Photo-induced charge separation in hydroxycoumarins on TiO2 and F–TiO2

The efficiency of photocatalytic charge separation is much higher for 7-hydroxycoumarin (7-CN) and 6,7-dihydroxycoumarin (6,7-CN) adsorbed on the surface modified TiO2 where the surface hydroxyl group was replaced by a fluorine atom (F–TiO2) than on TiO2. EPR measurements find 5- and 12-fold increas...

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Bibliographic Details
Published in:Dalton transactions : an international journal of inorganic chemistry 2019-08, Vol.48 (29), p.10881-10891
Main Authors: Gao, Yunlong, Lockart, Molly, Kispert, Lowell D, Bowman, Michael K
Format: Article
Language:English
Subjects:
Charge efficiency
Conduction bands
Donors (electronic)
Dyes
Electron transfer
Fluorine
Free radicals
Hydroxyl groups
Mathematical analysis
Separation
Titanium dioxide
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Summary:The efficiency of photocatalytic charge separation is much higher for 7-hydroxycoumarin (7-CN) and 6,7-dihydroxycoumarin (6,7-CN) adsorbed on the surface modified TiO2 where the surface hydroxyl group was replaced by a fluorine atom (F–TiO2) than on TiO2. EPR measurements find 5- and 12-fold increases in free radical yields for 7-CN and 6,7-CN, respectively. DFT calculations for the coumarins on TiO2 and F–TiO2 were performed to investigate these phenomena. The calculations show that when the coumarins act as the H-bond donors, the driving force for photo-induced electron transfer from the dyes to TiO2 is higher, and the dye's excited state mixes strongly with the TiO2 conduction band states. This is attributed to the shorter distance between the coumarins and the surface of TiO2 when the coumarins act as the H-bond donors. These calculations explain why the efficiency of charge separation of the coumarins is much higher on F–TiO2 than on TiO2.
ISSN:1477-9226
1477-9234
DOI:10.1039/c9dt01455a