Activation of Water in Titanium Dioxide Photocatalysis by Formation of Surface Hydrogen Bonds: An In Situ IR Spectroscopy Study

The hole‐driving oxidation of titanium‐coordinated water molecules on the surface of TiO2 is both thermodynamically and kinetically unfavorable. By avoiding the direct coordinative adsorption of water molecules to the surface Ti sites, the water can be activated to realize its oxidation. When TiO2 s...

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Bibliographic Details
Published in:Angewandte Chemie International Edition 2015-05, Vol.54 (20), p.5905-5909
Main Authors: Sheng, Hua, Zhang, Hongna, Song, Wenjing, Ji, Hongwei, Ma, Wanhong, Chen, Chuncheng, Zhao, Jincai
Format: Article
Language:English
Subjects:
Adsorption
Electron transfer
hydrogen bonds
Infrared spectroscopy
IR spectroscopy
Mathematical analysis
Oxidation
photocatalysis
Spectroscopy
Spectrum analysis
Surface chemistry
Titanium
Titanium dioxide
water oxidation
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Summary:The hole‐driving oxidation of titanium‐coordinated water molecules on the surface of TiO2 is both thermodynamically and kinetically unfavorable. By avoiding the direct coordinative adsorption of water molecules to the surface Ti sites, the water can be activated to realize its oxidation. When TiO2 surface is covered by the H‐bonding acceptor F, the first‐layer water adsorption mode is switched from Ti coordination to a dual H‐bonding adsorption on adjacent surface F sites. Detailed in situ IR spectroscopy and isotope‐labeling studies reveal that the adsorbed water molecules by dual H‐bonding can be oxidized to O2 even in the absence of any electron scavengers. Combined with theoretical calculations, it is proposed that the formation of the dual H‐bonding structure can not only enable the hole transfer to the water molecules thermodynamically, but also facilitate kinetically the cleavage of OH bonds by proton‐coupled electron transfer process during water oxidation. Switching the water adsorption mode on TiO2 to dual H‐bonding by the presence of fluorine atoms at the surface not only thermodynamically enables the hole transfer to the water molecules, but also facilitates the proton‐coupled electron transfer during water oxidation. This phenomenon is established by IR spectroscopy studies and calculations.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.201412035