Photocatalytic degradation of Rhodamine B on TiO2 nanoparticles modified with porphyrin and iron-porphyrin
Introduction
Titanium dioxide (TiO2) has been extensively studied in many applications such as organic pollutant degradation, air purification, deodorant, sterilization, and demister because of its nontoxicity, low cost, chemical stability and high catalytic activity [1], [2], [3]. Specially, it has been considered as the most promising environment protective photocatalyst. However, TiO2 can be activated only under UV light irradiation due to its wide band gap of 3.2 eV. It is known that the solar spectra usually contain about 4% UV light. Therefore, pure TiO2 cannot make use of the solar efficiently, the development of visible light photocatalysts is strongly urged for solving environmental and energy problems [4].
To overcome this problem, different approaches have been proposed in the literature in which the response of the semiconductor was extended towards the visible region. Among them, dye-sensitized TiO2 has been widely used either with dyes present in solution or grafted on TiO2 [5]. The dyes used are erythrosine B [6], rose bengal [7], metal porphyrin [8], [9], [10] etc., among which metal porphyrin may be an appropriate candidate because of its high absorption coefficient within the solar spectrum and its good chemical stability in comparison to that of other dyes. Recently, the photocatalytic activity of TiO2 powders impregnated with lipophilic copper porphyrins used as sensitizers for the decomposition of 4-nitrophenol has been investigated [10], [11], [12]. TiO2 samples impregnated with functionalized copper porphyrins are more efficient catalysts compared to bare TiO2 for the photodegradation of 4-nitrophenol.
In this article, the photocatalytic degradation of RhB on Pr/TiO2 and Fe(III)Pr/TiO2 under ultraviolet and visible light are both investigated. Considerable degradation of RhB over Pr/TiO2 under both light source is revealed, however, Fe(III)Pr/TiO2 has high activity only under ultraviolet light. It is necessary to clarify the different photocatalytic degradation mechanism in Pr/TiO2 nd Fe(III)Pr/TiO2.
Section snippets
Preparation
The synthesis of Pr/TiO2 and Fe(III)Pr/TiO2 nanoparticles involved the following steps: (1) 4 mL of acetic acid and 4 mL of tetrabutyl titanate(C16H36O4Ti) were dissolved into 20 mL of ethanol. (2) Appropriate amounts of HCl and water were dissolved in 10 mL ethanol. (3) Homogeneous solution prepared in step 2 was dropped into the step 1 mixture. After stirring for 3 h, a steady colloid solution was obtained. (4) The colloid was first dried at 100 °C and calcined in a muffle at 450 °C for 3 h. Then,
Spectroscopic properties of TiO2, Pr/TiO2 and Fe(III)Pr/TiO2 photocatalysts
Fig. 1 shows the UV–Vis diffuse reflectance spectra of TiO2, Pr/TiO2 and Fe(III)Pr/TiO2 samples. Obviously, there is no absorption above 400 nm for TiO2, while Pr/TiO2 and Fe(III)Pr/TiO2 show visible light absorption from 400 to 700 nm. It can be find Pr/TiO2 and Fe(III)Pr/TiO2 composites exhibit a broader absorption range than pure TiO2. For Pr/TiO2, the strong band appears at 412 nm arising from the transition of a1u()–(), and the less intense bands in the 500–650 nm region corresponding to
Conclusions
Two photocatalysts, Pr/TiO2 and FeIIIPr/TiO2 has been prepared successfully. Both photocatalysts were more efficient compared to TiO2 for degradation of RhB, the Pr/TiO2 shows high photocatalytic activity under either UV or visible light, however, FeIIIPr/TiO2 shows only high photocatalytic activity under UV light. We suggest that by injecting electrons from the photoexcited Pr to the conduction band of TiO2, Pr/TiO2 can effectively degraded RhB under UV light and visible light. The enhanced
Acknowledgments
This work was supported by the Natural Science Foundation of China (Grant No. 20603018) and Science Foundation of Jiangsu (Grant No. BM2007132), China. We gratefully acknowledge the anonymous reviewers whose comments helped to improve the manuscript.
References (21)
- et al.
Chem. Phys. Lett.
(1983) - et al.
Sol. Energy Mater. Sol. Cells
(1994) - et al.
Appl. Catal.
(2002) - et al.
Appl. Catal. B
(2002) - et al.
J. Catal.
(2003) - et al.
Appl. Catal. B
(2007) - et al.
Dyes Pigments
(2008) - et al.
Chem. Rev.
(1995) - et al.
Chem. Rev.
(1995) - et al.
J. Photochem. Photobiol.
(2001)