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Journal of Engineered Fibers and Fabrics 19 http://www.jeffjournal.org Volume 8, Issue 3 – 2013

[Copper (II)/Cellulose-Chitosan] Microspheres Complex for Dye Immobilization: Isotherm, Kinetic and

Thermodynamic Analysis

Mahjoub Jabli, Faouzi Aloui, Béchir Ben Hassine

Laboratory of Organic, Asymmetric Synthesis and Homogenous Catalysis, FSM, University of Monastir, TUNISIA

Correspondence to:

Béchir Ben Hassine email: [email protected] ABSTRACT Considered as ligands due to the presence of donor atoms in their chemical structures, and being also among the major pollutants of water, Eriochrome Black B (Erio), Calmagite (Calma) and Acid Blue 25 (AB25) were successfully immobilized on cellulose-chitosan microspheres loaded with copper ions. Prepared supports were characterized by Fourier Transform Infra-Red (FTIR) spectral study and Thermogravimetic analysis (TGA). The effect of experimental factors during dye immobilization such as pH, contact time, temperature, and initial dye concentration were studied. The experiments demonstrate that the adsorption capacities of dyes on [Cu(II)/cellulose-chitosan] are much higher than the unloaded microspheres. This indicates that these dyes can act as efficient ligands for coordinating metals already involved in [cellulose-chitosan]. At least, in the case of AB25, a 60% of difference in target removal was achieved at equilibrium. The kinetic adsorption fitted well to the intra-particle diffusion model and the corresponding rate constants were obtained. In addition, the interpretation of the equilibrium sorption data complies well with the Freundlich model. The thermodynamic parameters were also determined and the enthalpy change (ΔH°) was found to be low, between -5.93 and -20.68 Kj.mol-1, indicating that the adsorption phenomenon is exothermic and physical. A probable mechanism of the Dye/Copper(II)/cellulose-chitosan complex is also proposed. Keywords: Ligands, Erio; Calma; AB25; cellulose-chitosan, enthalpy change; Freundlich INTRODUCTION Color removal from textile effluents is one of the most serious environmental problems. In fact, various kinds of synthetic dyestuffs are discharged from a variety of industries such as textile, leather and paper during manufacture and processing operations [1,2]. Their visual effect and their undesirable impact make them toxic, mutagenic, and carcinogenic [3].

For this purpose, the development of unconventional methods and systems were investigated and a number of studies have been reported. Particular attention has been paid to adsorbents obtained from natural resources for their capacities to remove different dyes from aqueous solutions [4-8]. Our focus is to test various low-cost supports for the removal of pollutants from textile waste water. In previous experiments, we developed chitosan-cotton composite materials with differing %CH content for acid dye removal from aqueous suspension using an easy and economical technique [9]. In our further study, we reported the synthesis and characterization of a new ternary complex [10]. Due to the facile complexing of transition metal with functionalized polymers, it was very attractive to check the coordinating ability of some synthetic dyes towards transition metals by developing binary systems. This was done by complexing chitosan-Glutaraldehyde microspheres with Cu(II) ions, which could highly adsorb dyes. In other works, our data gleaned from chitosan microspheres supported [bis (2-ethylallyl) (1,5cyclooctadienne) ruthenium (II)] exhibited an excellent ability to oxidize several dyes in the presence of an ecological oxidant such as hydrogen peroxide [11]. In this framework, we also reported the synthesis and characterization of a new helically chiral palladium (II) and ruthenium (II) complexes [12,13]. The catalytic activity of such sample was evaluated for the first time in the degradation of organic azo dye solutions. The successful synthesis and characterization of these complexes will provide an interesting candidate for catalytic applications. Also a topic of great interest, polymer blending, has been considered as one of the suitable techniques that provide new desirable polymeric materials for practical applications. Chitosan blended with polyvinyl alcohol has been reported to have good mechanical, chemical properties and efficient removal of lead ions from aqueous solution [14].

Cellulose-chitosan has been also used for many


applications [15,10]. To our knowledge, no examples of transition metal-blended polymers complex have been previously used for the immobilization of dyes. For example, Jingling Shentu et al., have only investigated the use of chitosan microspheres as immobilized dye affinity support for catalase adsorption [16]. The works of Jun Sun et al., focused on the treatment of carboxymethyl chitosan nanoparticles with Zn (II), Cu(II) and Fe(III) ions solutions to obtain immobilized metal affinity magnetic nanoparticles. Then the prepared nanoparticles were conveniently applied for lysozyme adsorption [17]. The present investigation reports in detail the examination of cellulose-chitosan microspheres loaded with Cu(II) ions for their ability to immobilize Calmagite, Acid Blue 25 and Erio Black B as dye ligands in batch system. A probable sort of interaction, Dye/Copper(II)/cellulose-chitosan, has been proposed. The effect of pH, initial dye concentration, contact time, and temperature on color removal efficiency of prepared supports was investigated. The adsorption rates were determined quantitatively and compared for the loaded and unloaded supports with Cu(II) ions. The modelling of the kinetic data was performed by the pseudo-first order, pseudo-second order, Elovich and intra-particle diffusion equations; and the thermodynamic

parameters were also evaluated. The adsorption phenomenon is studied and fitted using either Langmuir or Freundlich models. EXPERIMENTAL Materials and Reagents Three different commercially available textile dyestuffs were tested as adsorbates in this study, Calmagite, Acid Blue 25, and Eriochrome Black B, referred to as Calma, AB25 and Erio, respectively, their characteristics and chemical structures are given in Table I. They were supplied by Hoechst (Frankfort, Germany) in the form of sodium salts and used without further purification. The presence of functional groups and electron donor atoms in their structure allows them to build complexes with metal ions. The stock dye solutions were prepared by dissolving an appropriate amount of dye in 500 mL of distilled water. The working solutions were obtained by diluting the dye stock solution to the required concentrations.

Cellulose powder (20 m) and chitosan flakes (DD = 72.5 %) were purchased from Sigma Aldrich (Sigma-Aldrich Chimie Sarl, Saint-Quentin Fallavier, France) and were used without further purification. All other chemicals were of reagent grade purity; and distilled water was used to prepare all solutions.

TABLE I. Chemical structures and characteristics of the ligands (AB25, Calma and Erio).

Dye

Referred to as

Chemical structure

λmax (nm)

Molar weight

(g.mol-1)

Eriochrome Blue

Black B

Erio N N SO3Na

HOOH

528

416.39

Acid Blue 25

AB25 O

SO3Na

NH

NH2O

600

416.39

Calmagite

Calma

CH3

N=N

OH

SO3Na

HO

526

358.37


Preparation of [Cellulose-Chitosan] Microspheres The preparation of cellulose-chitosan was realized using a coacervation/precipitation method [15]. This was based on the physicochemical property of chitosan since it is insoluble in alkaline pH medium, but precipitates/coacervates when it comes in contact with alkaline solution. A chitosan solution was prepared by adding an amount of the polymer into 100 mL [2% (w/w)] acetic acid under stirring at 70°C and 200 rpm until complete dissolution. Then, an equivalent amount of cellulose powder was added into the chitosan solution and the mixing was continued for another period at room temperature. The blended solution was further evacuated through a nozzle (inner diameter = 0.20 mm) and dropped into a bath containing a 2.0 mol L-1 NaOH solution and cellulose-chitosan microspheres were quickly prompted. Prepared microspheres were allowed to harden in this solution for 24h. Subsequently, chitosan microspheres were filtered and rinsed several times with distilled water up to neutral pH. As the sorption conditions required the use of the cellulose-chitosan microspheres in a wide range of pH, the prepared supports were also cross-linked with ethylene glycol diglycidyl ether to resolve the solubility of the plain polymers in acidic media. Loading of [Cellulose-Chitosan] With Cu(II) Ions Cellulose-chitosan microspheres were loaded with Cu(II) ions up to saturation by putting in contact a desired amount of the solid support with an aqueous solution of Cu(II) ions. The mixture was stirred for 24h at room temperature in a closed vessel. The pH was adjusted to the desired value with 0.10M HCl and/or 0.10M NaOH. Then, the wet cellulose-chitosan microspheres loaded Cu(II) were filtered off, washed with distilled water and stored in distilled water at 4°C until further use. The initially white color of cellulose-chitosan microspheres becomes blue turquoise after adsorption of Cu(II) ions. Indeed, the amine and hydroxyl groups present in cellulose-chitosan chains are the main effective bonding sites for metallic ions, resulting in complexes stabilized by coordination [18]. Characterization of the Prepared Solid Supports The prepared materials were characterized using FT-IR spectroscopy and TGA analysis. The FT-IR characterization of cellulose, cellulose-chitosan, Cu(II)/cellulose-chitosan and dye molecules/Cu(II)/cellulose-chitosan microspheres was performed using a FT-IR spectrometer (Perkin–Elmer FT-IR System 2000 Model spectrometer). Dry globules of unmodified and modified biopolymers

were crushed and ground in a mortar by pestle, and then the fine powder was dispersed in anhydrous spectrophotometric potassium bromide (KBr) in 1:10 ratio, pressed into a thin pellet, and placed in the sample holder of the spectrometer. For thermogravimetric analysis (TGA 2950 instrument), the measurements were achieved, with a heating rate of 10°C min-1, in a dynamic N2 atmosphere on 5–10 mg of the sample. The scanning temperature range was from 25 to 900°C for TGA. The concentration of Calma, AB25, and Erio was determined by an ultraviolet-visible spectrophotometer (U-2000 Hitachi) with 2 nm resolution using calibration curve at max. Batch Sorption Experiments The equilibrium adsorption isotherm was evaluated using batch studies. Experiments were carried out by varying the initial Calma, AB25 or Erio in a wide range of concentrations. The amount of adsorbent is maintained at 0.1 g. Thermodynamic parameters were estimated by examining a series of isotherms at different temperatures (25, 40, 60 and 80°C) and varying pH from 2 to 8. The mixtures in the bottles were stirred in an orbital shaker operated at 200 rpm. The pH was adjusted to a given value by the addition of HCl (1 mol L-1) or NaOH (1 mol L-1) and was measured using a pH-meter. The dye solutions were filtered using a Whatman No. 41 filter paper, and the concentrations of dyes were determined from its UV-Vis absorbance characteristic with the calibration method. The concentration of dye in each filtrate was determined at max wavelength (526 for Calma, 600 nm for AB25, and 528 nm for Erio, respectively). The quantity adsorbed of each dye per gramme of adsorbent was calculated by measuring the concentration of the solution before and after solute adsorption using equation (1):

)( 0

e m

VCCq e

(1)

Where eq is the dye sorption capacity of the

adsorbent (mg.g-1), 0C is the initial dye

concentration (mg.L-1), eC is the concentration of

the dye at the equilibrium (mg.L-1), m is the weight

of the adsorbent (g) and V is the volume of the dye solution used for sorption (L).


RESULTS AND DISCUSSION Characterization of the Prepared Supports Measurement of Water Content in the Prepared Microspheres The hydration rate relative to the prepared [cellulose-chitosan] microspheres was evaluated using the following equation:

100)(

(%)

wet

drywet

W

WWHydration (2)

Wwet and Wdry are the weight of the wet and dry [cellulose-chitosan] microspheres, respectively. Measuring error for water content value was 10-3%. It was observed that the calculated percent hydration rate was found to be equal to 94.01%. This value is lower than that determined in our previous experiments for chitosan-Glutaraldehyde (97.5 %) [10]. This result could be explained by the mechanical resistance property of cellulose polymer. FT-IR Analysis FT-IR spectra of cellulose, cellulose-chitosan, Cu(II)/cellulose-chitosan,] and the complexes Dye molecules/Cu(II)/cellulose-chitosan are shown in Figure 1. Results revealed the appearance of a new band at 1562 cm−1 which could be attributed to the N–H bending vibrations [Figure 1(b)]. This confirms the interaction of cellulose with chitosan chains. The strong broad band at 3300–3500 cm−1 is the characteristic of the N–H and –OH stretching vibrations [Figure 1(a-f)]. The change in the characteristic shape of the modified supports spectra as well as shifting of peak from 3449 to 3498 cm-1

due to hydrogen bonding between OH- of cellulose and OH- or NH2 of chitosan were observed in the blend microspheres [Figure 1(a-b)]. Narrow bands of CH group stretching vibrations at 2900 cm-1 were also seen and can be assigned to CH band. The bands

FIGURE 1. Spectrum of unmodified cellulose and cellulose-chitosan before and after the adsorption of Cu(II), AB25, Calma and Erio.


of deformational NH group vibrations were observed in the 1680-1400 cm-1 range [19,20]. The significant decrease in transmittance in this band after adsorption of copper(II) ions indicated that the bonding of metals with NH2 group was established. Thus the nitrogen atom of chitosan moiety acted as main adsorption site for Cu(II) adsorption on the [cellulose-chitosan]. Therefore coordination is possible by electron transfer. Transmission FT-IR spectrum, measured for Cu(II)/cellulose-chitosan before and after adsorption of AB25, Calma and Erio as ligands, were given in Figure 1(d-f). No significant change in the band intensity was observed after dyes adsorption. This implies a physical adsorption process and may not involve a chemical interaction. The similar observations were also reported in our previous work [10] and by Xue et al., [21] Wan Ngah et al., [22] and Dolphen, et al., [23] when the adsorption of acid dyes onto modified chitosan was evaluated.

Thermogravimetric Analysis (TGA) The typical TGA thermogram of chitosan microspheres (Figure 2), cellulose-chitosan (Figure 3) and Cu(II)/cellulose-chitosan (Figure 4) were detailed. The first stage exhibited a mass loss of 3.3 – 6.0%, which is due to the loss of the adsorbed water both on the surface and in the pores of the particles and could be observed for all supports. The second stage reached mass losses of 62.56% for chitosan microspheres, 60.59% for cellulose-chitosan and 66.98% for Cu(II)/cellulose-chitosan, respectively. The DTG curves revealed that chitosan decomposed at 304.64°C, whereas the cellulose-chitosan microspheres and loaded ones decomposed at 289.83 and 184.21°C, respectively. Comparing all decomposition temperatures, prepared supports were found to be less thermally stable than that of the plain chitosan microspheres. The variation in thermal events proved the formation of the new materials.

62.56%

6.090%

304.64°C

1.256%/°C

149.25°C

0.05674%/°C

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Der

iv. W

eigh

t (%

/°C

)

20

40

60

80

100

Weig

ht (

%)

0 100 200 300 400 500 600 700 800

Temperature (°C)

chitosan microspheres

Universal V4.3A TA Instrumen

FIGURE 2. TGA curves of chitosan microspheres obtained under nitrogen atmosphere flowing at a rate of 25 mL min-1 and at a 10°C min-1


60.59%

3.315%289.83°C

0.9883%/°C

0.0

0.2

0.4

0.6

0.8

1.0

De

riv.

We

igh

t C

han

ge (

%/°

C)

20

40

60

80

100

We

igh

t (%

)

0 100 200 300 400 500 600

Temperature (°C) Universal V4.3A TA Instruments

FIGURE 3. TGA curves of cellulose-chitosan microspheres obtained under nitrogen atmosphere flowing at a rate of 25 mL min-1 and at a 10°C min-1.

66.98%

1.029%/°C

184.21°C

0.0

0.2

0.4

0.6

0.8

1.0

1.2

De

riv.

We

igh

t C

ha

ng

e (

%/°

C)

20

40

60

80

100

Wei

ght

(%

)

0 100 200 300 400 500 600

Temperature (°C) Universal V4.3A TA Instruments

FIGURE 4. TGA curves of Cu(II)/cellulose-chitosan microspheres obtained under nitrogen atmosphere flowing at a rate of 25 mL min-1 and at a 10°C min-


FT-IR transmission analysis and thermal studies allow us to attribute the structure indicated in Figure 5 to the possible complex. In fact, the chitosan can coordinate with Cu(II) ions through both oxygen and nitrogen atoms present in the chitosan chains.

Moreover, when applied to the adsorption bath, the two ligands including donors’ atoms in their structure (Nitrogen or/and Oxygen) could bind Cu(II)/cellulose-chitosan throughout the d vacant orbital of the transition metal.

OH

O

O

O

H

O OOH

OH

OH

OH O

NH2

Cu

OH

N N

OH

SO3Na

OH2

OH2

OH

OHHOH2C

HONH2

O

O OO

NH2

O

O

OH

O

CH2OH

FIGURE 5. Proposal of associative structures between Cu(II)/cellulose-chitosan and Calma.

Factors Affecting the Adsorption of Dyes Effect of Ph Figure 6 represents the effect of the pH on the adsorption of Cu(II) ions, AB25, Calma and Erio molecules on the cellulose-chitosan microspheres. Results demonstrate that the adsorption of Cu(II) increased, when varying pH from three to six, and reached a maximum value at pH 6. However, the decrease in the adsorption capacities, when pH is lower than three, is explained by the possible protonation of the amine groups shielded by the [cellulose-chitosan] microspheres. Hence this protonation prevents their approach to the polymers surface. The same results were previously reported for the adsorption of Cu(II) ions on the surface of chitosan-Glut [10] and ED-cotton [7]. The removal of AB25, Calma and Erio by cellulose-chitosan as a function of pH revealed a different behavior. The high adsorption yield was obtained at pH 5, 4 and 4.2 for AB25, Calma and Erio, respectively. The explanation of this result is that, at very low pH, protonation of anionic sulfonate groups of these anionic dyes prevents their adsorption on the surface of the studied adsorbent. In addition most of the amine groups (-NH2) are protonated, which hinder

the electrostatic interactions between acid dyes and adsorbent. At basic conditions, the adsorption of both dyes decreased dramatically. This could be explained by the fact that at high pH, more OH- groups will be available in the aqueous solution and consequently this limits the protonation of amine groups of the adsorbent.

FIGURE 6. Effect of the initial pH on the adsorption of Cu(II) ions, AB25, Calma and Erio on the surface of cellulose-chitosan microspheres.


Effect of Time Contact Figures 7-9 show the time required to reach equilibrium for the adsorption of AB25, Calma and Erio on the surface of cellulose-chitosan and Cu(II)/cellulose-chitosan supports. As observed, the kinetics was characterized by a fast initial rate followed by stabilization at high time values. As demonstrated, fast rates of equilibration, about 50%, of dye-ion removal was achieved after 70 min of contact. Results also indicated that the adsorption of the studied dyes increased with agitation period and attained equilibrium at approximately 190 min. In addition, experimental data showed that Cu(II)/cellulose-chitosan microspheres have higher dye removal capacities than unloaded one. As example, for AB25, the dye removal from aqueous solution is about 6.8 mg g-1 on the surface of

Cu(II)/cellulose-chitosan while it doesn’t exceed 1.7 mg g-1 on cellulose-chitosan microspheres.

FIGURE 7. Effect of time contact on the adsorption of AB25 Calma on (a) cellulose-chitosan and (b) Cu(II)/cellulose-chitosan.

FIGURE 8. Effect of time contact on the adsorption of Calma on (a) cellulose-chitosan and (b) Cu(II)/cellulose-chitosan.

FIGURE 9. Effect of time contact on the adsorption of Erio Calma on (a) cellulose-chitosan and (b) Cu(II)/cellulose-chitosan.

(a)

(a)

(b)

(b)


Effect of the Initial Dye Concentration The effect of the initial concentration on the adsorption of AB25, Calma and Erio on the surface of Cu(II)/cellulose-chitosan and unloaded microspheres was studied in a wide range of concentration and given in Figure 10. All the experiments were realized at pH 6, where the highest adsorption of Cu(II) ions was registered. Data exhibited an increment in removal capacities with an increase in initial dye concentration. This proves that the effect of initial dye concentration on the sorption capacity is significant. The possible mechanisms of the adsorption process of cellulose-chitosan and these dyes in aqueous solution are likely to be ionic interactions of the dye molecules with the amine groups of chitosan [24]. More importantly, we observed an increase, in dye removal capacity, for Cu(II)/cellulose-chitosan microspheres as compared to unloaded ones. Maximum dye adsorption on the Cu(II)/cellulose-chitosan were 16.2 mg g-1, 20 mg g-1 and 17 mg g-1 for AB25, Calma and Erio, respectively. Under the similar conditions and when the unloaded cellulose-chitosan microspheres was used as adsorbent, retention capacities do not exceed 2 mg g-1 for AB25, 7 mg g-1 for Calma and 7.2 mg g-1 for Erio. These results indicate that the dyes can act as efficient ligands to coordinate metals already involved in cellulose-chitosan complex. Also, the absence of metal ions, at pH 6, in the filtrate confirms the strong complexation power of these dyes toward Cu(II)/cellulose-chitosan.

(a)

0

2

4

6

8

10

12

14

16

18

0 50 100 150 200 250 300

Concentration (mg.L-1

)

qe (m

g.g-1

)

Chitosan-Cellulose /Cu(II)

Chitosan-Cellulose

(b)

0

2

4

6

8

10

12

14

16

18

20

0 50 100 150 200 250 300


)

qe (m

g.g-1

)

Chitosan-Cellulose /Cu(II)

Chitosan-Cellulose

(c)

0

2

4

6

8

10

12

14

16

18

0 50 100 150 200 250 300Concentration (mg.L

-1)

qe (m

g.g-1

)

Chitosan-Cellulose/Cu(II)

Chitosan-Cellulose

FIGURE 10. Effect of initial concentration on the adsorption of (a) AB25, (b) Calma and (c) Erio on cellulose-chitosan and Cu(II)/cellulose-chitosan at room temperature and pH = 6.

(c)


Effect of the Temperature As known, temperature affects the two major aspects of the adsorption phenomenon: the equilibrium position in relation with the exothermicity or endothermicity of the process and the swelling capacity of the adsorbent. Thus, adjustment of temperature may be required in the adsorption process. The effect of the temperature on the adsorption of AB25, Calma and Erio on the surface of either cellulose-chitosan or cellulose-chitosan/Cu(II) is depicted in Figures 11-13. As observed for the three dyes, the adsorption capacity of the studied adsorbent decreases with increasing temperature. As example, at 80°C and when the complex Cu(II)/cellulose-chitosan was used as adsorbent, the adsorbed quantities attained 4.2 mg g-1 for AB25, 7 mg g-1 for Calma and 6.8 mg g-1 for Erio, respectively. This behavior could be explained by the enhanced magnitude of the reverse (desorption) step in the mechanism [7, 10] and the interactions established between adsorbents and dyes are therefore reversible in this case. This is possibly due to the exothermic effect of the surroundings during the sorption process.

(a)

0

2

4

6

8

10

12

14

16

18


-1)

qe (m

g.g-1

)

T = 25°CT = 40°CT = 60°CT = 80°C

(b)

0

0,5

1

1,5

2

2,5

3


-1)

qe (m

g.g-1

)

T = 25°CT = 40°CT = 60°CT = 80°C

FIGURE 11. Effect of temperature on the adsorption of AB25 on (a) Cu(II)/cellulose-chitosan and (b) cellulose-chitosan.

(a)

0

2

4

6

8

10

12

14

16

18

20

0 50 100 150 200 250 300


)

qe (m

g.g-1

)

T = 25°CT= 40°CT = 60°CT = 80°C

(b)

0

1

2

3

4

5

6

7

8

9

0 50 100 150 200 250 300


)

qe (m

g.g-1

)

T = 25°CT= 40°CT = 60°CT = 80°C

FIGURE 12. Effect of temperature on the adsorption of Calma on (a) Cu(II)/cellulose-chitosan and (b) cellulose-chitosan.

(a)

0

2

4

6

8

10

12

14

16

18

0 50 100 150 200 250 300


)

qe (m

g.g-1

)

T = 25°CT = 40°CT = 60°CT = 80°C

(b)

0

1

2

3

4

5

6

7

8

0 50 100 150 200 250 300


)

qe (m

g.g-1

)

T = 25°CT = 40°CT = 60°CT = 80°C

FIGURE 13. Effect of temperature on the adsorption of Erio on (a) Cu(II)/cellulose-chitosan and (b) cellulose-chitosan.


Kinetic Modelling In attempts to better understand the adsorption phenomenon of the studied dyes on the surface of the two supports cellulose-chitosan and [Cu(II)/cellulose-chitosan], the pseudo first-order, the pseudo second-order, the Elovich and the intra-particle diffusion equations were used to fit the experimental data. The corresponding equations in their linear forms are summarized in our previous work [10] and the validity of each model is checked in this work. The plots of log (qe-q) versus time were used to determine the first-order rate constant, k1. The plots of t/q versus time were used to calculate the second-order rate constant, k2. The plot of q versus Ln t yielded the Elovich constants; a [initial sorption rate (mg g-1 min-

1)] and b [extent of surface coverage (mg g-1 min-1)].

While the plots of q versus t1/2 yielded the intra-particle diffusion constant, ki (mg g-1 min1/2). The results of rate constant studies for different initial dye concentration from 10 to 40 mg L-1 were summarized in Table II cellulose-chitosan and Table III Cu(II)/cellulose-chitosan. The assessment of the kinetic models is controlled by the extent of the regression coefficient R2. As observed, the first order equation of Lagergen fits poorly to the whole range of contact time and is generally applicable over the initial stage of the adsorption processes of the studied dyes. Based on the regression coefficient (R2 > 0, 96, Table II and Table III), the intra-particle diffusion model was found to be adequate to describe the way of the retention of dyes on the studied supports.

TABLE II. Kinetic constants for the adsorption of studied dyes on cellulose-chitosan.


TABLE III. Kinetic constants for the adsorption of studied dyes on Cu(II)/cellulose-chitosan.

Analysis of the Adsorption of Dyes on the Surface of [Cellulose-Chitosan] and [Cu(II)/Cellulose-Chitosan] Microspheres Through Langmuir and Freundlich Models The data equilibrium could be also correlated by either common theoretical or empirical equations (Langmuir [25] and Freundlich [26] models). A more detailed discussion of these equations is given in the literature [27, 28]. The linearisation of Langmuir

isotherm can be obtained by plotting ee qc / as a

function of ec . The gradient of the plot yields the

maximum capacity ( mq ) and the adsorption constant

( La ). Whereas the Freundlich isotherm assumes

heterogeneous surface energies, in which the energy

term in the Langmuir equation varies as a function of

the surface coverage. A plot of ( ee qc ) versus ec

yields the Langmuir equilibrium constant, LK (L.mg-

1). While the plots of eqlog versus eclog yield the

Freundlich constant, FK . The parameters values for

the different studied [adsorbate/adsorbent] systems are assembled in Table IV and Table V. The high correlation coefficients (R2 > 0.97) obtained in this study strongly supports the fact that the adsorption of AB25, Calma and Erio closely follows the Freundlich

model. Moreover, in all cases, the value of n1 were

found to be less than 1 indicating that the adsorption was so favorable [26].


TABLE IV. Langmuir, Freundlich constants and thermodynamic parameters for the adsorption of the dyes on cellulose-chitosan microspheres.

Langmuir Constants

Freundlich Constants

Thermodynamic Parameters

T (°C)

aL (L.mg-1)

KL (L.g-1)

qmax

(.mg.g-1)

R2

KF (L.g -1)

1/n

R2

ΔH°

(Kj mol-1)

ΔS°

(j mol-1)

ΔG°

(Kj mol-1)

AB25

25 0.0175 0.0547 3.115 0.997 0.207 0.46 0.974

-20.68

-94.93

7.20

40 0.0093 0.0253 2.696 0.983 0.085 0.56 0.992 9.57

60 0.0124 0.0184 1.481 0.979 0.084 0.47 0.997 11.06

80 0.0204 0.014 0.906 0.993 0.087 0.40 0.973 12.53

Calma

25 0.0098 0.111 11.36 0.957 0.464 0.52 0.971

-16.20

-71.86

5.45

40 0.010 0.093 8.547 0.98 0.354 0.52 0.987 6.18

60 0.011 0.075 6.314 0.99 0.287 0.51 0.99 7.17

80 0.0096 0.038 3.998 0.993 0.112 0.59 0.976 9.60

Erio

25 0.0044 0.065 14.556 0.96 0.119 0.77 0.978

-12.99

-65.88

6.77

40 0.0056 0.055 9.813 0.971 0.130 0.70 0.988 7.55

60 0.0063 0.044 6.973 0.978 0.110 0.67 0.988 8.65

80 0.0065 0.028 4.37 0.927 0.099 0.60 0.997 10.50

TABLE V. Langmuir, Freundlich constants and thermodynamic parameters for the adsorption of the dyes on Cu(II)/cellulose-chitosan microspheres.

Langmuir Constants

Freundlich Constants

Thermodynamic Parameters

T (°C)

aL (L.mg-1)

KL (L.g-1)

qmax

(.mg.g-1)

R2

KF (L.g -1)

1/n

R2

ΔH°

(Kj mol-1)

ΔS°

(Kj mol-1)

ΔG°

(Kj mol-1)

AB25

25 0.0051 0.1419 27.472 0.937 0.261 0.75 0.971

-7.167

-40.22

4.84

40 0.0068 0.124 18.181 0.965 0.345 0.64 0.989 5.43

60 0.0121 0.11 11.481 0.971 0.632 0.47 0.982 6.11

80 0.0134 0.089 6.657 0.953 0.574 0.39 0.97 7.10

Calma

25 0.0079 0.16 28.735 0.963 0.73 0.59 0.981

-5.93

-35.38

4.54

40 0.0057 0.136 23.923 0.971 0.351 0.67 0.996 5.19

60 0.0065 0.116 17.699 0.917 0.427 0.58 0.992 5.96

80 0.0106 0.111 10.449 0.971 0.444 0.51 0.984 6.45

Erio

25 0.0043 0.135 31.25 0.906 0.209 0.81 0.977

-8.69

-45.34

4.96

40 0.0046 0.117 25.757 0.965 0.204 0.77 0.974 5.58

60 0.0061 0.10 17.699 0.978 0.217 0.72 0.975 6.38

80 0.0068 0.077 11.261 0.974 0.209 0.64 0.986 7.53


Thermodynamics of the Adsorption of Dyes on the Surface of Cellulose-Chitosan and Cu(II)/Cellulose-Chitosan Microspheres Figure 14 shows a plot of log KL versus 1/T for the adsorption of the three tested dyes on the cellulose-chitosan and Cu(II)/cellulose-chitosan microspheres. The values of ΔH° and ΔS° were estimated and the results were reported in Table IV and Table V. The negative heat of adsorption values suggests that the interaction of the dyes with either cellulose-chitosan or Cu(II)/cellulose-chitosan microspheres is exothermic, which is supported by the decreasing adsorption of the corresponding dyes with the increase in temperature. In addition, heat of adsorption values indicates that the adsorption of AB25, Calma and Erio on the supports is a physical manner. This is consistent with data discussed earlier in FT-IR analysis. The negative value of the entropy change (between -94.93 and -35.38) was found to be consistent with the decreased disorder at the solid-solution interface during the adsorption process.

(a)

-2,7

-2,5

-2,3

-2,1

-1,9

-1,7

0,0028 0,0029 0,003 0,0031 0,0032 0,0033 0,0034

1/T

Ln

KL

AB25 Calma Erio

(b)

-5

-4,4

-3,8

-3,2

-2,6

-20,0028 0,0029 0,003 0,0031 0,0032 0,0033 0,0034

1/T

Ln

KL

AB25 Calma Erio

FIGURE 14. Log KL versus reciprocal of temperature for (a) Cu(II)/cellulose-chitosan and (b) cellulose-chitosan microspheres.

CONCLUSION [Cellulose-chitosan] microspheres were found to be effective adsorbents for the removal of both metals and anionic dyes. Evidence of interaction between the two bio-polymers was confirmed by FT-IR spectrum. In addition, data depicted from thermal analysis

showed that the prepared supports were found to be less thermally stable than the native chitosan. A probable reaction mechanism of the Dye/Cu(II)/cellulose-chitosan complex formation was proposed. Kinetic experiments were detailed and the Intra-particle diffusion equation was shown to fit the experimental data. The modeling of the adsorption isotherms by Freundlich equation has been confirmed and the thermodynamic parameters were determined. These parameters allowed us to deduce some results related to the exothermic nature of the adsorption phenomenon and the evolution of the disorder during the adsorption of dyes. Both heat of adsorption values (between -5.93 and -20.68 Kj.mol-

1) and FT-IR interpretation confirmed that the adsorption of AB25, Calma and Erio on the surface of Cu(II)/cellulose-chitosan and cellulose-chitosan followed a physical mode. The rate of adsorption was found to be directly dependent on the dye concentration, pH, contact time and temperature. Globally, we have observed that the use of the chitosan-cellulose microspheres in binding either metal ions and/or ligands are worthy of exploration in the context of the synthesis of new complexes. This paper can provide quantitative and qualitative information on the binding characteristic of Cu(II) ions with a system Cu(II)/cellulose-chitosan or both Cu(II) ions and dyes with a complex Dye molecules/Cu(II)/cellulose-chitosan. Further experiments can be extended to include the removal of more toxic derivatives including pesticides. NOMENCLATURE qe Equilibrium dye concentration on adsorbent, mg.g-1 qt The amount of dye adsorbed per unit mass of the adsorbent at time, t, mg.g-1 C0 Initial dye concentration in aqueous solution, mg.L-1 Ce Concentration of the dye at equilibrium, mg.L-1

Ct Concentration of the dye at equilibrium, mg.L-1 M Weight of the adsorbent, g V The volume of the dye solution, L. λmax Maximum wavelength, nm t Time, s k1 The first order rate constant, min-1 k2 The second order rate constant, L.mg-1

h The Elovich constant (mg.g-1.min-1) Initial sorption rate (mg g-1 min-1) Extent of surface coverage (mg g-1 min-1) Ki The intra-particule diffusion constant (mg.g-1 min1/2) Ceq The residual equilibrium concentration,

mg.L-1


T The absolute temperature, K ΔS* Entropy change, J.mol-1.K-1 ΔH* Enthalpy change, kJ.mol-1 ΔG* Free energy, kJ.mol-1

aL Langmuir adsorption constant, L.mg-1

qm Theoretical maximum adsorption capacity, mg.g-1

KF The adsorption capacity of the used adsorbent, mg.g-1 (L.mg-1)1/n

KL Langmuir equilibrium constant, L.mg-1 R2 Linear regression coefficient REFERENCES [1] Vaidya, A. A., Date, K. V., Environmental

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AUTHORS’ ADDRESSES Béchir Ben Hassine Aloui Faouzi Faculty of Science of Monastir Department Chemistry Bd of Environment Monastir 9018 TUNISIA Mahjoub Jabli National School of Engineering, Monastir 5019 TUNISIA

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