Mechanism for Visible Light Responses in Anodic Photocurrents at N-Doped TiO₂ Film Electrodes

Abstract

Nitrogen doping of anatase TiO2 powder extended the photocurrent action spectrum for water oxidation from the UV-light region (≤400 nm) to the visible-light region (≤ ∼550 nm), as reported. Investigations of the effect of the addition of reductants such as methanol, SCN-, Br-, I-, and hydroquinone to the electrolyte have for the first time given clear experimental evidence to the mechanism that visible-light responses for N-doped TiO2 arise from an N-induced midgap level, formed slightly above the top of the (O-2p) valence band. The investigations, in combination with the above mechanism, have also shown that photocatalytic oxidation of organic compounds on N-doped TiO2 under visible illumination mainly proceed via reactions with surface intermediates of water oxidation or oxygen reduction, not by direct reactions with holes trapped at the N-induced midgap level.

Effect of N-doping on the photocatalytic activity of sol–gel TiO2

“…Visible light absorption through the addition of oxygen vacancies was also reported by Martyanov et al [2]. However there now appears to be some agreement regarding the fine electronic details of N doped visible light absorption as reported by Irie [8] and Nakamura [9]. It is now believed that oxygen lattice sites within the TiO 2 crystal are substituted by nitrogen atoms [10,11] form an occupied midgap (N 2p) level above the TiO 2 (O 2p) valence band.…”

“…It is now believed that oxygen lattice sites within the TiO 2 crystal are substituted by nitrogen atoms [10,11] form an occupied midgap (N 2p) level above the TiO 2 (O 2p) valence band. The N 2p band therefore acts as a step between the valence and the conduction band of the semiconductor, facilitating excitation of electrons from the N 2p mid-gap band to the conduction band upon irradiation with visible light [8,9]. Titanium dioxide is made up of TiO 6 octahedra [12].…”

Photoeletrochemical generation of hydrogen over carbon-doped TiO2 photoanode

“…The trapping of electrons effectively increases the lifetime of holes. Non-metallic elements such as nitrogen [9,10], carbon [11,12], sulfur [13], boron [14], and fluorine [15] have been used to impregnate the structure of TiO 2 . It was found that the substitutional carbon dopant incorporated into TiO 2 drastically affected the electronic structure of the material and hence improved its photoactivity due to significant overlap between O 2s 2 2p 4 and the carbon states near the valence band edge [16].…”

Synthesis of Ag/N-TiO2/SBA-15 Photocatalysts and Photocatalytic Reduction of CO2under Visible Light Irradiation

“…由直线外 推法可知 TS, ATS, NATS2, NATS3, NATS4 带边波长分 别为 385, 402, 408, 410, 419 nm. 根据公式 λ g ＝1240/E g 可计算出催化剂的禁带宽度 [1] , 式中 λ g 为带边波长(nm), [36,37] .…”