DOI

We report studies on photoinduced processes that take place in gas-solid heterogeneous systems. In particular, we examine the chemical reaction (i.e., chemical relaxation pathway) between hydrogen (or methane) and the surface of ZrO2 particles which occurs after the solid was preirradiated (vacuo or oxygen) and the intrinsic phosphorescence from zirconia had terminated. Introduction of H2 yields an after-glow (light pulse referred as photoinduced chesorluminescence, PhICL) that is caused by chemical interaction between the photoactivated surface of the photocatalyst and the H-containing molecules in the heterogeneous gas-solid system. Unlike hydrogen, methane does not yield a detectable PhICL emission. The PhICL emission for hydrogen decays via biphasic kinetics (τ1 = 0.9 s and τ2 = 10 s; ambient temperature). Reactions were also investigated in the temperature range of 75-600 K. For a nonpreirradiated surface, the H-containing molecules physisorb with binding energy Ephys = 33 kJ mol-1 (0.34 eV) for H2 and 52 kJ mol-1 (0.54 eV) for CH4. After preirradiation of ZrO2, the molecules chemisorb dissociatively yielding free radicals (Ḣ for H2, and CH3̇ for methane, the other Ḣ is trapped) through an activated process; activation energies Ea = 30 kJ mol-1 (0.31 eV) for H2 and 32 kJ mol-1 (0.33 eV) for CH4 if the process occurs by a Langmuir-type pathway; if the process occurs by an Eley-Rideal mechanism, Ea = 41 kJ mol-1 (0.43 eV) for H2 and 46 kJ mol-1 (0.48 eV) for CH4. The data were modeled through a sequence of differential equations. A mechanism is proposed that involves shallow traps and deep energy traps for electrons to explain the photophysical events triggered by the surface chemical reaction. In essence, surface chemical reactions cause the release of the energy stored during the preirradiation stage of the solid. This results in photoinduced formation of metastable defects in the solid (e.g., Os) together with deep electron traps (F centers) that lead to both chemical and physical relaxation of the system.

Язык оригиналаанглийский
Страницы (с-по)5956-5966
Число страниц11
ЖурналJournal of Physical Chemistry B
Том106
Номер выпуска23
DOI
СостояниеОпубликовано - 13 июн 2002

    Предметные области Scopus

  • Физическая и теоретическая химия
  • Поверхности, слои и пленки
  • Химия материалов

ID: 35143010