Removal of Methylene Blue from Aqueous Solution

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Oct 8, 2013 - International Journal of Modern Organic Chemistry ... Key words: removal of methylene blue, pyrazole derivatives, Antipyrine moiety. .... and because of the slow diffusion of MB molecules into the network of the pyrazole derivatives. ..... which indicated the pseudo-first order kinetic model was poor fit for the ...

International Journal of Modern Organic Chemistry, 2013, 2(2): 150-170 International Journal of Modern Organic Chemistry ISSN: 2166-0174 Florida, USA Journal homepage: www.ModernScientificPress.com/Journals/IJOrgChem.aspx Article

Removal of Methylene Blue from Aqueous Solution Using Some New Pyrazole Derivatives Yaser A. Soliman a, M. A. Goudab, c, Ammar N. Harmala,* a

Department of Chemistry, Faculty of Education, Amran University, Yemen

b

Department of Chemistry, Faculty of Science, Mansoura University, El-Gomhoria Street, Mansoura, 35516, Egypt.

c

Department of Chemistry, Faculty of Science and Arts, Ulla, Taibah University, KSA.

* Author to whom correspondence should be addressed; E-Mail: [email protected] Article history: Received 16 September 2013, Received in revised form 30 September 2013, Accepted 3 October 2013, Published 8 October 2013.

Abstract: A series of superabsorbent heterocyclic compound s based on pyrazole derivatives Incorporated Antipyrine moiety were tested for the removal of methylene blue (MB) from aqueous solutions via batch adsorption experiments. Studies concerning the factors influencing the adsorption capacities of pyrazole derivatives such as pH, adsorbent dosage, initial dye concentration, contact time, ionic strength and temperature were systematically investigated and discussed. Results of batch experiments showed that theses adsorbents exhibited high sorption capacities toward basic dyes. Experimental data were analyzed using first order kinetics, pseudo-second order kinetics and intra-particle diffusion models. It was found that kinetics followed a pseudo-second order equation. Equilibrium isotherm data were analyzed according to Langmuir and Freundlich

equations. The characteristic

parameters for each model have been determined. The thermodynamic parameters including ΔG°, ΔH° and ΔS° for the adsorption processes of MB on the pyrazole derivatives were also calculated, and the negative value of ΔG° indicated the spontaneous nature of adsorption. Key words: removal of methylene blue, pyrazole derivatives, Antipyrine moiety.

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1. Introduction In recent years, pollution from dye wastewater has become a serious environmental problem due to the vast and increasing uses of a variety of dyes [1-4]. Methylene blue (MB) is the most commonly used substance for dying cotton, wood and silk. It can cause eye burns which may be responsible for permanent injury to the eyes of human and animals. On inhalation, it can give rise to short periods of rapid or difficult breathing while ingestion through the mouth produces a burning sensation and may cause nausea, vomiting, profuse sweating, mental confusion and methemoglobinemia [5–7]. Numerous approaches have been applied for removal of dyes from wastewater such as biological treatment [8], coagulation/flocculation [9], ozone treatment [10], chemical oxidation [11], membrane filtration [12], ion exchange [13], photo catalytic degradation [14] and adsorption [15], have been developed to remove these compound s from colored effluents. Amongst the numerous techniques of dye removal, adsorption is a well-known equilibrium separation process and an effective method for water decontamination applications [16–19]. Nowadays, development of new adsorbents having superior properties such as high adsorption capacity, fast adsorption rate, and mechanical strength has generated great interests for wastewater treatment. Using of several heterocyclic compound s having different functional groups has gained great importance due to their high adsorption capacities, especially regeneration abilities and reuse for continuous processes. Pyrazole derivatives is chemically known as 4-((3-amino-5-methyl-1H-pyrazol4-yl)diazenyl)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one.[20],1,5-dimethyl-4-((E)-(5-methyl-3((E)-(2-oxo-2-phenyl-1-thiocyanatoethyl) diazenyl)-1H-pyrazol-4-yl)diazenyl)-2-phenyl-1H-pyrazol3(2H)-one [20] and 4-((3-(5-Benzoyl-2-imino-1,3,4-thiadiazol-3(2H)-yl)-5-methyl-1H-pyrazol-4yl)diazenyl)-1,5-dimethyl-2-phenyl-1H-pyr-azol-3(2H)-one [20] in scheme (1). It are used in the treatment of antitumor, cytotoxic and antioxidant [20]. The official method [21-23] recommends UV-spectrophotometric measurement of aqueous solution of (MB) at about 662nm, Ultra-violet spectrophotometry[24,25], fluorimetry [26], chemiluminescence spectrometry [27], ion-selective electrode-based potentiometry [28], polarography [29], high-performance liquid chromatography (HPLC)[30–22], gas chromatography (GC)[33], liquid chromatography–mass spectrophotometry [34], gas chromatography–mass spectrophotometry[35]and affinity chromatography[36] have been employed for determining (MB) in Aqueous Solutions. Many of these techniques are deficient in simplicity, cost-effectiveness and easy access. The most widely used technique for the assay of (MB) in Aqueous Solutions has been UV-Vis spectrophotometry. To our best knowledge, there is no literature focusing on the use of pyrazoles attached to antipyrine moiety for the removal of MB from aqueous solutions so the objective of this work is to develop ring of pyrazoles that contain different amounts of azo groups as a potential effective Copyright © 2013 by Modern Scientific Press Company, Florida, USA

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adsorbents to remove MB from aqueous solution attributing to their following unique properties: (i) azo groups increase mechanic strength to enhance the usable life. Moreover, the ring pyrazoles provide much larger specific surface area. The raw materials are low-cost and the synthetic approach is simple, which make these heterocyclic compounds potential commercializable. (iii) These heterocyclic compounds do not cause environmental pollution during the course of treatment. Indicating that pyrazoles attached to antipyrine moiety can be used as effective and practical heterocyclic compound s adsorbents.

2. Experimental 2.1. Materials and Instruments The pH measurements were made using a pH meter (Model 744, Metrohm). The concentrations of methylene blue were analyzed using UV-Vis spectrophotometer (SHIMADZUE, Japan) provided with 1-cm matched quartz cells were used for absorbance measurements. The adsorbents were weighed using analytical balance. Water bath shaker was used for adsorption experiments. All chemicals used in the experiment were of analytical reagent grade and distilled water was used to prepare the solutions. All chemicals were of analytical grade and used as received, compound (1) is: 4-((3-amino-5methyl-1H-pyrazol-4-yl)diazenyl)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one.[20], compound (2) is: 1,5-dimethyl-4-((E)-(5-methyl-3-((E)-(2-oxo-2-phenyl-1-thiocyanatoethyl) diazenyl)-1H-pyrazol-4yl)diazenyl)-2-phenyl-1H-pyrazol-3(2H)-one. [20] and compound (3) is: 4-((3-(5-Benzoyl-2-imino1,3,4-thiadiazol-3(2H)-yl)-5-methyl-1H-pyrazol-4-yl)diazenyl)-1,5-dimethyl-2-phenyl-1H-pyr-azol3(2H)-one prepared in Chemistry department, Faculty of science, Mansoura University, Mansoura, Egypt [20]. Methylene blue was purchased from Nile-Aldrich. A stock solution of methylene blue was prepared by dissolving the powder in distilled water. The working solutions of different initial concentrations of methylene blue were prepared by appropriate dilution of the stock solution. The required pH adjustments were made with buffer solutions. For pH 2–3, H3PO4/NaOH buffer solutions were used. The CH3COOH/CH3COONa buffer solutions were used to adjust pH in the range of 4–6, while Na2HPO4/NaH2PO4 buffer solutions were used for pH 7–10. All required solutions were prepared using deionized water, provided from a Milli-Q (Millipore, Bedford, MA, USA) purification system. CH3COOH, Na2HPO4, NaH2PO4, H3PO4, NaCl, HCl and NaOH were purchased from nile-Aldrich and used without further purification. Other chemicals such as NaOH are commercially available and used without further purification. 2.2. Procedure

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Batch sorption experiments were done by shaking 0.02 g of pyrazole derivatives with 50 ml aqueous solution of methylene blue in 250 ml-Erlenmeyer flasks placed in a temperature controlled shaking water bath at concentrations (1000 ppm), pHs (between 2 and 12), ionic strength (between 0.005 and 0.3 mole/l) and temperatures (between 25 and 45 ºC) at a constant shaking rate of 125 rpm. The absorbance of the resulting color was measured against the reagent blank at 662nm. 2.3. Adsorption Equilibrium Studies The amounts of dye removed by sorbents qe and percent extracted %E can be calculated using the following equations: (𝐶ₒ −𝐶𝑒 )𝑉

𝑞𝑒 =

(1)

𝑚

%𝐸 =

(𝐶ₒ −𝐶𝑒 ) 𝐶ₒ

× 100

(2)

Where qe is the amount of dye adsorbed (mg/g). Cₒ and Ce are the initial and equilibrium liquid-phase concentrations of dye (mg/g), respectively. V is the volume of the solution (l), and m is the weight of the sorbent used (g).

2.4. Adsorption Kinetic Studies The adsorption kinetics of methylene blue onto pyrazole derivatives were measured at one initial concentrations of MB, (1000 ppm) for pyrazole derivatives. 50 ml of aqueous methylene blue solutions was introduced into a 100 ml conical flask and mixed with 0.02 g of the adsorbents. The solution was stirred continuously at 25 °C and samples were taken from the solution by fast filtration at different time intervals. The concentration of methylene blue in the residual solution was analyzed spectrophotometrically using UV-Vis spectrophotometer at wavelength 662 nm and the amount of adsorption qt was calculated according to equation (1).

3. Results and Discussion 3.1. Effect of Contact Time on Adsorption Contact time is an important parameter of adsorption which can reflect the adsorption kinetics of pyrazole derivatives for MB solution. Figure 1 shows the effect of contact time on the adsorption capacity of pyrazole derivatives for MB. It is clear that the adsorption capacity of pyrazole derivatives increased rapidly with the increase of contact time from 0 to 35 min and more than 90% of the equilibrium adsorption capacity for MB occurred within 30 min. After 60 min, the adsorption capacity became

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constant and the adsorption reached equilibrium. Therefore, 60 min was selected as the contact time for the adsorption of MB onto the composites under our experimental conditions.

Fig. 1. Effect of the contact time on adsorption capacity of Compound (1), Compound (2) and Compound (3) at one concentrations 1000 ppm for MB. (Conditions: T=25°C; adsorbent dose = 0.02 g/50 ml; pH= 7).

As shown, the adsorption process was divided into three stages: (1) an initial stage with adsorption occurring instantly, (2) subsequently slow adsorption, and (3) a final stage with adsorption reaching equilibrium and remaining constant. The first stage can be attributed to the rapid attachment of MB to the rings of the pyrazole derivatives by surface mass transfer, high electric density in rings and high resonance in compound s. At this stage, more than 80% of MB adsorption was found in all cases. The second stage was slower, possibly because many of the available external sites was already occupied and because of the slow diffusion of MB molecules into the network of the pyrazole derivatives. An asymptotic trend was found after approximately 30 min regardless of the initial MB concentration applied to the adsorption system. The amount adsorbed did not vary significantly at contact times longer than the equilibrium time (60 min). The kinetics of the adsorption process indicates that the adsorption of MB onto the pyrazole derivatives can be considered as a fast adsorption process because more than 80% of MB was adsorbed within 30 min especially at MB concentration lower than the maximum adsorbed. Such finding reveals the benefits of using this low-cost adsorbent or so-called eco-adsorbent, for the treatment of wastewaters rich in dyes in general and MB in particular. 3.2. Effect of Ionic Strength

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The presences of ions lead to high ionic strength, which may significantly affect the performance of the adsorption process. Figure 2 presents the effect of ionic strength on the uptake of MB. It was observed that the adsorption capacity decrease with the increase in ionic strength. As the concentration of NaCl ions increased from 0.01 to 0.1 M, the adsorption capacities decreased from 1100 to 600 mg/g, from 1400 to 800 mg/g and from 1200 to 800 mg/g for Compound (1), Compound (2) and Compound (3), respectively. This may be due to the fact that, the presence of salt screens the electrostatic interaction between pyrazole derivatives and dye molecules. Also, the difference in ionic osmotic pressure, between the pyrazole derivatives and the external solution, reduces with increasing ionic strength of the salt solutions. Thus, the water absorbency decreases and MB uptake decrease. Further increase in ionic strength above 0.2 M decrease the adsorption capacities sharply until 0.4 M where any further increase cause steep increase in adsorption capacities because of salting out of dye molecules from aqueous solution. These results showed ionic strength had an adverse effect on the dyes adsorption, which may be induced by the competition between the cations and the dyes for the electron rich sites.

Fig. 2. Effect of ionic strength on the removal of MB by compound (1), compound (2) and compound (3). (Conditions: T=25°C; adsorbent dose = 0.02 g/50 mL; Cₒ = 1000 mg/L; time = 2 h).

3.3. Effect of the Temperature Table 1 shows the relationship between the temperature and the adsorption capacity of MB by the pyrazole derivatives. The adsorption capacity of the pyrazole derivatives increased with increasing of the temperature from 25 to 45 °C. This is attributed to the increase in the kinetic energy of MB with the temperature, and the flexibility of the azo group increases as well. Consequently, the rate of diffusion Copyright © 2013 by Modern Scientific Press Company, Florida, USA

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of MB molecules across the external boundary layer and in the internal pores in the pyrazole derivatives increases with temperature, and the amount of MB uptake increases. Also, it is found that the adsorption of MB is an endothermic reaction.

Table 1: Effect of temperature on maximum adsorption capacities of MB by compound (1), compound (2) and compound (3)

When the temperature increased from 25 °C to 45 °C, the maximum amounts of MB removed by Compound (1), Compound (2) and Compound (3) are found to be increased from 1071to 1134.117 mg/g, from 1401.333 to 1438.542 mg/g and from 1202.389 to 1266.051 mg/g, respectively. 3.4. Adsorption Isotherms Adsorption is usually described through isotherms, that is, the amount of adsorbate on the adsorbent as a function of its pressure or concentration (if liquid) at constant temperature. Adsorption isotherm is important to describe how adsorbates interact with adsorbents and so it is important in optimizing the use of adsorbents. Three most common isotherm equations namely, Langmuir, Freundlich and Redlich-Peterson were tested here (Arami et al., 2006). The basic assumption of the Langmuir model is that adsorption takes place at specific homogeneous sites within the adsorbent. It is further assumed that once a dye molecule occupies a site, no further adsorption can take place at that site (Baskaralingam et al., 2006). Moreover, the surface of the adsorbent is uniform, that is, all the adsorption sites are equivalent (only a monolayer is formed). Also, adsorbed molecules do not interact and all adsorption occurs through the same mechanism. The Langmuir equation can be written as follows (Arami et al., 2006): 𝑞𝑒 =

𝑄ₒ 𝐾𝑙 𝐶𝑒 1+ 𝐾𝑙 𝐶𝑒

(3)

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Where qe is the amount of dye adsorbed on pyrazoles at equilibrium (mg/g), Q0 is the maximum adsorption capacity (mg/g), KL is the Langmuir constant, and Ce is the concentration of dye solution at equilibrium (mg/L). The linear form of Langmuir equation is: 𝐶𝑒 𝑞𝑒

=

1 𝑄ₒ 𝐾𝑙

+

𝐶𝑒

(4)

𝑄ₒ

The monolayer adsorption capacity, Q and the Langmuir constant Kl can be obtained from the linear plot of Ce/qe against Ce. An essential characteristic of Langmuir isotherm can be expressed by a dimensionless constant called equilibrium parameter, RL (Webi and Chakravort, 1974), defined by: 𝑅𝑙 =

1 1 + 𝐾𝑙 𝐶ₒ

Where C0 is the highest initial dye concentration (mg/L), R L values indicate the type of isotherm to be either unfavorable (RL> 1), linear (Rl= 1), favorable (0 1). The Freundlich parameters can be obtained from the following linearized equation: ln 𝑞𝑒 = ln 𝐾𝑓 +

1 ln 𝐶𝑒 𝑛

By linear plotting ln qe as the function of ln Ce, the values of Kf and n can be obtained from the slope and the intercept of the plot. Figures (3) and (4) shows the linear plot of Langmuir and Freundlich isotherms for adsorption of MB on pyrazoles. The model parameters obtained by applying Langmuir and Freundlich models to the Copyright © 2013 by Modern Scientific Press Company, Florida, USA

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experimental data are given in Tables (2) and (3). It can be found that the regression coefficients R2 obtained from Langmuir model are closer to 1 than that of the Freundlich model, suggesting that the Langmuir isotherm fits better with the adsorption of MB on Compound (1), Compound (2), and Compound (3). In addition, the qmax values for the adsorption of MB onto the pyrazoles calculated from the Langmuir model are all the same as the experimental data. Also, RL values obtained are in all cases between 0 and 1, thereby confirming that the adsorption is a favorable process. It can be concluded that the monolayer Langmuir adsorption isotherm is more suitable to explain the adsorption of MB onto pyrazoles.

Fig. 3. Langmuir plot for the adsorption of MB by compound (1), compound (2) and compound (3) at three different temperatures (a) 25 °C, (b) 35 °C and (c) 45 °C.

Fig. 4. Freundlich plot for the adsorption of MB by compound (1), compound (2) and compound (3) at three different temperatures 25 °C, 35 °C and 45 °C. Copyright © 2013 by Modern Scientific Press Company, Florida, USA

Int. J. Modern Org. Chem. 2013, 2(2): 150-170 Table 2: Langmuir isotherm parameters and correlation coefficient for adsorption of MB by compound (1), compound (2) and compound (3) at different temperatures.

Table 3: Freundlich isotherm parameters and correlation coefficient for adsorption of MB by compound (1), compound (2) and compound (3) at different temperatures.

3.5. Intra-particle Diffusion Model

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Adsorption is a multi-step process involving transport of solute molecules from the aqueous phase to the surface of the solid particles of adsorbent, and then diffusion of the solute molecules into the interior of the pores, which is likely to be a slow process, and is therefore, rate determining. The intra-particle diffusion parameter, 𝐾𝑝 (mmol.g-1 h-0.5) is defined by equation

𝑞𝑡 = 𝐾𝑝 𝑡0.5 + 𝐶

(5)

Where kp is the intra-particle diffusion rate constant (mmol.g-1 h-0.5) and C is a constant. According to this model qt versus t0.5 should be linear if intra-particle diffusion is involved in the adsorption process [50]. From Eq. (5), if pore diffusion is the rate limiting step, then a plot of qt against t0.5 must give a straight line with a slope that equals kp and the intercept value c represents the resistance to mass transfer in the external liquid film. Fig (5) shows the plot of qt against t0.5 of compound (1), compound (2) and compound (3) for MB at three different initial concentrations, the plots are multilinear, containing at least three linear segments which indicate that three steps occur during adsorption process. The first sharper portion is transport of dye molecules from the bulk solution to the adsorbent external surface by diffusion through the boundary layer (film diffusion). The second portion is the diffusion of the dye molecules from the external surface into the pores of the adsorbent. The third portion is the final equilibrium stage, where the dye molecules were adsorbed on the active sites on the internal surface of the pores and the intraparticle diffusion starts to slow down due to the solute concentration getting lower and lower in solution [51, 52].

Fig. 5. Intra-particle diffusion plots for adsorption of MB on compound (1), compound (2) and compound (3) at different initial dye concentrations.

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Also, the linear portions of curves did not pass through the origin, suggesting that pore diffusion is not the step controlling the overall rate of mass transfer at beginning of adsorption. In Table (4), the correlation coefficients (R 2 ) for the linear segment intra-particle diffusion model were between 0.9286 and 0.9939, indicating that the intra-particle diffusion was not the only rate controlling step, other process could control the rate of adsorption. The boundary layer effect may control the rate of mass transfer in the time period of the first linear segment. This conclusion could be corroborated by the analysis of data from Boyd's model [53-55].

Table 4: Intraparticle diffusion parameters for adsorption of MB (1), compound (2) and compound (3) at different concentrations.

The model of Boyd is expressed as: 𝐹 =1−

6 exp (1 − 𝐵𝑡) 𝜋2

(6)

Where F is the fractional attainment of equilibrium, at different times, t, and Bt is a function of F 𝐹=

𝑞𝑡 𝑞𝑒

Where qt and qe are the dye uptake (mmol g−1) at time (t) and at equilibrium, respectively. Eq. (6) can be rearranged to 𝐵𝑡 = −0.4977 − ln (1 − 𝐹)

(7)

Fig. 6 shows the values of Bt were calculated from Eq. (7) and plotted against time t. The linearity of this plot can provide available information to distinguish intra-particle diffusion and boundary layer effect (film diffusion) rates of adsorption. If a plot of Bt versus t is a straight line passing through the origin, then adsorption will fit layer effect. The plots are linear only in the initial period of adsorption Copyright © 2013 by Modern Scientific Press Company, Florida, USA

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and do not pass through the origin, indicating that external mass transfer is the rate limiting process in the beginning of adsorption and then is the intra-particle diffusion.

Fig. 6. Bt versus t plot for MB adsorption onto compound (1), compound (2) and compound (3) at three different initial dye concentrations.

3.5. Adsorption Kinetics 3.5.1. The pseudo-first order equation and the pseudo-second order equation In order to investigate the controlling mechanism of adsorption process of compound (1), compound (2) and compound (3) for MB, the pseudo-first order and the pseudo-second order kinetic models were cited to evaluate the experimental data obtained from batch MB removal experiments. The pseudo-first order kinetic model has been widely used to predict metal adsorption kinetics. It was suggested by Lagergren [48] for the adsorption of solid/liquid systems and its linear form can be formulated as

log(𝑞𝑒 − 𝑞𝑡 ) = log 𝑞𝑒 −

𝐾1 𝑡 2.303

Where qe is the adsorption uptake of copper at time t (mol g-1) and k1 (min-1) is the rate constant of the pseudo-first-order adsorption. A plot of log (qe - qt) versus t should be linear; the parameters k1 and R2 (correlation coefficient) calculated from the data (Fig. 7) are listed in Table 5. It can be seen that the Copyright © 2013 by Modern Scientific Press Company, Florida, USA

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linear correlation coefficients (R2) for the pseudo-first order kinetic model are very high. However, there are large differences between the experimental qe values (qe,exp) and the calculated qe values (qe,cal), which indicated the pseudo-first order kinetic model was poor fit for the adsorption processes of Compound (1), Compound (2) and Compound (3) for MB.

Fig. 7. Pseudo-first-order kinetic model for the adsorption of MB by Compound (1), Compound (2) and Compound (3) at three different initial concentrations 1000 ppm.

Table 5: First order kinetic parameters for adsorption of (1), compound (2) and compound (3) at different concentrations.

The kinetic data were further analyzed using Ho's pseudo-second-order kinetic model [49]. It can be expressed as

𝑡 1 𝑡 = + 2 𝑞𝑡 𝐾2 𝑞𝑒 𝑞𝑒

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Where k2 (g mol-1 min-1) is the rate constant of pseudo-second-order adsorption. Fig. 8 shows the plot of t/q versus t for MB onto compound (1), compound (2) and compound (3). It can be observed from Table 6 that R2 for the pseudo-second order kinetic model are all over 0.9994. These suggested that the adsorption processes of compound (1), compound (2) and compound (3) for MB can be well described by the pseudo-second order kinetic model.

Fig. 8. Pseudo-second-order kinetic model for the adsorption of MB by compound (1), compound (2) and compound (3) at three different initial concentrations 1000 ppm.

Table 6: Second order kinetic parameters for adsorption of MB by compound (1), compound (2) and compound (3) at different concentrations.

3.6. Thermodynamic Study The data obtained from the temperature study were used for thermodynamic analysis. Thermodynamics analysis focused on the Gibbs free energy, which is presented in Eq. (8). The Gibbs

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free energy can also be expressed using enthalpy and entropy at a constant temperature (Eq. (9). The linearized form Esq. (8) and (9) results in Eq. (10) which is the van't Hoff equation [56]: ΔG° = -RT ln Kc

(8)

Δ G° = ΔH° - TΔS°

(9)

𝑙𝑛 𝑘𝐶 =

∆𝑆 𝑅



∆𝐻 𝑅𝑇

(10)

where ΔG° (kJ/mol) is the change in Gibbs Free Energy, ΔH° (kJ/mol) is the enthalpy change of MB adsorption, ΔS° (J/molK) is the entropy change of MB adsorption, R is the universal gas constant (8.314J/mol K) Tis the absolute temperature (K) and Kl is the Langmuir constant. By plotting a graph of ln Kc versus 1/T (Figure 9) the values of ΔH° and ΔS° can be estimated from the slope and intercept of van't Hoff plots, respectively. The thermodynamic parameters are given in Table 8. It is clear from the table that the values of ΔG° are negative for Compound (1), Compound (2) and Compound (3). The negative values of ΔG° at various temperatures indicate the spontaneous nature of the sorption process. The fact that the values of the ΔG° decrease with increasing temperature indicates the increase of spontaneous effect. For all the sorbents, the positive value of ΔH° suggested the endothermic nature of the adsorption process. Moreover, the positive values of ΔS° point out the increased randomness at the solid/liquid interface during the sorption of dye on compound (1), compound (2) and compound (3).

Fig. 9. The plots of lnKa versus T−1 for estimations of thermodynamic parameters of the adsorption reactions. Copyright © 2013 by Modern Scientific Press Company, Florida, USA

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4. Conclusion The result of the present study reveals that some new pyrazole derivatives attached to antipyrine moiety can be used as effective and practical heterocyclic compounds adsorbents based on polarization of carbonyl groups, the ring pyrazoles provide much larger specific surface area and azo groups increase mechanic strength to enhance the usable life may be an extremely viable adsorbent for application in the treatment of water and industrial wastewater contaminated with dyes. The amount of MB adsorbed was found to increase with increasing the carbonyl groups and azo groups. Moreover, the adsorption of MB was dependent on initial concentration, reaction temperature and pH. The MB adsorption capacity increased with the increase of pH in the range of 3–8, where ionization of carbonyl group occurs. The adsorption of MB onto the pyrazole derivatives reached equilibrium within about 60 min. The adsorption equilibrium could be well described by Langmuir adsorption isotherms, namely monolayer adsorption on a homogenous surface. The adsorption kinetics followed a pseudo-second order kinetic model and intra-particle diffusion was involved in the adsorption process. Thermodynamic results indicated that the adsorption process was spontaneous and endothermic in nature.

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