Synthesis, characterization, and theoretical study of N, S-codoped nano-TiO₂ with photocatalytic activities

Abstract

Nitrogen and sulfur doped titanium dioxide photocatalysts were prepared by the sol-gel method. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV-visible diffuse reflectance spectra (DRS). Photocatalytic activities of the samples were investigated on the degradation of methyl orange (MO). The effect of the dopants on the electronic structure of TiO₂ was studied by the first-principles calculations based on the density functional theory (DFT). The orbital hybridization resulted in energy gap narrowing and electronic delocalization in the crystal of doped TiO₂. Mobile electrons of varied energetic states could offer enhanced electron transfer, together with optical absorption improvement. The results show that the doping elements of N and S play a cooperative role in the modification of electronic structure, which enhances the photocatalytic performance. The experimentally observed absorption edges of N-doped TiO₂, S-doped TiO₂, and N, S-codoped TiO₂ are 420, 413, and 429 nm, respectively, which can be explained by the theoretical calculation results.

Keywords

titanium dioxide / doping / electronic structure / red shift / photocatalysis / nanoparticles

References

[1] Sun J.H., Qiao L.P., Sun S.P., Wang G.L. Photocatalytic degradation of orange G on nitrogen-doped TiO₂ catalysts under visible light and sunlight irradiation. J. Hazard. Mater., 2008, 155(1–2): 312.

[2] Dai K., Peng T.Y., Chen H., et al. Photocatalytic degradation and mineralization of commercial methamidophos in aqueous titania suspension. Environ. Sci. Technol., 2008, 42(5): 1505.

[3] Jagadale T.C., Takale S.P., Sonawane R.S., et al. N-doped TiO₂ nanoparticle based visible light photocatalyst by modified peroxide sol-gel method. J. Phys. Chem. C, 2008, 112(37): 14595.

[4] Khan S.U.M., Al-Shahry M., Ingler W.B.Jr. Efficient photochemical water splitting by a chemically modified n-TiO₂. Science, 2002, 297(5590): 2243.

[5] Huo Y.N., Bian Z.F., Zhang X.Y., et al. Highly active TiO_2−xN_x visible photocatalyst prepared by N-doping in Et₃N/EtOH fluid under supercritical conditions. J. Phys. Chem. C, 2008, 112(16): 6546.

[6] Tang X.H., Li D.Y. Sulfur-doped highly ordered TiO₂ nanotubular arrays with visible light response. J. Phys. Chem. C, 2008, 112(14): 5405.

[7] Zhou J.K., Lv L., Yu J.Q., et al. Synthesis of self-organized polycrystalline F-doped TiO₂ hollow microspheres and their photocatalytic activity under visible light. J. Phys. Chem. C, 2008, 112(14): 5316.

[8] Su W.Y., Zhang Y.F., Li Z.H., et al. Multivalency iodine doped TiO₂: preparation, characterization, theoretical studies, and visible-light photocatalysis. Langmuir, 2008, 24(7): 3422.

[9] Sato S. Photocatalytic activity of NO_x doped TiO₂ in the visible light region. Chem. Phys. Lett., 1986, 123(1–2): 126.

[10] Asahi R., Morikawa T., Ohwaki T., et al. Visible-light photocatalysis in nitrogen-doped titanium oxides. Science, 2001, 293(5528): 269.

[11] Qiu X.F., Burda C. Chemically synthesized nitrogen-doped metal oxide nanoparticles. Chem. Phys., 2007, 339(1–3): 1.

[12] Colpini L.M.S., Alves H.J., Santos O.A.A., Costa C.M.M. Discoloration and degradation of textile dye aqueous solutions with titanium oxide catalysts obtained by the sol-gel method. Dyes Pigm., 2008, 76(2): 525.

[13] Zhu J.F., Zheng W., He B., et al. Characterization of Fe-TiO₂ photocatalysts synthesized by hydrothermal method and their photocatalytic reactivity for photodegradation of XRG dye diluted in water. J. Mol. Catal. A, 2004, 216(1): 35.

[14] Kim Y.J., Chai S.Y., Lee W.I. Control of TiO₂ structures from robust hollow microspheres to highly dispersible nanoparticles in a tetrabutylammonium hydroxide solution. Langmuir, 2007, 23(19): 9567.

[15] Seifried S., Winterer M., Hahn H. Nanocrystalline titania films and particles by chemical vapor synthesis. Chem. Vapor Depos., 2000, 6(5): 239.

[16] Hsieh C.S., Zhu H., Wei T.Y., et al. Applying the experimental statistical method to deal the preparatory conditions of nanometric-sized TiO₂ powders from a two-emulsion process. J. Eur. Ceram. Soc., 2008, 28(6): 1177.

[17] Zhang Z.H., Yuan Y., Shi G.Y., et al. Photoelectrocatalytic activity of highly ordered TiO₂ nanotube arrays electrode for azo dye degradation. Environ. Sci. Technol., 2007, 41(17): 6259.

[18] Ryu Y.B., Lee M.S., Jeong E.D., et al. Hydrothermal synthesis of titanium dioxides from peroxotitanate solution using different amine group-containing organics and their photocatalytic activity. Catal. Today, 2007, 124(3—4): 88.

[19] Hidalgo M.C., Aguilar M., Maicu M., Navío J.A., Colón G. Hydrothermal preparation of highly photoactive TiO₂ nanoparticles. Catal. Today, 2007, 129(1–2): 50.

[20] Colón G., Hidalgo M.C., Navío J.A., et al. Influence of amine template on the photoactivity of TiO₂ nanoparticles obtained by hydrothermal treatment. Appl. Catal. B, 2008, 78(1–2): 176.

[21] Liu Y., Chen X., Li J., Burda C. Photocatalytic degradation of azo dyes by nitrogen-doped TiO₂ nanocatalysts. Chemosphere, 2005, 61(1): 11.

[22] Lettmann C., Hildenbrand K., Kisch H., et al. Visible light photodegradation of 4-chlorophenol with a coke-containing titanium dioxide photocatalyst. Appl. Catal. B, 2001, 32(4): 215.

[23] Lopez T., Gomez R., Sanchez E., et al. Photocatalytic activity in the 2,4-dinitroaniline decomposition over TiO₂ sol-gel derived catalysts. J. Sol Gel. Sci. Technol., 2001, 22(1–2): 99.

[24] Yu J.G., Liu S.W., Zhou M.H. Enhanced photocalytic activity of hollow anatase microspheres by Sn4+ incorporation. J. Phys. Chem. C, 2008, 112(6): 2050.

[25] J. Taylor, H. Guo, and J. Wang, Ab initio modeling of open systems: Charge transfer, electron conduction, and molecular switching of a C₆₀ device, Phys. Rev. B, 63(2001), No.12, art. No.121104.

[26] Valentin C.D., Pacchioni G., Selloni A. Theory of carbon doping of titanium dioxide. Chem. Mater., 2005, 17(26): 6656.

[27] Yang K.S., Dai Y., Huang B.B., Whangbo M.H. Density functional characterization of the band edges, the band gap states, and the preferred doping sites of halogen-doped TiO₂. Chem. Mater., 2008, 20(20): 6528.

[28] Kamisaka H., Adachi T., Yamashita K. Theoretical study of the structure and optical properties of carbon-doped rutile and anatase titanium oxides. J. Chem. Phys., 2005, 123(8): 1.

[29] Valentin C. D., Pacchioni G., Selloni A., et al. Characterization of paramagnetic species in N-doped TiO₂ powders by EPR spectroscopy and DFT calculations. J. Phys. Chem. B, 2005, 109(23): 11414.

[30] Gao H., Zhou J., Dai D., Qu Y. Photocatalytic activity and electronic structure analysis of N-doped anatase TiO₂: a combined experimental and theoretical study. Chem. Eng. Technol., 2009, 32(6): 867.

[31] Tian F.H., Liu C.B. DFT description on electronic structure and optical absorption properties of anionic S-doped anatase TiO₂. J. Phys. Chem. B, 2006, 110(36): 17866.