Scholarly article on topic 'Degradation of the Reactive Black 5 by Fenton and Fenton-like system'

Degradation of the Reactive Black 5 by Fenton and Fenton-like system Academic research paper on "Chemical engineering"

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Abstract of research paper on Chemical engineering, author of scientific article — Xuanmo Liu, Muqing Qiu, Chengcai Huang

Abstract This study investigated Fenton and Fenton-like reactions to oxidize the commercial zao dye of Reactive Black 5. The parameters of ratio affecting the decolorization efficiency of Reactive Black 5 such as initial concentration of Fe2+, Fe3+ and H2O2 and initial pH value of dye solution were investigated. The results showed that the decolorization efficiency of Reactive Black 5 in Fenton oxidation was much faster than that of the Fenton-like oxidation in the initial stages and the decolorization efficiency was similar for both systems after 45min. For the two oxidation systems, the decolorization efficiency of Reactive Black 5 depends on [Dye]0, [Fe2+]0 or [Fe3+]0, [H2O2]0 and pH.

Academic research paper on topic "Degradation of the Reactive Black 5 by Fenton and Fenton-like system"

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Procedía Engineeri ng 15 (2011) 40835 - 4840

Procedía Engineering

www.elsevier.com/Iocate/procedia

Advanced in Control Engineeringand Information Science

Degradation of the Reactive Black 5 by Fenton and Fenton-

like system

Xuanmo Liu, Muqing Qiu, Chengcai Huanga*

College of Life Science, Shaoxing University, Shaoxing, 312000, P.R. China

Abstract

This study investigated Fenton and Fenton-like reactions to oxidize the commercial zao dye of Reactive Black 5. The parameters of ratio affecting the decolorization efficiency of Reactive Black 5 such as initial concentration of Fe2+, Fe3+ and H2O2 and initial pH value of dye solution were investigated. The results showed that the decolorization efficiency of Reactive Black 5 in Fenton oxidation was much faster than that of the Fenton-like oxidation in the initial stages and the decolorization efficiency was similar for both systems after 45 min. For the two oxidation systems, the decolorization efficiency of Reactive Black 5 depends on [Dye]0, [Fe2+]0 or [Fe3+]0, [H2O2]0 and pH.

© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of [CEIS 2011]

Key words: Decolorization; Reactive Black 5; Fenton and Fenton-like reaction

1. Introduction

The dyes used in the textile dyeing and printing industriesnot only can impart colour to water sources but also can causeenvironmental damage to living organisms by stopping the reoxygenation capacity of water and also blocking sunlight, thereby disturbing the natural growth activity of aquatic life. Azo dyes, which contain at least one azo group (-N=N-), which is attached to at least one aromatic moiety, are commonly used in textile coloration. These dyes are resistant to biodegradation under aerobic conditions. Discharge of azo dyes can cause aesthetic problems and their breakdown products are toxic to

* Corresponding author. Tel.: +86-575-88345001; fax: +86-575-88345001.

E-mail address: chengcai@usx.edu.cn.

1877-7058 © 2011 Published by Elsevier Ltd. doi:10.1016/j.proeng.2011.08.902

aquatic life [1]. Many different approaches have been proposed to remove dyes from aqueous solution such as physical adsorption, electrochemical oxidation, chemical oxidation, chemical coagulation/precipitation, and biological anaerobic/aerobic decomposition [2-6].

In recent years, advanced oxidation processes using ozone, photocatalytic process UV/TiO2, and Fenton's reagent (H2O2 and ferrous ion) have received considerable attention as effective pretreatment processes of less biodegradable wastewater [7, 8]. Among them, Fenton's process has been widely used because it is cost effective, easy to treat, reacts well with organic compounds and does not produce toxic compounds during oxidation [9]. The main drawback of this Fenton's reaction technique is represented by the cost of the reactants, i.e. H2O2 and Fe2+. For this reason, various methods have been introduced to use the lower cost Fe3+ salts rather than Fe2+ salts, which have resulted in photo-Fenton and electro-Fenton techniques [10]. While Fenton-like oxidation should also be effective, little work has been reported on the Fenton-like oxidation of dyes. Several studies have shown that the decomposition rate of decomposition of H2O2 and the oxidation rate of oxidation of organic solutes are much slower using Fe3+/H2O2 than Fe2+/H2O2 and the pH values are optimal at pH 3.0[11]. However, as the solution pH in many cases is neutral or alkaline, the necessity to acidify the reaction medium limits the applicability of the Fenton's process in wastewater treatment environmental technology. Moreover, despite numerous studies of the Fe3+/H2O2 system, the chemistry and kinetics of the oxidation of organic compounds by Fe3+/H2O2 have not been well elucidated [12].

In this paper, this study was conducted to understand the system of Fenton and Fenton-like to oxidize the commercial zao dye of Reactive Black 5. The ratio of parameters affecting the decolorization such as initial concentration of Fe2+, Fe3+, H2O2 and initial pH value of dye solution were investigated.

2. Materials and Methods

2.1. Mnterinls

The Reactive Black 5 was chosen as the model dye. The Reactive Black 5 was commercial samples and was used without further purification. Fig.1 depicts the chemical structure of Reactive Black 5. The pH of the solutions was adjusted using H2SO4 and NaOH solutions.

2.2. Experimental procedures

All tests experiments were conducted in a 500mL Erlenmeyer flask as a batch reactor. Each experiment was performed by the addition of ferrous ion or ferric ion and dilution with deionized water to 200mL. Batch experiments of the Reactive Black 5 decolorization were performed by adding H2O2 to the dye solution and then the pH was adjusted to the desired value by the addition of a few drops of either 0.1 mol/L H2SO4 or 0.1 mol/L NaOH. Following the pH adjustment, the Fe2+ ions or Fe3+ ion were quickly added to the dye solution. The flask was then placed in a thermostated water-bath shaker and agitation was provided at 150rpm. The samples were taken out from the conical flask periodically using a pipette and were analyzed immediately. Each experiment was replicated three times.

2.3. Analytical methods

The UV-vis spectra of Reactive Black 5 solution were recorded from 200 to 800nm using a UV/Vis spectrophotometer with a spectrometric quartz cell (UV752, China). The maximum absorbance wavelength of Reactive Black 5 was found at 553nm. In the whole reaction process, it was found that the measure of concentration of Reactive Black 5 is not interfered by the decolorization products. Therefore,

the concentration of Reactive Black 5 in reaction mixture at different reaction times was determined by measuring the absorption intensity of solution at 598nm and using a calibration curve. In order to decrease the experimental error, the sampling and measurement of the absorbance of reaction solutions were finished in 1 minute [10].

The decolorization efficiency of Reactive Black 5 was defined as follows:

Decolorization efficiency =1-C0/Ct *100% (1)

Where C0 is the initial concentration of Reactive Black 5, and Q is the concentration of Reactive Black 5 at reaction time t (minute).

3. Results and discussion

3.1. Fenton and Fenton-like systems

A comparison of the dye decolorization of Reactive Black 5 with Fe2+/ H2O2 and Fe7+/ H2O2 was investigated at 40mg/L[dye], 0.05mmol/L [Fe2+] or 0.05mmol/L [Fe7+], 2.0mmol/L [H2O2], pH3.5 and 70 °C. As seen form from Fig.2, it was showed that both Fenton and Fenton-like oxidations were effective in dye decolorization. The decolorization efficiency was 97% after 45min. However, the decolorization efficiency exhibited different reaction rates for the Fenton and Fenton-like oxidations. The decolorization efficiency in Fenton oxidation was much faster than that of the Fenton-like oxidation in the initial stages and the variation of decolorization efficiency was similar for both systems after 45min. It is known that the hydroperoxyl radical has lower oxidation capability than •OH [17]. Several investigations into regarding to the Fenton oxidation of organic compounds have shown that the initial mineralization rate of Fenton mineralization is faster with Fenton than with Fenton-like reagents, due to the immediate formation of hydroxyl radicals in the case of Fenton reagent [14].

Fig.1 Chemical structure of Reactive Black 5 Fig.2 The decolorization efficiency of dye by Fenton

and Fenton-like systems

3.2. Effect of pH

The effect of pH was studied by varying pH value in the solution from 2.5 to 6.0 with 0.05mmol/L of [Fe2+] or 0.05mmol/L of [Fe7+], 40mg/L of dye solution, 2.0mmol/L [H2O2], pH0=7.5, reaction time of 20minutes and 70 C . Fig. 7 shows that lower pH resulted in higher decolorization rates of dye decolorization. For the Fenton reaction, 92% of decolorization was achieved in 20minutes at a pH<7.5 and when the pH was further decreased, the similar variation of decolorization efficiency was observed similar. However, in the Fenton-like reaction, 75% of decolorization efficiency was obtained after

20minutes at pH<3.5. It is considered that more Fe(OH)+ is formed at low pH and the activity of Fe(OH)+ is higher than Fe2+ in Fenton oxidation. In contrast, ferrous ions are unstable at a pH above 4.0 and they easily form ferric ions, which have a tendency to produce ferric hydrogen complexes. Hydrogen peroxide is also unstable may decompose to give oxygen and water in basic solution and may decompose to give oxygen and water and lose its oxidation ability. Thus, hydrogen peroxide and ferrous ions have difficulty in establishing an effective redox system and their decolorization is also less effective [15].

3.3. Effect of H2O2 concentration

The effect of H2O2 was studied by varying the amount of H2O2 used for the experiment from 1.0mmol/L to 4.0mmol/L with 0.05mmol/L of [Fe2+] or 0.05mmol/L of [Fe3+], 40mg/L of dye solution, pH0=3.5, reaction time of 20minutes and 30°C. Fig.3 shows the relationship between decolorization of the dye at different initial H2O2 concentrations. As seen from Fig.4, it indicated that the decolorization of the dye increased with increasing H2O2 concentration. When the H2O2 concentration increased to 2mmol/L, in the Fenton reaction the decolorization efficiency of Fenton reaction could reach to 92% after 20minutes. H2O2 concentration above 2mmol/L would not induce significant change in decolorization efficiency. In Fenton-like reaction, 73% of decolorization efficiency could be achieved after 20minutes when the H2O2 concentration was 2mmol/L. The un-reacted H2O2 will act as a scavenger of •OH and produces a less potent perhydroxyl radical, resulting in less dye decolorization.

Fig.3 Effect of initial pH on decolorization of Fig.4 Effect of [H2O2]0 on decolorization of dye by Fenton and Fenton-like reaction dye by Fenton and Fenton-like reaction

3.4. Effect of the initial dye concentration

The effect of the initial dye concentration on Fenton processes and Fenton-like processes was investigated with pH0=3.5, 0.05mmol/L of [Fe2+] or 0.05mmol/L of [Fe3+], 2.0mmol/L of [H2O2], reaction time of 20minutes and 30 C. The influence of the initial dye concentration is shown in Fig.5. It was observed that higher the initial dye concentration, lower decreased the decolorization efficiency of Reactive Black 5 by Fenton oxidation and Fenton-like reaction. This means that with constant [H2O2]0 and [Fe2+]0/[Fe3+]0, more hydrogen peroxide was consumed because of a higher dye concentration.

3.5. Effect of Fr2+ and Fr3+ concentrations

A series of experiments were conducted with different [Fe2+] or [Fe3+] from 0.01mmol/L to 0.1mmol/L, pH0=3.5, 40mg/L of dye solution, 2.0mmol/L of [H2O2], reaction time of 20minutes and 30°C . The results obtained are presented in Fig.6. It was observed that the decolorization efficiency of the Reactive Black 5 by Fenton oxidation and Fenton-like reaction increased with increasing Fe2+ or Fe3+ concentrations. In the case of Fenton oxidation, the decolorization efficiency of the Reactive Black 5 was very small poor when with the Fe2+ concentration was < below 0.025 mmol/L. When the Fe2+ concentration was 0.05mmol/L, the decolorization efficiency of the Reactive Black 5 was 92%. For Fenton-like oxidation, when the Fe3+ concentration was 0.025mmol/L, the decolorization efficiency of the Reactive Black 5 was 38% at Fe3+ concentration 0.025mmol/L. By contrast, When the Fe3+ concentration was 0.05mmol/L, the decolorization efficiency of the Reactive Black 5 was increased to 73% with increasing of Fe3+ concentration to 0.05mmol/L.

Fig.5 Effect of [dye]0 on the decolorization of dye by Fig.6 Effect of [Fe2+] and [Fe3+] on the decolorization of Fenton oxidation and Fenton-like reaction dye by Fenton oxidation and Fenton-like reaction

4. Conclusions

Fenton and Fenton-like oxidation can effectively decolorize Reactive Black 5 in aqueous solution under neutral acid conditions. The decolorization efficiency in Fenton oxidation was much faster than that of the Fenton-like oxidation in the initial stages and the decolorization efficiency was similar for both systems after 45min. For the two oxidation systems, the decolorization efficiency of Reactive Black 5 depends on [Dye]0, [Fe2+]0 or [Fe3+]0, [H2O2]0 and pH.

Acknowledgements

The author gratefully acknowledges the financial support from the Innovation Program of College student in Shaoxing University.

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