(Bi, C and N) codoped TiO2 nanoparticles
Introduction
A great deal of effort has been devoted in recent years to developing heterogeneous photocatalysts with high activities for environmental applications, such as air purification, water disinfection, hazardous waste remediation, and water purification [1], [2]. Among various oxide semiconductor photocatalysts, titania has proven to be the most suitable for environmental applications for its chemical inertness, strong oxidizing power, cost effectiveness, and long-term stability [3], [4].
The primary event occurring on the illuminated TiO2 is the generation of ecb− and hvb+. In these reactions, the organic pollutants are oxidized by the photogenerated holes or by reactive oxygen species such as OH and O2− radicals formed on the irradiated TiO2 surface. However, a problem in the application of TiO2 as a photocatalyst is the large band gap energy, i.e. anatase only shows photocatalytic activity under UV-light irradiation of wavelengths <387 nm, corresponding to its band gap value of 3.2 eV.
Many studies have revealed that doping TiO2 with nonmetal atoms, such as N [5], S [6], C [7], I [8], Br and Cl [9] shifts the optical absorption edge of TiO2 to lower energies, thereby increasing the photoactivities. Another way of extending the TiO2 spectral response and of improving its photoreactivity is doped with transition metals. Doping of transition metal ions including Cr [10], V [11] and Fe [12] have been investigated. Recently, we found that the photoreactivity of TiO2 was greatly improved when doping with Bi [13]. Choi et al. [14] found that the photoreactivity of doped TiO2 appears to be a complex function of the dopant concentration, the energy level of dopants within the TiO2 lattice, their d electronic configuration, the distribution of dopants, the electron donor concentration, and the light intensity.
However, the effect of codoping by both cation and anion on the photocatalytic activity was seldom reported. Zhao et al. studied the TiO2 doping with both a nonmetal element, boron, and a metal oxide, Ni2O3 [15]. They found that incorporation of B into TiO2 extended the spectral response to the visible region and that the photocatalytic activity was greatly enhanced as it was further loaded with Ni2O3.
Recently, a number of Bi-based photocatalysts, such as NaBiO3 [16], Bi3O4Cl [17], Bi4Ti3O12 [18] and Bi2WO4 [3], were synthesized; these materials showed high photocatalytic activities even under visible light irradiation. It seems that bismuth maybe a proper candidate dopant element to extend the TiO2 spectral response and thus to improve its photoreactivity. Another goal of the paper is to study the synergistic effects of codoping by both cation and anion on the photocatalytic activity of TiO2. Here we report on doped TiO2 with both Bi3+ and SCN− by a simple method of modified sol–gel synthesis.
Section snippets
Catalyst synthesis
Titanium n-butoxide (TTBO), KSCN, BiCl3 and phenol were obtained from Shanghai. Chemical Co., China. The target dye pollutants, RhB (Fig. 1), was obtained from Acros Chem. Co. Commercial P25 (Degussa, 50 m2/g, 80% anatase and 20% rutile) was used as reference sample. Doubly distilled water was used throughout this study, and the pH of the solution was adjusted by diluted aqueous solutions of HClO4 and NaOH.
The catalyst (Bi,SCN)-TiO2, were prepared by the sol–gel method. In a typical preparation
Measurements of XRD, TEM, DRS, XPS and FT-IR
XRD was usually used for identification of the crystal phase and to estimate the anatase to rutile ratio as well as the crystallite size of each of the phases present. The XRD peaks at around 2θ = 25.25°(1 0 1) in the spectrum of TiO2 are identified as the anatase form, whereas the XRD peaks at 2θ = 27.42°(1 1 0) are taken as the rutile form [19]. Fig. 2 shows the XRD patterns of TiO2. It could be seen that the prepared pure TiO2 was of pure anatase form (Fig. 2b). However, the intensity of the peaks
Conclusions
The goals both of extending the TiO2 spectral response to the visible region and of improving its photocatalytic activity are realized by modification with BiCl3 and KSCN. The photocatalyst shows much higher photoreactivity than p25 TiO2 on the degradation of organic pollutants (RhB and phenol) both under UV and visible light irradiation. Doping of TiO2 with Bi3+ resulted in the formation of BixTiOy, and the heterojunction effects of BixTiOy/TiO2 maybe responsible for the higher photoreactivity
Acknowledgements
The authors are grateful to the Natural Science Foundation of China (20577070) and Science Foundation of South-Central University for Nationalities (YZZ06019) for funding received.
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