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Coumarin as a Quantitative Probe for Hydroxyl Radical Formation in Heterogeneous Photocatalysis
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0002-4782-4969
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0003-0663-0751
2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 11, p. 6667-6674Article in journal (Refereed) Published
Abstract [en]

In this work, we have assessed coumarin as a quantitative probe for hydroxyl radical formation in heterogeneous photocatalysis. Upon reaction with the hydroxyl radical, coumarin produces several hydroxylated products, of which one, 7-OH-coumarin, is strongly fluorescent. The fluorescence emission is strongly affected by inner filtering due to the presence of coumarin. Therefore, we performed a series of calibration experiments to correct for the coumarin concentration. From the calibration experiments, we could verify that the inner-filtering effect can be attributed to the competing absorption of the fluorescence excitation light between coumarin and 7-OH-coumarin. Through judicious calibration for the inner-filtering effects, the corrected results for the photocatalytic system show that the rate of hydroxyl scavenging is constant with time for initial coumarin concentrations of ≥50 μM under the conditions of our experiments. The rate increases linearly with coumarin concentration, as expected from the Langmuir–Hinshelwood model. Within the coumarin concentration range used here, the photocatalyst surface does not become saturated. Given the fact that the highest coumarin concentration used (1 mM) in this work is quite close to the solubility limit, we conclude that coumarin cannot be used to assess the full photocatalytic capacity of the system, i.e., surface saturation is never reached. The rate of hydroxyl radical scavenging will, to a large extent, depend on the affinity to the surface, and it is therefore not advisable to use coumarin as a probe for photocatalytic efficiency when comparing different photocatalysts.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2019. Vol. 123, no 11, p. 6667-6674
National Category
Chemical Sciences
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URN: urn:nbn:se:kth:diva-249493DOI: 10.1021/acs.jpcc.9b00337ISI: 000462260700040Scopus ID: 2-s2.0-85062883293OAI: oai:DiVA.org:kth-249493DiVA, id: diva2:1304493
Note

QC 20190426

Available from: 2019-04-12 Created: 2019-04-12 Last updated: 2019-04-26Bibliographically approved

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Leandri, ValentinaGardner, James M.Jonsson, Mats

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