Synthesis of porous adsorbent using microwave assisted combustion method and dye removal

Journal of Alloys and Compounds 602 (2014) 210–220

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Synthesis of porous adsorbent using microwave assisted combustion method and dye removal Niyaz Mohammad Mahmoodi ⇑, Omeleila Masrouri, Aimr Masoud Arabi Department of Environmental Research, Institute for Color Science and Technology, Tehran, Iran

a r t i c l e

i n f o

Article history: Received 16 November 2013 Received in revised form 20 February 2014 Accepted 25 February 2014 Available online 13 March 2014 Keywords: Nanostructured materials Chemical synthesis Scanning electron microscopy, SEM X-ray diffraction

a b s t r a c t Zinc aluminum hydroxide (ZAH) as a porous adsorbent was synthesized using microwave assisted combustion method and its dye removal ability from single and binary systems was studied. The ZAH characteristics were investigated using XRD, FTIR, and SEM. Acid Blue 92(AB92), Acid Red 14 (AR14), and Direct Red 23 (DR23) were used. The effect of ZAH dosage and initial dye concentration on dye removal was investigated. Adsorption isotherm and kinetic was evaluated. The capacity of ZAH to remove AB92, AR14, and DR23 was 95 mg/g, 84 mg/g and 75 mg/g, respectively. Dye removal fitted with the Langmuir model and pseudo-second order kinetics. Ó 2014 Elsevier B.V. All rights reserved.

1. Introduction Dyes are released into wastewater from several industries such as textile, paper and plastic. Textile industry uses dyes for dyeing of goods. However, the first known use of a dye was much later, being nearly 4000 years ago, when indigo was found in the wrappings of mummies in Egyptian tombs. Till the late nineteenth century, all the dyes were more or less natural with main sources like plants, insects and mollusks, and were generally prepared on small scale. It was only after 1856 that with Perkin’s historic discovery of the first synthetic dye, mauveine, that dyes were synthesized on a large scale. About 15% of the total world dyes production is lost during textile dyeing which is released in textile effluents. Several methods were used to remove dyes from wastewater. Adsorption process as one of the effective treatment methods is used to remove dyes from wastewater. Several adsorbents are synthesized and used [1–11]. The synthesis of adsorbents by conventional methods is more complex and high cost. Thus, the synthesis of materials by a low cost and simple method is an important task. Synthesis and modification of materials using microwave radiation has attracted considerable attention as a green technology. Microwave radiation has both electrical and magnetic properties. The radiation of material by microwave results in vibration of molecules by induced or permanent dipoles. The quantity of microwave energy absorbed by the materials determines the intensity ⇑ Corresponding author. Tel.: +98 021 22969771; fax: +98 021 22947537. E-mail addresses: [email protected], [email protected], nm_mahmoodi@ yahoo.com (N.M. Mahmoodi). http://dx.doi.org/10.1016/j.jallcom.2014.02.155 0925-8388/Ó 2014 Elsevier B.V. All rights reserved.

of vibration. The size, shape and polarizability of the molecules, as well as, extent of intermolecular bonding of the materials are main factors on the intensity of vibration [12]. A literature review showed that anionic dye removal ability of zinc aluminum hydroxide (ZAH) as a porous adsorbent from binary (bin.) system was not studied in details. In this paper, ZAH was synthesized using microwave assisted combustion method and characterized. The dye adsorption capacity of ZAH from single (sin.) and binary (bin.) systems was studied. Acid Blue 92(AB92), Acid Red 14 (AR14), and Direct Red 23 (DR23) were used as anionic dyes. The isotherm of dye removal and kinetics were investigated. 2. Experimental 2.1. Materials Acid Blue 92(AB92), Acid Red 14 (AR14), and Direct Red 23 (DR23) were achieved from Ciba and applied. Fig. 1 shows the structure of dyes. The other materials were obtained from Merck. 2.2. Synthesis of ZAH Microwave assisted combustion synthesis method was used to synthesis of porous adsorbent (ZAH). Microwave assisted combustion synthesis of oxide materials was introduced by Patil et al. [13] which is well-known as propellant chemistry. In this method, oxidizer to fuel ratio (W) is calculated as an effective parameter. The P oxidizer to fuel ration (O/F) is calculated by dividing the ratio of (coefficient of P metal nitrate elements)  (valence) to  (coefficient of fuel elements)  (valence). Nitrogen in combustion is ineffective and role of this specie of compound on combustion reaction is negligible so the valence number of N is equal to zero. In this study, urea as a suitable fuel was selected. Stoichiometric reaction of metal nitrates and urea fuel is shown as follows:

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N N

N H

OH

SO3Na

Absorbance

NaO3S

NaO3S

OH NaO3S

N N

250

325

SO3Na

OH

475

550

625

700

OH N N

NHCOCH3

SO3Na

Absorbance

O N C N H H

Fig. 1. The chemical structure of dyes.

ZnðNO3 Þ2 þ 2AlðNO3 Þ3 þ WCH4 N2 O ! ZnAl2 O4 þ WCO2 þ 2WH2 O þ 1:6WN2

ð1Þ

The W value which is determined by O/F ratio of propellant chemistry was equal to 6.67. The combustion synthesis of aluminate structure has different steps. In first step, mix solution of 0.26 M zinc nitrate and 0.52 M aluminum nitrate was prepared. Second step was addition of ammonium chloride (0.18 g) to the metal nitrate solution. The main role of NH4Cl is enhancement of exhaust gases and improvement of sponge-like structure of products. Next step was addition of urea with respect to the calculated O/F ratio (0.35 mol, 2.11 g). Fourth step before combustion reaction was the conversion of solution to the viscose gel. The formation of well distribution of metal in an organic structure is the main goal of gelation. For this purpose, solution was gradually heated at 70 °C until the gelation process was completed. The gel complex of metal nitrates and urea fuel was transferred to the microwave oven and combustion process was quickly happened less than 3 min with the power of 900 W. The intense ignition under microwave irradiation leads to straight formation of porous structure of zinc aluminum hydroxide.

250

325

400

475

550

625

Wavelength (nm)

Absorbance

N N NaO3S

400

Wavelength (nm)

2.3. Physicochemical characterization of ZAH The synthesized ZAH was characterized using X-ray diffraction (XRD) (PW1800 Philips), Fourier transformation infra-red (FTIR) (Perkin–Elmer) and Scanning electron microscope (SEM) (UK 1455VP Leo). 2.4. Adsorption studies

250

325

400

475

550

Wavelength (nm)

Fig. 2. UV–VIS spectrum of dyes.

The dye removal using ZAH was done by mixing of adsorbent in 250 mL of dye solution (50 mg/L) in jars. The solution samples were taken from sample point during the dye removal process at certain time intervals and centrifuged. The residual concentration of dyes in supernatant solution was measured at the maximum wavelength (kmax) of dyes. The kmax of AB92, AR14, and DR23 was 580 nm, 517 nm and 504 nm, respectively (Fig. 2). Perkin–Elmer Lambda 25 UV–VIS spectrophotometer was used to measure of dye absorbance in samples. The dye removal data were verified with the adsorption isotherm and kinetics. The effect of ZAH dosage on dye adsorption from single and binary systems was studied by contacting 250 mL of dye solution (50 mg/L) at room temperature (25 °C) for 60 min. The effect of initial dye concentration on dye adsorption was investigated by contacting 250 mL of dye solution with ZAH at room temperature (25 °C) for 60 min. Dye concentrations in a binary system of components A and B at wavelengths of k1 and k2, respectively, to give optical densities of d1 and d2 were measured as follows [14]:

d1 ¼ kA1 C A þ kB1 C B

ð1Þ

d2 ¼ kA2 C A þ kB2 C B

ð2Þ

C A ¼ ðkB2 d1  kB1 d2 Þ=ðkA1 kB2  kA2 kB1 Þ

ð3Þ

Fig. 3. X-ray diffraction pattern of ZAH.

625

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Fig. 4. FTIR spectra of viscose gel before ignition process and the product of ignition (ZAH).

C B ¼ ðkA1 d2  kA2 d1 Þ=ðkA1 kB2  kA2 kB1 Þ

ð4Þ

where kA1, kB1, kA2 and kB2 are the calibration constants for components A and B at the two wavelengths k1 and k2, respectively.

3. Results and discussion 3.1. Characterization of ZAH XRD pattern of the sample synthesized by combustion process has been illustrated in Fig. 3. The amorphous phase is the major

structure with a few weak peaks below 30° which can be related to the intermediate zinc aluminum hydroxide phase as a minor phase. This intermediate phase has a non-cubical structure and closely resembles a phase of aluminum hydroxide. It appears that this intermediate phase is a mixture of aluminum hydroxide and zinc hydroxide [15]. It seems that the formation of zinc aluminum oxide (ZnAl2O4) from complex of metal nitrate–urea fuel has been divided into two special processes: (1) transformation of complex to intermediate zinc aluminum hydroxide during the combustion process and (2) the formation of zinc aluminum oxide by the calcination of hydroxide powder above 400 °C [15]. Although, the combustion reaction leads to formation of high adiabatic temperature which is high enough to the formation of zinc aluminum hydroxide structure, but the straight preparation of ZnAl2O4 is impossible. Because of high residual amine groups of urea fuel and ammonium chloride on the surface of porous intermediate structure of synthesized sample, porous powder of intermediate zinc aluminum hydroxide structure can be used for dye removal. The accurate information on the change of chemical composition during the combustion reaction can be useful to investigate the method of functionalization of porous structure of obtained powder as a result of decomposition of organic compounds. FTIR spectrum of metal nitrate–urea complex and the synthesized sample is illustrated in Fig. 4. Chemical composition of gel indicates the formation of metal nitrate–urea complex. Moreover, high temperature of ignition during the combustion causes the vital effect on chemical bonds. Combustion process leads to weaken of all organic bonds and enhancement of oxide, hydroxide and nitrate bonds. The chemical composition of viscose gel consists of carbonyl, amino,

Fig. 5. SEM images of sponge-like structure of ZAH (b, d and e show the feature of sponge’s walls).

N.M. Mahmoodi et al. / Journal of Alloys and Compounds 602 (2014) 210–220

Fig. 6. The effect of adsorbent dosage (g) on dye removal by ZAH from single and binary systems.

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Fig. 7. The effect of dye concentration on dye removal by ZAH from single and binary systems.

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N.M. Mahmoodi et al. / Journal of Alloys and Compounds 602 (2014) 210–220 Table 1 Linearized isotherm coefficients of dye removal using ZAH at different adsorbent dosages from single and binary systems. System

Langmuir Q0

Single system

AB92 95 AR14 84 DR23 75

Binary system AB92 + AR14

AB92 104 AR14 84

AB92 + DR23

AB92 76 DR23 77

Freundlich

Tempkin

KF

1/n

R

KT

B1

R2

0.999

92

0.008

0.609

2.05727E + 48

1

0.609

3.305

0.999

71

0.054

0.692

13791112

4

0.680

0.486

0.956

50

0.092

0.488

2734

6

0.480

1.136

0.997

77

0.085

0.455

15 375

8

0.452

0.369

0.995

80

0.0217

0.070

2.66E + 20

2

0.066

1.639

0.980

96

0.063

0.360

2.57E + 08

5

0.380

1.000

0.984

96

0.062

0.411

1.78E + 08

5

0.428

KL

R

6.275

2

hydroxide, nitrate and metal–oxygen bonds. The wide shoulder and weak peaks appeared at 3400 and 1580 cm1 can be assigned to OAH stretch and bend bands, respectively. Two peaks around 3400–3200 cm1 can be related to NH2 group bands of urea. The fuel molecules coordinate to the cations either by their carboxyl oxygen or amino nitrogen. The intense peak at 1640 cm1 is due to C@O bonds of urea and shift of this peak from 1678 cm1 in urea itself can be related to coordination of fuel molecules with metal cations [16]. Moreover, the bands at 824, 1383 and 2430 cm1 originate from the presence of nitrates [17]. After ignition of viscose gel, the sponge-like particles consist of OH groups (3443 cm1), carbonyl groups (1640 cm1), NAH bands (3237 cm1), nitrate ions (830, 1400 cm1), ZnAO and AlO4 bands (below 700 cm1). The peaks of synthesized sample are narrower than viscose gel which can be related to the enhancement of purity in the obtained sample. The prediction of structure and chemical composition of obtained sample with respect to FTIR spectra (Fig. 4) and XRD pattern (Fig. 3) leads to introduce the zinc aluminum hydroxide as a structure of particles with a large amount of carbonyl, and amine groups in the chemical composition of obtained sample which can be used as a functionalized particles for dye removal. The high adiabatic temperature of ignition, ultrahigh rate of reaction and the high volume of exhaust gases (CO2, H2O and N2) cause the creation of sponge-like structure. By controlling the mentioned parameters, the thickness of walls, the type, shape, size and distribution of pores and linkages of pores are designed. Different features of combustion synthesis sample are illustrated by SEM images in Fig. 5. Sponge-like structure of obtained sample consists of micro-size pores which connected to each other in all directions. Surface roughness in higher magnification figure (Fig. 5e) can be related to the initial stage of the formation of zinc aluminum hydroxide nanoparticles. These observations are in good agreement with the weak crystallization of zinc aluminum hydroxide in the X-ray pattern (Fig. 3). Thus, sponge-like morphology of zinc aluminum hydroxide with good functional organic groups on the surface of porous structure was synthesized by combustion synthesis method.

3.2. Effect of operational parameter on dye removal The effect of ZAH dosages (g) on adsorption of dye from single and binary systems at different time intervals was shown in Fig. 6. The dye removal increases with adsorbent dosage due to the increase of adsorbent surface and availability of more adsorption sites. The capacity of adsorbent to remove pollutant was

2

expressed in mg adsorbed per gram of material. The adsorbent capacity decreases with the increasing amount of ZAH because of overlapping or aggregation of adsorption sites. In addition the total adsorbent surface area available to the dye decreases and diffusion path length increases [18,19]. Pollutants accumulate at the interface between two phases during the adsorption process [19,20]. The effect of initial dye concentration of dye adsorption by ZAH from single and binary systems was shown in Fig. 7. The dye removal ability of ZAH decreases at the higher initial dye concentration. The adsorbed dye onto ZAH increases by increasing in the initial dye concentration of solution if the amount of adsorbent is kept unchanged. It can be attributed to the increasing of the driving force at the higher initial dye concentration. At low initial dye concentration, adsorption of dye onto ZAH reaches equilibrium very quickly. The moles of dye to the available adsorbent sites are low at lower dye concentrations and subsequently the fractional adsorption becomes independent of initial concentration [21–24]. 3.3. Isotherm study Adsorption isotherm studies the relation between the mass of the dye adsorbed onto adsorbent and the dye concentration in liquid phase. Adsorption data of several pollutants were fitted to Langmuir, Freundlich and Tempkin isotherms. The Langmuir isotherm explains the adsorption of pollutant onto adsorbent. It assumes adsorption takes place at specific sites of the adsorbent surface [1,25,26,20]. The Langmuir equation is:

C e =qe ¼ 1=K L Q 0 þ C e =Q 0

ð5Þ

where qe, Ce, KL and Q0 are the amount of dye adsorbed onto adsorbent at equilibrium (mg/g), the equilibrium concentration of dye solution (mg/L), Langmuir constant (L/g) and the maximum adsorption capacity (mg/g), respectively. The data dye removal using ZAH at different adsorbent dosages from single and binary systems was fitted to the Langmuir isotherm by linear plotting of Ce/qe versus Ce. The isotherm constants (Q0, KL, and R2 (correlation coefficient values)) were indicated in Table 1. Also, Isotherm data were tested with Freundlich isotherm that can be expressed by [1,27]:

log qe ¼ log K F þ ð1=nÞ log C e

ð6Þ

where KF and 1/n are the adsorption capacity at unit concentration and adsorption intensity, respectively.

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2

2

log (qe-qt )

1 0.5

0.125

1

0.05 0.075

0.5

0.1

0

0.125

0

0 0

10

20

30

10

20

30

40

50

-0.5

50

40

-0.5

-1

t (min)

t (min)

2

2 Adsorbent (g)

1

0.075 0.1

0.5

0.125 0.15

Adsorbent (g)

1.5

log (qe-qt )

1.5

log (qe-qt )

Adsorbent (g)

1.5

log (qe-qt )

Adsorbent (g) 0.05 0.075 0.1

1.5

0.05

1

0.075

0.5

0.1 0.125

0 0

0 0

10

20

30

20

30

40

50

-0.5

50

40

10

-0.5

-1

t (min)

t (min)

2.5 2

2

Adsorbent (g)

0.5

0.1 0.125

0 -0.5 -1

log (qe-qt )

0.05 0.075

1

0

10

20

30

40

1

0.05 0.075

0.5

0.1 0.125

0

50

0

10

20

30

40

50

-0.5

t (min)

t (min)

2 Adsorbent (g)

1.5 log(qe-qt )

log (qe-qt )

1.5

Adsorbent (g)

1.5

0.05

1

0.075 0.1

0.5

0.125

0 0 -0.5

10

20

30

40

50

t (min)

Fig. 8. The pseudo-first order kinetics of on dye removal by ZAH from single and binary systems.

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N.M. Mahmoodi et al. / Journal of Alloys and Compounds 602 (2014) 210–220 Table 2 Linearized kinetics coefficients of dye removal using ZAH at different adsorbent dosages from single and binary systems. Dye

Single system

AB92

AR14

DR23

Binary system

AB92 + AR14 AB92

AR14

AB92 + DR23 AB92

DR23

Adsorbent (g)

(qe)Exp

Pseudo-first order (qe)Cal.

k1

R

k2

R

kp

I

R2

95 94 93 92 84 82 81 75 77 60 65 57

39 52 44 39 31 25 27 30 13 39 46 37

0.044 0.085 0.053 0.046 0.051 0.048 0.071 0.080 0.083 0.074 0.055 0.053

0.815 0.961 0.890 0.848 0.904 0.737 0.887 0.935 0.790 0.900 0.968 0.950

96 99 95 94 84 85 83 77 77 63 70 60

0.004 0.037 0.003 0.004 0.007 0.008 0.008 0.008 0.026 0.004 0.002 0.003

0.996 0.998 0.996 0.997 0.999 0.999 0.999 0.999 0.999 0.995 0.993 0.992

4 5 5 5 3 3 3 3 1 4 6 4

59 57 56 58 60 63 62 54 69 32 23 23

0.960 0.930 0.970 0.980 0.916 0.930 0.934 0.888 0.899 0.990 0.980 0.990

0.050 0.075 0.100 0.125 0.050 0.075 0.100 0.125

101 100 99 86 85 87 88 80

54 54 48 54 44 39 38 38

0.055 0.062 0.060 0.104 0.060 0.055 0.097 0.083

0.926 0.939 0.920 0.958 0.932 0.890 0.940 0.954

103 105 104 89 86 89 91 83

0.010 0.003 0.003 0.004 0.003 0.002 0.007 0.005

0.996 0.998 0.998 0.998 0.996 0.997 0.999 0.999

6 6 6 5 5 5 4 4

53 55 60 53 47 52 63 53

0.973 0.959 0.970 0.954 0.985 0.936 0.843 0.949

0.050 0.075 0.100 0.125 0.050 0.075 0.100 0.125

82 72 80 85 82 73 80 85

47 36 58 55 45 40 39 51

0.076 0.055 0.069 0.053 0.092 0.067 0.037 0.046

0.948 0.898 0.933 0.937 0.973 0.880 0.833 0.930

86 74 87 89 85 75 81 89

0.003 0.004 0.002 0.002 0.004 0.004 0.003 0.002

0.997 0.997 0.993 0.990 0.999 0.996 0.992 0.992

5 4 5 6 5 4 5 6

47 43 37 34 48 43 37 33

0.900 0.950 0.960 0.960 0.908 0.950 0.964 0.968

ð7Þ

where

B1 ¼ RT=b

(qe)Cal.

Intraparticle diffusion 2

0.050 0.075 0.100 0.125 0.075 0.100 0.125 0.150 0.050 0.075 0.100 0.125

1/n values indicate the type of isotherm to be irreversible (1/n = 0), favorable (0 < 1/n < 1) and unfavorable (1/n > 1). The Freundlich isotherm of dye removal from single and binary systems was studied by linear plotting of log qe against log Ce at different ZAH dosages. Table 1 presents the isotherm constants (KF, 1/n and R2). Tempkin isotherm assumes the heat of molecule adsorption in the layer decreases linearly with coverage because adsorbent interacts with adsorbate. In addition, the adsorption is characterized by a uniform distribution of binding energies, up to some maximum binding energy [28,29]. The Tempkin isotherm is given as:

qe ¼ B1 ln K T þ B1 ln C e

Pseudo-second order 2

ð8Þ

where KT is the equilibrium binding constant (L/mol) corresponding to the maximum binding energy and constant B1 is related to the heat of adsorption. In addition, R and T are the gas constant (8.314 J/mol K) and the absolute temperature (K), respectively. The applicability of Tempkin isotherm on dye removal by ZAH was studied by linear plotting of qe against ln Ce at different ZAH dosages from single and binary systems. The isotherm constants (KT, B1 and R2) were indicated in Table 1. The data show that isotherm of dye adsorption onto ZAH does not conform the Freundlich and Tempkin isotherms. The R2 values and the linearity between the Ce/qe against Ce show that the dye removal isotherm follows Langmuir model (Table 1) because the dye adsorption onto ZAH takes place at specific homogeneous sites and a one layer adsorption.

3.4. Kinetics study Several models can be used to express the mechanism of solute sorption onto an adsorbent. In order to investigate the mechanism of adsorption, characteristic constants of adsorption were determined using intraparticle diffusion, pseudo-first order equation and pseudo-second order equation [29–34]. A linear form of pseudo-first order model is [33]:

logðqe  qt Þ ¼ logðqe Þ  ðk1 =2:303Þt

ð9Þ

where qt and k1 are the amount of the adsorbed dye at time t (mg/g) and the equilibrium rate constant of pseudo-first order kinetics (1/min), respectively. The pseudo-first order dye removal kinetics was studied by linear plotting of log(qe–qt) against t (Fig. 8) at different ZAH dosages from single and binary systems. The pseudo-first order kinetics constants (k1, R2 and the calculated qe ((qe)Cal.) were shown in Table 2. Linear form of pseudo-second order model, was illustrated as [34]:

t=qt ¼ 1=k2 q2e þ ð1=qe Þt

ð10Þ

where k2 is the equilibrium rate constant of pseudo-second order (g/mg min). The applicability of pseudo-second order kinetics on dye removal at different ZAH dosages from single and binary systems was studied by linear plotting of t/qt against t (Fig. 9). The pseudo-second order kinetics constants (k2, R2 and the calculated qe ((qe)Cal.) were indicated in Table 2. The intraparticle diffusion kinetics of dye adsorption was investigated using the intraparticle diffusion model as [30–34]:

qt ¼ kp t 1=2 þ I

ð11Þ

where kp and I are the intraparticle diffusion rate constant and intercept, respectively.

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Fig. 9. The pseudo-second order kinetics of dye removal by ZAH from single and binary systems.

N.M. Mahmoodi et al. / Journal of Alloys and Compounds 602 (2014) 210–220

Fig. 10. The intraparticle diffusion kinetics of dye removal by ZAH from single and binary systems.

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The intraparticle diffusion kinetics of dye removal from single and binary systems at different ZAH dosages was studied by linear plotting of qt against t1/2 (Fig. 10). Table 2 shows the intraparticle diffusion kinetics constants (kp, I and R2). The R2 values showed that dye adsorption by ZAH did not follow pseudo-first order and intraparticle diffusion kinetics (Table 2). The linearity between the t/qt versus t and the R2 values show that the kinetics of dye removal followed pseudo-second order (Table 2). In addition, the qe values (experimental ((qe)Exp) and the calculated ones ((qe)Cal.)) agree with each other. 4. Conclusion In this paper, zinc aluminum hydroxide (ZAH) as a porous adsorbent was synthesized and its dye adsorption capacity from binary system was investigated. Three anionic dyes (Acid Blue 92(AB92), Acid Red 14 (AR14), and Direct Red 23 (DR23)) were selected. The ZAH adsorption capacity (Q0) for AB92, AR14, and DR23 were 95 mg/g, 84 mg/g and 75 mg/g, respectively. The data show that isotherm of dye adsorption onto ZAH does not conform the Freundlich and Tempkin isotherms. The R2 values showed that dye adsorption by ZAH did not follow pseudo-first order and intraparticle diffusion kinetics. Adsorption data showed that isotherm and kinetics of adsorption onto ZAH confirm Langmuir isotherm and pseudo-second order kinetics, respectively. The results showed that the ZAH was as an adsorbent to remove dyes from multicomponent systems.

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