Preparation of (Ga 1-xZn x)(N 1-xO x) photocatalysts from the Reaction of NH 3 with Ga 2O 3/ZnO and ZnGa 2O 4: In situ time-resolved XRD and XAFS studies

Haiyan Chen, Wen Wen, Qi Wang, Jonathan C. Hanson, James T. Muckerman, Etsuko Fujita, Anatoly I. Frenkel, José A. Rodriguez

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Abstract

Gallium zinc oxynitrides (Ga 1-xZnx)(N 1-xO x) are important due to their visible-light photocatalytic activity. Using in situ time-resolved X-ray diffraction (XRD), we have monitored the formation of wurtzite (Ga 1-xZn x)(N 1-xO x) compounds during the solid-state reaction of NH 3 with Ga 2O 3/ZnO mixtures or a ZnGa 2O 4 spinel. The ZnGa 2O 4 spinel was found to be a key intermediate in the formation of (Ga 1-xZn x)(N 1-xO x) and imposes a limit on the zinc content in the gallium zinc oxynitrides. Furthermore, after its formation, a wurtzite (Ga 2/3Zn 1/3)(N 2/3O 1/3) phase evolves to (Ga 0.9Zn 0.1)(N 0.9O 0.1) with increasing nitridation reaction time as a result of the removal of Zn and O atoms from the system. Once (Ga 2/3Zn 1/3)(N 2/3O 1/3) is formed, one must minimize exposure of the compound to NH 3. Zinc and gallium K-edge X-ray absorption fine structure (XAFS) data revealed that the local structures around gallium and zinc atoms in the (Ga 1-xZn x)(N 1-xO x) systems are similar to those of GaN and ZnO, respectively, with relatively minor distortions in the Ga-N and Zn-O bond lengths. The Zn-O/N bonds prefer to align along the c-axis of the lattice, in agreement with the findings of DFT calculations reported in the literature. The corresponding Zn K-edge XANES spectra of (Ga 1-xZn x)(N 1-xO x) display a position red-shifted toward lower energies by ̃ 0.5 eV with respect to that of ZnO, indicating a lower oxidation state of Zn in (Ga 1-xZn x)(N 1-xO x). N K-edge NEXAFS data show that the bonding geometry and electronic properties of the nitrogen atoms in (Ga 1-xZn x)(N 1-xO x) are similar to those in GaN. However, the O K-edge spectra exhibit a pre-edge feature not seen for ZnO or Ga 2O 3. This unique property of the oxygen atoms in (Ga 1-xZn x)(N 1-xO x) may be related to the existence of holes and affect visible light absorption and surface chemistry.

Original languageEnglish
Pages (from-to)3650-3659
Number of pages10
JournalJournal of Physical Chemistry C
Volume113
Issue number9
DOIs
Publication statusPublished - Mar 5 2009

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ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

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