Sulfur-doping of rutile-titanium dioxide by ion implantation: Photocurrent spectroscopy and first-principles band calculation studies

Abstract

Sulfur (S)-doped titanium dioxide (TiO2) was synthesized by ion implantation and subsequent thermal annealing. The S ions were implanted into the single crystals of rutile TiO2 at a fluence of 8×1015 ions/cm2. According to the results of Rutherford backscattering spectroscopy and ion channeling analysis, the irradiation damage recovered by annealing at 600 °C in air. In the annealed crystal, the S atoms occupied oxygen sites for form Ti-S bonds, as confirmed by x-ray photoelectron spectroscopy. Compared to the pure TiO2, a photocurrent was observed in the lower-energy regions for the S-doped TiO2. Based on the theoretical analyses by the first-principles band calculations using the full potential linearized augmented plane-wave methods within the generalized gradient approximation, the mixing of the S 3p states with the valence band (VB) was found to contribute to the increasing width of the VB. This leads to the band gap narrowing in the S-doped TiO2. Therefore, the photon-to-carrier conversion was induced during irradiation by visible light above 420 nm (<2.9 eV).

Nanomaterials for renewable energy production and storage

“…106 Yuan et al found that in nitrogen (N)-doped TiO 2 samples the N was presented in the state of both molecularly chemisorbed N 2 and substituted N; while both of them contributed to the response to visible light, the substituted N was responsible for the hydrogen evolution under visible light. 110 S dopant induced a similar bandgap narrowing as nitrogen: 89 the mixing of the sulfur 3p states with the valence band was found to contribute to the increased width of the valence band, leading to the narrowing of the bandgap, 91,93 the strong absorption in the region from 400 to 600 nm. 99 In Asahi's study, C dopant introduced deep states in the gap.…”

Improved High-Temperature Stability and Sun-Light-Driven Photocatalytic Activity of Sulfur-Doped Anatase TiO2

“…20,21 Recent literature reports indicate that sulphur could either add to the TiO 2 matrix as a cation or an anion depending upon the sulphur source employed. [22][23][24][25][26][27] Umebayashi et al…”

“…[22][23][24] This anion doping shifts the absorption spectrum of titania to a lower energy and effectively leads to visible light activity. Ohno It should also be noted that upon 10 wt% addition of CuSO 4 , copper segregated as bonattite (CuSO 4 ·3H 2 O) after annealing the sample at 400 °C or lower temperature and as antierite (Cu 3 SO 4 (OH) 4 ) after annealing the sample at 800 °C.…”

“…26 It has been previously reported that sulphur can be doped either as a cation or an anion depending on the precursor used. [22][23][24][25][26] Yu et al reported that anionic sulphur doping is difficult to achieve because the ionic radius of S 2-(1.7 Å) has a larger value than O 2-(1.22 Å). .…”

Identification of bulk and surface sulfur impurities in TiO2 by synchrotron x-ray absorption near edge structure

“…4,5 Enhanced photocatalysis is seen when TiO 2 is doped with some elements, such as C, N, and F, which are claimed to substitute for O in the bulk, and S doping may have similar effects. [6][7][8][9][10][11] On the other hand, S impurities are known to inhibit photocatalytic reactions, so unwanted S impurities might limit photocatalytic performance.…”