Enhanced photocatalytic activity of nitrogen doped TiO2 photocatalysts sensitized by metallo Co, Ni-porphyrins
Highlights
► Four kinds of metalloporphyrin sensitized nitrogen-doped titanium dioxide composites have been prepared successfully. ► Four composites as photocatalysts have been investigated and contrasted for the first time. ► The mechanisms of higher degradation efficiency for cobalt porphyrins sentisized N-TiO2 are reduced.
Introduction
Recently, much attention has been paid to improve the photocatalytic properties of TiO2 under irradiation of visible light. To realize this, many strategies have been developed including doping of transitional metal ions and non-metal elements [1], [2], [3], [4]. Nitrogen doping has been confirmed to be one of the effective ways in improving the photocatalytic properties of TiO2 [5], [6]. When the nitrogen was doped in TiO2, the band gap of TiO2 was decreased due to the replacement of TiO bonds by TiN or TiNO bonds, thus widening the absorption spectrum and improving the photocatalytic efficiency. Surface sensitizing with dyes was another effective way to widen the absorption spectrum of TiO2. Metal porphyrin was an effective sensitizer because of its high absorption coefficient within the solar spectrum and its good chemical stability [7]. It was believed that porphyrins coupled on the surface of TiO2 can serve as the light absorption channel. When the light was exposed on the surface of the porphyrin-coupled TiO2, the electrons of porphyrins were excited to create photo-induced electrons, and then these electrons were injected into the conduction band of TiO2. Subsequently, the active electrons will further generate peroxyl radicals (·OH) with oxygen absorbed on the surface of TiO2, resulting in the oxidation of organic compound [8], [9], [10].
Obviously, the two methods mentioned above were completely different in mechanism of enhancing the photocatalytic efficiency of TiO2. If the porphyrin sensitization and nitrogen doping could be combined together, the photocatalytic activity of TiO2 would be further increased. However, this kind of research has been rarely reported [11].
In this article, we reported several novel composite photocatalysts, the N doped TiO2 powders sensitized by four metallo Co, Ni-porphyrins. Results showed that these kinds of composite photocatalysts exhibited higher photocatalytic activity than that of unsentisized N-doped TiO2.
Section snippets
Reagents and materials
All reagents (titanium sulfate, formaldehyde, benzene, and metal acetate) were analytical grade and used as received without further purification except pyrrole, which was distilled before use. Ammonia was chemical grade.
Characterization
X-ray diffraction was performed on XRD-7000s (Shimadzu, Japan) between 20° and 80° with Cu Kα at 40 KV and 40 mA. The transmission electron microscopy (TEM) images were recorded on a JEM-3010 (JEOL, Japan). X-ray photoelectron spectroscopy (XPS) was recorded with PHI 5000C ESCA
XRD analysis
It is well known that anatase TiO2 shows a higher photocatalytic activity than the brookite or rutile one. Fig. 1 shows the XRD patterns of N-TiO2 and four kinds of metalloporphyrin sensitized N-TiO2 catalysts. For N-TiO2, the 2θ angles located at 25.4°, 37.8°, 48.1°, 53.9°, 55.2°, 62.8° and 75.3° were observed, indicating its nature of anatase structure. Based on the Scherrer formula D = Kλ/β cos θ, the average diameter of N-TiO2 crystallites was calculated to be 15.1 nm.
Fig. 1b–e is XRD patterns
Conclusions
The four kinds of metalloporphyrin sensitized nitrogen-doped titanium dioxide (N-TiO2) composite photocatalyst, NiTPP, CoTPP, NiTHPP and CoTHPP, have been successfully prepared by solvent reflux method. The existing of metalloporphyrin improved the spectral response of N-TiO2 in the visible region. Metallo Co, Ni-porphyrins sensitized N-TiO2 exhibit higher photocatalytic activity than non-sensitized N-TiO2 under visible light irradiation. CoTPP and CoTHPP sensitized N-TiO2 show better catalytic
Acknowledgements
This work is supported by the National Natural Science Foundation of China (21276208 and 51102195), Special Research Fund for the Doctoral Program of Higher Education (20096118110008), the Support Scheme of Xi’an Science and Technology Innovation (CXY09025(1)), Innovation of Science and Technology Fund of Xi’an University of Technology (108-211303), Scientific Research Program Funded by Shaanxi Provincial Education Department (11JK0842, 12JK0606) and Xi’an University of Technology Doctoral Fund
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