Accepted Manuscript Adsorption behaviour of direct yellow 50 onto cotton fiber: equilibrium, kinetic and thermodynamic profile L.F.M. Ismail, H.B. Sallam, S.A. Abo Farha, A.M. Gamal, G.E.A. Mahmoud PII: DOI: Reference:

S1386-1425(14)00471-5 http://dx.doi.org/10.1016/j.saa.2014.03.060 SAA 11893

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

18 November 2013 13 March 2014 21 March 2014

Please cite this article as: L.F.M. Ismail, H.B. Sallam, S.A. Abo Farha, A.M. Gamal, G.E.A. Mahmoud, Adsorption behaviour of direct yellow 50 onto cotton fiber: equilibrium, kinetic and thermodynamic profile, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.2014.03.060

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Adsorption behaviour of direct yellow 50 onto cotton fiber: equilibrium, kinetic and thermodynamic profile a

L. F. M. Ismail*, aH. B. Sallam, aS. A. Abo Farha, aA. M. Gamal, and a G. E. A. Mahmoud a Al-Azhar University - Faculty of Science (Girls), Chemistry Department, Nasr City, Cairo, Egypt. Abstract This study investigated the adsorption of direct yellow 50 onto cotton fiber from aqueous solution by using parameters, such as pH, temperature, contact time, initial dye concentration and the effect of sodium sulphate, tetrasodium edate and trisodium citrate. The extent of dye adsorption increased with increasing contact time, temperature and solution concentration. The experimental data were analysed by the Langmuir and Freundlich models of adsorption. It was found that the Langmuir equation fit better than the Freundlich equation. The results show that the presence of SE and SC significantly enhance the dye adsorption onto cotton fiber. In addition, the adsorption data obtained at different temperatures of DY50 onto cotton fiber were applied to pseudo first-order, pseudo second-order and intraparticle diffusion models. The rates of adsorption were found to conform to pseudo second-order kinetics with good correlation. Also, free energy of adsorption (G#), enthalpy (H#), and entropy (S#) changes were determined to predict the nature of adsorption. The positive value of the enthalpy change indicated that the adsorption is endothermic process. The activation energy, Ea, is ranged between 1.9- 3.9 kJ mol-1 indicated that the adsorption process is a physisorption. This low value of Ea generally indicates diffusion controlled process. Keywords: Cotton fiber, Adsorption, Isotherm, Kinetics, Thermodynamics. _____________________________________________________________________ * Corresponding author. E-mail address: [email protected] 1. Introduction Direct dyes are one of the most popular types of colorant used for the dyeing and printing of cellulosic fibres and their blends. Because of the ease of their application and the wide gamut of products available at a modest cost, direct dyes are still a popular dye class [1, 2]. The name ʻdirect dyeʻ alludes to the fact that these dyes do not require any form of ʻfixingʻ. They are almost always azo dyes, with some similarities to acid dyes. Most direct dyes have disazo and trisazo structures, with each hue dominated by unmetallized structures [3, 4]. They also have sulphonate functionality, but in this case, it is only to improve solubility, as the negative charges on dye and fibre will repel each other. Their flat shape and their length enable them to lay along-side cellulose fibres and maximise the Van-der-Waals, dipole and hydrogen bonds. Moreover, the dyeing is a heterogeneous process which takes place at the interphase between the dyeing solution and the fiber. Its proceeding includes (i) diffusion of the dye in the bulk liquid phase; (ii) adsorption of the dye on the fibers outer surface; (iii) diffusion in the bulk of the fibers; (iv) adsorption on the inner surface of the fibers [5]. Depending on the dyeing conditions each one of these steps can become limiting and hence determining the overall rate and the kinetic relations

1

of the process. The last step- the fixation of the dye on the fibrous material presents definite interest. Consequently, the present work aims to study a convenient and economic method for the adsorption of direct yellow 50 (DY50) onto cotton fiber, to gain an understanding of the adsorption kinetics, to describe the rate and mechanism of adsorption, to determine the factors controlling the rate of adsorption and to calculate the activation energy of the system. The effects of initial DY50 concentration, solution pH, effect of nonbiodegradable inorganic salt (sodium sulphate) and biodegradable organic salts (tetrasodium edate and trisodium citrate) and temperature on DY50 adsorption rate have been evaluated. The best-fit equilibrium isotherms are determined by Freundlich and Langmuir models. Adsorption kinetic models are employed to analyse the kinetics and mechanisms of DY50 adsorption onto cotton fiber. 2. Experimental 2.1. Adsorbate and adsorbent C.I. Direct Yellow 50 (DY50) is diazo dye (Scheme 1). The dye is purchased from Ciba-Geigy. It is a water-soluble dye. The stock solution of DY50 is prepared by dissolving the accurately weighed amount of dye in 1 L of distilled water. All working solutions are prepared by diluting the stock solution with distilled water. In the investigations Mill desized, scoured and bleached cotton fabric (Poplin) is supplied by Misr Company for spinning and weaving, Mehala El-kubra, Egypt. Short specification of cotton fabric is listed in Table 1. H3 C

NaO 3 S

H N

H N CO

CH3

N

N

N

N

SO 3Na

SO 3Na

NaO 3 S

Scheme 1: C.I. Direct Yellow 50 (DY50)

Table.1: Cotton fabric (Poplin) construction. Threads (cm)

Count

Warp fill warp 109 72 04 (100% Cotton Poplin)

fill 04

Width (cm)

Weight (g/m2)

160

120

Other chemicals (sodium sulphate (SS), tetrasodiumedate (SE) trisodiumcitrate (SC), detergent nastapon, sodium hydroxide, nitric acid) from BDH or Merk are used as received. 2.2. Equilibrium and kinetic studies Adsorption experiments are conducted in batch mode to evaluate the effects of various parameters, such as initial dye concentration (22.00 - 1056.15mg/l), effect of inorganic salt (sodium sulphate [SS] = 40 g/l at pH 7.03) and organic salts (sodium edate [SE] = 30 g/l at pH 7.11 and sodium citrate [SC]= 20 g/l at pH 7.09 and temperature (40-90ºC)). pH and contact time, on the adsorption of DY50. In each 2

adsorption experiment, 1.0 g of the cotton fiber is added to 30 ml of DY50 solution into 100 ml conical flasks (L: R 1:30) with adjusting the pH (DATALOGGER 6209; JENCO ELECTRONICS – LTD pH meter, U.S.A.) with sodium hydroxide or nitric acid. The flasks are placed in the thermostatic shaker (Elphin 358 S, Poland) and agitated at a constant speed of 170 rpm at 25 ◦C for 2 hours. The sample was withdrawn from the shaker at the end of the adsorption period, and the adsorbent was separated from the solution. The absorbance of the residual solution was measured to enable calculation of the dye concentration. The equilibrium amount of adsorbed dye per unit mass, qe (mg /g), and the amount of dye adsorbed on the adsorbent at time t, qt (mg/ g), are calculated using the following equations Eqs. (1) and (2)[1, 6]: qe = ((C0 − Ce)/W)V (1) qt = ((C0 – Ct)/W)V (2) where C0 and Ce are the concentrations of the dye in the solution at initial and equilibrium (mg/l), respectively; V is the volume of the solution (ml); W is the mass of the dry cotton fiber (g). The dye concentrations are measured at the maximum absorbance wavelength (λmax = 397 nm) using a JENWAY- 6300 UV-Visible spectrophotometer. The absorbance of solutions measured using a 1cm quartz cell. 2.3. Kinetics and isotherm studies The kinetics of the adsorption is determined by analyzing the quantity of dye adsorbed from aqueous solution at different time intervals. The initial dye concentration in the test solution is varied to investigate their effects on the adsorption kinetics. Isotherms of the adsorption at various dosages are analyzed to determine the equilibrium adsorption capacity. Thermodynamic parameters were calculated from the equilibrium adsorption data at different temperatures. 3. Results and discussion 3.1. Effect of contact time on adsorption In order to determine the adsorption equilibrium time, the adsorption of DY50 dye onto cotton fiber is studied as a function of contact time. The contact time between adsorbate and the adsorbent is of significant importance in the adsorption process. Therefore, the contact time experiment for DY50 dye has been carried out with a constant initial dye concentration of 113.366mg/l, L.R. 1:30 at pH 7.03 used in aqueous medium and in presence of 40g/l SS, 30g/l SE at pH 7.11 and in presence of 20g/l SC at pH 7.09 and at different temperature. The effect of contact time of DY50 adsorbed on cotton fiber in aqueous and in presence of 40g/l SS at pH 7.03 is shown in Figure 1. Figure 1 shows that the required contact time to reach the equilibrium of DY50 is 120 min. The contact time curve shows that the dye removal rate is rapid in the first 80min due to surface adsorption, and remained almost unchanged after 120 min., indicating an equilibrium state. The curve of contact time is single, smooth and continuous leading to saturation due to intraparticle diffusion process. This curve indicates the possible monolayer coverage of dye on the surface of cotton fiber [7, 8]. Similar results are obtained in presence of 30g/l SE at pH 7.11 and in presence of 20g/l SC at pH 7.09. 3. 2. Effect of temperature of the dye solution on adsorption The effect of temperature on the adsorption rate of DY50 on cotton fiber is investigated at 40, 50, 60, 70, 80 and 90 ◦C. The temperature has two major effects on the adsorption process. Increasing the temperature is known to increase the rate of diffusion of the adsorbate molecules across the external boundary layer and in the internal pores of the adsorbent, owing to the decrease in the viscosity of the solution. In addition, changing the temperature will change the equilibrium capacity of the adsorbent for a particular adsorbate [9]. Figure 1 presents the contact time versus

3

adsorbed amount at different temperatures, and indicates that with the increase in temperature the amount of adsorbed dye increases, indicating the process to be endothermic. This kind of temperature dependence of the adsorbed amount of DY50 may reflect the increase in the case with which the dye penetrates into the cotton fiber because of its larger diffusion coefficient. In fact, a possible mechanism of interaction is the reaction between the chromophore groups of the dye molecule and the groups in cotton fiber; such a reaction could be favored at higher temperatures. Hydrogen bond can occur between OH groups of cotton fiber and nitrogen atom of dye. 3.3. Effects of the initial concentrations of the dye solution on adsorption The initial concentration provides an important driving force to overcome all mass transfer resistances of all molecules between the aqueous and solid phases [10, 11]. The initial concentrations of DY50 solutions are changed from 22.009 to 1056.153 mg/l and time intervals are assessed until no adsorption of adsorbate on cotton fiber takes place. Figure 2 shows the effects of the amount of DY50 adsorbed by cotton fiber under different initial DY50 concentrations in presence of 40g/l SS at pH 7.03, in presence 30g/l S.E. at pH 7.11 and in presence of 20g/l S.C. at pH 7.09 and temperature 90ºC. The results show that the adsorption increases with increasing initial DY50 concentration. The adsorption of dye is found to be rapid at the initial period of contact time and remained almost unchanged after 120 min., indicating an equilibrium state. In order to ensure complete adsorption equilibrium, 2 h is chosen as the contact time in each batch equilibrium adsorption experiment. This is caused by attractive forces between the dye molecule and the adsorbent such as van der Waals forces and electrostatic attractions; fast diffusion onto the external surface is followed by fast pore diffusion into the intraparticle matrix, which contains the chromophere groups, to attain rapid equilibrium. The increase in loading capacity of the adsorbent with relation to dye ions is probably due to a high driving force for mass transfer. In fact, the more concentrated the solution, the better the adsorption [12]. In other words, an increase in the surface loading led to a decrease in the adsorption rate. Generally, when adsorption involves a surface reaction process, the initial adsorption is rapid. Then, a slower adsorption would follow as the available adsorption sites gradually decrease [13]. 3. 4. Effects of the initial pH of the dye solution on adsorption The pH is one of the most important factors controlling the adsorption of dye onto cotton fiber. The pH of the solution affects the surface charge of the adsorbents. Change of pH affects the adsorptive process through dissociation of functional groups on the adsorbent surface active sites [14]. This subsequently leads to a shift in reaction kinetics and equilibrium characteristics of adsorption process. Figure 2 shows the adsorption of DY50 reaches maximum values at pH values 7.03, 7.11 and 7.09 in presence of SS, SE and SC, respectively. When the initial solution pH is between 6.0 and 7.1 the adsorption of DY50 is favored, with the increase of the solution pH the dye adsorption efficiency decreased slightly in this pH range. However, a significant decline in dye adsorption occurred when the pH is greater than 7.1. 3.5. Effect of SS, SE and SC on adsorption Figure 4 shows that the adsorption capacity increases as the concentration of SS, SE and SC increases with initial dye concentration 113.366mg/l and L.R 1:30 for 2 hour dyeing time. For dyeing with DY50, the function of electrolyte in dyeing cellulosic fabrics with direct dye is to neutralize the negative surface charge of the cellulose, reduce the electrostatic repulsion of ionic direct dye and allow the dye to exhaust. Direct dye which requires lower levels of salt have been recently described [15]. Figure 4 shows

4

that maximum adsorption capacity of DY50 on cotton fabric reaches at 40g/l SS, 30g/l SE and 20g/l SC. The penetration rate depends on the penetrate reaction with hydroxyl group [16]. As a result of complicated interaction arising, diffusion coefficients of many dyes increase with salt concentrations to a maximum values and then being to decrease at high concentration. The molecules of direct dyes are made large so as to build up the physical attraction between fabric and dye, thus making them more substantive. Moreover, adsorption capacity of DY50 increases as the concentration of SE or SC is increased up to 30g/lg/l and 20g/l respectively. Also Figure 4 shows comparative results of the adsorption capacity in presence of 30g/l and 20g/l from SE, SC and 40g/l from SS. It’s clear that SE and SC are an effective fixing agent for direct dyeing. In the case of the substantive direct dyestuffs, the function of salt is to increase the size of the colloidal aggregates of the dyestuff and thus to make easier their coagulation on the fabric [17]. Taking into account that the amount of SS, compared to that of SE and SC used to produce the same depth of shade is ~ 1: 0.75: 0.5 respectively, this reduce the overall raw material costs. 3.6. Adsorption isotherms The correlation of equilibrium adsorption data by either theoretical or empirical equations is important in the design and operation of adsorption systems. Adsorption isotherms demonstrate the relationships between equilibrium concentrations of adsorbate in the solid phase q, and in the liquid phase C at constant temperature [18]. Adsorption isotherms are described in many mathematical forms. They are often obtained in the laboratory using batch tests in which the equilibrium data are attempted by various isotherm models such as Langmuir and Freundlich isotherms [18 – 20]. The Langmuir isotherm has been widely used to describe single-solute systems. This isotherm assumes that intermolecular forces decrease rapidly with distance and consequently it can predict monolayer coverage of the adsorbate on the outer surface of the adsorbent. Further assumption is that adsorption occurs at specific homogeneous sites within the adsorbent and there is no significant interaction among adsorbed species. The Langmuir isotherm is given by the following Eq. (3) [21]: qe= QbCe / (1 + bCe) (3) a linear form of this expression is: 1/qe= (1/Q) + (1/QbCe) (4) where qe is the amount of dye adsorbed per gram of cotton fiber (mg/g) at equilibrium; Ce denotes the equilibrium concentration of dye in solution (mg/l); b represents the Langmuir constant (l/mg) that relates to the affinity of binding sites and Q is the theoretical saturation capacity of the monolayer (mg/g). The values of Q and b are calculated from the intercept and slope of the linear plot of 1/qe versus 1/Ce. Furthermore, the effect of the isotherm shape is considered with a view to predict whether an adsorption system is favorable or unfavorable. Another important parameter, RL, called the separation factor or equilibrium parameter, also evaluated in this study from the relation (Eq. 5) [22]: RL=1/ (1+bCo) (5) where b is the Langmuir constant (l/mg) and C0 is the initial dye concentration. Ho and McKay [23] established that (i) 0 < RL < 1 for favorable adsorption, (ii) RL > 1 for

5

unfavorable adsorption, (iii) RL = 1 for linear adsorption and (iv) RL = 0 for irreversible adsorption. Moreover, the Freundlich model is an empirical equation that assumes heterogeneous adsorption due to the diversity of adsorption sites. The Freundlich equation is (Eq. 6) [24]: qe = Qf Ce1/n (6) Eq. 6 can be linearized as (Eq. 7): lnqe = lnQF + 1/n(lnCe) (7) where qe is the equilibrium dye concentration (mg/g); Ce the equilibrium dye concentration in solution (mg/l); Qf and n are the Freundlich constants, which represent the adsorption capacity and the adsorption strength, respectively. Qf and 1/n can be obtained from the intercept and slope of the linear plot of ln(qe) versus ln(Ce). The magnitude of 1/n quantifies the favorability of adsorption and the degree of heterogeneity of cotton fiber surface. If 1/n is less than unity, indicating favorable adsorption, then the adsorption capacity increases and new adsorption sites occur [25 15]. Figures 5 and 6 display the adsorption isotherms of Langmuir and Freundlich for DY50 on cotton fiber in aqueous and in presence of 40 g/l SS (other condition not shown), which revealed the relationship between the amount of DY50 adsorbed per unit mass of cotton fiber (qe) and the equilibrium concentration in solution (Ce). Table 2 summarized the coefficients of the Langmuir and Freundlich isotherms at different temperatures at dye concentration 113.366 mg/l and in presence of SS, SE and SC. Most of the r values exceed 0.99 for both the Langmuir and the Freundlich models, suggesting that both models closely fitted the experimental results. However, the regression results demonstrated that the Langmuir isotherm fitted the experimental data better than the Freundlich suggesting monolayer coverage of DY50 on surfaces of cotton fiber. Table 2 shows that b value increase with temperature. The results implied that the affinity of the binding sites for DY50 increased with the temperature. RL lied between zero and unity, suggesting that the adsorption of DY50 on cotton fiber is favorable. Both the Langmuir and the Freundlich models suggest that increasing temperature increased adsorption capacity, revealing that the adsorption is endothermic. Moreover, Tables 2 shows that the presence of organic salts (SE and SC) significantly enhance the dye adsorption (high Q, b and Qf values) onto cotton fiber compared with the results obtained in aqueous and in the presence of SS. Thus, presence SE and SC is an alternative way to subsequently increase the affinity between DY50 dye and the cotton fiber. 3.7. Adsorption kinetics Representative concentration-time profile for the sorption of DY50 dye on cotton fiber with initial dye concentration 113.366mg/l and L.R. 1:30 at pH 7.03 used in aqueous medium and in presence of 40g/l SS is shown in Figure 1. Evidently, cotton fiber shows high efficiencies to adsorb DY50 dye from its aqueous solutions. The adsorption process attained equilibrium gradually. Three consecutive mass transport steps are associated with the adsorption of a solute from solution [26, 27]. First, the solute migrates through the solution to the external surface of the sorbent particles by molecular diffusion (film diffusion), followed by solute movement from particle surface to interior sites (pore diffusion) and finally the solute adsorbed onto these sites. Figure 1 depicts that the time profile of dye uptake is a single, smooth and continuous curve leading to saturation, suggesting also the possible monolayer

6

coverage of dyes on the sorbent surface. Figure 1 show also that the contact time required to attain equilibrium is almost 2 h for the dye and cotton fiber. 3.7.1. First order kinetic model The kinetic adsorption data are processed to understand the dynamics of the adsorption process in terms of the order of the rate constant. Kinetic data are treated with the pseudo-first order kinetic model of Lagergren based on solid capacity [2832]. The Lagergren first-order model [32] is given by the following differential Eq. (8): dqt = k1(qe - qt) (8) where qe and qt refer to the amount of dye adsorbed (mg/g) at equilibrium and at time t (min), respectively, and k1 (min-1) is the equilibrium rate constant of the pseudo-first order reaction. Integrating Eq. (8) for the boundary conditions t =0 to t= t and qt =0 to qt, gives Eq. (9) which is the integrated rate law of pseudo-first order reaction. ln(qe1 - qt) = ln qe1 - k1t (9) Values of the rate constant k1 and the equilibrium adsorption capacity qe could be respectively obtained from the slope and the intercept of the straight line representing the adsorption data. Figure 7 shows representative plots of ln (qe - qt) versus t at initial dye concentrations of 113.36 mg/l, L: R 1:30 and pH 7.03 in aqueous and in presence of 40 g/l SS at different temperatures ranges from 40oC to 90oC. The calculated values of k1 and qe1 at different concentrations and temperatures are given in Tables 3 and 4. Although the correlation coefficients, r1 , for the application of the pseudo first-order model are reasonably high in some cases, all of the intercepts of the straight line plots do not yield predicted qe values equal, or even values reasonably close to experimental qe values (Tables 3 and 4) [21]. 3.7. 2. Second order kinetic model Kinetic data are further treated with pseudo second-order kinetic model [32, 33]. The differential equation is (Eq. 10): dqt /(qe2 - qt)2 = k2 dt (10) where k2 is the equilibrium rate constant of the pseudo-second order adsorption (g/mg min). Integration of Eq. (10) for the boundary conditions t= 0 to t= t and q =0 to q t gives (Eq. 11) [1, 34]: t/(qe - qt) = 1/k2qe2 + t/qe (11) If pseudo second-order kinetics is applicable, the plot of t/qt versus t should show a linear relationship. The plot of the linearised form of the second-order model at 113.366 mg/l, L.R. 1:30 and pH 7.03 used in aqueous medium and in presence of 40g/l SS is given in Figure 8. The straight lines in the plot of t/qt versus t show good agreement of experimental data with the second-order kinetic model for the DY50 (Table 3 and 4). The slopes and intercepts of plots of the t/qt versus t are used to calculate the k2 and qe2. The correlation coefficients (r2 ) for the second order rate kinetic model are higher than 0.99. The calculated qe2 values agree very well with the experimental data (Tables 3 and 4). These indicate that the adsorption of DY50 from aqueous solution on cotton fiber obeys pseudo second-order kinetic model [1, 33, 34]. 3.8. Adsorption mechanism The prediction of the rate-limiting step is an important factor to be considered in sorption process. For solid–liquid sorption process, the solute transfer process was usually characterized by either external mass transfer (boundary layer diffusion) or intraparticle diffusion or both. The mechanism for the adsorption of DY50 by cotton fiber may be assumed to involve the following steps [35]: 1. Migration of dye from the bulk of the solution to the surface of adsorbent. 2. Diffusion of dye through the

7

boundary layer to the surface of adsorbent. 3. Adsorption of dye at an active site on the surface of adsorbent. 4. Intraparticle diffusion of dye into the interior pore structure of adsorbent. The boundary layer resistance will be affected by the rate of adsorption and increase in contact time, which will reduce the resistance and increase the mobility of dye during adsorption [36]. The adsorption of DY50 at the active sites of cotton fiber can mainly be governed by either liquid phase mass transfer rate or intraparticle mass transfer rate. 3. 8.1. Intraparticle diffusion The adsorbate species are most probably transported from the bulk of the solution into the solid phase through an intraparticle diffusion process, which is often the rate-limiting step in many adsorption processes. The possibility of intraparticle diffusion is explored by using the intraparticle diffusion model [14, 36]. An empirically found functional relationship, common to adsorption processes defines that the uptake varies almost proportionally with t1/2, the Weber-Morris plot, rather than with the contact time t (Eq. 12) [37]. qt = ki√t + C (12) where ki is the intraparticle diffusion rate constant (mol g-1 min-1/2). According to Eq. (12), a plot of qt versus t1/2 should be a straight line with a slope ki and intercept C when adsorption mechanism follows the intraparticle diffusion process. For intraparticle diffusion model, Ho [38] pointed out that it is essential for the qt versus t1/2 plots to go though the origin if the intraparticle diffusion is the sole rate-limiting step. The intraparticle diffusion plot at different temperatures with initial dye concentration 113.366mg/l, L.R. 1:30 and pH 7.03 used in aqueous medium and in presence of 40g/l SS is given in Figure 9. In the present study, any plot does not passed through the origin. This indicates that although intraparticle diffusion is involved in the adsorption process, it is not the sole rate-controlling step. This also confirms that adsorption of DY50 on the adsorbent is a multi-step process, involving adsorption on the external surface and diffusion into the interior [14]. From Figure 9, at all conditions, the sorption process tends to be followed by two phases. It was found that an initial linear portion ended with a smooth curve followed by a second linear portion. The two phases in the intraparticle diffusion plot suggest that the sorption process proceeds by surface sorption and the intraparticle diffusion. The initial curved portion of the plot indicates boundary layer effect while the second linear portion is due to intraparticle or pore diffusion. The slope of second linear portion of the plot has been defined as the intraparticle diffusion parameter ki [39]. Tables 3 and 4 show the corresponding model fitting parameters, indicating the adsorption mechanism follows the intraparticle diffusion process. It is found that the values of ki increased with increasing initial DY50 concentration (Table 4). The driving force of diffusion is very important for adsorption processes. Generally, the driving force changes with the adsorbate concentration in the bulk solution. The increase of adsorbate concentration results in an increase of the driving force, which will increase the diffusion rate of DY50 [31].On the other hand, the intercept of the plot reflects the boundary layer effect. Larger the intercept, greater is the contribution of the surface sorption in the rate-limiting step. The calculated intraparticle diffusion coefficient ki value at different initial dye concentrations is shown in Table 4. Since the double nature of intraparticle diffusion plot confirms the presence of both surface adsorption and intraparticle diffusion [30]. 3.9. Activation parameters

8

The activation energy of dye adsorption onto the adsorbent can be calculated by Arrhenius relationship [40, 41] ln k = ln A - Ea/RT (13) -1 -1 where k is either the pseudo-second-order constant (k2, g mol min ) or intraparticle diffusion rate constant (ki , mol g-1 min-1/2), A the Arrhenius factor which is a temperature independent factor, Ea is activation energy of adsorption (J mol-1), R is the gas constant (8.314 Jmol-1 K-1), T is the solution temperature (K). Plotting of ln k against the reciprocal temperature gives a reasonably straight line, the gradient of which is -Ea/R. From Eq. 13, the activation energy, Ea, is ranged between 1.9-3.9 kJ mol-1 (Tables 5 and 6). The magnitude of activation energy gives an idea about the type of adsorption which is mainly physical or chemical. Low activation energies (< 4.20 kJ mol-1 [42]) are characteristics for physical adsorption. The result obtained for the adsorption of DY50 onto cotton fiber indicates that the adsorption process is a physisorption. Therefore, the affinity of DY50 for cotton fiber may be ascribed to Van der Waals forces and electrostatic attractions between the dye and the surface of the fiber. This low value of Ea generally indicates diffusion controlled process. We can therefore conclude that the Ea value calculated from data suggest a diffusioncontrolled process, which is a physical step in the adsorption process. Moreover, to calculate the activation parameters such as enthalpy (H#), entropy (S#) and free energy (G#), the Eyring equation is applied (Eq. 14)[43], ln (k/T) = ln(Kb/h) + ΔS#/R - ΔH#/ RT (14) where kb is the Boltzmann constant (1.3807×10−23 J K−1), h is the Planck constant (6.6261×10−34 J s), k is the pseudo-second-order constant (k2) or intraparticle diffusion rate constant (ki). Plotting of ln k/T against the reciprocal temperature also gives a reasonably straight line. Moreover, Gibbs energy of activation may be written in terms of entropy and enthalpy of activation: ΔG# = ΔH# − TΔS# (15) # # # The calculated values of (ΔG ), (ΔH ) and (ΔS ) for DY50 at different dye concentrations, L: R 1:30, at pH 7.03 in aqueous medium and in presence of different salts, and at different temperature and constant initial dye concentration of 113.366mg/l are listed in Tables 5 and 6. The positive ΔG# value suggests that adsorption reactions require energy to convert reactants into products. The ΔG# value determines the rate of the reaction, rate increases as ΔG# decreases, and hence the energy requirement is fulfilled, the reaction proceeds. The positive value of ΔH# confirms the endothermic process, meaning the reaction consume energy. The negative value of ΔS# indicates that the adsorption leads to order through the formation of activated complex suggesting that DY50 adsorption on cotton fiber surface is an associated mechanism. Also the negative value of ΔS* normally reflects that no significant change occurs in the internal structure of the adsorbent during the adsorption process [44]. Conclusion This investigation examined the equilibrium and the dynamic adsorption of direct yellow 50 onto cotton fiber. The adsorption capacity is determined at different operation parameters that affect the adsorption of direct yellow 50 onto cotton fiber (initial dye concentration, pH, effect of inorganic salt (sodium sulphate (SS)) and organic salts (sodium edate (SE) and sodium citrate (SC)) and temperature. The adsorbed amount of direct yellow 50 increased with increasing dye concentration, pH and temperature. Moreover, presence of SE and SC increases the adsorbed amount. The adsorption of direct yellow 50 onto cotton fiber in presence of SE and SC was successively achieved, and these results are also promising for the use SE and SC to

9

increase adsorption capacity and offer the potential as an exhausting and fixing agent for direct dyeing of cotton. The data obtained from adsorption isotherms are well fitted to Langmuir model. The applicability of the Langmuir isotherm suggests monolayer coverage of direct yellow 50 on surfaces of cotton fiber. The results obtained in batch adsorption of direct yellow 50 onto cotton fiber showed that the adsorption kinetics can be explained by a second order equation better than Lagergren’s first order. The values of k2, qe,exp and qe,cal all increased with the temperature, suggesting that increasing the temperature increased the adsorption capacity and the adsorption rate. The regression results of the intraparticle diffusion model suggested that intraparticle diffusion is not the only rate-controlling step. The activation energies (Ea) for the pseudo second-order kinetics and intraparticle diffusion kinetics for direct yellow 50 are energetically favorable with different salts at different dye concentration and the adsorption process is a combination of physical and diffusion processes. References [1] S. M. Burkinshaw, N. Kumar, Dyes and Pigments 85 (2010) 124-132. [2] J. S. Bae, H. S. Freeman, Fibers and Polymers, 3 (2002) 140-146. [3] J. Shore, Colorants and Auxiliaries, 1 (1990) 174. [4] W. Bauer, J. Ritter in “Chemistry of Functional Dyes”. 2 (1993) 649. [5] V. Vassileva, E. Valcheva, Z. Zheleva, J. the University of Chem. Technol. and Metall. 43 (2008) 323-326. [6] Y. Bulut, N. Gozubenli, H. Aydın, J. Hazard. Mater. 144 (2007) 300-306. [7] M. Dogan, M. Alkan, J. Coll. Interf. Sci. 267 (2003) 32-41. [8] P.K. Malik, Dyes and Pigments, 56 (2003) 239-249. [9] M. Alkan, M. Dogan, Y. Turhan, Ö. Demirbas¸ , P. Turan, Chem. Eng. J. 139 (2008) 213-223. [10] Y.S. Ho, T.H. Chiang, Y.M. Hsueh, Process Biochem. 40 (2005) 119-124. [11] M. Dogan, M. Alkan, Ö. Demirbas, Y. Ozdemir, C. Ozmetin, Chem. Eng. J. 124 (2006) 89-101. [12] Y. Bulut, H. Aydın, Desalination, 194 (2006) 259-267. [13] C. H. Weng, Y. F.Pan, Colloids Surf. A: Physicochem. Eng. Aspects 274 (2006) 154-162. [14] M. Dogan, H. Abak, M. Alkan, J. of Hazard. Mater. 164 (2009) 172-181. [15] K. M. Chen, L. H. Lin, C. F. Wang, M. C. Hwang, Colloids and Surfaces A: Physicochem. Eng. Aspects, 356 (2010) 46-50. [16] R. H. Peters, Textile chemistry, in: The Physical Chemistry of Dyeing. Elsevier Scientific, New York, III (1975) 379. [17] A. Johnson, The theory of Coloration of Textiles, 2nd ed. Bradford: SDC, (1989) 121. [18] V. Gokmen, A. Serpen, J. Food Eng. 53 (2002) 221-227. [19] M. d. T. Uddin , M. D. A. Islam, S. Mahmud, M. d. Rukanuzzaman, J. Hazard. Mater. 164 (2009) 53–60 [20] O. Nitzsche, H. Vereecken, Mine Water Environ. 21 (2002) 15-23. [21] I. Langmuir, J. Am. Chem. Soc. 40 (1918) 1361-1403. [22] C. H. Wu, J. Hazard. Mater. 144 (2007) 93-100. [23] Y. S. Ho, G. McKay, Chem. Eng. J. 70 (1998) 115-124. [24] H. Freundlich, Z. Phys. Chem. 1906; 57 : 384-470. [25] A. S. Ozcan, B. Erdem, A. Ozcan, J. Coll. Interf. Sci. 280 (2004) 44-54. [26] D. C. Faust, M. O.Aly, (1983) Butterworth, London.

10

[27] S. S. Ashour, J. Saudi Chem. Soc. 14 (2010) 47-53. [28] M. Arami, N. Y. Limaee, N. M. Mahmoodi, N. S. Tabrizi, J. Hazard. Mater. 135 (2006) 171-179. [29] C. Namasivayam, S. Sumithra, J. Environ. Manag. 74 (2005) 207-215. [30] S. J. Allen, Q. Gan, R. Matthews, P.A. Johnson, J. Coll. Interf. Sci. 286 (2005) 101-109. [31] P. K. Malik, J. Hazard. Mater. 113 (2004) 81-88; [32] S. Lagergren, Zur theorie der sogenannten adsorption geloster stoffe, K. Sven. Vetenskapsakad. Handl. 24 (1898) 1-39 . [33] G. Blanchard, M. Maunaye and G. Martin, Water Res. 18 (1984) 1501-7. [34] Y. S. Ho, Dyes and Pigments 72 (2007) 134-6. [35] A. P. Mathews, W. J. Weber, Effects AIChE Symp. Ser. 1976; 73: 91-98. [36] Y. Bulut, H. Aydın, Desalination, 194 (2006) 259-267. [37] W. J. Weber, J. C. Morris, J. Sanit. Div. Am. Soc. Civ. Eng., 89 (1963) 31- 60. [38] Y. S.Ho, Water Res. 37 (2003) 2323-2330. [39] K. V. Kumar, A. Kumaran, Biochem. Eng. J. 27 (2005) 83-93. [40] M. Al-Ghouti, M. A. M. Khraisheh, M. N. M. Ahmad, S. Allen, J. Coll. Interf. Sci. 287 (2005) 6-13. [41] W. J. Thomas, B. Crittenden, Adsorption Technology and Design, Reed Educational and Professional Publishing, Oxford. (1998) pp. 27, 32, 68. [42] E. I .Unuabonah, K. O. Adebowale, B. I. Owolabi, J. Hazard. Mater. 144 (2007) 386-395. [43] K. J. Laidler, J. M. Meiser, Physical Chemistry, Houghton Mifflin, New York. (1999) p. 852. [44] T. S. Anirudhan, P. G. Radhakrishnan, J. Chem. Therm. 40 (2008) 702-709.

11

1.6 O

40 C in Aq. O 50 C in Aq. O 60 C in Aq. O 70 C in Aq. O 80 C in Aq. O 90 C in Aq. O 40 C in S.S. O 50 C in S.S. O 60 C in S.S. O 70 C in S.S. O 80 C in S.S. O 90 C in S.S.

1.4

qt (mg/g cotton)

1.2 1.0 0.8 0.6 0.4 0.2 0.0 0

40

80

120

160

200

240

Time (min)

Figure 1: The effect of contact time and temperature of DY50 with initial dye concentration 113.366mg/l and L.R. 1:30 at pH 7.03 used in aqueous medium (…) and in presence of 40g/l SS (—).

30 -5

qt in SS 2.045X10

25

-5

G

H

qt in SS 5.190X10

I

-5

qt in SS 7.070X10

F

-4

qt in SS 1.002X10

E

20

-4

qt in SS 5.021X10

qt (mg/g cotton)

-3

qt in SS 1.002X10

-5

qt in SE 2.045X10

D

-5

qt in SE 5.190X10

15

-5

qt in SE 7.070X10

-4

C 5

B

10

7

6

8

qt in SE 1.002X10

9

-4

qt in SE 5.021X10

-3

qt in SE 1.002X10

4

A

-5

qt in SC 2.045X10

3

-5

qt in SC 5.190X10

2

5

1

-5

qt in SC 7.070X10

-4

qt in SC 1.002X10

0 0

50

100

150

Time (min)

15

200

-4

1

qt in SC 5.021X10

A

qt in SC 1.002X10

250

-3

Figure 2: Effect of different concentrations of DY50 on q t at L.R.1:30 for 2 hour dyeing time in presence of 40g/l SS at pH 7.03, 30g/l S.E. at pH 7.11 and in presence of 20g/l S.C at pH 7.09 and temperature 90ºC.

2.4 S.S. S.E. S.C.

qt (mg/g cotton))

2.3 2.2 2.1 2.0 1.9

6

7

8

9

10

11

pH

Figure 3: Effect of pH on qt in presence of 40g/l SS, 30g/l S.E. and 20g/l S.C. with initial dye concentration 113.366mg/l , L.R. 1:30 for 2 hours dyeing time and temperature 90ºC

2.4

qt (mg/g cotton)

2.0 in S.S. in S.E. in S.C.

1.6

1.2

0.8 0

10

20

30

40

50

60

[Salt] g/l

Figure 4: Effect of different SS, SE and SC concentrations on qt of DY50 on cotton fabric with initial dye concentration 113.366mg/l, L.R.1:30 for 2 hours dyeing time at temperatures 90.

16

6

5

4

3

2

1

0 0

30

60

90

120

150

180

1/Ce(ml/mg)

Figure 5: Langmuir adsorption isotherm of DY50 at different temperatures with L.R.1:30 and pH 7.03 in aqueous medium (…) and in presence of 40g/l SS (—). 4.5 3.6 2.7 O

40 C in Aq. O 50 C in Aq. O 60 C in Aq. O 70 C in Aq. O 80 C in Aq. O 90 C in Aq. O 40 C in S.S. O 50 C in S.S. O 60 C in S.S. O 70 C in S.S. O 80 C in S.S. O 90 C in S.S.

1.8 ln qe

1/qe(g cotton/mg)

O

40 C in Aq. O 50 C in Aq. O 60 C in Aq. O 70 C in Aq. O 80 C in Aq. O 90 C in Aq. O 40 C in S.S. O 50 C in S.S. O 60 C in S.S. O 70 C in S.S. O 80 C in S.S. O 90 C in S.S.

0.9 0.0 -0.9 -1.8 -2.7 -6

-5

-4

-3

-2

-1

0

1

2

3

ln Ce

Figure 6: Freundlich adsorption isotherm of DY50 at different temperatures with L.R.1:30 and pH 7.03 in aqueous medium (…) and in presence of 40g/l salt SS (—).

17

O

40 C in Aq. O 50 C in Aq. O 60 C in Aq. O 70 C in Aq. O 80 C in Aq. O 90 C in Aq. O 40 C in S.S. O 50 C in S.S. O 60 C in S.S. O 70 C in S.S. O 80 C in S.S. O 90 C in S.S.

0.6 0.0

-1.2 -1.8 -2.4 -3.0 -3.6 0

20

40

60

80

100

120

Time (min)

Figure 7: The pseudo first-order plot of DY50 at different temperatures with initial dye concentration 113.366mg/l, L.R. 1:30 and pH 7.03 used in aqueous medium (….) and in presence of 40g/l SS (―). O

40 C in Aq. O 50 C in Aq. O 60 C in Aq. O 70 C in Aq. O 80 C in Aq. O 90 C in Aq. O 40 C in S.S. O 50 C in S.S. O 60 C in S.S. O 70 C in S.S. O 80 C in S.S. O 90 C in S.S.

400

t/qt (g cotton min/mg)

Ln (qe- qt)

-0.6

300

200

100

0 0

40

80

120

160

200

240

Time (min)

Figure 8: The pseudo second-order plot of DY50 at different temperatures with initial dye concentration 113.366mg/l, L.R. 1:30 and pH 7.03 used in aqueous medium (….) and in presence of 40g/l SS (—).

18

2.4 O

40 C in Aq. O 50 C in Aq. O 60 C in Aq. O 70 C in Aq. O 80 C in Aq. O 90 C in Aq. O 40 C in S.S. O 50 C in S.S. O 60 C in S.S. O 70 C in S.S. O 80 C in S.S. O 90 C in S.S.

2.0

qt (mg/g cotton)

1.6

1.2

0.8

0.4

0.0 4

6

8

10 1/2

12

14

16

1/2

Time , ( min )

Figure 9: The intraparticle diffusion kinetics plot of DY50 at different temperatures with initial dye concentration 113.366mg/l, L.R. 1:30 and pH 7.03 used in aqueous medium (…) and in presence of 40g/l SS (—).

19

Table 2: Langmuir and Freundlich isotherm constants of adsorption of DY50 onto cotton fabric at different temperatures, and different salts. Langmuir isotherm Salt add

Aqueous and pH =7.03

[SS] = 40g/l, pH= 7.03

[SE] = 30g/l and pH= 7.11

[SC] = 20g/l and pH =7.09

Freundlich isotherm

Temp ºC

40 50 60 70 80 90 40 50 60 70 80 90 40 50 60 70 80 90 40 50 60 70 80 90

Q (mg/g) 4.405 4.651 4.608 4.444 5.208 5.780 20.002 13.510 15.625 16.949 16.666 23.809 18.181 22.222 19.607 25.000 25.640 20.010 26.315 28.571 20.000 22.222 18.518 15.625

b (l/mg) 1.258 1.387 1.327 1.247 1.611 1.302 2.560 2.481 2.703 2.722 2.971 2.882 2.663 2.508 2.683 2.800 2.887 2.827 2.743 2.789 2.366 2.785 3.251 2.697

RL

0.0039 0.0032 0.0030 0.0027 0.0026 0.0026 0.0032 0.0024 0.0023 0.0020 0.0019 0.0019 0.0036 0.0033 0.0025 0.0024 0.0020 0.0014 0.0042 0.0041 0.0023 0.0021 0.0015 0.0007

12

r

0.997 0.998 0.998 0.998 0.999 0.998 0.997 0.998 0.998 0.998 0.998 0.997 0.997 0.999 0.998 0.999 0.999 0.998 0.998 0.998 0.999 0.998 0.999 0.998

Qf (mg/g) 4.889 5.088 4.632 5.754 12.420 7.242 28.388 30.631 36.929 42.734 45.558 47.465 31.000 37.675 37.675 52.562 60.642 63.943 37.225 41.058 47.655 57.397 64.974 83.179

1/n 0.916 0.907 0.909 0.910 0.904 0.886 0.771 0.768 0.730 0.776 0.722 0.791 0.932 0.908 0.905 0.896 0.894 0.873 0.931 0.921 0.917 0.914 0.889 0.865

r

0.995 0.996 0.996 0.996 0.997 0.996 0.995 0.996 0.998 0.996 0.996 0.995 0.995 0.999 0.996 0.997 0.997 0.996 0.998 0.996 0.997 0.996 0.997 0.996

Table 3: Kinetic parameters for DY50 at different temperatures with initial dye concentration 113.366mg/l and L.R. 1:30 by using different salts. Salt add

Aqueous and and pH =7.03

[SS] = 40g/l, and pH= 7.03

[SE] = 30g/l and pH= 7.11

[SC] = 20g/l and pH =7.09

Temp . o C

qe,exp mg/g cotto n

40 50 60 70 80 90 40 50 60 70 80 90 40 50 60 70 80 90 40 50 60 70 80 90

0.712 0.742 0.756 0.849 0.888 0.95 1.456 1.581 1.925 2.039 2.126 2.239 1.646 1.769 2.007 2.266 2.329 2.381 1.884 2.031 2.126 2.255 2.332 2.532

Pseudo first-order model qe1 , cal

mg/g cotton 0.821 0.760 0.752 0.795 0.807 0.982 1.698 1.661 1.872 1.944 2.017 2.166 3.016 3.872 3.781 4.604 4.632 4.673 6.546 6.986 7.322 10.372 16.776 50.463

Pseudo second-order model qe2, cal

k1 x102 min-1 2.127 2.395 2.430 2.471 2.632 2.811 2.384 2.671 2.774 2.800 3.041 3.162 4.603 4.822 4.832 5.002 5.193 5.432 6.482 7.142 7.332 8.741 10.317 11.880

r 0.998 0.983 0.985 0.993 0.996 0.997 0.988 0.967 0.983 0.997 0.991 0.998 0.998 0.998 0.999 0.999 0.995 0.998 0.994 0.994 0.993 0.981 0.989 0.987

mg/g cotton 0.684 0.735 0.774 0.924 0.933 0.965 1.487 1.504 1.836 1.983 2.093 2.136 1.575 1.692 1.957 2.077 2.155 2.279 1.701 2.084 2.197 2.299 2.506 2.367

k2 x102g cotton/ mg min

Intraparticle diffusion model

r

11.401 11.903 12.411 12.582 12.831 12.950 5.922 6.035 6.418 6.657 6.769 7.011 5.831 5.981 6.262 6.676 6.822 6.951 5.552 5.671 5.882 6.141 6.409 6.851

0.958 0.969 0.977 0.978 0.978 0.979 0.990 0.982 0.977 0.979 0.979 0.984 0.991 0.990 0.991 0.991 0.985 0.977 0.990 0.988 0.976 0.976 0.980 0.991

ki x10g/m min-1 1.182 1.250 1.282 1.353 1.391 1.451 2.536 2.641 2.879 2.941 3.011 3.112 2.781 2.883 2.972 3.021 3.099 3.211 2.951 3.004 3.081 3.132 3.200 3.271

r 0.994 0.996 0.998 0.998 0.998 0.994 0.993 0.993 0.988 0.992 0.997 0.998 0.980 0.990 0.993 0.995 0.992 0.988 0.996 0.986 0.993 0.997 0.992 0.992

Table 4: Kinetic parameters for DY50 at different initial dye concentration and L.R. 1:30 by using different salts. Salt add

Aqueous and pH =7.03 [SS] = 40g/l,and pH= 7.03 [SE] = 30g/l and pH= 7.11 [SC] = 20g/l and pH =7.09

[Dye] mg/l

22.009 50.361 73.003 113.366 533.669 1056.153 22.009 50.361 73.003 113.366 533.669 1056.153 22.009 50.361 73.003 113.366 533.669 1056.153 22.009 50.361 73.003 113.366 533.669 1056.153

qe,exp mg/g cotton 0.216 0.482 0.655 0.955 2.951 4.362 0.460 1.044 1.487 2.239 10.354 19.351 0.496 1.199 1.696 2.381 11.198 21.883 0.522 1.283 1.878 2.532 12.782 23.841

Pseudo first-order model qe1, cal

mg/g cotton 0.175 0.703 0.572 0.859 5.206 7.028 2.353 1.081 1.410 2.021 9.934 19.010 0.679 2.275 2.992 3.892 23.196 39.330 0.972 2.466 2.933 6.202 45.361 98.214

k1 x102 min-1 2.374 2.123 2.453 2.456 3.201 2.504 3.342 3.671 3.352 2.951 3.152 3.362 4.251 5.404 5.243 4.778 5.694 5.124 4.921 6.201 5.781 6.762 9.151 10.83

Pseudo second-order model qe2, cal

r 0.998 0.998 0.998 0.995 0.998 0.997 0.997 0.998 0.996 0.994 0.997 0.997 0.995 0.994 0.992 0.995 0.996 0.997 0.992 0.997 0.995 0.995 0.995 0.997

13

mg/g cotton 0.203 0.396 0.578 0.965 2.732 4.789 0.442 0.990 1.353 2.036 8.342 17.55 0.484 1.119 1.597 2.167 11.874 18.797 0.526 1.299 1.767 2.267 11.999 22.459

k2 x102g cotton/ mg min 31.030 20.663 16.321 13.088 3.112 2.663 18.921 11.571 9.102 7.221 5.142 1.173 14.371 9.162 8.113 6.674 2.016 0.763 12.631 7.342 6.920 6.842 1.312 0.537

Intraparticle diffusion model

r 0.989 0.973 0.974 0.979 0.981 0.988 0.986 0.991 0.990 0.984 0.986 0.988 0.9952 0.990 0.988 0.995 0.972 0.991 0.978 0.988 0.983 0.994 0.974 0.990

ki x10g/m min-1 0.271 0.599 1.091 1.452 6.271 11.453 0.563 1.311 2.125 3.112 13.506 25.661 0.668 1.513 2.250 3.211 15.602 27.952 0.756 1.679 2.467 3.271 16.461 30.001

r 0.997 0.988 0.992 0.997 0.992 0.990 0.992 0.994 0.991 0.997 0.998 0.994 0.992 0.989 0.991 0.995 0.992 0.996 0.989 0.993 0.996 0.997 0.992 0.994

Table 5: Activation parameters for pseudo second-order kinetic model of DY5 with initial dye concentration 113.366mg/l and L.R. 1:30 by using different salts. Salt add

Aqueous medium and pH 7.03

[S.S.] = 40g/l, pH 7.03

[S.E.] = 30g/l and pH 7.11

[S.C.] = 20g/l and pH 7.09

Temp. o C

∆G#2 (kj/mol)

313 323 333 343 353 363 313

82.388 85.039 87.689 90.339 92.990 95.640 84.142

323

86.815

333

89.489

343 353 363 313 323 333 343 353 363 313 323 333 343 353 363

92.162 94.836 97.509 84.179 86.844 89.510 92.176 94.841 97.507 84.362 87.016 89.670 92.324 94.979 97.633

∆H#2 (kj/mol)

∆S#2 (j/mol K)

r2

Ea2 (kj/mol)

r2

-0.566

-265.033

0.892

2.369

0.974

0.460

-267.353

0.881

3.316

0.988

0.745

-266.563

0.889

3.595

0.986

1.284

-265.424

0.926

3.918

0.979

Table 6: Activation parameters for intraparticle diffusion kinetic model of DY50 with initial dye concentration 113.366mg/l and L.R. 1:30 by using different salts. Salt add

Aqueous medium and pH 7.03

[S.S.] = 40g/l, pH 7.03

[S.E.] = 30g/l and pH 7.11

[S.C.] = 20g/l and pH 7.09

Temp. o C

∆G#i (kj/mol)

22.009 50.361 73.003 113.366 533.669 1056.153 22.009

82.328 84.926 87.525 90.124 92.723 95.322 80.347

50.361

82.884

73.003

85.420

113.366 533.669 1056.153 22.009 50.361 73.003 113.366 533.669 1056.153 22.009 50.361 73.003 113.366 533.669 1056.153

87.957

90.493 93.030 80.103 82.672 85.240 87.809 90.378 92.947 79.963 82.545 85.127 87.709 90.291 92.873

∆H#i (kj/mol)

∆S#i (j/mol K)

ri

Eai (kj/mol)

ri

0.985

-259.881

0.988

3.786

0.996

0.924

-253.652

0.943

3.891

0.978

-0.299

-256.877

0.884

2.511

0.999

-0.851

-258.191

0.997

1.942

0.997

14

2.4 O

40 C in Aq. O 50 C in Aq. O 60 C in Aq. O 70 C in Aq. O 80 C in Aq. O 90 C in Aq. O 40 C in S.S. O 50 C in S.S. O 60 C in S.S. O 70 C in S.S. O 80 C in S.S. O 90 C in S.S.

2.0

qt (mg/g cotton)

1.6

1.2

0.8

0.4

0.0 4

6

8

10 1/2

12 1/2

Time , ( min )

14

16

 The adsorption capacity is determined at different operation parameters that affect the adsorption of direct yellow 50 onto cotton fiber in presence of biodegradable salts (sodium edate (SE) and sodium citrate (SC)).  Presence of SE and SC increases the adsorbed amount.  The activation energies (Ea) for the pseudo second-order kinetics and intraparticle diffusion kinetics for direct yellow 50 are energetically favorable with different salts at different dye concentration and the adsorption process is a combination of physical and diffusion processes.