Solar photocatalytic degradation of eight commercial dyes in TiO2 suspension

doi:10.1016/S0043-1354(99)00210-9

Water Research

Volume 34, Issue 3, 15 February 2000, Pages 990-994

https://doi.org/10.1016/S0043-1354(99)00210-9 Get rights and content

Abstract

The photocatalytic degradation of eight commercial dyes with different structure and containing different substitute groups has been investigated using TiO₂ as photocatalyst in aqueous solution under solar irradiation. Decolorization rate, TOC decrease and inorganic ion production of the dye solution were detected. The experimental results indicate that eight commercial dyes could be degradated efficiently at different levels. The comparison of chloride and sulfate ions production rate from the cleavage of substitute groups in different structure positions reveals the dye compounds degradation pattern and decomposition pathway.

Introduction

Dyes are an abundant class of colored organic compounds that represent an increasing environmental danger. During dye production and textile manufacturing processes a large amount of wastewater containing dyestuffs with intensive color and toxicity can be introduced into aquatic systems. Due to the large degree of aromatics present in these molecules and the stability of modern dyes, conventional biological treatment methods are ineffective for decolorization and degradation (Souther and Alspaugh, 1957, Hamza and Hamoda, 1980, Sheng and Chi, 1993. This had led to the study of other methods. Recent studies have demonstrated that photocatalysis can be used to destroy dye compounds using semiconductors such as the anatase form of titanium dioxide and UV light irradiation (Al-Ekabi et al., 1991, Blake, 1994, Hoffmann et al., 1995). Lately, the utilization of combining photocatalysis and solar technologies has been attracted increasing attention. It may be developed to a useful process for the reduction of water pollution caused by dying compounds because of the mild conditions required and their efficiency in the mineralization (Minero et al., 1993, Minero et al., 1996, Daoxin et al., 1994, Lindner et al., 1995, Li and Zhang, 1996). In order to elucidate the photocatalytic decolorization mechanism and decomposition pattern of dye compounds in details, our study focus on the investigation of inorganic ion production from degradation of substitute groups. It will provide the reaction pathways for eight commercial dyes with different molecular structures and containing different substitute groups under solar irradiation.

Section snippets

Materials

Seven commercial dyes were obtained from the Dye Plant in Shanghai without further purification. Methylorange was purchased from the Beijing Chemical Industrial Company as an analytical reagent grade. Their classification and molecular formulas were listed in Table 1. The catalyst used in all testes was titanium dioxide reagent powder (from Beijing Chemical Industrial Company; predominantly anatase with specific surface areas of 9 m² g⁻¹).

Irradiation experiment

All photocatalytic experiments were carried out at the

Photocatalytic degradation of eight dyes

The experimental data of different photocatalytic degradation of eight dyes with different structures after 4 h solar irradiation are shown in Table 2. It indicates that, in general, the decolorization rate of the dye solution was more rapid than the mineralization rate identified by TOC removal. The latter will take longer time for further oxidation. The release of chloride ions and sulfate ions points to molecular structure cleavage during the solar photodegradation process. Nitrate and

Summary and conclusion

This study demonstrates that certain commercial dyes with different structure and different substitute groups can be decolorized and mineralized by solar photocatalysis. The experimental results indicate that during the photocatalytic degradation, the decolorization rate is faster than the mineralization rate. For chloride substituted dye, the chloride in the side chain is more active with respect to cleavage than the one connected with the benzene ring. The triazine ring and the groups

Acknowledgements

This research has been supported by the National Natural Foundation of China (No. 29637010; 59878051) and partly supported by the Chinese Academy of Sciences (No: KZ952-S1-231). Liu Nian, a student of Beijing Industrial University, took part in the research within a training program.

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D.M. Blake

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Solar photocatalytic degradation of eight commercial dyes in TiO2 suspension

Abstract

Introduction

Section snippets

Materials

Irradiation experiment

Photocatalytic degradation of eight dyes

Summary and conclusion

Acknowledgements

Water Sci. Technol.

Chemosphere

Solar Energy

Advanced technology for water purification by heterogeneous photocatalysis

Int. J. Environ. Pollut.

Solar photocatalytic degradation of eight commercial dyes in TiO₂ suspension