Ionics

, Volume 24, Issue 4, pp 1211–1219 | Cite as

Towards sustainable energy: photocatalysis of Cr-doped TiO2. 5. Effect of segregation on surface versus bulk composition

  • Kazi Akikur Rahman
  • Tadeusz Bak
  • Armand Atanacio
  • Mihail Ionescu
  • Rong Liu
  • Janusz Nowotny
Original Paper

Abstract

The present chain of five papers considers the concept of solar-to-chemical energy conversion using TiO2-based semiconductors. The series reports the effect of chromium on the key performance-related properties of polycrystalline TiO2 (rutile), including electronic structure, photocatalytic activity, intrinsic defect disorder, electrochemical coupling and surface versus bulk properties. This work considers the effect of oxygen activity on segregation-induced surface versus bulk composition for both polycrystalline and single-crystal specimens of Cr-doped TiO2. It has been documented that annealing of Cr-doped TiO2 at 1273 K in oxidising conditions results in an enrichment and depletion of the surface layer with chromium. It is shown that the segregation-induced enrichment factor for single crystal is substantially larger than that for polycrystalline specimen. The effect is considered in terms of a theoretical model showing that surface segregation of solute in polycrystalline specimen is encumbered by its segregation to grain boundaries. It is also shown that the segregation-induced enrichment is profoundly influenced by oxygen activity. The new insight of this work involves (i) the determination of well-defined chromium segregation in Cr-doped TiO2, including single-crystal and polycrystalline specimens, after annealing in the gas phase of controlled oxygen activity, and (ii) identification of the predominant driving force of segregation of chromium in Cr-doped TiO2 that is based on electrostatic interactions between the low-dimensional surface structure (LDSS) and electrically charge segregating species.

Graphical abstract

Keywords

Titanium dioxide Segregation Oxygen activity Cr-doped TiO2 

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Copyright information

© Springer-Verlag GmbH Germany 2017

Authors and Affiliations

  • Kazi Akikur Rahman
    • 1
  • Tadeusz Bak
    • 1
  • Armand Atanacio
    • 2
  • Mihail Ionescu
    • 2
  • Rong Liu
    • 3
  • Janusz Nowotny
    • 1
  1. 1.Solar Energy Technologies, School of Computing, Engineering and MathematicsWestern Sydney UniversityPenrithAustralia
  2. 2.Australian Nuclear Science and Technology OrganisationInstitute of Environmental ResearchKirrawee DCAustralia
  3. 3.Secondary Ion Mass Spectrometry Facility, Office of the Deputy Vice Chancellor (Research and Development)Western Sydney UniversityPenrithAustralia

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