TY - JOUR

T1 - Catalytic role of TiO2 terminal oxygen atoms in liquid-phase photocatalytic reactions

T2 - Oxidation of aromatic compounds in anhydrous acetonitrile

AU - Montoya, J.F.

AU - Bahnemann, D.W.

AU - Peral, J.

AU - Salvador, P.

N1 - Copyright: Copyright 2014 Elsevier B.V., All rights reserved.

PY - 2014/8/4

Y1 - 2014/8/4

N2 - On the basis of experiments carried out with controlled amounts of residual oxygen and water, or by using oxygen-isotope-labeled Ti 18O 2 as the photocatalyst, we demonstrate that 18O s atoms behave as real catalytic species in the photo-oxidation of acetonitrile-dissolved aromatic compounds such as benzene, phenol, and benzaldehyde with TiO 2. The experimental evidence allows a terminal-oxygen indirect electron-transfer (TOIET) mechanism to be proposed, which is a new pathway that involves the trapping of free photogenerated valence-band holes at O s species and their incorporation into the reaction products, with simultaneous generation of oxygen vacancies at the TiO 2 surface and their subsequent healing with oxygen atoms from either O 2 or H 2O molecules that are dissolved in the liquid phase. According to the TOIET mechanism, the TiO 2 surface is not considered to remain stable, but is continuously changing in the course of the photocatalytic reaction, challenging earlier interpretations of TiO 2 photocatalytic phenomena. A stable surface? TiO 2- assisted photocatalytic oxidation of organic compounds involves the exchange of surface oxygen on the catalyst, the generation of a surface oxygen vacancy, and the final incorporation of a water molecule to heal the vacancy.

AB - On the basis of experiments carried out with controlled amounts of residual oxygen and water, or by using oxygen-isotope-labeled Ti 18O 2 as the photocatalyst, we demonstrate that 18O s atoms behave as real catalytic species in the photo-oxidation of acetonitrile-dissolved aromatic compounds such as benzene, phenol, and benzaldehyde with TiO 2. The experimental evidence allows a terminal-oxygen indirect electron-transfer (TOIET) mechanism to be proposed, which is a new pathway that involves the trapping of free photogenerated valence-band holes at O s species and their incorporation into the reaction products, with simultaneous generation of oxygen vacancies at the TiO 2 surface and their subsequent healing with oxygen atoms from either O 2 or H 2O molecules that are dissolved in the liquid phase. According to the TOIET mechanism, the TiO 2 surface is not considered to remain stable, but is continuously changing in the course of the photocatalytic reaction, challenging earlier interpretations of TiO 2 photocatalytic phenomena. A stable surface? TiO 2- assisted photocatalytic oxidation of organic compounds involves the exchange of surface oxygen on the catalyst, the generation of a surface oxygen vacancy, and the final incorporation of a water molecule to heal the vacancy.

KW - isotopic labeling

KW - oxidation

KW - photophysics

KW - reaction mechanisms

KW - surface chemistry

UR - http://www.scopus.com/inward/record.url?scp=84904878800&partnerID=8YFLogxK

U2 - 10.1002/cphc.201402043

DO - 10.1002/cphc.201402043

M3 - Article

VL - 15

SP - 2311

EP - 2320

JO - CHEMPHYSCHEM

JF - CHEMPHYSCHEM

SN - 1439-4235

IS - 11

ER -