Photoelectrocatalytic degradation of 4-chlorophenol at Bi2WO6 nanoflake film electrode under visible light irradiation

doi:10.1016/j.apcatb.2006.10.006

Applied Catalysis B: Environmental

Volume 72, Issues 1–2, 8 March 2007, Pages 92-97

https://doi.org/10.1016/j.apcatb.2006.10.006 Get rights and content

Abstract

To efficiently utilize the solar light and improve the photooxidation technique for wastewater purification, a new type of photoelectrode, visible light responsive Bi₂WO₆ nanoflake film, was covered onto the indium–tin oxide glass substrate via the electrostatic self-assembly deposition. The photocatalytic oxidation, electro-oxidation, and photoelectrocatalytic (PEC) oxidation of 4-chlorophenol (4-CP) in aqueous solution using the film electrode were investigated and compared under visible light irradiation (λ > 400 nm). The experimental results demonstrated that 4-CP could be degraded by the nanoflake film under visible light irradiation or by applying a bias potential greater than 0.8 V. Based on X-ray photoelectron spectra (XPS) analysis of the electrode after electrochemical reaction, the electropolymerization was suggested to occur in the electro-oxidation process. Furthermore, degradation efficiency of 4-CP was largely increased by combined electro-oxidation and photocatalysis. And, it is the largest at the bias potential of 2.0 V. The characteristics of the PEC degradation of 4-CP were also investigated by electrochemical impedance spectroscopy (EIS). It is shown from the EIS that the PEC degradation appears to be a simple reaction on the electrode surface, suggesting that only one step of charge transfer is involved in the electrode process. The total organic carbon analysis indicated that 4-CP could be efficiently mineralized during the PEC process.

Introduction

Photoelectrocatalytic (PEC) oxidation has proven to be an efficient method in degrading organic contaminants in aqueous solution using the TiO₂ based film electrode [1], [2], [3], [4], [5]. However, the wide band gap of TiO₂ can only capture less than 5% of solar irradiance at the Earth's surface. To obtain a more efficient utilization of solar irradiation, many attempts were made to shift its photocatalytic activity to the visible region [6], [7]. In another way, some novel photocatalyst with can absorb visible light and degrade organic pollutants are developed [8], [9].

Bi₂WO₆ is the simplest members of the aurivillius family of structurally related oxides with the layer structure and interesting physical properties [10]. Kudo found Bi₂WO₆ had photocatalytic activities for O₂ evolution [11], and Zou and coworkers revealed the Bi₂WO₆ could degrade CHCl₃ and CH₃CHO under visible light irradiation [12]. Our recent work reveals that nanoflake Bi₂WO₆ have high photocatalytic activity in degrading rhodamine B compared with that of solid samples [13]. Bi₂WO₆ with nanoflake structure has exhibited novel or enhanced physical properties such as large blue shift of the absorption edge and high specific surface areas [14], [15], [16]. These specific properties are beneficial for the photocatalytic degradation of organic contaminants.

Herein, Bi₂WO₆ nanoflake film electrode was prepared onto indium–tin oxide (ITO) glass via electrostatic self-assembly deposition (ESD) according to the method described in the literature [17]. The resultant Bi₂WO₆ nanoflake film exhibits photocatalytic activities towards degrading 4-CP under visible light irradiation. The removal efficiency of 4-CP was increased by applying a bias potential to the Bi₂WO₆ nanoflake film electrode. Moreover, a synergetic effect was observed in the degradation of 4-CP by the combined electro-oxidation and photocatalysis. The synergetic mechanism was further investigated.

Section snippets

Materials

ITO glass employed as a substrate was purchased from China Southern Class Co. Ltd., with a thickness of 1.1 mm and a sheet resistance of 15 Ω/□. It was cleaned by sonication in acetone, ethanol, and ultrapure water for 30 min each and stored in water until use. All other chemicals are analytical grade reagents and used without further purification. Deionized water was used throughout the experiment.

Preparation and characterization of the Bi₂WO₆ nanoflake film

Bi₂WO₆ nanoflake powder was synthesized through hydrothermal process according to previously

Characterization of the Bi₂WO₆ nanoflake film electrode

Fig. 1(A) shows the Raman patterns of the Bi₂WO₆ nanoflake film as well as the ITO substrate. The Raman analysis shows that the Bi₂WO₆ is well crystallized with the orthorhombic structure. Fig. 1(B) represents the UV–vis diffuse transmittance spectra of the Bi₂WO₆ nanoflake film coated on quartz glass. The steep shape of the spectra indicated that the visible light absorption was not due to the band-gap transition. The band gap of the Bi₂WO₆ film is estimated to be 2.80 eV from the onset of the

Conclusions

The experimental results demonstrated that 4-CP could be degraded by the Bi₂WO₆ nanoflake film under visible light irradiation. The bias potential with various values applied to the Bi₂WO₆ film electrode increase the degradation efficiency of 4-CP. The bias potential below 0.8 V promotes the separation of electron and holes, leading to the increase of degradation rate of 4-CP. At the potential higher than 0.8 V, combined electro-oxidation and photocatalysis lead to the synergetic degradation of

Acknowledgements

This work was supported by the National Science Foundation of China (Nos. 20507011 and 20433010), Trans-Century Training Program Foundation for the Talents by the Ministry of Education, P.R.C., the Excellent Young Teacher Program of MOE, P.R.C., and the Chinese Postdoctoral Science Foundation (023204337).

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Photoelectrocatalytic degradation of 4-chlorophenol at Bi2WO6 nanoflake film electrode under visible light irradiation

Abstract

Introduction

Section snippets

Materials

Preparation and characterization of the Bi2WO6 nanoflake film

Characterization of the Bi2WO6 nanoflake film electrode

Conclusions

Acknowledgements

Sep. Purif. Technol.

Catal. Lett.

Water. Res.

Electrochim. Acta

J. Phys. Chem.

Environ. Sci. Technol.

Environ. Sci. Technol.

Environ. Sci. Technol.

Science

Chem. Commun.

Nature

J. Phys. Chem. B

Phys. Status Solidi, A

Photoelectrocatalytic degradation of 4-chlorophenol at Bi₂WO₆ nanoflake film electrode under visible light irradiation

Preparation and characterization of the Bi₂WO₆ nanoflake film

Characterization of the Bi₂WO₆ nanoflake film electrode