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Adsorption and photo-oxidation of acetaldehyde on TiO2 and sulfate-modified TiO2: Studies by in situ FTIR spectroscopy and micro-kinetic modeling
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
2013 (engelsk)Inngår i: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 307, s. 265-274Artikkel i tidsskrift (Fagfellevurdert) 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.

sted, utgiver, år, opplag, sider
Elsevier, 2013. Vol. 307, s. 265-274
Emneord [en]
Acetaldehyde, TiO2, Photocatalysis, In situ Fourier transform infrared spectroscopy, Micro-kinetic modeling, Acid–base properties, Surface functionalization
HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot nanoteknologi och funktionella material; Teknisk fysik med inriktning mot fasta tillståndets fysik
Identifikatorer
URN: urn:nbn:se:uu:diva-209690DOI: 10.1016/j.jcat.2013.08.004ISI: 000327903900029OAI: oai:DiVA.org:uu-209690DiVA, id: diva2:659634
Forskningsfinansiär
EU, European Research Council, ERC Advanced Grant 267234Swedish Research Council, VR 2010-3514Tilgjengelig fra: 2013-10-26 Laget: 2013-10-24 Sist oppdatert: 2017-12-06bibliografisk kontrollert
Inngår i avhandling
1. Photocatalysis for Indoor Air Cleaning: In situ FTIR and DFT Study of Acetaldehyde Photo-Oxidation on TiO2 and Sulfate-Modified TiO2
Åpne denne publikasjonen i ny fane eller vindu >>Photocatalysis for Indoor Air Cleaning: In situ FTIR and DFT Study of Acetaldehyde Photo-Oxidation on TiO2 and Sulfate-Modified TiO2
2013 (engelsk)Licentiatavhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Uppsala: Uppsala universitet, 2013. s. 72
Emneord
TiO2, acetaldehyde, crotonaldehyde, dimer, adsorption, DFT, FTIR, photocatalysis, micro-kinetic modeling, acid–base properties, surface functionalization
HSV kategori
Forskningsprogram
Fasta tillståndets fysik; Materialvetenskap
Identifikatorer
urn:nbn:se:uu:diva-210004 (URN)
Presentation
2013-11-21, Å2001, Lägerhyddsv. 1, Uppsala, 13:15 (engelsk)
Veileder
Tilgjengelig fra: 2013-11-25 Laget: 2013-10-29 Sist oppdatert: 2013-11-25bibliografisk kontrollert
2. Photocatalytic TiO2 thin films for air cleaning: Effect of facet orientation, chemical functionalization, and reaction conditions
Åpne denne publikasjonen i ny fane eller vindu >>Photocatalytic TiO2 thin films for air cleaning: Effect of facet orientation, chemical functionalization, and reaction conditions
2015 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Uppsala: Acta Universitatis Upsaliensis, 2015. s. 148
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1307
Emneord
titanium dioxide, photocatalysis, thin films, surface functionallization, acetaldehyde, indoor air cleaning, sputter deposition, crystallographic modifications, preferential orientation, self-cleaning surfaces
HSV kategori
Forskningsprogram
Teknisk fysik med inriktning mot fasta tillståndets fysik
Identifikatorer
urn:nbn:se:uu:diva-265056 (URN)978-91-554-9387-5 (ISBN)
Disputas
2015-12-11, Polhemssalen, Lägerhyddsv. 1, Uppsala, 09:15 (engelsk)
Opponent
Veileder
Prosjekter
GRINDOOR
Forskningsfinansiär
EU, European Research Council, ERC Grant Agreement No. 267234 (“GRINDOOR”)
Tilgjengelig fra: 2015-11-19 Laget: 2015-10-21 Sist oppdatert: 2016-01-13

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