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Photocatalysis for Indoor Air Cleaning: In situ FTIR and DFT Study of Acetaldehyde Photo-Oxidation on TiO2 and Sulfate-Modified TiO2
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
2013 (English)Licentiate 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.

Place, publisher, year, edition, pages
Uppsala: Uppsala universitet, 2013. , 72 p.
Keyword [en]
TiO2, acetaldehyde, crotonaldehyde, dimer, adsorption, DFT, FTIR, photocatalysis, micro-kinetic modeling, acid–base properties, surface functionalization
National Category
Chemical Process Engineering Inorganic Chemistry Theoretical Chemistry
Research subject
Solid State Physics; Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-210004OAI: oai:DiVA.org:uu-210004DiVA: diva2:660732
Presentation
2013-11-21, Å2001, Lägerhyddsv. 1, Uppsala, 13:15 (English)
Supervisors
Available from: 2013-11-25 Created: 2013-10-29 Last updated: 2013-11-25Bibliographically approved
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

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