Scholarly article on topic 'Decolorization of Azo Dye C.I. Direct Black 38 by Photocatalytic Method Using TiO2 and Optimizing of Process'

Decolorization of Azo Dye C.I. Direct Black 38 by Photocatalytic Method Using TiO2 and Optimizing of Process Academic research paper on "Chemical sciences"

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Abstract of research paper on Chemical sciences, author of scientific article — Kambiz Seyyedi, Mohammad Ali Farbodnia Jahromi

Abstract Dye wastewaters are considered as major pollutants to surface waters. The dye C.I. Direct Black 38 is one of the most important azo dyes used in dying industry and contaminated waters containing this harmful material are produced in large volumes. The purpose of this study is investigation removing of C.I. Direct Black 38 by photocatalytic method as one of advanced oxidation processes (AOPs) using TiO2 as photocatalyst and determination of optimum values of effective parameters against color removing efficiency. Spectrophotometric results showed that photocatalytic process has decolorization ability of wastewaters containing C.I. Direct Black 38 in different dye concentrations. The operating conditions for 90% decolorization of C.I. Direct Black 38 were obtained for initial dye concentration of 50ppm, hydrogen peroxide dosage of 26.56mM, TiO2 dosage of 0.75g/l and pH of 5. TiO2 can’t be used in basic solution. The proper addition of hydrogen peroxide improved the decolorization, while the excess amount of hydrogen peroxide could quench the formation of hydroxyl radicals.

Academic research paper on topic "Decolorization of Azo Dye C.I. Direct Black 38 by Photocatalytic Method Using TiO2 and Optimizing of Process"

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ScienceDirect Procedia

APCBEE

APCBEE Procedia 10 (2014) 115 - 119

www.elsevier.com/locate/procedia

ICESD 2014: 19-21 February 2014, Singapore

Decolorization of azo dye C.I. Direct Black 38 by Photocatalytic method using TiO2 and optimizing of process

Kambiz Seyyedi a*, Mohammad Ali Farbodnia Jahromi b

a Department of Chemistry, Faculty of Science, Islamic Azad University, Tabriz Branch, Tabriz 5157944533, Iran b Medicinal Plants Processing Research Center, Shiraz University of Medical Sciences, Shiraz, Iran

Abstract

Dye wastewaters are considered as major pollutants to surface waters. The dye C.I. Direct Black 38 is one of the most important azo dyes used in dying industry and contaminated waters containing this harmful material are produced in large volumes. The purpose of this study is investigation removing of C.I. Direct Black 38 by photocatalytic method as one of advanced oxidation processes (AOPs) using TiO2 as photocatalyst and determination of optimum values of effective parameters against color removing efficiency. Spectrophotometric results showed that photocatalytic process has decolorization ability of wastewaters containing C.I. Direct Black 38 in different dye concentrations. The operating conditions for 90% decolorization of C.I. Direct Black 38 were obtained for initial dye concentration of 50 ppm, hydrogen peroxide dosage of 26.56 mM, TiO2 dosage of 0.75 g/l and pH of 5. TiO2 can't be used in basic solution. The proper addition of hydrogen peroxide improved the decolorization, while the excess amount of hydrogen peroxide could quench the formation of hydroxyl radicals.

© 2014TheAuthors. PublishedbyElsevierB.V. This isanopenaccessarticleunder theCCBY-NC-NDlicense (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society Keywords: Decolorization, Direct Black 38, Photocatalytic, TiO2, Optimization

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1. Introduction

Dyes widely used in textiles, paper, rubber and plastics industries often create severe environmental pollutions in the form of colored wastewater discharged into environmental water bodies [1]. Over 700,000 tons of approximately 10,000 types of dyes and pigments are produced annually worldwide. From this amount, about 20% are discharged as industrial effluents during the textile dyeing and finishing processes

* Corresponding author. Tel.: +984113363669; fax: +984113376064. E-mail address: ka_seyyedi@yahoo.com

2212-6708 © 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society doi: 10.1016/j.apcbee.2014.10.027

without previous treatment [2, 3]. The colour and toxicity of dyes influence the quality of life by causing health problems besides influencing the efficiency of some water treatment techniques [4, 5].

Considering the volume and chemical composition of the effluent discharge, the textile dyeing and finishing industry is one of the major polluters among industrial sectors. Therefore, establishing removal technologies for dyes is an urgent problem. The commonly used methods for the treatment of wastewater such as: biological oxidation, physical-chemical, ozonation, chemical precipitation and electrocoagulation have been reported in recent years [6]. However, these processes are quite ineffective in colour removal of wastewater because azo dyes aren't biodegradable due to their aromatic structure, and physical-chemical treatments and other similar methods provide only a phase transfer of dyes and produce large quantities of sludge. Chemical oxidation aims at the mineralization of contaminants to carbon dioxide, water and inorganic components or, at least, their transformation into biodegradable or harmless products. During the last two decades, advanced oxidation process (AOPs) has been applied for the removal of organic pollutants [7, 8].

In the past decade, considerable attention has focused on using nanocrystalline TiO2 as a photocatalyst for the degradation of organic pollutants. Several papers have discussed the fundamentals of the photocatalytic degradation process. The photocatalyst, titanium dioxide, is a wide band gap (3.2 eV) semiconductor, corresponding to radiation in the near-UV range. Upon the absorption of this UV energy, TiO2 particles will form a paired electron (e-) and hole (h+), in the conduction band and valence band. The positive hole is apparently able to oxidize a water molecule to hydroxyl radical. The hydroxyl radical, in turn, is a powerful oxidant. Moreover, the possible use of vis-light has recently drawn attention [9]. Some authors demonstrated how the photobleaching dyes could be achieved by sunlight irradiation using TiO2 as photocatalyst [10]. In the present study the optimum conditions of experimental parameters for the removal of C.I. Direct Black 38 (DB38) have been determined which can be extensively used in textile, foodstuff and pharmaceutical industries.

2. Experimental

2.1. Materials

Azo dye C.I. Direct Black 38 was obtained from Sigma-Aldrich Chemical Co., and used without further purification. The structure of C.I. Direct Black 38 is shown in Fig. 1. Hydrogen peroxide solution (30% w/w), NaOH and H2SO4 were provided by Merck. Titanium dioxide (Degussa P25) with average primary particle size around 30 nm and purity above 97% was utilized as a photocatalyst.

Fig. 1. The structure of DB38. 2.2. Procedure

Concentration of dye solution was selected 50 ppm. The pH values of solutions were adjusted at desired level using dilute NaOH and H2SO4 and measured by using Metrohm 744 digital pH meter. The radiation

source was a low pressure mercury UV lamp (15W, UV-C, Xmax= 254 nm, manufactured by Philips, Holland), which was placed above a batch photoreactor. In each experiment, a known amount of H2O2 and TiO2 were added to 200 ml of the solution and a magnetic stirrer was used in order to achieve a homogeneous mixture. Sampling of solution was done at certain time intervals for spectrophotometry analysis. The concentration of dye in solution at different times was obtained by measuring absorbance of solution and computing it from calibration curve. UV-Vis spectrophotometer (Cam Spec M 550) was employed for absorbance measurements. The effect of each parameter was studied by fixing the values of other parameters.

2.3. Chemical analyses

Photodegradation of The DB38 was monitored by spectrophotometer in the visible region of electromagnetic spectrum (1=200-800 nm). Maximum wavelength of dye is 520 nm that is used to monitor the decolorization of the dye. The equation used to calculate the colour removal efficiency in the treatment experiments is as follow:

R %=( I-C/C0) *100 (1)

In this equation C0 and C are the initial and present concentrations of the dye in solution (ppm), respectively.

3. Results and discussion

3.1. Effect of amount of TiO2 on decolorization process

Concentration of TiO2 as a photocatalyst has an important role in the efficiency of the photocatalytic process. The effect of different doses of catalyst from 0.15 to 1 g/l was tested. As shown in Fig. 2, with increasing catalyst concentration to 0.75 g/l reaction rate increases because with increasing amount of catalyst more dye molecules are adsorbed to the catalyst surface and dye concentration in the area of irradiation increases. Increasing of catalyst concentration up to 0.75 g/l is caused reaction rate decreases. In high concentration of catalyst, TiO2 particles form a dense mass and so the active sites of catalyst surface is reduced. Also the photons maybe in collision with catalyst particles were scattered or reflected and couldn't penetrate into the solution. Therefore amount of 0.75 g/l TiO2 was selected as optimum amount of photocatalyst in other experiments [11].

Fig. 2. Effect of T1O2 amount on photodegradation efficiency of DB38, [DB38] = 50 ppm, [H2O2] = 16.6 mM, pH= 7

3.2. Effect of pH

The results showed that the pH of the solution to achieve maximum removal is very effective, so that changes in pH of solution have a significant impact on the decolorization process. In this work, to investigation the effect of pH on decolorization process, pH of solution was evaluated from 1 to 11 using NaOH and H2SO4 0.1N. According to Fig. 3 the highest efficiency is observed at pH = 5. The isoelectric point of TiO2 is 6.6, so in pH lower than the pH of the isoelectric point, TiO2 surface will be positively charged. Since the dye molecules due to having the sulfonic groups (SO3-) are negatively charged, the electrostatic interactions between the catalyst surface and color may occur. The electrostatic interaction leads to greater absorption of dye on TiO2 surface at acidic pH and increased decolorization efficiency. At alkaline pH, TiO2 surface due to adsorption of OH- will be negatively charged, therefore, the electrostatic repulsion between the dye and the catalyst occurs. Due to repulsion, less dye molecules can be absorbed on the catalyst and decolorization efficiency is reduced [12].

s 40 A * -*-pH=i

<3 30 / yS -B-pH-3

20 r^^ jr^ —pH=5

10 ITf^ -w-pH=7

if —w— pH = 10

20 40 60 SO 100 120 140

Time(min)

Fig. 3. Effect of pH on photodegradation efficiency of DB38, [DB38] = 50 ppm, [H2O2] = 16.6 mM, [TiO2] = 0.75 g/l 3.3. Effect of initial H2O2 concentrations

As shown in Fig. 4 the results indicated that degradation of dye increases with increasing of H2O2 concentration. This can be explained by the effect of the additionally produced hydroxyl radicals. When the H2O2 concentration increased to 26.56 mM, decolorization after 2h of irradiation could be achieved 90.54%. In higher concentrations than 26.56 mM reduction in decolorization efficiency is observed. This indicates that the excess amount of H2O2 is decomposed without promoting further degradation or maybe due to recombination of hydroxyl radicals and also reaction of hydroxyl radicals with H2O2, the concentration of Off and so decolorization efficiency is decreased. Further experiments were carried out using 26.56 mM H2O2 as optimum value. Selecting the appropriate concentration of H2O2 is commercially affordable [12].

0 £ 60 50

a O 40 30 20 10 [H202]=6.65mM -»-[H202]=13.3mM -^[H2021=16.6mM —[H202|=2G.56mM -*-[H202]=33.23mM

20 40 60 Time(r SO nin) 100 120 140

Fig. 4. Effect of H2O2 concentration on photodegradation efficiency of DB38, [DB38] = 50 ppm, pH= 5, [TiO2] = 0.75 g/l

4. Conclusions

The results presented in this paper indicated that photocatalytic oxidation process is an effective method for decolorization of C.I. Direct Black 38 in aqueous solution. TiÜ2 and UV light had a negligible effect when they were used lonely. The results indicated that decolorization of DB38 was obviously affected by the initial concentration of the dye, concentration of H2O2, amount of TiÜ2 and value of pH. The optimum condition for the decolorization of DB38 in photocatalytic process were observed at pH=5, TiÜ2 concentration of 0.75 g/l and H2O2 concentration of 26.56 mM with dye concentration of 50 ppm. Under these conditions, decolorization efficiency after 2h UV irradiation was obtained 90%. TiÜ2 can't be used in basic solution. The proper addition of hydrogen peroxide could improve the photodegradation rate, but in its high concentration decolorization efficiency decreases.

Acknowledgements

The authors are very thankful to the Islamic Azad University-Shiraz branch for providing laboratory facilities for conducting this project.

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