Anatase (101)-like Structural Model Revealed for Metastable Rutile TiO₂(011) Surface

Abstract

Titanium dioxide has been widely used as an efficient transition metal oxide photocatalyst. However, its photocatalytic activity is limited to the ultraviolet spectrum range due to the large bandgap beyond 3 eV. Efforts to reduce the bandgap to achieve a broader spectrum range of light absorption have been successfully attempted via the experimental synthesis of dopant-free metastable surface structures of rutile-type TiO (011) 2 × 1. This new surface phase possesses a reduced bandgap of ∼2.1 eV, showing great potential for an excellent photocatalyst covering a wide range of visible light. There is a need to establish the atomistic structure of this metastable surface to understand the physical cause for the bandgap reduction and to improve the future design of photocatalysts. Here, we report computational investigations in an effort to unravel this surface structure via swarm structure-searching simulations. The established structure adopts the anatase (101)-like structure model, where the topmost 2-fold O atoms form a quasi-hexagonal surface pattern and bond with the unsaturated 5-fold and 4-fold Ti atoms in the next layer. The predicted anatase (101)-like surface model can naturally explain the experimental observation of the STM images, the electronic bandgap, and the oxidation state of Ti. Dangling bonds on the anatase (101)-like surface are abundant making it a superior photocatalyst. First-principles molecular dynamics simulations have supported the high photocatalytic activity by showing that water and formic acid molecules dissociate spontaneously on the anatase (101)-like surface.

Interface structure prediction via CALYPSO method

“…However, the photoreaction efficiency of TiO 2 is severely limited by its large intrinsic band gap (>3 eV). Various approaches including noble metal loading [45], doping with nonmetal atoms [46], hydrogenation [47], and surface modification [48] have been used in attempts to narrow the band gap and enhance the visible-light photoactivity of TiO 2 . Recently, the introduction of Ti 3+ originating from O defects in reduced TiO 2 has been shown to be an effective strategy to improve the photocatalytic performance [49,50].…”

Cu and Zr surface sites in photocatalytic activity of TiO2 nanoparticles: The effect of Zr distribution

“…Despite the progress made in the material chemistry of TiO 2 [1,2] there are still obstacles in using solar light for efficient photocatalytic water purification and disinfection processes. The efficient applicability of TiO 2 for environmental purposes, which is restricted by its limited activity under the solar light, is strongly connected to TiO 2 visible light sensitivity.…”

Atomically Thin 2D Transition Metal Oxides: Structural Reconstruction, Interaction with Substrates, and Potential Applications

“…They claimed that both the simulated STM images and electronic structures are in agreement with those of experimental observations, as shown in Figure d,e. Meanwhile, by means of CALYPSO, Xu et al proposed an anatase (101)‐like structural model (Figure f) . It is found that this anatase (101)‐like structure could explain not only the observed STM images and the electronic bandgap, but also the measured oxidation state of Ti 4+ .…”

“…Due to inherent limitations of experimental techniques, some information about the materials of interest, e.g., detailed atomistic structures, might not always be obtained at ease. Theoretical investigations as a complement to the experiment may facilitate understanding experimental observations …”

“…Atoms in light gray and red colors represent the H and O atoms of water, respectively. f,g) Reproduced with permission . Copyright 2017, American Chemical Society.…”