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Photocatalytic TiO2 thin films for air cleaning: Effect of facet orientation, chemical functionalization, and reaction conditions
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.ORCID iD: 0000-0002-1017-7067
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 [en]
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: urn:nbn:se:uu:diva-265056ISBN: 978-91-554-9387-5 (print)OAI: oai:DiVA.org:uu-265056DiVA: diva2:862338
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
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, 77-88 p.Article 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
Keyword
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, 265-274 p.Article 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
Keyword
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, UNSP 012011- p.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
Keyword
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, 587-601 p.Article 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.

Keyword
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, 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
Keyword
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: 2017-12-04Bibliographically 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, 187-196 p.Article 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: 2017-12-01Bibliographically 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, 678-682 p.Article 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.

Keyword
Chemical Engineering, General Public, Photocatalysis, Gases, Photochemistry, Reactions, Nanotechnology, Laboratory Equipment/Apparatus
National Category
Physical Sciences 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: 2017-12-04Bibliographically approved

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  • apa
  • ieee
  • modern-language-association-8th-edition
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  • en-GB
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