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    Degradation of anthraquinone dyes by ozone

    LIU Jia-le(刘佳乐), LUO Han-jin(罗汉金), WEI Chao-hai(韦朝海)

    College of Environmental Science and Engineering, South China University of Technology,

    Guangzhou 510640, China

    Received 17 November 2006; accepted 25 May 2007

    Abstract: The decolorization of three kinds of anthraquinone dyes by ozone was investigated and the residues in the degradation solution were analyzed. The results indicate that the decolorizing effects are obvious with the decolorization efficiency of dyes all above 96% in 40 min. The pH value and TOC concentration decline while the conductivity increases with the lapse of reaction time. The complicated dye molecules are decomposed to simple compounds with SOH, Cl in the dye molecules transformed into 3?2? ? Cl, and nitrogen partially degrades into according to the bases of different groups. The organic acids are found in theSO , NO 4 3 degradation solutions and dyes with larger relative molecular mass are decomposed into substances with larger relative molecular mass.

    Key words: decolorization; anthraquinone dye; ozone; residue

    ?initiated by hydroxyl ions (OH)[13]. But few studies

    have been carried out on the comparative research on the 1 Introduction

    decolorization efficiency of different dyes by ozone and

    the residues of dye aqueous solutions. Therefore, the Wastewater derived from dye industry is

    objective of the present work is to compare the ozonation characterized by deep color, high chemical oxygen

    demand(COD) content and pH value varying from 2 to decolorization efficiency of different types of 12;which is very toxic and resistant to physicochemical anthraquinone dyes. Moreover, the variation of pH value, treatments and not easily biodegradable[1?6]. The color conductivity, TOC in the reaction process, and the of dye results from conjugated chains or rings that can residues in the degradation solutions are analyzed for absorb UV light of different wavelengths. The researching the ozone degradation of anthraquinone chromophores of dyes are usually composed of CC, =dyes.

    NN, CN, and aromatic and heterocyclic rings ==

    containing oxygen, nitrogen or sulfur[7?8]. Some 2 Experimental

    chemicals such as hypochlorite, ozone, and hydrogen

    peroxide, in the absence and in the presence of UV light 2.1 Materials

    and hydrogen peroxide with ferrous ions, have been used The chemical structures and properties of for pretreatment of dye-bearing wastewater[9?10]. anthraquinone dyes used were represented in Table 1[14].

    Ozone is very effective in decolorizing dye The types of dyes used involved direct, cationic and wastewater because it attacks conjugated double bonds reactive dyes, and the experimental dyes were all that are often associated with color[11?12]. Ozone reacts analytically pure.

    with aqueous compounds in two paths: a direct path

    corresponding to the action of molecular ozone, and an 2.2 Apparatus and experimental methods indirect path resulting from the decomposition of ozone The experimental set-up included an oxygen to radicals. Decomposition favored by basic pH is concentrator (Sim Oplus, China), a HF-3 model ozone 2

    Foundation item: Project(50278036) supported by the National Natural Science Foundation of China; Project(2006AA06Z378) supported by the National High-Tech Research and Development Program of China

    Corresponding author: LUO Han-jin; Tel: +86-20-87114142; Fax: +86-20-87114142; E-mail:

    LIU Jia-le, et al/Trans. Nonferrous Met. Soc. China 17(2007) 881 Table 1 Structures and properties of dyes


    molecular Name of dye Structure Type λ/nm max mass

    Reactive brilliant Reactive 637 580 blue X-BR

    Cationic blue Cationic 463 606 FGL

    Direct fast blue Direct 941 568 B2RL

    generator (Ozonetek Ltd, China) that was used to obtain decolorization efficiency was calculated by the equation:

    a maximum producing rate of ozone, 3 g/h, an ozonation η = ( A? A)/A× 100%(1) 0 1 0 chamber with a capacity of 800 mL and two gas

    where η is the decolorization efficiency of dye, Ais 0 absorption bottles. It was provided with a sample port at

    the absorbance of initial aqueous solution, and Ais the 1 various times, an ozone gas inlet at the bottom. Excess

    absorbance of sample after decolorizing for certain time. ozone was passed into two gas absorption bottles

    The O-I-Analytical TOC analyzer (1020A, USA) containing 2% KI solution.

    was used to measure TOC concentration by directly 500 mL of dye solutions at concentration of 300

    injecting the samples to characterize the mineralization mg/L were prepared and exposed to ozonation in the

    of dyes. The Bruker infrared spectrometric analyzer ozonation chamber. 5 mL of the solution was sampled at

    (Tensor 27, Germany) was used to analyze the variation 0, 1, 3, 5, 10, 15, 20, 25, 30 and 40 min, respectively.

    of dye molecules. Besides, the solutions after ozonation The pH value and conductivity were measured.

    were measured by Dionex ion chromatography For the preparation of GC-MS samples, the

    (ICS-2000, USA). degradation aqueous solutions were extracted three times

    The Shimadzu GC-MS spectrometer (QP2010, with 30 mL trichloromethane at pH value of 2 and 11

    Japan) was used to confirm the identity of the adjusted by HCl and NaOH, respectively. The extracted

    degradation products. The capillary column used was an phase was purged to 1 mL using pure nitrogen gas at

    HP-5 (cross linked 5% phenyl methyl siloxane, 30.0 m× 25 ?, and then adjusted to 5 mL by adding acetone for

    0.25 mm × 0.25 µm). 1 µL of the solution was GC-MS analysis.

    chromatographed under the following conditions:

    injector temperature was 280 ?, the initial column 2.3 Analytical methods

    temperature was held constant at 40 ? for 2 min, The samples were determined by testing absorbance

    ramped at 10 ?/min to 150 ? and held constant for at maximum wavelength(λ) of the dyes on Hitachi max

    2 min, then ramped further at 5 ?/min to 250 ? and UVvisible spectrophotometer (U-3210, Japan). The

    LIU Jia-le, et al/Trans. Nonferrous Met. Soc. China 17(2007) 882

    held constant for 2 min, at last ramped at 10 ?/min to decreases with increasing reaction time. The final pH

    value of reactive brilliant blue X-BR, direct fast blue 280 ? and held constant for 3 min.

    B2RL and cationic blue FGL are 3.64, 4.21 and 3.61, and

    ?pH are 1.86, 2.74 and 1.46, respectively. Besides, the 3 Results and discussion higher the pH value of the original solution is, the more

    steeply it declines. As shown in Fig.2, the downtrend of 3.1 Comparison of decolorization efficiency

    pH value is obvious when the decolorization rate Fig.1 shows the time variation of decolorization

    increases rapidly in 20 min, but it slows down with the efficiency of dyes. It can be seen from Fig.1 that the

    decrease in decolorization rate after 20 min, thus it can decolorization efficiencies of all dyes reach over 87.1%

    be considered that the trend of the pH change is in 20 min, indicating that ozone is very effective for + consistent with the decolorization efficiency, and that Hdecolorizing the anthraquinone dyes. After 20 min, the

    is released in the reaction and the dye molecules can be increase of decolorization rate slows down gradually,

    possibly decomposed to organic acid or inorganic acid in while the decolorization efficiencies of reactive brilliant

    the degrading process. blue X-BR, direct fast blue B2RL and cationic blue FGL

    are respectively 99.8%, 98.9% and 96.0% in 40 min,

    which means that the chroma of solution are almost

    wiped off. Fig.1 also indicates although the experimental

    dyes are all anthraquinone ones, their decolorization

    efficiencies are different. This relates to the chemical

    structure and relative molecular mass of dyes. The

    larger the relative molecular mass, the smaller the

    molar concentration, and the larger the decoloriza-

    tion rate. Reactive brilliant blue X-BR and cationic blue

    FGL both have one chromophore ( ), and the

    relative molecular mass of reactive brilliant blue X-BR

    (637) is larger than that of cationic blue FGL (463), so

    Fig.1 Decolorization efficiency of samples vs reaction time the decolorization rate of reactive brilliant blue X-BR is

    higher than that of cationic blue FGL. Although direct

    fast blue B2RL has two chromophores( ),

    because is easier to be degraded than

    and its relative molecular mass(941) is

    about twice as large as that of cationic blue FGL, the

    decolorization rate of direct fast blue B2RL is also higher

    than that of cationic blue FGL. According to the

    dynamics of chemical reaction, the decolorization rate is

    high in 0?20 min, which belongs to the quick reaction

    step, but it decreases in 21?40 min, causing decrease of

    Fig.2 pH value of samples vs reaction time decolorization rate with the increase in reaction time.

    3.2 Analysis of pH value and conductivity Fig.3 shows the time variation of conductivity of

    In order to examine how the solution changes with dyes. It can be seen that the conductivity of dyes its properties, its pH value and conductivity were increases with increasing reaction time and climbs up measured. more quickly in the first 20 min than after 20 min, and

    The time variation of pH value of samples is shown the change trend is consistent with the decolorization in Fig.2, which indicates that the pH value of the samples efficiency and pH value. After reaction, the increments of

    LIU Jia-le, et al/Trans. Nonferrous Met. Soc. China 17(2007) 883

    evaporates from the solution. The downtrend of pH value

    is more obvious as a whole when the pH value of

    original solution is larger, showing the possibility of the

    increase in the concentration of carbonic acid.

    3.4 Variation of dye molecules

    Fig.5 shows the infrared spectra of fore-and-aft

    degradation of three anthraquinone dyes. As shown in

    Fig.5, the fore-and-aft degradation variation of dye

    molecules is obvious by comparing the two curves of

    fore-and-aft degradation[16]. In the initial aqueous

    solutions, the strong absorption peak of C=O that is the

    ?1chromophore of anthraquinone dye is near 1 675 cm ?1and the absorption peak of C?O exists near 1 280 cm.

    Because of the decomposition from cyclic compound to

    Fig.3 Conductivity of samples vs reaction time acyclic compound, the IR absorption peak of carbonyl is

    ?1in the region of 1 650?1 700 cm. Similarly, all three

    conductivity of reactive brilliant blue X-BR, cationic anthraquinone dyes contain the complex aromatic

    blue FGL and direct fast blue B2RL are 249, 380 and 72 structure, thus the bands of aromatic compound in the

    µS/cm, respectively, which means that ions in the five regions are seen in Fig.5, but after reaction the

    solution augment with increasing reaction time and the characteristic absorption peaks are weakened evidently

    dye molecules have been decomposed to ions and other or disappear, indicating that complicated compounds of

    benzene ring are decomposed into simple ones. Besides, substances.

    the peak of free ?OH in the region of 3 400?3 664 ?1 cmis lower than that after degradation, probably due to 3.3 Analysis of TOC

    the descent of pH value; and the characteristic absorption As shown in Fig.4, TOC concentration decreases ?1 peaks of COin the region of 2 360?2 300 cmin the air with increasing reaction time, reaching over 24.9% in 40 2

    are generated in the infrared spectra of degradation min and the variation trend is consistent with that of the

    solutions in Fig.5. So it can be concluded that decolorization efficiency and pH value. By comparing

    complicated molecules of anthraquinone dyes are Fig.1 with Fig.4, it shows that the variation of TOC is

    decomposed to simple organic compounds after reaction. rather large when the change of decolorization efficiency

    is less, which indicates that besides chromophores, other

    3.5 Analysis of inorganic residues parts of dye molecules also participate in the reaction,

    It is considered that the degraded aqueous solutions generating COor volatile organic compounds[13,15] 2 probably contain inorganic anions of N, S and Cl, that cause the decrease in the TOC concentration. Part

    because the structural formulas of dyes contain N, S and of COproduced changes into carbonic acid and the rest 2 Cl. As shown in Table 2, by means of comparing the

    theoretical concentration of N that is calculated by using

    chemical measuring method with the practical ? ? concentration of NO , NO that measured by using 2 3

    ion chromatography, we can observe that the practical

    concentration is much less than the theoretical one,

    indicating that N in the dye molecule is not decomposed ? ? to NO , NO completely, and some other compounds 2 3

    containing N are produced. the practical concentrations ?in degradation solutions of all dyes are equal of NO 2 ? to zero, indicating that NO is oxidized by ozone 2 ? ? to NO . Table 2 shows that NO only exists in reactive 3 3

    brilliant blue X-BR and cationic blue FGL solutions after

    degradation, probably because the compounds containing

    N=N or Ar?NHare oxidized by ozone to Nor Ar? 2 2

    NO, whose oxidative products cannot be transformed 2Fig.4 TOC concentration of samples vs reaction time

    LIU Jia-le, et al/Trans. Nonferrous Met. Soc. China 17(2007) 884

    Table 2 Comparison of theoretical concentrations of N, S and Cl elements with practical ones

    ?1?1Theoretical concentration/(mmol?L) Practical concentration/(mmol?L) Dye ? ? 2? ? NO NOSOCl N S Cl 234

     Reactive brilliant blue X-BR 2.826 0.942 0.942 0 0.009 0.940 0.940

    Cationic blue FGL 1.944 0.650 0 0 0.041 0.554 0

    Direct fast blue B2RL 2.232 1.275 0 0 0 1.450 0

    ? to NO . However,is oxidized easily to 3

    and because of space resistance of R, 1

    Rand Ar,disengages from benzene ring and 2

    ? then is partially oxidized to NO . After reaction, 3

    ?SOH and ?Cl in the dye molecules are transformed 32? ?into SO and Cl, respectively. It is deduced that there 4

    is organic acid in the degradation solution, because the + Hcontent in the degraded aqueous solution is much +higher than inorganic acid produced by combining H ? ? 2? ? with NO , NO , SO and Cl . 2 3 4

    3.6 Analysis of organic residues

    The purpose of GCMS analysis is to identify

    some intermediates produced from the degradation

    processes and organic residues in the degradation

    solutions. The GCMS chromatograms of the blank

    and the samples are displayed in Fig.6, and the organic

    residues are listed in Table 3. Compared the

    chromatogram of samples with that of blank, the

    degradation solutions of three anthraquinone dyes all

    contain organic residues No.1, 2, 3 and 4. In addition,

    the degradation solution of reactive brilliant blue X-BR

    contains organic residues No.5 and 6, direct fast blue

    B2RL contains organic residue No.7, and cationic blue

    FGL also contains No.6 and 8, and naphthalin ring. In

    addition, it is notable that organic residue No.2, 5, 7 are

    organic acids, so it validates adequately, where there are

    organic acids in the degradation solution. Through

    analysis, dyes with larger relative molecular mass are

    decomposed into other substances with comparatively

    larger molecular mass.

    4 Conclusions

    1) Ozone treatment is very effective in

    decolorization of anthraquinone dyes, and the

    decolorization efficiency reaches over 87.1% in 20 min.

    Fig.5 Infrared spectra of fore-and-aft degradation of samples: Some acids are produced, causing pH value to reduce.

    (a) Reactive brilliant blue X-BR; (b) Cationic blue FGL; (c) The final pH values of reactive brilliant blue X-BR,

    Direct fast blue B2RL direct fast blue B2RL and cationic blue FGL are 3.64,

    LIU Jia-le, et al/Trans. Nonferrous Met. Soc. China 17(2007) 885

    Fig.6 GCMS spectra of three kinds of blank and anthraquinone dyes: (a) Blank; (b) Reactive brilliant blue X-BR; (c) Cationic blue FGL; (d) Direct fast blue B2RL

    Table 3 Organic residues determined by GSMS

    No. Molecular formula Relative molecular mass No. Molecular formula Relative molecular mass

    1 204 5 278

    2 278 6 274

    3 85 7 278

    4 83 8 128

LIU Jia-le, et al/Trans. Nonferrous Met. Soc. China 17(2007) 886

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