KINETIC STUDY OF ACID BLUE 1 DISCOLORATION WITH PERSULFATE KINETIC STUDY OF ACID BLUE 1 DISCOLORATION

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  • Journal of Chemical Technology and Metallurgy, 52, 5, 2017

    812

    KINETIC STUDY OF ACID BLUE 1 DISCOLORATION WITH PERSULFATE

    Zeinab Ali Ayoub, Ogarite Ali Yazbeck, Mouhiaddine Mohamed El Jamal

    ABSTRACT

    The discoloration of the food colorant Acid Blue 1 (AB1) by persulfate is mainly investigated by UV-VIS spectroscopy. The rate of discoloration is proportional to increase of persulfate and Fe (II) concentration, as well as temperature, whereas it decreases slightly with increase of food colorant and chloride ion concentration. The blue color disappearance is first order with respect to the food colorant and persulfate. The thermodynamic parameters of discoloration of AB1 (Ea, ∆H

    #, ∆S#, ∆G#) in presence and absence of Fe(II) are calculated. Discoloration of AB1 can be accomplished in both acidic and basic medium, with formation of one or more intermediate(s) depending on the [dye]/[persulfate] ratio and the reaction mixture pH. However, even a 100-fold excess of persulfate does not result in AB1 mineralization. The mechanism(s) of AB1 discoloration based on UV-VIS spectra and comparison to other triphenylmethane dyes degradation patterns are advanced.

    Keywords: Acid Blue 1, persulfate, discoloration, advanced oxidation, kinetic.

    Received 05 February 2017 Accepted 28 April 2017

    Journal of Chemical Technology and Metallurgy, 52, 5, 2017, 812-824

    Inorganic and Organometallic Coordination Chemistry Laboratory LCIO Faculty of Sciences (I), Lebanese University Rafic Hariri Campus El Hadath, Lebanon E-mail: mjamal@ul.edu.lb

    INTRODUCTION

    Bread, margarine, juice, candies are just some of the food products which can lead to numerous problems for human health, including cancer and weakens in the im- mune system, because these foods are hiding a number of harmful organic (colorants) and inorganic (bromates, sulphite, and persulfate) compounds. Nowadays, pre- servatives, which are actually designed to keep food edible for a longer time, are in a high concentration not only in various exotic foods, but in foods we consume daily, too. A number of studies have focused on the use of additives and their influence on humans and on the environment [1 - 3].

    Acid Blue 1 (AB1), also called Sulfan Blue 5 or E131 VF, is a synthetic triphenylmethane dye (Fig. 1). It is structurally very similar to the food colorant Patent Blue V (E131 V, or PBV), Brillian Blue FCF (E133), Malachite Green (MG), and Crystal Violet (CV) to mention a few (Fig. 1). All these dyes have one or more

    alkylamine which can stabilize the triphenylmethyl cation by electron donation through resonance becom- ing an imine. Bromothymol Blue (BTB) belongs also to the same dye group but it has fairly different functional groups, two bromines on the aryl rings and an oxide anion instead of an amine stabilizing the triphenylmethyl cation (Fig. 1).

    Food dyes are one of the most widely used and dangerous additives. Triphenylmethane dyes find large applications in food industry (beverages, jelly sweets, candies, ice-cream, etc.). For example, there is a great concern about the thyroid peroxidase-catalyzed oxida- tion of the triphenylmethane dyes because the reactions might form various N-dealkylated primary and second- ary aromatic amines, whose structures are similar to those of aromatic amine carcinogens [4]. The European Union placed regulations on labeling food dyes to inform consumers of the health risks.

    Many dyes are environmentally persistent and have strong absorption bands in the visible light region; and

  • Zeinab Ali Ayoub, Ogarite Ali Yazbeck, Mouhiaddine Mohamed El Jamal

    813

    when released into water bodies generally reduce light transmission thereby affecting aquatic biota. An envi- ronmental regulation applied in most countries requires discoloring industrial wastewater prior to its discharge. The problem to choose a suitable treatment in this respect is old and not yet solved. Furthermore, it is important to note that color removal is not attributed to the com- plete mineralization of the organic dye as it may simply involve transformation of the chromophore groups into non-chromophore ones. A number of techniques of dyed wastewater purification based on biodegradation [5 - 7], and photocatalytic degradation [9 - 11] are investigated. Other purification strategies include electrochemical treatment [12 - 16], adsorption [17], and advanced oxidation [18 - 21]. The latter processes, which involve in situ chemical oxidation (ISCO) generating powerful oxidants, have emerged as an important and cheaper class of technologies for removal of a wide range of organic contaminants in wastewater, and for remediation of organic contaminants in polluted soil and ground- water [22, 23]. These oxidation methods use oxidants like K2S2O8 [24 - 27], KBrO3 [28], KIO4 [29], Fenton’s reagent [30, 31], photo Fenton [32, 33], H2O2 [34] and ozone, which is a strong non-selective oxidizer [35, 36]. Potassium persulfate, K2S2O8 (KPS, E923) is one of the strongest oxidants used in an aqueous solution and has a higher reduction potential (Eo of S2O8

    2- / SO4 2- = 2.01 V)

    than that of H2O2 (E o of H2O2 / H2O = 1.76 V) [37]. It

    offers some advantages over other oxidants as a solid chemical at ambient temperature with ease of storage and transport, high stability, high aqueous solubility and a low cost [25]. It has great capability for degrad- ing numerous organic contaminants through powerful free radical oxidants as SO4

    -* and OH* which are gener- ated in the persulfate system [38]. To enhance further the oxidation strength KPS may be activated in order to produce sulfate radicals (SO4

    -*) of a higher standard reduction potential (Eo = 2.6 V) capable of acting as a much stronger oxidant towards organic contaminants [39]. Persulfate activation can be accomplished by heat

    [40, 41], UV irradiation [42] and reactions with transition metals (Eq. (2)) [43, 44]. These activation mechanisms are well described.

    2 * 2 8 4( , , ) 2S O heat UV OH SO

    − − −+ → (1)

    2 * ( 1) 2 8 42 2 2

    n nS O M SO M− + − + ++ → + (2)

    2 2 * * 2 8 2 4 4 22 2 3 4S O H O OH SO SO O H

    − − − − − ++ + → + + +

    (3) Strong alkaline pH has also been used [22, 45] to acti-

    vate KPS (Eq. (3)). The sulfate radicals obtained are very reactive in aqueous solution, as they can initiate a cascade of reactions [45] leading to the formation of other oxidants

    N

    HO

    -O3S

    N

    -O3S

    Patent BlueV

    N

    N

    N

    N

    N

    Crystal VioleteMalanchite Green

    N

    -O3S

    N

    -O3S

    Acid Blue 1

    O

    Bromothymol Blue

    N

    NBrilliant Blue FCF

    -O3S

    SO3-

    SO3-

    Br

    O-Br

    -O3S

    Fig. 1. Structurally similar triphenylmethylene dyes with either an amine or oxide group stabilizing the triphenylmethyl cation by resonance.

  • Journal of Chemical Technology and Metallurgy, 52, 5, 2017

    814

    (H2O2) and other radicals like hydroxyl radical (E o =2.7 V)

    and hydrogen peroxide, as shown in Eqs. (4 - 6): * *

    4 2 4 * * 2

    4 4 *2

    SO H O HO HSO SO OH HO SO

    HO HOOH

    − −

    − − −

    + → +

    + → +

    (4) (5) (6)

    The addition of persulfate to colored foods causes alteration of the food color as well as undesirable reac- tions with time. The purpose of this work is to investigate the parameters that influence Acid Blue 1 discoloration by K2S2O8. The parameters studied refer to the concen- tration of the food colorant and the oxidant, the solution pH, the presence of Fe (II), the matrix effect, and the temperature. The UV-VIS absorption spectra obtained and the pathway of AB1 discoloration will be compared with those of some other triphenylmethane dyes (Fig. 1).

    EXPERIMENTAL

    Materials and analytical procedures The food colorant Acid Blue 1 (AB1) was used as

    purchased from Sigma Aldrish (C27H31N2O6S2Na, purity of 50 %, molecular mass of 565.67 g). Na2SO4 and NaCl were the main inorganic salts in the food colorant as confirmed by an ionic chromatography analysis. The other chemical reagents used were of analytical grade. Dilute solutions of AB1 were prepared from an initial solution (40 mg/L) aiming to draw a calibration curve. Solutions of 1 M KCl were prepared to study the effect of the ionic force on the discoloration rate constant. A solution of 10-2 M Fe (II) in 10-2 M H2SO4 was prepared to study iron catalytic effect on AB1 discoloration rate.

    The kinetic study of AB1 discoloration by KPS was carried out on a double beam spectrophotometer, Specord 200 (Analytical Jena). The relation found be- tween the absorbance A640 and the mass concentration of AB1 was A640 = 0.07x [AB1] (mg/L) with R

    2 = 0.999. HPLC analysis was performed using a RP-C18

    stationary phase and a mobile phase composed of 50 % methanol and 50 % H2O (or 25 mM aqueous (NH4)2SO4, the flow rate was 1 ml/min, while the injection volume was 20.0 µL [9].

    Method of discoloration The kinetic study aiming to determine the reaction

    order with