Ab initio design of GaN-based photocatalyst: ZnO-codoped GaN nanotubes

ZnO-codoped GaN nanotubes are designed and studied for their application as photocatalyst on the basis of first-principles calculations. The codoped nanotubes are semiconducting with their band structures controllable by the doping concentration. It is found that the codoping and its effects on the band gaps strongly depend on the chirality of the nanotubes. For armchair nanotubes, the ZnO codoping prefers to the radial direction of the nanotube, and a minimum of band gap at 1.27 eV is achievable at the concentration of 31 at.%. For zigzag nanotubes, the codoping is energetically more stable in the axial direction, and a reduction of 21% in band gap can be obtained by optimizing the doping concentration. The calculated potentials of the conduction band bottoms of the codoped nanotubes are more negative than H-2/H2O level, and those of their valence band tops are more positive than O-2/H2O level. The calculated electronic properties of the codoped nanotubes evidence the widely tunable band gap, enhanced mobility, and better band edges' alignments, satisfying basic prerequisites as a new class of high efficiency photocatalysts for water splitting and other avenues of solar energy utilization. (C) 2013 Elsevier B.V. All rights reserved.