Water Air Soil Pollut (2010) 206:225–236 DOI 10.1007/s11270-009-0098-5

Preparation, Characterization, and Environmental Application of Crosslinked Chitosan-Coated Bentonite for Tartrazine Adsorption from Aqueous Solutions Wan Saime Wan Ngah & Noorul Farhana Md Ariff & Megat Ahmad Kamal Megat Hanafiah

Received: 3 December 2008 / Accepted: 13 May 2009 / Published online: 31 May 2009 # Springer Science + Business Media B.V. 2009

Abstract The preparation, characterization, and environmental application of crosslinked chitosancoated bentonite (CCB) beads for tartrazine adsorption have been investigated. CCB beads were characterized by using Fourier transform infrared spectrophotometer (FTIR), scanning electron microscope (SEM), and Brunauer–Emmett–Teller (BET) surface area and Barrett–Joyner–Halenda (BJH) pore size distribution analyses were also determined. The values of pH of the aqueous slurry and pH of zero point charge (pHZPC) were almost equal. The adsorption at equilibrium of tartrazine was found to be a function of pH of the solution, stirring rate, contact time, and tartrazine concentration. The optimum conditions for tartrazine adsorption were pH 2.5, stirring rate of 400 rpm and contact time of 80 min. Pseudo-first-order and pseudo-second-order models were used to analyze the kinetics of adsorption with the latter found to agree well with the kinetics data, suggesting that the rate determining step may be chemisorption. The two most common isotherm models, Langmuir and Freundlich, were used to describe the adsorption equilibrium data. On the basis of Langmuir isotherm model, the maximum adsorption capacities were determined to be 250.0, 277.8, and 294.1 mg g−1 at W. S. Wan Ngah (*) : N. F. M. Ariff : M. A. K. M. Hanafiah School of Chemical Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia e-mail: [email protected]

300, 310, and 320 K, respectively. Desorption studies were carried out at different concentrations of EDTA, H2SO4, and NaOH. All desorbing solutions showed poor recovery of tartrazine. Keywords Adsorption . Crosslinked chitosan-coated bentonite . Desorption . Isotherm . Kinetic . Tartrazine

1 Introduction An increase in human population and rapid growth of industries has triggered a high demand for dyes and pigments. Approximately 10,000 different dyes and pigments are used by industries and over 7×105 tons of dyes are annually produced worldwide (Mane et al. 2007). It is well known that most of dyes and pigments are produced from organic substances. Unfortunately, the release of synthetic dyes and pigments into water bodies resulted in bad odor, bad taste, and unsightly color (Ravikumar et al. 2007). Dyes and pigments, if not properly treated, can also have detrimental effects on human health. Therefore, these soluble colored contaminants must be removed from aqueous solutions. Tartrazine, IUPAC name trisodium-5-hydroxy-1-(4sulfonatophenyl)-4-(4-sulfonatophenylazo)-H-pyrazole-3-carboxylate (Fig. 1), consists of an azo (–N=N–) group which is very harmful to living things. Tartrazine is widely used in food materials, confectionary

226

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Fig. 1 Molecular structure of tartrazine

O

O S

Na

O N

OH

N O

N

Na

N O

O

Na

S O

products, drugs, cosmetics, textile, electroplating, and pharmaceuticals (Monser and Adhoum 2008; Mittal et al. 2006). This is due to the lower price of this dye compared to beta carotene (Mittal et al. 2007). Tartrazine is very soluble in water; therefore, it is commonly found in wastewater (Mittal et al. 2006). Tartrazine is also highly toxic and can act as catalyst in hyperactivity and other behavioral problems. It has been reported that exposure to tartrazine may cause asthma, migraines, eczema, thyroid cancer, and lupus (Mittal et al. 2006). For the past two decades, adsorption techniques have been found to be superior for tartrazine removal to other techniques in terms of cost, design, ease of operation, and insensitivity to toxic substances (Mittal et al. 2005; Wawrzkiewicz and Hubicki 2009). Various types of waste materials have been used to remove dyes such as bagasse fly ash (Mane et al. 2007), bottom ash and de-oiled soya (Mittal et al. 2006), hen feather (Mittal et al. 2007), eucalyptus bark (Morais et al. 1999), activated carbon (Al-Degs et al. 2008; Hameed et al. 2007), palm kernel fiber (Ofomaja and Ho 2007), chitosan bead (Bekçi et al. 2008), and bentonite (Eren and Afsin 2008). Chitosan or poly (β-1-4)-2-amino-2-deoxy-D-glucopyranose is synthesized through the deacetylation of chitin, a material that is widely spread among marine and terrestrial invertebrates and in lower forms of the plant kingdom (Wan Ngah and Fathinathan 2008). Chitosan is well known for its high adsorption capacity for contaminants, and with physical or chemical modifications, chemical stability in acidic media and resistance to microbiological degradation of chitosan can be enhanced (Guibal et al. 2000; Yang and Yuan 2001). In this study, both physical and chemical modifications have been carried out on the raw chitosan. The physical modification was performed by embedding chitosan with bentonite which

O

can provide physical support and increase the accessibility of binding sites (Boddu et al. 2003). In previous studies, various types of solids have been coated with chitosan such as bentonite (Gecol et al. 2006), perlite (Hasan et al. 2006; Kalyani et al. 2005), montmorillonite (Fan et al. 2006; Wang and Wang 2007), alumina (Boddu et al. 2003, 2008), activated clay (Chang and Juang 2004), calcium alginate (Vijaya et al. 2008), and silica (Vijaya et al. 2008). However, the application of chitosan-coated bentonite in the adsorption of tartrazine has not been studied. Chemical modification was carried out by using epichlorohydrin as a crosslinking agent. Crosslinking is an important step that enhances resistance of chitosan to acids, alkali, and chemicals in general (Wan Ngah et al. 2005). The main objectives of this study were to prepare and to evaluate the potential of an adsorbent, crosslinked chitosan-coated bentonite (CCB) beads as an adsorbent for tartrazine. Characterization of CCB beads was performed and the effects of several physicochemical parameters on tartrazine adsorption such as pH, stirring rate, tartrazine concentration, and temperature were also investigated.

2 Materials and Methods 2.1 Adsorbents and other Chemicals Samples of medium molecular weight chitosan powder with 85% degree of deacetylation and bentonite were supplied by Sigma-Aldrich. Tartrazine (E102 or Acid Yellow 23), an anionic dyestuff with C. I. Number 19140, empirical formula C16H9N4O9S2Na3, and molecular weight 534.4 g/ mol, was purchased from R & M Chemicals. All

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chemicals used were of analytical grade and were used without any purification. Distilled water was used throughout the adsorption experiments. 2.2 Preparation of CCB Beads A mixture of 2 g chitosan powder and 3 g bentonite was suspended in 80 mL (5% v/v) acetic acid and left overnight. The mixture was then dropped into a 500 mL (0.50 M) NaOH solution under continuous stirring at 100 rpm. The resulting beads were later stirred at 200 rpm and 125 mL (0.01 M) epichlorohydrin (ECH) was added, stirred for another 2 h at 50°C before being rinsed thoroughly with hot distilled water followed by cold distilled water for several times. The crosslinked chitosan-coated bentonite (hereafter called CCB) beads were then air dried before being finally ground and sieved to obtain adsorbent size of <200 µm. This adsorbent size was used throughout the adsorption experiments. 2.3 Characterization of CCB Beads The pH of the aqueous slurry was determined by adding 1 g of CCB beads in 50 mL distilled water, stirred for 24 h, filtered, and the final pH measured. The pH of zero point charge (pHZPC) was determined by immersing 1 g of CCB beads in 50 mL (0.01 M) KNO3 solutions in which the initial pH values were adjusted from 2 to 9 and left for 24 h. The final pH of the solutions was determined after 24 h. The pHZPC value can be determined from the curve that cuts the pHo (initial pH of the solutions) line of the plot of ∆pH (difference between initial pH and the final pH) versus Fig. 2 Plot of pHZPC

pHo (Wan Ngah and Hanafiah 2008). The Fourier transform infrared (FTIR) spectra were obtained by FTIR spectrophotometer (PerkinElmer 2000 Model). The average pore diameter and surface area of CCB beads were determined by using a gas adsorption surface analyzer (Micromeritics ASAP 2010). 2.4 Batch Adsorption Studies A stock solution of 250 mg L−1 tartrazine was prepared freshly each time the adsorption experiment was conducted. The stock solution was then diluted to 20 mg L−1 (unless otherwise stated). In general, adsorption experiments were conducted by adding 0.01 g of CCB beads (unless otherwise stated) into 50 mL tartrazine solutions in 100 mL beakers. Preliminary experiments indicated that, at this adsorbent dosage, more than 98% tartrazine could be removed. After adsorption, the solutions were filtered and analyzed at a wavelength of 428.4 nm using UV– visible spectrophotometer (Hitachi U-2000 Model). The effect of initial pH on adsorption of tartrazine was studied over pH range 1 to 8. The pH of the solution was adjusted by adding drops of 0.10 M HCl or 0.10 M NaOH solutions. The pH study was performed at 400 rpm for 80 min (equilibrium time). The effect of stirring rate was studied by fixing the pH of the solution at the optimum condition (pH 2.5) while the stirring rate was varied from 100 to 600 rpm, and left stirring for 80 min. The effect of tartrazine concentration and contact time was conducted at three different tartrazine concentrations (20, 40, and 60 mg L−1) while the pH and stirring rate were kept at pH 2.5 and 400 rpm, respectively. The

6 5 4 3 2 1 0

0

2

4

6

-1

pH o

8

10

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Table 1 Characteristics of CCB beads Characteristics

Value

pH of aqueous slurry

8.52

pHZPC

8.88

SBETa (m2 g-1)

3.64

SLb (m2 g-1)

5.40

Dpc (nm)

19.51

Beads size (μm)

<200

Color

Gray

a

BET surface area

b

Langmuir surface area

c

Average pore diameter

maximum adsorption capacity was determined from the isotherm study. This was done by adding 0.01 g of CCB beads into 50 mL tartrazine solutions at various concentrations (20–300 mg L−1) and stirred for 80 min. The amount of tartrazine adsorbed, qe (mg g−1), was calculated by using the following mass balance equation: qe ¼

Co
Ce V m

ð1Þ

where Co and Ce are the concentration of tartrazine before and after adsorption (mg L−1), V is the volume of the adsorbate used (L), and m is weight of adsorbent used (g). For the desorption studies, three desorbing solutions (EDTA, H2SO4, and NaOH) were used. After contacting the adsorbent with 50 mL (20 mg L−1) tartrazine solution for 80 min, the mixture was filtered and dried Fig. 3 N2 adsorption–desorption isotherm plot

at room temperature overnight. The beads were mixed with 50 mL of different concentrations (0.025 to 0.100 M) of desorbing solutions and stirred for 60 min.

3 Results and Discussion 3.1 Characterization of CCB Beads According to Wan Ngah and Hanafiah (2008), at pH ZPC value, adsorbent surface will have net electrical neutrality. At pH lower than pHZPC, the adsorbent surface is positively charged while at pH higher than the pH value of the pHZPC, negatively charged species will dominate the adsorbent surface (Monser and Adhoum 2008). As shown in Fig. 2, the pH value of the pHZPC of CCB beads is 8.88, which is very close to the pH value of the aqueous slurry (Table 1). Therefore, one can assume that the pH value of the aqueous slurry can be taken as the value of pHZPC. Meanwhile, the N2 adsorption–desorption measurement was conducted to study the mesoporosity of CCB beads. The N2 isotherm plot (Fig. 3) shows a typical type-IV sorption behavior with type-H3 hysteresis loop representing a mesoporous structure characteristic (Gregg and Sing 1982). The type-H3 hysteresis loop corresponds to adsorbents having slit-shaped pores. The values of BET surface area, Langmuir surface area, and average pore diameter are 3.64 m2 g−1, 5.40 m2 g−1, and 19.51 nm, respectively (Table 1). Pore sizes are classified in accordance with the classification adopted by the International Union of Pure and

14 12

Volume adsorbed (cm3 g-1 STP)

10 8 6 4 2 0 0

0.2

0.4 0.6 Relative pressure (P/Po)

0.8

1

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229

Fig. 4 SEM images of CCB beads at a ×1,000 and b ×3,000 magnifications

Figure 4 shows SEM images of the CCB beads at 1,000× and 3,000× magnifications. The beads have porous and irregular structure and the pores with diameter smaller than 2 μm can be clearly observed on the adsorbent surface. The internal surface area and the presence of pores provide suitable sites for

Applied Chemistry (IUPAC), that is, micropores (diameter (d) <2 nm), mesopores (2 nm < d < 50 nm), and macropores (d>50 nm). Since the value of average pore diameter of CCB beads lies between 2 and 50 nm, the beads can be classified as mesoporous adsorbent.

74.6 CCB beads loaded with tartrazine 1478

1638 70

2929 2925

1345

1384

CCB beads

1561 1314

66

3612

1646

3619

1384

3430

62 3426

%T

1123 58

54 1045 50

46 4000

1046 3600

3200

2800

2400

2000

1800

1600 cm-1

Fig. 5 FTIR spectra of CCB beads before and after tartrazine adsorption

1400

1200

1000

800

600

400

230

Water Air Soil Pollut (2010) 206:225–236

1,646 cm−1 corresponds to N–H bending vibrations. This peak was shifted to 1,638 cm−1 after tartrazine adsorption, again suggesting the involvement of amine groups in the binding of tartrazine molecules. No significant shift in wavenumber was observed for the peak at 1,046 cm−1 corresponds to C–O–C groups; therefore, it is likely that no chemical interaction occurs between C–O–C groups of chitosan and tartrazine molecules. The FTIR spectrum of CCB beads loaded with tartrazine shows that a new peak at 1,478 cm−1 corresponds to –SO3− groups, thus confirming the presence of tartrazine molecule.

Table 2 Amount of tartrazine adsorbed at different stirring rates Stirring rate (rpm)

Tartrazine adsorbed (mg g-1)

100

76.89

200

94.71

300

97.96

400

98.50

500

98.67

600

98.59

tartrazine adsorption. Infrared spectroscopy, on the other hand, is a useful tool for identifying the functional groups present in the adsorbent and for obtaining information on the nature of possible interactions between functional groups in CCB beads and tartrazine molecules. The FTIR spectra for CCB beads before and after tartrazine adsorption are shown in Fig. 5. The broad peak at 3,426 cm−1 in CCB beads can be assigned to stretching vibration of hydroxyl group. A small shift in wavenumber from 3,426 to 3,430 cm−1 suggests a possible hydrogen bonding between tartrazine and –OH group of chitosan. The peak at 3,619 cm−1 is due to stretching vibration of amine (–NH2) which is consistent with the peak at 1,123 cm−1 assigned to C–N stretching vibration. After adsorption, the peak at 3,619 cm−1 was shifted to 3,612 cm−1, suggesting that the amine groups in CCB beads had been changed to protonated amine. This also explained the possible ionic attraction between R′–NH3+ and R–SO3− groups. The peak at 2,925 cm−1 is assigned to C–H stretching vibration of –CH2 and –CH3 groups. The peak observed at Fig. 6 Effect of initial pH on the adsorption of tartrazine onto CCB beads

3.2 Effect of pH of Tartrazine Solution pH of the tartrazine solution plays an important role in the adsorption process. As shown in Fig. 6, the adsorption at equilibrium was low at pH 1 (47.6 mg g−1) but increased drastically at pH 2.5 (98.58 mg g−1), then became low after pH 3 and remained almost constant until pH 8. Thus, pH 2.5 was selected as the optimum condition for subsequent adsorption experiments. As stated before, at pH lower than pHZPC, the surface of the adsorbent will be positively charged. The anionic (R–SO3−) groups in the tartrazine molecule will be attracted to the positive charge of the adsorbent surface. However, the repulsion between R–SO3− groups and adsorbent surface would increase as the pH increased, thus adsorption at equilibrium would be greatly decreased especially at pH >7. The adsorption of tartrazine at pH 1 was found to be low most likely due to protonation of both of CCB beads and tartrazine. Based on the FTIR spectra and results

120 100

qe (mg g-1)

80 60 40 20 0 0

1

2

3

4

5 pH

6

7

8

9

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231

obtained from the pH dependence study, the mechanism of tartrazine adsorption process can be represented by the following equations:

NH

H+

+

2

NH 3 +

ð2Þ (CCB beads)

NH3+

(protonated CCB beads)

+

-

O3S

-

NH3+

R

O3S

R

ð3Þ (protonated CCB beads)

(tartrazine)

(CCB-tartrazine complex)

However, tartrazine also contains hydroxyl (–OH), carboxylate (–COO−), and azo (–N=N–) groups. Therefore, binding of tartrazine on CCB surface via coulombic, hydrogen bonding and van der Waals forces cannot be ruled out as suggested by Wawrzkiewicz and Hubicki 2009. 3.3 Effect of Stirring Rate Stirring rate determines the frequency of the collision between tartrazine and the adsorbent surface. The more frequently tartrazine touches the surface, the Fig. 7 Effect of initial concentration and contact time on adsorption of tartrazine onto CCB beads

more tartrazine can be adsorbed. A higher stirring rate can also reduce the boundary layer that surrounds the adsorbent surface. Based on Table 2, the lowest stirring rate applied was 100 rpm which resulted in 76.89 mg g−1 tartrazine being adsorbed. Adsorption at equilibrium increased to 94.71 mg g−1 at 200 rpm and slightly increased to 97.96 mg g−1 at 300 rpm speed. Beyond 400 rpm, the capacities remained almost constant. Based on these results, stirring rate of 400 rpm was chosen for subsequent adsorption studies since it records a high adsorption at equilibrium, which was 98.67 mg g−1.

300 250

qt (mg g-1)

200 150 100 20 mg/L 50

40 mg/L 60 mg/L

0 0

50

100 t (min)

150

200

232

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Fig. 8 Pseudo-first-order plots of adsorption of tartrazine onto CCB beads

2.5 2.0 1.5 log (qe-qt)

1.0 0.5 0.0

20 mg/L 40 mg/L

-0.5

60 mg/L

-1.0 0

3.4 Effect of Initial Tartrazine Concentration and Contact Time

10

20

30

40

50 t (min)

60

70

80

90

3.5 Adsorption Kinetic Studies

The study on initial concentration and contact time was performed at room temperature (300 K) while the pH and stirring rate were fixed at pH 2.5 and 400 rpm, respectively. Three concentrations (20, 40, and 60 mg L−1) were used for this study and the adsorption data are shown in Fig. 7. A rapid adsorption for 20 mg L−1 tartrazine solution occurred in the first 20 min and 30 min for 40 and 60 mg L−1 solutions. According to Crini (2008), there are four common steps involved in an adsorption process. The first step is bulk diffusion process in which adsorbates migrate from bulk solution onto the surface of the adsorbent. Secondly is the film diffusion where the adsorbates diffused through boundary layer to the adsorbent surface. Pore diffusion or intraparticle diffusion then takes place which allows adsorbates to diffuse from the surface to the inner part of the adsorbent particles and finally adsorbed on the active sites. Figure 7 also shows that the highest adsorption at equilibrium was recorded by 60 mg L−1 tartrazine.

The kinetics of the tartrazine adsorption onto CCB beads can be depicted using pseudo-first-order and pseudo-second-order models. Pseudo-first-order model is used to describe the reversibility of the equilibrium between liquid and solid phases (Vijaya et al. 2008). The pseudo-first-order model of Lagergren can be expressed as (Ho and McKay 1998): logðqe
qt Þ ¼ log qe


k1 t 2:303

ð4Þ

where qe and qt are the amounts of tartrazine adsorbed (mg g−1) at equilibrium and at time t (min), and k1 is the rate constant of the pseudo-first-order adsorption process (min−1). Linear plots of log (qe −qt) versus t was used to predict the rate constant (k1) and adsorption at equilibrium (mg g−1), which were obtained from the slope and intercept, respectively (Fig. 8). The high correlation coefficient (R2) values for each tartrazine concentration showed that these plots have a good linearity. However, the values of calculated (qe, cal) and adsorption at equilibrium

Table 3 Comparison between pseudo-first-order and pseudo-second-order rate constants and calculated and experimental adsorption loads at equilibrium for three different tartrazine concentrations [Tartrazine]

Pseudo-first-order

Pseudo-second-order

(mg L−1)

qe, cal (mg g−1)

k1 (min−1)

R2

20

1.794

0.0279

40

2.078

60

2.120

qe,

exp

(mg g−1)

R2

qe, cal (mg g−1)

k2 (g mg−1 min−1)

h (mg g−1 min−1)

0.9973

102.2

2.333×10−3

24.27

0.9996

0.0168

0.9802

204.1

6.453×10−4

26.88

0.9978

187.8

0.0147

0.9493

263.2

6.222×10−4

43.10

0.9982

245.9

97.60

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233

Fig. 9 Pseudo-second-order plots of adsorption of tartrazine onto CCB beads

2.0

t/qt (min g mg-1)

1.6 1.2

0.8 20 mg/L

0.4

40 mg/L 60 mg/L

0.0 0

50

(qe, exp) are not similar. Therefore, the adsorption process did not follow the pseudo-first-order model (Table 3). The pseudo-second-order equation assumes that ratelimiting step might be due to the chemical adsorption and the equation can be expressed as (Ho and McKay 2000): t 1 1 ¼ þ t 2 qt k 2 qe qe

ð5Þ

where k2 is the rate constant of pseudo-second-order adsorption (g mg−1 min−1). If the adsorption kinetic obeys the pseudo-second-order model, a linear plot of t/ qt versus t can be observed (Fig. 9). The slope of the plot will give the value of calculated adsorption at equilibrium (qe, cal), while the intercept gives the value of the rate constant (k2). The values of correlation coefficients for these plots are much higher than the pseudo-first-order plots. Based on Table 3, the calculated adsorption at equilibrium (qe, cal) also agreed well

Fig. 10 Amounts of tartrazine adsorbed versus equilibrium concentration

100 t (min)

150

200

with the experimental adsorption at equilibrium (qe, exp). Both conditions proved that the adsorption of tartrazine onto CCB beads follows the pseudo-second-order adsorption model. 3.6 Adsorption Isotherm Adsorption isotherm study was carried out at optimum conditions by varying tartrazine concentrations from 20 to 300 mg L−1. This study was done at three different temperatures which were 300, 310, and 320 K. The adsorption isotherm plots showed the adsorption at equilibrium increased with increase in its equilibrium concentration and temperature (Fig. 10). The two most common isotherm models were further applied for describing the adsorption data, which were Langmuir and Freundlich. Langmuir equation is based on several assumptions which are: (1) the adsorbent surface is homogeneous, (2) there is

350 300

qe (mg g-1)

250 200 150 100 300 K 50

310 K 320 K

0 0

50

100

150 Ce (mg L-1)

200

250

300

234

Water Air Soil Pollut (2010) 206:225–236

no interaction between adsorbates in the plane of the surface, and there is a (3) monolayer type of adsorption. The linearized Langmuir equation is given as: Ce 1 Ce þ ¼ Qmax b Qmax qe

ð6Þ

where Ce is the equilibrium tartrazine concentration (mg L−1), qe is the amount of tartrazine adsorbed at equilibrium (mg g−1), Qmax is the capacity (mg g−1), and b is a constant (L mg−1). The value of b reflects the binding strength between tartrazine molecules and adsorbent surface. From the linear plots of Ce/qe against Ce (plots not shown), the values of Qmax and b can be calculated from the slope and the intercept, respectively. From Table 4, the Qmax values increased as the temperature increased from 250.0 mg g−1 (300 K) to 294.1 mg g−1 (320 K). The theoretical adsorption capacities (Qmax) predicted from Eq. (6) is also very close to the experimental values for all temperatures studied. In addition, the values of Langmuir constants (b) increased as the temperature increased from 0.520 L mg−1 (300 K) to 1.214 L mg−1 (320 K), suggesting stronger binding of tartrazine on CCB beads at higher temperature. High correlation Table 4 Langmuir and Freundlich isotherm constants and correlation coefficients Model

Temperature

Parameters

Value

Langmuir

300 K

Qmax (mg g−1)

250.0

310 K

b (L mg−1)

0.520

R2

0.999

Qmax (mg g−1) b (L mg−1) R

320 K

Freundlich

300 K

310 K

2

294.1 1.214

R2

0.999

CCB beads

294.1

This study

Activated carbon

121.3

Monser and Adhoum 2008

Hen feathers

64.1

De-oiled soya

24.6

Mittal et al. 2007 Mittal et al. 2006

Bottom ash

12.6

Mittal et al. 2006

coefficients (R2 >0.999) for all temperatures suggest that isotherm data followed the Langmuir model well. The Freundlich model is expressed as: log qe ¼ log KF þ

1 log Ce n

ð7Þ

where KF represents Freundlich constant (mg g−1) and n is considered as the heterogeneity of the adsorbent surface and its affinity for the adsorbate (Chen et al. 2003). The most important parameter from this equation is the n value. A higher n value (or smaller value of 1/n) indicates a stronger bond between adsorbent and adsorbate. All the n values were larger than unity, an indication that the bond between tartrazine and CCB is strong (Table 4). However, based on the correlation coefficient values (R2), adsorption of tartrazine was best fitted by the Langmuir than the Freundlich model. A comparison of tartrazine adsorption capacity of CCB beads with previously employed adsorbents is given in Table 5.

131.9

Table 6 Percentage of tartrazine desorbed by EDTA, H2SO4, and NaOH solutions Desorbing solution Concentration (mol L−1) Desorption (%) EDTA

0.025

7.248

n

7.260

0.050

R2

0.780

0.100

12.20

0.025

19.99

0.050

21.41

0.100

26.08

0.025

20.70

0.050

25.36

0.100

20.60

KF (mg g−1) n KF (mg g ) R2

H2SO4

0.981 −1

n

182.0 10.95

R2 320 K

Qmax (mg g−1) Reference

1.161

b (L mg−1) KF (mg g−1)

Adsorbent

277.8 0.999

Qmax (mg g−1)

Table 5 Comparison of CCB beads with previous employed adsorbents for tartrazine removal

198.6 11.51 0.967

NaOH

10.97

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3.7 Desorption Studies One of the important characteristics of an adsorbent is its ability to be regenerated. Desorption studies help to elucidate the nature of the adsorption process and the recovery of tartrazine from CCB beads. All desorbing solutions showed poor recovery (<30%) of tartrazine although the concentration was increased from 0.025 to 0.100 M (Table 6). EDTA recorded the lowest recovery while a slightly higher recovery was achieved by 0.100 M H2SO4. These results indicated that tartrazine molecules were strongly attached to the CCB surface and therefore the beads are likely to be used for one cycle only rather than reusing them for several cycles.

4 Conclusion This study demonstrates that CCB beads are a promising adsorbent for the removal of tartrazine from aqueous solution. This is due to the rapid uptake of tartrazine and a very high maximum adsorption capacity recorded especially at 320 K, which was 294.1 mg g−1. The adsorption process however was affected by several physicochemical factors such as pH, stirring rate, tartrazine concentration, and temperature. The kinetic study indicated that the tartrazine adsorption obeyed pseudo-second-order model better than pseudo-first-order model. The adsorption process was best fitted by the Langmuir than the Freundlich model. The interaction between tartrazine molecules and adsorbent surface was confirmed by FTIR analysis and the FTIR spectra revealed amine as the main functional group involved in the adsorption of tartrazine molecules. The low recovery of tartrazine by desorbing solutions indicated the strong bonding between tartrazine and CCB beads. Acknowledgement The authors are very grateful to the Universiti Sains Malaysia (Grant No. 304/229/PKIMIA/ 638166) for financial support of this work.

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