Enhanced photocatalytic activity of (Mo,C)-codoped anatase TiO 2 nanoparticles for degradation of methyl orange under si
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Shu Yin IMRAM, Tohoku University, Aoba-ku, Sendai 980-8577, Japan (Received 2 July 2010; accepted 20 September 2010)
C-doped, Mo-doped, and (Mo, C)-codoped TiO2 photocatalysts were prepared by a sol-gel process. The photocatalytic activity was evaluated by the photocatalytic degradation of methyl orange (MO) under simulated solar irradiation. Results indicated that both monodoped and codoped TiO2 exhibited better visible light absorption behavior and narrower energy gap than pure TiO2, and codoped TiO2 showed a slightly higher adsorption property in the dark because of higher Brunauer–Emmett–Teller-specific surface area. The photocatalytic activity of monodoped TiO2 was also enhanced, and the (0.04% Mo, C)-codoped sample had the best photocatalytic activity for degrading MO among all of the samples. The reason can be ascribed to the synergistic effect due to Mo and C doping. Furthermore, the transfer pathways of photoinduced carriers and photocatalytic reaction mechanism of (Mo, C)-codoped TiO2 was first investigated.
I. INTRODUCTION
Titanium dioxide (TiO2) has been widely studied and used as a photocatalyst in virtue of its strong photocatalytic activity, chemical stability, nontoxicity, favorable optoelectronic properties, and low cost. During the past 20 years, TiO2 has been widely taken as a photocatalyst in the photodegradation of organic pollutants. However, only a small ultraviolet (UV) fraction of solar light (3–5%) could be used because of the wide band gap of TiO2. Therefore, it was urgent to develop a particular photocatalyst sensitive to sunlight.1 The shift of the optical response of TiO2 from UV to the visible spectral range will have a profound positive effect on the efficient use of solar energy in photocatalytic reactions.2 So far, much effort has been directed toward the development of visible-light active photocatalysts.3 One approach to synthesizing visible-light active photocatalysts is the doping of various metal and nonmetal elements, such as Fe,4 La,5 Ce,6 Mo,7 N,8,9 C,10–12 F,13 etc. Moreover, researchers have reported that the introduction of metal or nonmetal atoms into a photocatalytic system is effective for enhancing the photocatalytic activity of TiO2. Among these studies, Xiao et al.11 reported that C-doped TiO2 exhibited obviAddress all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/JMR.2010.0307 2392
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J. Mater. Res., Vol. 25, No. 12, Dec 2010 Downloaded: 13 Mar 2015
ous absorption in the visible light range. They found the sample of C-doped TiO2 calcined at 873 K showed the highest photocatalytic activity under solar irradiation, and it can be used to degrade methylene blue solution. Wang et al.12 showed that the C-doped TiO2 obtained by the thermal treatment at 400 C had high crystalline and was visible light responsive. Devi and Murthy7 found a significant enhancement on photocatalytic activity of TiO2 powders by doping with 0.06 at.% Mo6þ ions under visible light irradiation. All of these ef
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