Mechanisms of Visible Light Photocatalysis in N-Doped Anatase TiO2with Oxygen Vacancies from GGA+U Calculations

Hsuan-Chung Wu,Syuan-Wei Lin,Yu-Siang Lin

doi:10.1155/2013/289328

Hsuan-Chung Wu, Syuan-Wei Lin + Show 1 more

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https://doi.org/10.1155/2013/289328

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Abstract

We have systematically studied the photocatalytic mechanisms of nitrogen doping in anatase TiO2using first-principles calculations based on density functional theory, employing HubbardU(8.47 eV) on-site correction. The impurity formation energy, charge density, and electronic structure properties of TiO2supercells containing substitutional nitrogen, interstitial nitrogen, or oxygen vacancies were evaluated to clarify the mechanisms under visible light. According to the formation energy, a substitutional N atom is better formed than an interstitial N atom, and the formation of an oxygen vacancy in N-doped TiO2is easier than that in pure TiO2. The calculated results have shown that a significant band gap narrowing may only occur in heavy nitrogen doping. With light nitrogen doping, the photocatalysis under visible light relies on N-isolated impurity states. Oxygen vacancies existence in N-doped TiO2can improve the photocatalysis in visible light because of a band gap narrowing and n-type donor states. These findings provide a reasonable explanation of the mechanisms of visible light photocatalysis in N-doped TiO2.

Highlights

Photocatalytic mechanisms are created with an electron-hole pair by exciting an electron from the valence band to the conduction band through absorption of the electromagnetic radiation
Etot and Etot are the total energies of defective models and pure TiO2; μN and μO represent the chemical potentials of the N and O atoms; m and n are the numbers of doped nitrogen and removed oxygen atoms; m = 1 and n = 1 for Ns model, and m = 1, n = 0 for Ni model, m = 0, n = 1 for oxygen vacancy (Ov) model, m = 1, n = 2 for NsOv model, m = 1, n = 1 for N-doping with oxygen vacancy (NiOv) model
Using the generalized gradient approximation (GGA)+U method, this study calculated impurity formation energy, charge density, and electronic properties of an N-doped anatase TiO2 with oxygen vacancies system to investigate the photocatalytic mechanisms of N-doped TiO2 under visible light

Summary

Introduction

Photocatalytic mechanisms are created with an electron-hole pair by exciting an electron from the valence band to the conduction band through absorption of the electromagnetic radiation. The nitrogen doping is considered more effective and widely studied, the photocatalytic mechanisms under visible light are still debatable. Valentin et al [20] employed theoretical calculations to show that nitrogen doping led to a substantial reduction of energy costs to form oxygen vacancies in TiO2. This suggested that nitrogen doping was likely to be accompanied by the formation of oxygen vacancies. The mechanisms of N-doping in TiO2 under visible light region have three views: (1) band gap narrowing, (2) impurity energy levels, and (3) oxygen vacancies. The calculated results were analyzed and compared with the previous literature

Calculation Models and Methods

Results and Discussion

Conclusions