TY - JOUR

T1 - Catalytic role of bridging oxygens in TiO2 liquid phase photocatalytic reactions

T2 - Analysis of H216O photooxidation on labeled Ti18O2

AU - Montoya, J.F.

AU - Bahnemann, D.W.

AU - Salvador, P.

AU - Peral, J.

N1 - Publisher Copyright: © 2017 The Royal Society of Chemistry. Copyright: Copyright 2017 Elsevier B.V., All rights reserved.

PY - 2017/2/21

Y1 - 2017/2/21

N2 - Experiments of photocatalytic oxidation of H 2 16O with a suspended oxygen-isotope labelled Ti 18O 2 photocatalyst are presented here for the first time. The photo-induced evolution of 18O 16O demonstrates that bridging surface oxygens (> 18O br 2-) behave as real catalytic species of the global water splitting photocatalytic reaction (2H 2O + 4h + → O 2(g)↑ + 4H +). The experimental results are interpreted according to a previously developed water redox photooxidation (WRP) mechanism (Salvador, P. Prog. Surf. Sci. 2011, 86, 41-58), opening a new mechanistic pathway that involves the participation of terminal >O br 2- bridging oxygens as real photocatalytic species. In the primary step, one-fold coordinated - 18O br - radicals are generated from the direct photooxidation of > 18O br 2- oxygens with valence band holes (> 18O br 2- + h + → - 18O br -). In the second step, a couple of adjacent - 18O br - radicals chemically react, giving rise to peroxo species (2 18O br - → 18O 2 2-), which are further photooxidized with photogenerated valence band holes, initially leading to 18O 2(g) evolution according to the global photoreaction 18O 2 2- + 4h + → 2V[> 18O br 2-] + 18O 2(g)↑. Terminal oxygen vacancies (V[> 18O br 2-]) become further healed via dissociative adsorption of H 2 16O water molecules (2V[> 18O br 2-] + 2H 2 16O → 2(> 16O br 2-) + 2H +), in such a way that > 18O br 2- bridging ions are progressively substituted by > 16O br 2- and the initially evolved 18O 2(g) is further replaced by 16,18O 2(g) and finally by 16O 2(g).

AB - Experiments of photocatalytic oxidation of H 2 16O with a suspended oxygen-isotope labelled Ti 18O 2 photocatalyst are presented here for the first time. The photo-induced evolution of 18O 16O demonstrates that bridging surface oxygens (> 18O br 2-) behave as real catalytic species of the global water splitting photocatalytic reaction (2H 2O + 4h + → O 2(g)↑ + 4H +). The experimental results are interpreted according to a previously developed water redox photooxidation (WRP) mechanism (Salvador, P. Prog. Surf. Sci. 2011, 86, 41-58), opening a new mechanistic pathway that involves the participation of terminal >O br 2- bridging oxygens as real photocatalytic species. In the primary step, one-fold coordinated - 18O br - radicals are generated from the direct photooxidation of > 18O br 2- oxygens with valence band holes (> 18O br 2- + h + → - 18O br -). In the second step, a couple of adjacent - 18O br - radicals chemically react, giving rise to peroxo species (2 18O br - → 18O 2 2-), which are further photooxidized with photogenerated valence band holes, initially leading to 18O 2(g) evolution according to the global photoreaction 18O 2 2- + 4h + → 2V[> 18O br 2-] + 18O 2(g)↑. Terminal oxygen vacancies (V[> 18O br 2-]) become further healed via dissociative adsorption of H 2 16O water molecules (2V[> 18O br 2-] + 2H 2 16O → 2(> 16O br 2-) + 2H +), in such a way that > 18O br 2- bridging ions are progressively substituted by > 16O br 2- and the initially evolved 18O 2(g) is further replaced by 16,18O 2(g) and finally by 16O 2(g).

UR - http://www.scopus.com/inward/record.url?scp=85021719973&partnerID=8YFLogxK

U2 - 10.1039/c6cy02457b

DO - 10.1039/c6cy02457b

M3 - Article

VL - 7

SP - 902

EP - 910

JO - Catalysis Science and Technology

JF - Catalysis Science and Technology

SN - 2044-4753

IS - 4

ER -