Kinetic and Thermodynamic Studies of Adsorption of cationic dye on Wood Cores of Jujube in Aqueous Solution

Kinetic and Thermodynamic Studies of Adsorption of cationic dye on Wood Cores of Jujube in Aqueous Solution

Noureddine El Messaoudi 1, Abdellah Lacherai 1, Mohamed El Khomri1

Safae Bentahar1, Mohamed Ezahri 2

1. Laboratory of Biotechnology and Valuation of Natural Resources, Faculty of Science, Ibno Zohr University, BP 8106, 80000 Agadir, Morocco

2. Laboratory of Materials and Environment, Faculty of Science, Ibno Zohr University, BP 8106, 80000 Agadir, Morocco

Abstract—- This work is a contribution to the search for new efficient and less expensive adsorbents on the one hand, on the other hand to the valuation of a natural material, namely wood cores jujube (WCJ). The efficiency of this material was tested on a dye widely used in the textile industry the methylene blue (MB), in aqueous solution. Thus, in this study, the support used is prepared and characterized by different techniques (FTIR, TGA and DTA). Also, we studied isotherms (Langmuir, Freundlich, Temkin), kinetic and thermodynamic of the adsorption phenomenon involved. The various results obtained showed that the adsorption of MB on WCJ is an endothermic reaction, spontaneous, follows a second order kinetics, and better described by the Langmuir isotherm.

Key words —- Jujube, Adsorption, Methylene blue, Kinetic, Thermodynamic, Isotherm models

1. INTRODUCTION

   Preserving the environment requires the development and optimization of technologies to reduce pollution of air, soil, and especially water. So far, in spite of the efforts deployed the industrial effluents contain a significant amount of pollutants of all kinds which is released into the environment.

   Several techniques were used for the removal of dyes from industrial effluents [1, 2]. Adsorption is one of the most exploited phenomena for highlighting these removal techniques. So the activated carbon material is widely used, only it is very expensive and requires more regeneration [3, 4]. This limits its use in developing countries. What brings to remedy it by searching for new cheaper adsorbents and in particular from materials which are not classics, in particular from plant waste.

   Much research has been conducted in this area by using materials of vegetable origin [5- 8].

   In this perspective we were interested in a material of plant origin present in our region namely wood cores jujube WCJ, and to test its effectiveness we have chosen as a model pollutant methylene blue (MB).

   The latter is a cationic dye widely used in the textile industry. MB is toxic and causes upon exposure nausea, vomiting, ocular lesions, and methemoglobinemia [9].

   In this study we set ourselves the aim of studying the kinetics and thermodynamics of adsorption involved the one hand and the other hand the valorization of the material studied.

2. MATERIAL AND METHODS

   1. Preparation and characterization of biosorbent

      Wood cores jujube WCJ (Zizyphus lotus) was provided from region of Tata (south of Morocco). It was collected and washed with distilled water to remove the surface adhered particles, then dried in oven at 110°C for 24 h.. It was then milled and sieved to obtain a particle size in diameter range of 0.5 to 1mm. After drying for several hours the fine powder of WCJ was preserved in tight glass for use as adsorbents.

      We have characterized WCJ by transform infrared spectroscopic (FTIR), Thermogravimetric analysis (TGA) and the differential thermal analysis (DTA).

   2. Preparation of dye solutions

      1g of methylene blue dye ( Chemical formula: C16H18N3SCl, molecular weight 319.85 g/mol, maximum wavelength 661 nm and IUPAC name : 3,7-bis (dimethylamino)-phenothiazin-5-ium chloride. The structure of BM is shown in Fig.1 [10]) was dissolved in 1L distilled water (stock solution). All working solutions of varying concentrations were obtained by successive dilution. Adsorption studies were conducted with desired dilution of the stock solution.

      Fig.1. Structure of methylene blue.

   3. Batch adsorption experiments

   Adsorption of BM dye solution was carried out using batch experiment and the effect of various parameters like contact times (30-240min), initial dye concentration C0 (10-60 mg/L) and temperature (15- 60°C) on the removal of BM were studied.

   The adsorption studies were carried out by adding to 0,3g of WCJ powder to 50ml of dye solutions to of known concentrations. The solutions were stirred using a magnetic stirrer at predetermined times intervals and are kept in a bath at different temperature (15- 60°C) by a thermostat with external circulation [11,12].The mixture is stirred using a magnetic stirrer to different contact times (30- 240min), in these sorption experiments.

   The adsorbent was then removed by filtration the equilibrium concentrations of the samples were analyzed using spectrophotometer (UV-visible 2300- TECHCOMP). Calibration curve were obtained with standard MB solutions by recording the absorbance values of various concentration of methylene blue dye at maximum absorbance of wavelength max=661nm.

   Each experiment was carried out in duplicate and the average results are presented.

   The adsorption capacity qe (mg/g) and color removal efficiency R(%) were calculated using following equations (1) and (2), respectively.

   (1)

   (2)

   Where,C0 (mg/L) and Ce (mg/L) are the initial and equilibrium concentrations of MB solution, respectively, V

   (L) is the volume of solution, and W(g) is the mass of biosorbent used.

3. RESULTS AND DISCUSSION

   1. Characterization of biosorbent

      The FTIR spectrum (JASCO FT/IR 4100) of the WCJ before dye adsorption is shown in Fig.2. The absorption with maxima at 3343 cm1 is assigned to the OH group stretching vibration and the band about 2901 cm1 is attributed to stretching of CH. The band observed at 1703cm1 is assigned to a carbonyl band (C=O) of

      unionized carboxylate stretching of carboxylic acid or ester [13], while the peak at 1552 cm1 is attributed to C=O stretching of carboxylic acid with intermolecular hydrogen bond [13] .The band in the 1210 cm1 is due to the bending modes of OCH, CCH and COH. The band at 1021 cm1 is attributed to C-O stretching.

      The FTIR results indicated that the biosorbent studis presented functional groups such as, OH, COO and CO, that could be potential adsorption sites for interaction with the cationic MB dye also conrmed the lignin presence of the lignin on the wood cores [14].

      The WCJ was analyzed by TGA and DTA (SHIMADZU D60) between 25 ° and 600 ° C with a heating rate of 10° C / min. The TGA and DTA curves are shown in Fig. 3. The analysis of these curves shows that they can be divided into four phases in function of the temperature [15]. The first endothermic corresponds to loss of water (T <270 ° C). The second is exothermic (270 <T> 360 ° C) and the third endothermic (360 <T> 500 ° C). The latter two may be due to the decomposition of organic matter. The last phase is the formation of carbon (> 500 °

      C) at an exothermic process.

   2. Adsorption Kinetic studies

      Figure 4 shows the effect of contact time on the retention rate at three different initial concentrations of the dye. For the three used concentrations, the retention rate grows with reaction by following two different slopes. One is rapid and is located in the first 180 minutes, whereas the second is slow and could express the equilibrium between the fractions retained dye and those desorbed.

      Overall retention is comparable fo all three concentrations with a yield that decreases when the concentration increases, with the values of 94.09, 76.71 and 56.93% respectively for concentrations 10, 25 and 40 mg / l.

      Most of transferred dye onto the adsorbent is obtained in the third hour with amounts on the order of 91.94, 76.07 and 55.68% respectively for concentrations 10, 25 and 40 mg / l. The adsorption capacity increases, too, with the increase in concentration of the solution to reach values of about 1.56, 3.19 and 3.79 mg / g for the respective concentrations of 10, 25 and 40 mg / L.

      The mechanism of adsorption and the potential rate controlling steps involved in the process of adsorption had been investigated using kinetic models such as pseudo- first-order, pseudo-second-order and intra particle diffusion model.

      Pseudo first-order model

      The pseudo first-order equation is generally expressed as [16]:

      (3)

      Where, k1 is the constant pseudo-first order (min-1). The constants of pseudo-first order were determined by

      extrapolation of the plot of log (qe-qt) vs. t. The results are shown in Fig. 5.

      The adsorbed quantities qecal values, the constants k1 pseudo-first order and R2 regression coefficients for the three concentrations used are given in Table 1. R2 values were found relatively low and between 0.823 and 0.981.

      The calculation of qe for the three concentrations shows that the adsorbed amounts of dye are rather low compared with experimental quantities. These observations lead us to say that the adsorption of methylene blue does not express a diffusion process controlled since it does not follow the of pseudo-first order equation.

      Fig.2.FTIR spectra of WCJ

      Fig.3. Curves TGA and DTA of WCJ

      Fig.4.Effect of contact time on the amount adsorbed (C0 =10-40 mg /L; T = 30° C; biosorbent dose =6g/L).

      amounts (qecal) in equilibrium are in the order of 1 .71,

      3.75 and 4.26 mg / g respectively for the concentrations 20, 30 and 40 mg / L and are very close to the values found experimentally, the order of 1.56 , 3.19 and 3.79 mg / g.

      These two last finding suggests that the adsorption process follows the model of pseudo-second order

      Fig.6. Pseudo-Second-Order kinetic of MB adsorption by WCJ (C0 =10-40 mg / L; T = 30°C; biosorbent =6g/L).

      Intraparticle diffusion model

      The possibility of intraparticle diffusion was examined using Weber-Morris theory [17]. According this theory the intraparticle diffusion model can be expressed as

      Fig.5.Pseudo-First-Order kinetic of MB adsorption by WCJ (C0

      =10-40 mg / L; T = 30° C; biosorbent dose=6g/L).

      Pseudo second -order model

      The equation of the pseudo-second-order can be expressed as follows [16]:

      (4)

      Where K2 is the constant of pseudo-second order rate (g

      .mg-1.min-1).Figure 6 shows the application of the kinetic model of pseudo-second order to the results for the adsorption of methylene blue. The constants of the pseudo- second-order have been determined by extrapolating the plot of t / qt vs. t. The values of the adsorbed quantities qecal, constants pseudo second order K2 and regression coefficients R2 for the three concentrations used are given in Table 1.

      In view of these results, it appears that the amount adsorbed at equilibrium (qecal), increases with initial concentration. Moreover, the R2 values are very high and are all above 0.99. They surpass significantly those obtained with the model of pseudo-first order. The fixed

      (5)

      Where, qt is the amount adsorbed (mg/g) at time t, and

      kint is the rate constant for intraparticle diffusion (mg.g1.min1/2).

      Figure 7 shows plots of the model used for the three values dye concentrations (10, 25 and 40 mg / L) . The intraparticle diffusion constant and R2 are given in Table 1. From figure 7, it is easy to see that the intraparticle diffusion is a significant step in the process of adsorption of methylene blue on wood cores jujube, especially after 180 minutes. This latency can be explained by the movement of

      dye molecules in the channels of the adsorbent cellulose. However, the chemical surface reaction, which begins in the first few minutes of contact with the experimental points are aligned to the pseudo-second order with very high regression coefficients R2, indicates that the most influential step in the adsorption the dye on WCJ is the intraparticle diffusion process, since it can be considered as limiting step that controls the transfer of the dye at each time t.

      Fig.7.Intraparticle diffusion of MB adsorption by WCJ (C0 =10-40 mg / L; T = 30° C; biosorbent dose =6g/L).

      Table1.Kinetic parameters for adsorption of MB by WCJ

      Fig.8. Adsorption isotherm of MB on WCJ at different T°C (C0 =10-60 mg / L; t = 180 min; biosorbent dose=6g/L).

      It is important to study the equilibrium adsorption isotherm for the conception of the system adsorption. Three isotherm models of adsorption were used for this study namely Langmuir, Temkin and Freundlich.

      The Langmuir equation can be described by the linearized form

      Pseudo-rst-order model
      C0 (mg/L)	qeexp (mg/g)	qecal (mg/g	K1 (min-1)	R2
      10	1.56	1.08	0.021	0.981
      25	3.19	6.65	0.027	0.823
      25	3.19	4.26	0.020	0.923
      Pseudo-second-order model
      C0 (mg/L)	qecal (mg/g)		K2 (g .mg-1.min-1)	R2
      10	1.71		0.027	0.999
      25	3.79		0.743	0.993
      40	4.32		0.115	0.998
      Intraparticle diffusion model
      C0 (mg/L	Kint		C	R2
      10	0.017		1.299	0.987
      25	0.147		1.065	0.968
      40	0.158		1.498	0.973

      Where, KL

      (6)

      is the Langmuir constant (L/mg) and qm

      is the

   3. Isotherms studies

      The adsorption process was carried out at different temperatures of 15-60 ° C with an initial concentration of between 10 MB and 60 mg / L, stirring for a period of 180 minutes was used for all concentrations of BM in this study. Figure 8 shows that the adsorption capacity of MB on WCJ increased with temperature elevation from 15 to 60

      ° C, due to an increased surface activity and an increase in kinetic energy of the dye molecule.

      Since the adsorption increases with temperature, therefore, the system is endothermic.

      maximum amount of adsorbate retained on the medium used (mg/g).

      This isotherm (Fig.9) has several advantages. The value of KL is related to the strength of interaction between the adsorbed molecules and the solid surface on the one hand, and on the other hand the value qm expresses the quantity of solute fixed per gram of solid, the surface is considered completely covered by a monomolecular layer [18]. In addition the parameters KL and qm have a physical meaning.

      Equilibrium parameter «or» separation factor, which characterizes the adsorption, is defined by the following equation [19]:

      (7)

      Where, C0 is the initial concentration of the adsorbate (mg

      / L).

      The RL value indicates the mode of sorption of the isother process, if the process is unfavorable (RL> 1) or linear (RL = 1) or favorable (0 < RL <1) or irreversible (RL = 0).

      Fig.9. Langmuir isotherm of MB on WCJ at different T°C (C0 =10-60 mg / L; t = 180 min, biosorbent dose =6g/L).

      The linearzed Freundlich (Fig.10) equation is represented by the following equation [19]:

      Temkin isotherm contains a factor which takes into account explicitly the adsorptive interactions of species of adsorbents [20].

      The values of the parameters qm, KL, RL, KF, 1 / n, KT, Aq and R2 for the removal of methylene blue are given in Table 2.

      (8)

      Where, KF is the Freundlich constant ((mg/g)(l/mg) 1/n) and 1/n is the intensity of adsorption.

      Fig.10.Freudlich isotherm of MB on WCJ at different T°C (C0 =10-60 mg / L; t = 180 min; biosorbent dose =6g/L).

      The isotherm Temkin (Fig.11) also used in this studies t and may be represented

      (9)

      Where KT is the Temkin constant (L/mg), Q is the energy variation (J.mol-1), R is the ideal gas constant 8.31447 (J.mol-1.k-1), T is the temperature (K).

      Fig.11.Temkin isotherm of MB on WCJ at different T°C (C0 =10-60 mg / L; t = 180 min; biosorbent dose =6g/L).

      By adjusting the experimental points on the three isotherm models, it appears that the Langmuir model best describes the adsorption type involved. And from the RL value obtained we can conclude that the process is favourable (0 <RL <1). Thus, the molecules of the dye may be adsorbed monolayers, without any dye-dye interactions. This hypothesis is reinforced by the thermodynamic results which indicate that during adsorption the order increases to give, ultimately, a organized distribution of dye molecules at the adsorption sites.

      Table2.Parameters isotherms for the removal of MB dye.

      Langmuir
      T (C°)	KL (L/mg)	qm (mg/g)	RL	R2
      15	0.314	3.46	0.050-0.241	0.991
      30	0.173	3.47	0.087-0.366	0.992
      45	0.140	3.59	0.106-0.415	0.992
      60	0.090	4.20	0.144-0.501	0.997
      Freundlich
      T (C°)	KF ((mg/g)(l/mg) 1/n)		1/ n	R2
      15	1.202		0.278	0.959
      30	1.603		0.210	0.978
      45	1.734		0.202	0.979
      60	1.866		0.235	0.947
      Temkin
      T (C°)	KT (L/mg)		Q (kj/mol)	R2
      15	5.359		3.982	0.989
      30	25.750		5.170	0.990
      45	36.598		5.448	0.995
      60	21.769		4.456	0.961

   4. adsorption Thermodynamics

   Thermodynamic behavior of the bisorption of MB on WCJ is evaluated by the thermodynamic parameters. These parameters, such as the change in Gibbs energy (G), the enthalpy change (H) and entropy (S, reflect the feasibility and spontaneous nature of adsorption process [21].

   The thermodynamic relationship G=H-TS associated with the relationship VantHoff G =-RTLn Kd

   [22] allows us to reach the Eyring equation [23]:

   (10)

   Where, R is the ideal gas constant 8.31447 (J.mol-1.k-1), T is the absolute temperature (K) , Kd=Cad/Ce is the distribution coefficient, and Cad is the concentration of MB dye adsorbed (mg/L) .

   A plot of Ln kd versus 1/T is linear (Fig.12). The Values G, H, S and R2 for the removal of methylene blue are given in Table 3.

   The negative value of G indicates the biosorption is favorable and spontaneous. The positive value of change in enthalpy (H) indicates the endothermic nature of adsorption process. The positive (S) value suggests the increased disorder and randomness at the solid interface of MB with the adsorbent. Provides positive value implies that the conscious choice.

   The increase of adsorption capacity of the biosorbent at higher temperatures was due to enlargement of pore size and activation of adsorbent surface [24]

   From these results, we can conclude that the adsorption of methylene blue on WCJ was favorable.

   T (k)	G (kj/mol)	H (kj/mol)	S (j.mol-1.k-1)	R
   288	-3.407	22.653 91.99 0.877
   303	-5.836
   313	-6.867
   323	-7,.551

   Fig.12. Plot of lnKd vs. 1/T for adsorption of MB on WCJ. Table 3.Thermodynamic parameters for the adsorption of MB by WCJ

4. CONCLUSION

The parameters such initial dye concentration, contact time and temperature have shown significant effect on the removal of MB by CWJ from aqueous solutions.

The Langmuir, Freundlich and Tempkin isotherm models were used for the mathematical description of the biosorption equilibrium of MB onto CWJ. The l Langmuir isotherm model was found to provide the best fit of the experimental data in the temperature range studied.

The Kinetic studies showed that the adsorption process followed the pseudo-second-order model.

The thermodynamic results indicated the feasibility, endothermic and spontaneous nature of the adsorption process involved at 1560 °C.

The various results obtained indicated that the adsorbent chosen for this study was efficient and could be used as an economical sorbent for the industrial effluents.

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