Visible-light photocatalytic activity of nitrogen-doped TiO2 thin film prepared by pulsed laser deposition

doi:10.1016/j.apsusc.2008.01.069

Applied Surface Science

Volume 254, Issue 15, 30 May 2008, Pages 4620-4625

https://doi.org/10.1016/j.apsusc.2008.01.069 Get rights and content

Abstract

Nitrogen-doped titanium dioxide (TiO_2−xN_x) thin films have been prepared by pulse laser deposition on quartz glass substrates by ablated titanium dioxide (rutile) target in nitrogen atmosphere. The x value (nitrogen concentration) is 0.567 as determined by X-ray photoelectron spectroscopy measurements. UV–vis spectroscopy measurements revealed two characteristic deep levels located at 1.0 and 2.5 eV below the conduction band. The 1.0 eV level is attributable to the O vacancy state and the 2.5 eV level is introduced by N doping, which contributes to narrowing the band-gap by mixing with the O2p valence band. The enhanced degradation efficiency in a broad visible-light range was observed from the degradation of methylene blue and methylene orange by the TiO_2−xN_x film.

Introduction

Titanium dioxide (TiO₂) is a well-known photocatalytic material and has received great attention as a photocatalyst since it is a wide-gap semiconductor and exhibits strong oxidation activity and hydrophilicity under UV irradiation [1]. However, TiO₂ can only be activated by irradiating with ultraviolet (UV) light due to its high band-gap energies (for example, 3.0 eV for rutile phase or 3.2 eV for anatase phase) [2]. Therefore, only a small fraction (∼5%) of the solar energy (<390 nm) can be utilized in practical application. Therefore, the modification of TiO₂ to render its sensitivity to visible-light became one of the most important goals to increase the utility of TiO₂. Many techniques have been proposed to achieve this purpose. Earlier investigations investigated the doping of transition metals of Fe, Ni, and Cr into TiO₂, which can increase the absorption of visible-light, but these doped materials suffer from thermal instability and an increased number of carrier recombination centers [3], [4], [5], [6]. Recently, the doping of nonmetal atoms such as N [7], [8], [9], [10], [11], S [12], [13], and C [14], [15] into the TiO₂ lattice were reported, which can shift the absorption edge or band-gap to lower energies and hence increase the visible absorption. Particularly, the substitution doping of nitrogen was found to be effective in narrowing the band-gap through mixing of N with O2p states [7].

Many techniques have been explored to fabricate TiO₂ thin films, such as chemical vapor deposition (CVD) [16], sol–gel process [17], [18], radio-frequency sputtering [19], pulse laser deposition (PLD) [20]. Among them, pulse laser deposition method has become a widely used technique for the deposition of thin films due to its advantages including simple system setup, wide range of deposition conditions, wider choice of materials and high laser energy or instantaneous deposition rates.

In the present work, we prepared TiO_2−xN_x thin films by PLD method using TiO₂ targets under nitrogen and oxygen atmosphere. The structure, surface morphology and nitrogen-doping state of the TiO_2−xN_x films were investigated with X-ray diffraction (XRD), field emission scan electronic microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS), respectively. The visible-light photocatalytic activity was estimated by the degradation of methylene blue and methylene orange with the TiO_2−xN_x films. Relationship between the nitrogen-doping state and visible-light photocatalytic activity was discussed.

Section snippets

Experiment

TiO_2−xN_x films were prepared on quartz glass substrate by pulse laser deposition and TiO₂ films without doping was also prepared for comparison. Pulsed Nd:YAG laser with a wavelength of 1064 nm was used. The repetition rate is 20 Hz and the fluency on target was set at 60 J/cm² for all samples. A target of TiO₂ with rutile phase was used. The distance between the target and the quartz substrate was kept at 2.5 cm. The chamber was evacuated first to a base pressure (below 5 × 10⁻⁴ Pa) using a turbo

Result and discussion

Fig. 1 shows XRD patterns of the TiO_2−xN_x and TiO₂ film. Diffraction peaks of TiO₂ film at 25.28°, 37.9° and 53.89° are corresponding, respectively, to the (1 0 1), (0 0 4) and (1 0 5) planes of the anatase TiO₂ phase. Compared with the standard anatase structure XRD spectrum (from JADE card) it could be clearly seen that the TiO₂ film exhibits the preferred orientation of (0 0 4). The diffraction peaks of TiO_2−xN_x film at 25.28° and 48.05° are corresponding, respectively, to the (1 0 1) and (2 0 0) planes

Conclusion

1,
TiO_2−xN_x film was deposited on quartz glass substrates by pulsed laser deposition. The TiO_2−xN_x film shown single anatase crystal phase. The x value (N-doping concentration) was 0.567 determined from X-ray photoelectron spectroscopy measurements.
2,
The TiO_2−xN_x film deposited by PLD is a broad-spectrum UV–vis-light absorption film (about 200–700 nm) characterized by its optical absorption spectrum. The film shows two deep levels located at 1.0 eV and 2.5 eV. The 1.0 eV level is attributed to O vacancy

Acknowledgments

This work was supported by Foundation of National Key Basic Research and Development Program (No.2004CB619301) and Project 985-automotive engineering of Jilin University.

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Visible-light photocatalytic activity of nitrogen-doped TiO2 thin film prepared by pulsed laser deposition

Abstract

Introduction

Section snippets

Experiment

Result and discussion

Conclusion

Acknowledgments

Appl. Catal. B

Appl. Sur. Sci.

Surf. Coat. Technol.

Thin Solid Films

Surf. Coat. Technol.

Appl. Surf. Sci.

Appl. Surf. Sci.

Appl. Catal. B: Environ.

Thin Solid Films

Nature

Phys. Rev. B

J. Phys. Chem. B

J. Electrochem. Soc.

J. Phys. Chem.

Chem. Rev. (Washington, DC)

Science

J. Phys. Chem. B

Visible-light photocatalytic activity of nitrogen-doped TiO₂ thin film prepared by pulsed laser deposition