation, chemical functionalization, and reaction conditions
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. 148 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1307
Keyword
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

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Stefanov, BozhidarGunnar, NiklassonGranqvist, Claes-GöranÖsterlund, Lars

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