Photodegradation treatment of azo dye wastewater by UV/TiO2 process

doi:10.1016/j.dyepig.2004.12.002

Dyes and Pigments

Volume 68, Issues 2–3, 2006, Pages 191-195

https://doi.org/10.1016/j.dyepig.2004.12.002 Get rights and content

Abstract

In this study the photocatalytic decomposition of a synthetic dye, C. I. Acid Yellow 17, was investigated. The TiO₂ photocatalyst prepared by chemical vapor deposition (CVD) for UV/TiO₂ process was prepared by annealing at 550 °C for 24 h and anatase type crystalline (under XRD and SEM analysis) was obtained. The more important factors affecting the dye wastewater treatment in terms of dye removal ratio, color removal ratio, and mineralization ratio in this study were pH value of the solution, initial concentration of the dye wastewater, flow rate of the wastewater inflow and light intensity. Chloride and sulfate were detected in C. I. Acid Yellow 17 decomposition process while ammonium and nitrate were not detected.

Introduction

Dyestuff and dyeing industry have long been the important traditional industries in Taiwan. The wastewater that is characterized with high color, high chemical oxygen demand, low biodegradability and high variability has seriously polluted the drain water. Among the problems it causes, color is the most critical and dyestuff is the primary source of color. Most of dyestuffs are complicated aromatic compounds and are chemically stable. Though the wastewater possesses low BOD/COD ratio, the color, COD and residual dye level are still high even after traditional biological treatment or chemical coagulation treatment. Without further treatment, the wastewater will not meet the ever stricter environmental standards of discharged water.

The advanced oxidation process to oxidize the organic pollutants in wastewater with free radicals had been valued in recent years. There were some related articles published. Matthews [3] treated Methylene Blue, Rhodamine B, Methyl Orange and salicylic acid with fixed bed UV/TiO₂ process. The results indicated that the half-life of decomposition of the four compounds were around 21–22 min and the faster the flow rate of the wastewater circulation, the better the reaction. Shu et al. [5] treated the wastewater of Acid Red 1 and Acid Yellow 23 with UV/H₂O₂ and found that the color removal ratio reached 98% and 96% in 30 min with the initial concentration of 22.4 mmol/L and 23.5 mmol/L, respectively, at pH 5.7. Tang and An [6] investigated the treatment of five commercial dyes with suspended UV/TiO₂ photocatalytic process. The result showed that the color removal ratio varied a lot among those dyes at different pH values and suggested that the azo number in the dye molecules might be the factor related.

Most of the studies done on the wastewater treatment with TiO₂ photocatalyst or H₂O₂ addition to enhance the color removal effect used suspended TiO₂. However, suspension of TiO₂ requires further filtration or centrifugation to isolate TiO₂ from the solution, which added both costs and difficulties of the treatment technique. This study used fixed UV/TiO₂ photocatalytic treatment procedures for a batch experiment to investigate the parameters of solutions pH value, dye concentration, wastewater inflow rate and light intensity on the effects of dye wastewater treatment with photocatalytic decomposition. More than 50% of dyestuffs used in Taiwan textile and dyeing industrials are azo dyes. This study selected the widely used C. I. Acid Yellow 17 as the target of synthetic dye wastewater.

Section snippets

Methods

For the preparation of photocatalyst a chemical vapor deposition (CVD) method was used. Tetraisopropyl orthotitanate (Merck) and deionized water were put in two aeration bottles, respectively, heated up to 60 °C in a water bath, then induced to a pyrex glass tube (outer diameter of 3 cm, inner diameter of 2.6 cm, length of 70 cm) with nitrogen as the carrier gas. TiO₂ was deposited on the inner wall of the pyrex glass tube in the furnace, then the reactor was placed in a box furnace to eliminate

Qualitative analysis of the catalyst

X-ray diffractometer was used to identify the quality and crystalline phase of the catalysts at various annealing temperatures (450 °C, 550 °C, 650 °C, 750 °C and 850 °C) and the results were compared with JCPDS database. It indicated that the TiO₂ crystal formed was of anatase type at 450–750 °C while rutile type appeared when the annealing temperature reached 850 °C. Zhang et al. [8] also found that anatase crystalline changed into rutile type at 600–1100 °C in the preparation of TiO₂ from TiCl₄.

Conclusions

In the preparation of TiO₂ photocatalyst with chemical vapor deposition, anatase crystalline was obtained by annealing at 550 °C for 24 h. To obtain maximum dye removal, color removal and mineralization ratios, low pH value, high light intensity and low initial concentration are required. The full spectrum scanning results indicate that C. I. Acid Yellow 17 is decomposed in this reaction system and chloride and sulfate are detected too. In the 9 h of reaction time, the COD level of original

Acknowledgements

This work was supported by the research grant no. NSC89-2211-E-005-005 from the National Science Council in Taiwan.

References (8)

R.W. Matthews
Kinetics of photocatalytic oxidation of organic solutes over titanium dioxide
Journal of Catalyst
(1988)
H.Y. Shu et al.
Decolorization of mono-azo dyes by advanced oxidation process: a case study of Acid Red 1 and Acid Yellow 23
Chemosphere
(1994)
W.Z. Tang et al.
UV/TiO₂ photocatalytic oxidation of commercial dyes in aqueous solution
Chemosphere
(1995)
Y. Wang
Solar photocatalytic degradation of eight commercial dyes in TiO₂ suspension
Water Research
(2000)

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Photodegradation treatment of azo dye wastewater by UV/TiO2 process

Abstract

Introduction

Section snippets

Methods

Qualitative analysis of the catalyst

Conclusions

Acknowledgements

Journal of Catalyst

Chemosphere

Chemosphere

Water Research

Photodegradation treatment of azo dye wastewater by UV/TiO₂ process