Increasing the Photocatalytic Activity of Anatase TiO₂ through B, C, and N Doping

Abstract

We utilized density functional theory (DFT) to systematically investigate the ability of B, C and N interstitial and O substitutional surface and near-surface dopants in TiO 2 to facilitate O 2 reduction and adsorption. Periodic boundary condition calculations based on the PBE+U DFT functional show that dopants that create filled band gap states with energies higher than that of the near surface O 2 π z * molecular orbital enable O 2 adsorption and reduction. Sites that create unoccupied band gap states with energies below that of the O 2 π z * orbital reduce TiO 2 's reduction ability as these states result in photoexcited electrons with insufficient reduction potential to reduce O 2 . B dopants in interstitial and relaxed substitutional sites, whose gap states lie > 1.5 eV above the valence band maximum (VBM) and hence above O 2 's π z * level, facilitate the reduction of O 2 to the peroxide state with adsorption energies on TiO 2 of -1.22 to -2.77 eV.However, N dopants, whose gap states lie less than ~1 eV above the VBM impede O 2 adsorption and reduction; O 2 on N doped (101) anatase relaxes away from the surface. Interstitial and substitutional N dopants require two photoexcited electrons to enable O 2 adsorption. C doping, which introduces gap states between those introduced by N and B, aids O 2 adsorption as a peroxide for interstitial doping, although substitutional C does not facilitate O 2 adsorption. Dopants for enhancing the photocatalytic reduction of O 2 in order of predicted effectiveness are interstitial B, relaxed substitutional B, and interstitial C. In contrast, substitutional C, and interstitial and substitutional N hinder O 2 reduction despite increasing visible light absorption.Dopants within the surface layer likely deactivate quickly due to the high exothermicity of O 2 reacting with them to form BO 2 , CO 2 , and NO 2 .

Doping Effects on the Adsorption of a Nitric Oxide Molecule on an Anatase (101) Surface

“…This peak does not appear in the DOS of the N‐doped sample. An empty state inside the band gap introduced by p‐type doping was previously reported by Muhich et al …”

“…This peak does not appear in the DOS of the N-doped sample. An empty state inside the band gap introduced by ptype doping was previously reported by Muhich et al [45] 2.2. Adsorption of aNOM oleculeonaClean Anatase (101) Surface Twoa dsorption configurations of aN Om olecule on ac lean anatase (101)s urface are considered.…”

Photocatalytic decomposition of N2O over TiO2/g-C3N4 photocatalysts heterojunction

“…silver [2,3,7], cerium [4]) or non-metallic elements (e.g. B, C, N) [8], and coupling with other narrow band gap semiconductor materials.…”

Exploring the effect of boron and tantalum codoping on the enhanced photocatalytic activity of TiO2

“…This is mostly attributed to the fast recombination of electron-hole pairs and a relatively large energy gap of TiO 2 (E g = 3.2 eV for anatase phase and E g = 3.0 eV for rutile phase), limiting its light absorption to the ultraviolet fraction of the solar energy spectrum [1,2,5]. Numerous efforts have been devoted to extending the optical response regime of TiO 2 toward visible region, and/or suppress the charge carrier recombination [1,2,[6][7][8][9][10][11][12][13][14][15].…”

“…One frequently used method involves the incorporation of nonmetal [6,7,[16][17][18][19], or metal dopants [8,[20][21][22][23]. However, monodoping has inadvertently increased recombination losses, and thus did not always lead to significant improvement of photocatalytic activities companying the extension of photo-response region [10,24,25].…”