Photocatalytic Activity of Neodymium Ion Doped TiO2 for 2-Mercaptobenzothiazole Degradation under Visible Light Irradiation

Fang Bai Li; Xiang Zhong Li; Kok Wai Cheah

doi:10.1071/EN05008

RESEARCH ARTICLE

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Photocatalytic Activity of Neodymium Ion Doped TiO₂ for 2-Mercaptobenzothiazole Degradation under Visible Light Irradiation

Fang Bai Li ^A ^B , Xiang Zhong Li ^A ^D and Kok Wai Cheah ^C

+ Author Affiliations

- Author Affiliations

^A Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hong Kong, China.

^B Guangdong Key Laboratory of Agricultural Environment Pollution Integrated Control, Guangdong Institute of Eco-Environment and Soil Science, Guangzhou 510650, China.

^C Department of Physics, Hong Kong Baptist University, Hong Kong, China.

^D Corresponding author. Email: cexzli@polyu.edu.hk

Environmental Chemistry 2(2) 130-137 https://doi.org/10.1071/EN05008
Submitted: 2 February 2005 Accepted: 6 April 2005 Published: 24 June 2005

Environmental Context. Conventional titanium dioxide catalysts can assist oxidation reactions upon ultraviolet light irradiation. Such photocatalysts are used to degrade organic pollutants in water to less harmful inorganic materials. By modifying the catalyst with luminescent lanthanide ions, the pollutant degradation reaction takes place upon visible light illumination. 2-Mercaptobenzothiazole, a poorly biodegradable and malodourous pollutant used both as a corrosion inhibitor and antifungal agent, is shown to be efficiently mineralized to carbon dioxide, water, ammonium, nitrate, and sulfate with this new catalyst.

Abstract. A series of neodymium ion-doped titanium dioxide (Nd³⁺-TiO₂) catalysts were prepared by means of a sol–gel method. The physical and chemical properties of the catalysts were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) N₂ sorbtion method, UV-visible diffusive reflective spectroscopy (DRS), and photoluminescence (PL) analyses. The adsorption behaviour and photocatalytic activity of Nd³⁺-TiO₂ under visible light irradiation were evaluated for aqueous 2-mercaptobenzothiazole (MBT) solution. The analytical results of XRD and BET demonstrate that the neodymium ion doping could reduce the crystallite size and increase the specific surface area of TiO₂ catalysts. The analytical results of DRS show that Nd³⁺ doping did not shift the main absorption band edge significantly, but some new absorption peaks attributable to 4f internal electron transition existed in the visible region. It was further confirmed that significant PL emission occurred in the visible range of 350–700 nm, attributable to the electron transfer between Nd³⁺ and TiO₂ owing to introduction of a Nd 4f level. The experimental results of adsorption isotherm tests demonstrate that both the saturated adsorption amount (Γ_max) and adsorption equilibrium constant (K_a) of Nd³⁺-TiO₂ catalysts increased significantly with the increased Nd³⁺ dosage. Furthermore, the Nd³⁺-TiO₂ catalysts demonstrated significant activity towards photocatalytic degradation of MBT in aqueous solution under visible light irradiation, whereas the TiO₂ catalyst did not. An optimal dosage of Nd³⁺ doping was found to be 0.7%. We propose that the introduction of the Nd 4f level plays a crucial role in visible photosensitization and enhancement of the electron–hole separation.

Keywords. : neodymium — photocatalysis — titanium dioxide — visible light — water treatment

Acknowledgements

The authors would like to thank financial support from The Hong Kong Polytechnic University as the Postdoctoral Fellowship Grant to F.B.L. (Project No.: G-YW69/02).

References

Photocatalytic Activity of Neodymium Ion Doped TiO2 for 2-Mercaptobenzothiazole Degradation under Visible Light Irradiation

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Photocatalytic Activity of Neodymium Ion Doped TiO₂ for 2-Mercaptobenzothiazole Degradation under Visible Light Irradiation