A hybrid density functional study on the visible light photocatalytic activity of (Mo,Cr)–N codoped KNbO₃

Abstract

To improve the photocatalytic performance of KNbO3 for the decomposition of water into hydrogen and oxygen, the electronic structure of KNbO3 should be modified to have a suitable bandgap with band edge positions straddling the water redox level so as to sufficiently absorb visible light. Hybrid density functional theory has been used to calculate the electronic structures of pure, N-, Mo-, and Cr-monodoped, and Mo-N and Cr-N codoped KNbO3. In particular, the influence of the relative positions of Mo-N or Cr-N codopants on the electronic structure of KNbO3 is discussed in detail to account for the possible difference in the photocatalytic activity of the codoped samples prepared by different experimental techniques. The defect formation energy calculations indicate that a N-doped system is difficult to form under any conditions and the codoped systems are energetically favorable under Nb-poor and O-rich conditions. It is interesting to find that the effective bandgap and stability for codoped systems decrease with the increase of the dopant concentration and/or the distance between dopants. Furthermore, the suitable bandgap and band edge position with respect to the water redox level make the Mo-N codoped systems good candidates for visible light photocatalytic decomposition of water to generate hydrogen.

Recent Progress in the Development of Semiconductor‐Based Photocatalyst Materials for Applications in Photocatalytic Water Splitting and Degradation of Pollutants

“…In addition, the PDOS analysis of Mo‐doped NaNbO 3 revealed that the VBM consist of O 2p states and the CBM was controlled by Nb 4d and Mo 4d states. In NNd codoped KNbO 3 , the VBM was found to compose of O 2p states and the Nb 4d states contributed to the CBM …”

Rotation Tunable Photocatalytic Properties of ZnO/GaN Heterostructures

“…Hydrogen generation by water splitting using semiconductor photocatalysts is a promising approach to develop renewable energy. As a desired water‐splitting photocatalyst, it must have an appropriate bandgap for using visible light . In addition, it must possess suited band alignments, i.e., the valence band maximum (VBM) and conduction band minimum (CBM) must be separately below the O 2 /H 2 O potential and above the H + /H 2 potential .…”

Tunable Photocatalytic Properties of GaN‐Based Two‐Dimensional Heterostructures

“…2D materials ignite increasing interest owning to their intriguing mechanical, thermal, and optical properties. A desired photocatalyst for water splitting must own the conduction band minimum (CBM) above the (H + /H 2 ) reduction level and the valance band maximum (VBM) below the water oxidation level (H 2 O/O 2 ) . With the consideration of the additional overpotential accompanied with the overall water redox processes, the bandgap needed for effective water splitting must be larger than 1.23 eV .…”