Photochemistry of Carboxylate on TiO2(110) Studied with Synchrotron Radiation Photoelectron Spectroscopy

Forskningsoutput: TidskriftsbidragArtikel i vetenskaplig tidskrift

Abstract

We present a dedicated synchrotron radiation photoelectron spectroscopy (SR-PES) study of a photochemical reaction on the surface of rutile TiO2(110). The photoreaction kinetics of carboxylate species (trimethyl acetate, TMA) upon irradiation by UV and soft X-rays were monitored, and we show that it is possible to control the reaction rates from UV light and soft X-rays independently. We directly observe Ti4+ A Ti3+ conversion upon irradiation, attributed to electron trapping at Ti sites close to surface OH groups formed by deprotonation of the parent molecule, trimethylacetic acid (TMAA). TMA photolysis on two surface preparations with different oxygen vacancy densities shows that the vacancy-related charge quenches the amount of charge that can be trapped at hydroxyls upon irradiation. During the initial stages of reaction the correlation between the amount of photodepleted TMA and the amount of charge trapped in the Ti 3d band gap state is nearly 1:1. A first-order kinetics analysis reveals that the reaction rate decreases with decreasing TMA coverage. There is also a coverage-dependent difference in the electronic structure of TMA moieties, primarily involving the carboxyl anchor group. These changes are consistent with a decreased hole affinity of the adsorbed TMA and hence a decreased reaction rate. This discovery adds to the previously presented picture of a reactivity that is inversely proportional to the number of surface hydroxyls, suggesting that the balance between the amounts of TMA, OH, and trapped charge needs to be considered.

Detaljer

Författare
  • A. Sandell
  • D. Ragazzon
  • A. Schaefer
  • M. H. Farstad
  • A. Borg
Enheter & grupper
Externa organisationer
  • Uppsala universitet, Historiska institutionen
  • Norwegian University of Science and Technology
Forskningsområden

Ämnesklassifikation (UKÄ) – OBLIGATORISK

  • Oorganisk kemi
Originalspråkengelska
Sidor (från-till)11456-11464
Antal sidor9
TidskriftLangmuir
Volym32
Utgivningsnummer44
StatusPublished - 2016 nov 8
PublikationskategoriForskning
Peer review utfördJa