Change search
ReferencesLink to record
Permanent link

Direct link
Silver enhanced TiO2 thin films: photocatalytic characterization using aqueous solutions of tris(hydroxymethyl)aminomethane
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0003-2672-0041
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
Show others and affiliations
2014 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 43, no 1, 344-351 p.Article in journal (Refereed) Published
Abstract [en]

The photocatalytic activity in aqueous solutions of TiO2 and Ag enhanced TiO2 sol-gel produced films was characterized using tris(hydroxymethyl)aminomethane (Tris) under black light (365 nm) and the observed differences in efficiency were further investigated by O-2 adsorption studies using the same probe. Hydrogen abstracting species, such as hydroxyl radicals formed upon photocatalysis, are able to abstract hydrogen from Tris. This reaction leads to the formation of formaldehyde which was detected and quantified through a modified version of the Hantzsch reaction. It was found that the Ag enhanced TiO2 film increased the apparent quantum yield from 7% to 12%, partly as a result of a Schottky barrier formation at the metal-semiconductor interface and partly as the sensitizing effect of Ag nanoparticles extends the visible light absorption, which through electron transfer processes enable an efficient charge separation in the TiO2 by attracting acceptor species more efficiently than pure TiO2. The O-2 adsorption studies in this paper showed that the Ag enhanced TiO2 film has a stronger adsorption affinity than pure TiO2 towards O-2, which make the reduction of O-2 more efficient with a subsequent enhanced electron-hole lifetime. It was also found that the Ag enhanced TiO2 film had a poorer adsorption affinity for Tris than the pure TiO2 film, which is a consequence of fewer available surface adsorption sites due to the Ag coverage at 64% which agrees well with the obtained adsorption equilibrium constants (K-LH(TiO2) = 615 M-1 and KLH(Ag-TiO2) = 320 M-1).

Place, publisher, year, edition, pages
2014. Vol. 43, no 1, 344-351 p.
Keyword [en]
Adsorption affinity, Adsorption equilibrium constants, Electron transfer process, Metal semiconductor interface, Photocatalytic activities, Sensitizing effects, Trishydroxymethylaminomethane, Visible light absorption
National Category
Chemical Sciences
URN: urn:nbn:se:kth:diva-134314DOI: 10.1039/C3DT52270AISI: 000327665200044ScopusID: 2-s2.0-84889678813OAI: diva2:665856

QC 20140109

Available from: 2013-11-21 Created: 2013-11-21 Last updated: 2014-01-09Bibliographically approved
In thesis
1. Heterogeneous TiO2 Photocatalysis: Fundamental Chemical Aspects and Effects of Solid Phase Alterations
Open this publication in new window or tab >>Heterogeneous TiO2 Photocatalysis: Fundamental Chemical Aspects and Effects of Solid Phase Alterations
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Heterogeneous photocatalysis on TiO2 is an emerging green technology for water disinfection. The rationale for this technology is based on in-situ generation of highly reactive transitory species for degradation of organic and inorganic pollutants as well as microorganisms. Recent research has concentrated on improving the efficiency of the photocatalytic process, however, some fundamental information on the mechanistic aspects and rate limiting properties still remain elusive. 

   The focus of this thesis has been to identify the primary oxidant in heterogeneous TiO2 photocatalysis and to create prerequisites for further evaluation of how selected internal (material specific) and external (system specific) alterations influence the photocatalytic activity. Furthermore, an attempt to induce visible light activity to a modified TiO2 film was also made.

   Production of H2O2 was used to probe the existence of the hydroxyl radical as the primary oxidizing species in aqueous TiO2 photocatalysis. The only possible pathway to produce H2O2 in an oxygen free environment is through hydroxyl radical recombination. A significant amount of H2O2 could be detected in deoxygenated solutions confirming the existence of hydroxyl radicals. To further elucidate the origin of the H2O2, experiments with the hydroxyl radical scavenger Tris(hydroxymethyl)aminomethane (Tris) were performed. The results further support the hypothesis that the hydroxyl radical is the primary oxidant in TiO2 photocatalysis.

   Tris was evaluated as a probe in aqueous photocatalysis. Hydrogen abstracting species such as hydroxyl radicals are able to abstract hydrogen atoms from Tris, which leads to formation of formaldehyde. Formaldehyde was detected and quantified by a modified version of the Hantzsch reaction. This route to probe the photocatalytic efficiency allows for assessment of the maximum photocatalytic efficiency with high accuracy and sensitivity and was further used to study how selected solid phase alterations and dissolved electron acceptors affect the photocatalytic efficiency. The results showed that the surface area of immobilized photocatalysts affects the efficiency and a high surface area is advantageous for photocatalysis. It was also shown that TiO2 enhanced with Ag nanoparticles significantly increases photocatalytic activity. This is explained partly by an increased O2 adsorption and reduction process on the Ag enhanced TiO2 compared to pure TiO2 and partly as a Schottky barrier formation at the metal-semiconductor interface. These processes lead to a prolonged charge separation in the photocatalyst, which is advantageous for the efficiency. Moreover, the effect of the external, dissolved electron acceptors H2O2 and O2 were also evaluated by Tris. The results showed an increased photocatalytic activity upon addition of the electron acceptors. It was also shown that the adsorption affinity of a reactant to the photocatalyst is rate controlling and governs the kinetics.

   An attempt to induce visible light activity into a TiO2 film was also made by a post-treatment in liquid NH3. The slightly narrowed bandgap of the resulting film caused a red-shift in the absorption band and the film showed visible light activity under illumination by white light with a cut-off filter at 385 nm.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. v, 77 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2013:48
National Category
Physical Chemistry
urn:nbn:se:kth:diva-134003 (URN)978-91-7501-930-7 (ISBN)
Public defence
2013-12-12, E3, Osquarsbacke 14, KTH, Stockholm, 10:00 (English)

QC 20131121

Available from: 2013-11-21 Created: 2013-11-14 Last updated: 2013-11-21Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textScopus

Search in DiVA

By author/editor
Diesen, VeronicaÖsterberg, ElinJonsson, Mats
By organisation
Applied Physical Chemistry
In the same journal
Dalton Transactions
Chemical Sciences

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 104 hits
ReferencesLink to record
Permanent link

Direct link