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INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 1, No 5, 2011 © Copyright 2010 All rights reserved Integrated Publishing Association Research article

ISSN 0976 – 4402

Removal of methylene blue, a basic dye from aqueous solutions by adsorption using teak tree ( Tectona grandis) bark powder Satish Patil 1 , Sameer Renukdas 2 , Naseema Patel 2 1 Department of Chemistry, K.E.S.A.P.Science College, Nagothane, Maharashtra 2 Department of Chemistry, Yashwant College,Nanded, Maharashtra. [email protected] ABSTRACT Systematic batch mode studies of adsorption of methylene blue (MB) on teak tree bark powder (TTBP) were carried out as a function of process of parameters includes initial MB concentration, dose of adsorbent, pH, agitation time, agitation speed, temperature and particle size. TTBP was found to have excellent adsorption capacity. Freundlich, Langmuir and Temkin isotherm models were used to test the equilibrium data. The best fitting isotherm models was found to be Langmuir and Freundlich. The linear regression coefficient R 2 was used to elucidate the best fitting isotherm model (R 2 ≈ 0.99).The monolayer (maximum) adsorption capacity (qm) was found to be 333.333 mg g 1 for TTBP. The dimensionless separation factor (RL) values lie between 0.015 to 0.3289 indicated favourable adsorption. Lagergen pseudo –first order, Lagergen pseudo second order, Natrajan and Khalaf first order, Bhattacharya Venkobachar first order and Elovich kinetic models were tested for the kinetic study. Lagergen pseudo second order model best fits the kinetics of adsorption (R 2 = 1, q e(the) ≈ q e(exp)). Intra particle diffusion model showed boundary layer effect and larger intercepts indicates contribution of surface adsorption was high in rate controlling step. Adsorption was found to increase on increasing pH, increasing temperature and decreasing particle size. Thermodynamic analysis showed negative values of ∆G indicating adsorption was favourable and spontaneous, positive values of ∆H indicating endothermic physical adsorption and positive values of ∆S indicating increased disorder and randomness at the solid solution interface of MB with the adsorbent TTBP. Key words: Adsorption isotherm, methylene blue(MB), Teak tree bark powder (TTBP), kinetic and thermodynamic parameters 1. Introduction High production and use of dyes generates coloured wastewater and pollute the environment. Textile, paper and food industries, tanneries, electroplating factories discharge coloured wastewater (Mckay, et al. 1998). Colour or dye being one of the recalcitrant, persist for long distances in flowing water, retards photosynthesis, inhibit growth of aquatic biota by blocking out sunlight and utilising dissolved oxygen. Some dyes may cause allergic dermatitis, skin irritation, cancer and mutation in man. The methods of colour removal from industrial effluents include coagulation, floatation, biological treatment, hyper filtration, adsorption and oxidation. Among these options, adsorption is most preferred method and activated carbon is most effective adsorbent widely employed to treat wastewater containing different classes of dyes, recognizing the economical drawback of commercial activated carbon.

Received on November, 2010 Published on December 2010

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Removal of methylene blue, a basic dye from aqueous solutions by adsorption using teak tree ( Tectona grandis) bark powder

Many researchers have studied the applicability of low cost alternative materials like saw dust, coir pith, olive stone, pine bark, coconut shell, tropical grass almond shells etc as carbonaceous precursors from the removal of dyes from wastewater (Arivoli, et al. 2007; Sekar, et al. 1995; Selvarani, et al. 2000).

The present study undertaken to evaluate the efficiency of teak tree bark powder as an adsorbent for the removal of MB dye from aqueous solutions. The kinetic, equilibrium and thermodynamic data on batch adsorption studies were carried out to understand the process of adsorption. The effect of adsorption parameters such as initial dye concentration, temperature, pH, adsorbent dose, contact time, agitation time has been studied. 2. Materials and Methods 2.1 Adsorbent Adsorbent used in the present study is Teak tree bark powder (TTBP). Mature dried bark of teak tree were collected from one of the forest of western region of Maharashtra state in India and washed thoroughly with distilled water to remove dust and other impurities. Washed bark was dried for 5 days in sunlight. Dried bark was grounded in a domestic mixer grinder. After grinding, the powders were again washed and dried. Different sized TTBP’s were stored in plastic container for further use. 2.2 Dye ( Adsorbate ) MB (C6H18ClN3S ) was used as an adsorbate in the present study, is a monovalent cationic dye. In dye classification it is classified as C.I.Basic blue 9 and C.I.52015. It has a molecular weight of 373.9 and was supplied by S.D.Fiine Chemicals, Mumbai, India. A stock solution of 1000 mg l 1 was prepared in double distilled water and the experimental solutions of the desired concentration were obtained by successive dilutions. 2.3 Adsorption Experiments Absorbance of 10 mg l 1 was determined at different wavelengths using Equiptronics single beam u.v. visible spectrophotometer to obtained a plot of absorbance verses wavelength. The wavelength corresponding to the maximum absorbance (λmax= 665 nm) as determined from the plot, was noted and this wavelength was used for measuring the absorbance of residual concentration of MB. pH of solutions were adjusted using 1M HCl and 1M NaOH. Equiptronics pH – meter was used to adjust the pH of MB solution as per the requirement. By conducting batch mode experimental studies the efficiency of the adsorbent TTBP was evaluated. Specific amount of adsorbent were shaken in 25 ml aqueous solution of dye of varying concentration for different time periods at natural pH and temperature. At the end of predetermined time intervals, adsorbent was removed by centrifugation at 10000 rpm and supernant was analysed spectrophotometrically for the residual concentration of MB, at 665 nm wavelength. The values of percentage removal and amount of dye adsorbed were calculated using following relationships :

Satish Patil, Sameer Renukdas, Naseema Patel International Journal of Environmental Sciences Volume 1 No.5, 2011

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Percentage removal = [(Ci – Cf) / Ci] × 100 Amount adsorbed = (Ci – Cf )/ m Where, Ci = Initial dye concentration (mg l 1 ), Cf = Final dye concentration (mg l 1 ), m= Mass of adsorbent (g l 1 ) Experiment (1) Effect of initial dye concentration and contact time 25 mg of adsorbent of ≥ 120 mesh size with 25 ml of dye solution was kept constant. Batch experiments for initial MB concentration of 100, 150, 200, 250, 300, 350 and 400 mg l 1 were performed at nearly 303K on a oscillator at 230 rpm for 5,10, 15, 20, 30, 40, 50 and 60 minutes at pH = 7. Then optimum contact time was identified for further batch experimental study. Experiment (2) Effect of adsorbent dosage and initial dye concentration Initial MB concentrations of 400, 500, 600 and 700 mg l 1 were used in conjunction with adsorbent dose of 1, 2, 3, 4, 5, and 6 g l 1 . Contact time = 30 minutes, pH = 7, agitation speed = 230 rpm, temperature = 303K and particle size ≥ 120 mesh were kept constant. Experiment (3) Effect of pH Initial pH of MB solutions were adjusted to 3, 4, 5, 6, 7, 8, 9, 10 and 11 for 250 mg l1 concentration. Contact time= 30 minutes, adsorbent dose = 1 g l1, agitation speed = 230 rpm, temperature = 303K and particle size ≥ 120 mesh were kept constant. Experiment (4) Effect of particle size and initial dye concentration Three different sized particles of ≥ 120, 120 ≤ 85 and 85 ≤ 60 mesh were used in conjunction with 100, 150, 200, 250, 300 and 350 mg l1 MB concentration. Contact time= 30 minutes, adsorbent dose = 1 g l1, agitation speed = 230 rpm, temperature = 303K and pH = 7 were kept constant. Experiment (5) Effect of temperature and initial dye concentration 303K, 313K and 323K temperatures were used in conjunction with 100, 150, 200, 250, 300 and 350 mg l1 MB concentration. Contact time = 30 minutes, adsorbent dose 1 g l1, pH = 7, agitation speed = 230 rpm and particle size ≥ 120 mesh were kept constant. Experiment (6)Effect of agitation speed 100, 170 and 230 rpm agitation speeds were used in conjunction with initial MB concentration of 250 mg l1 for 5,10, 15, 20, 30, 40, 50 and 60 minutes. Adsorbent dose = 1 g l1, agitation speed = 230 rpm, temperature = 303K and pH = 7 were kept constant. 3. Results and Discussions 3.1 Investigation of sorption parameters 3.1.1 Effect of initial dye concentration and contact time Satish Patil, Sameer Renukdas, Naseema Patel International Journal of Environmental Sciences Volume 1 No.5, 2011

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Effect of initial dye concentration with contact time on adsorption of MB is presented in Figures 1. Uptake of MB was rapid in first 5 minutes and after 30 minutes amount of MB adsorbed was almost constant. Therefore, for batch experiments 30 minutes equilibrium time was used. Percentage sorption decreased (from 99.4 to 81.25%) but amount of MB adsorbed per unit mass of adsorbent increased (from 99.4 to 325 mg g1) with increase in MB concentration from 100 to 400 mg l1. 3.1.2 Effect of adsorbent dosage and initial dye concentration The adsorption of MB on TTBP was studied by varying the adsorbent dosage. The amount of MB adsorption increased with increase in dosage of adsorbent. Percentage removal of MB decreased with increase in concentration, Figure 2. This is due to the increase in availability of surface active sites resulting from the increased dose and conglomeration of the adsorbent (Kannan and Karuppasamy, 1998). For above 95% removal of MB, adsorbent dosage of 3, 3, 4, 5 g l1 for TTBP were needed for initial MB concentrations 400, 500, 600 and 700 mg l1 respectively.

Figure 1: Effect of initial dye concentration and contact time on adsorption of MB on TTBP.

Figure 2 : Effect of adsorbent dosage and initial dye concentration on adsorption of MB on TTBP.


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3.1.3 Effect of pH pH is an important factor in controlling the adsorption of dye onto adsorbent. The adsorption of MB from 250mg l1 concentration on TTBP was studied by varying the pH from 3 to 11. The amount of dye adsorbed per unit mass of adsorbent at equilibrium (qe) increased from 120 to 246.2 mg g1 (48% to 98.48%) by variation in pH from 3 to 11, Figure 3. 3.1.4 Effect of particle size and initial dye concentration Adsorption of MB on three sized particles ≥ 120, 120 ≤ 85 and 85 ≤ 60 mesh of TTBP was studied for 100 to 350 mg l1 concentrations of MB. The results of variation of these particle sizes on dye adsorption are shown in Figure 4. It can be observed that as the particle size increases the adsorption of dye decreases and hence the percentage removal of dye also decreases. This is due to the decrease in available surface area. For larger particles, the diffusion resistance to mass transfer is high and most of the internal surface of the particle may not be utilized for adsorption and so the amount of dye adsorbed is small.

Figure 3 : Effect of pH on adsorption of MB From initial concentration 250 mg l 1 MB solution on TTBP.

Figure 4 : Effect of particle size and initial dye concentration on % removal of MB on TTBP.


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3.1.5 Effect of temperature and initial dye concentration Temperature has important effects on adsorption process. Thermodynamic parameters like heat of adsorption and energy of activation play an important role in predicting the adsorption behaviour and both are strongly dependent on temperature. Adsorption of MB at three different temperatures (303K, 313K and 323K) onto TTBP was studied for 100 to 350 mg l1 initial MB concentrations. It is observed that as the experimental temperature increases from 303K to 323K, the dye adsorption also increases. As the temperature increases, rate of diffusion of adsorbate molecules across external boundary layer and internal pores of adsorbent particle increases 7. Changing the temperature will change the equilibrium capacity of the adsorbent for particular adsorbate. 3.1.6 Effect of agitation speed The sorption is influenced by mass transfer parameters. The sorption kinetics of MB by TTBP for different agitation speeds ranging from 100 to 230 rpm was studied. The amount adsorbed at equilibrium was found to increase from 213, 224.5 and 229.5 mg g1 of TTBP with increased in agitation speed from 100, 170 and 230 rpm of an oscillator from 250 mg l1 initial MB solution. This is because with low agitation speed the greater contact time is required to attend the equilibrium. With increasing the agitation speed , the rate of diffusion of dye molecules from bulk liquid to the liquid boundary layer surrounding the particle become higher because of an enhancement of turbulence and a decrease of thickness of the liquid boundary layer. 3.2 Adsorption Kinetics To investigate the mechanism of adsorption, pseudo first order and pseudo second order models were used. The Lagergen (Singh et al., 1998) pseudo first order rate expression is given as log (qe qt) = log qe – (k1 / 2.303) t

(1)

Where qe and qt are amounts of dye adsorbed (mg g1) on adsorbent at equilibrium and at time t, respectively and k1 is rate constant of pseudo first order adsorption (min1). The slope and intercept values of plot log(qe qt) against t , Figure 5 were used to determine pseudo first order rate constant (k1) and theoretical amount of dye adsorbed per unit mass of adsorbent qe(the), respectively. qe(the)were compared with the qe(exp) values in Table(1). qe(exp) values differ from the corresponding qe(the) values and also correlation coefficient values (R2 ) values were not high for all concentrations showed that pseudo first order equation of Langergen does not fit well with whole range of contact time and is generally applicable for initial stage of adsorption (Ho and Mckay, 1999). The Langergen pseudo second order kinetic model (Ho and Mckay, 1999) is given as t/qt = 1/(k2qe2) + t/qe (2) Where k2 is rate constant of second order adsorption (g mg1 min1). The slopes and intercepts of plot of t/qt against t , Figure 6, were used to determine qe(the) and k2 respectively. From highly linear plots it is cleared that there may be a possibility of chemisorptions playing a significant role in the rate determining step. The pseudo second


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order parameters, qe(the), h and k2 obtained from the plot are represented in Table (1). Where h is initial adsorption rate (mg g1.min), h = k2 qe2

Figure 5 : Pseudo first order plot of effect of initial dye concentration and contact time on adsorption of MB on TTBP.

Figure 6 : Pseudo second order plot of effect of initial dye concentration and contact time on adsorption of MB on TTBP.

The correlation coefficient R2 for second order adsorption model has very high values for both the adsorbents (R2 = 1) and qe(the) values are consistent with qe(exp) showed that pseudo second order adsorption equation of Langergen fit well with whole range of contact time and dye adsorption process appears to be controlled by chemisorptions. The linearized form of Natarajan and Khalaf first order kinetic equation is presented as log (Co/Ct) = (K /2.303) t

(3)

Where Co and Ct are concentration of MB (mg l1) at time zero and time t respectively. K is first order adsorption rate constant (min1) which was calculated from slope of the plot log(Co/Ct) against t, Figure 7 (R2 = 0.766 to 0.984) Table 2.


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The linearized form of Bhattacharya and Venkobachar first order kinetic equation is presented as log [ 1 – U(T) ] = (k /2.303) t

(4)

Where U(T) = [(CoCt) / (CoCe)], Ce is equilibrium MB concentration (mg l1) K is first order adsorption rate constant (min1) which was calculated from slope of the plot log [ 1 – U(T) ] against t, Figure 8 (R2 = 0.894 to 0.974) Table 2. Correlation coefficient values (R2 ) values were not high for all concentrations showed that Natarajan and Khalaf as well as Bhattacharya and Venkobachar first order equations does not fit well with whole range of concentration for adsorption of MB on TTBP.

Figure 7 : Natarajan and Khalaf first order plot of effect of initial dye concentration and contact time on adsorption of MB on TTBP.

Figure 8: Bhattacharya and Venkobachar first order plot of effect of initial dye concentration and contact time on adsorption of MB on TTBP.

Steps involved in sorption of the dye by adsorbent includes transport of solute from aqueous to surface of solid and diffusion of solute into the interior of pores, which is generally a slow rate determining process. According to Weber and Morris, the intra particle diffusion rate constant (Ki) is given by the following equation qt = Ki t 1/2 (5) Satish Patil, Sameer Renukdas, Naseema Patel International Journal of Environmental Sciences Volume 1 No.5, 2011

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Ki (mg g1 min1/2 ) values can be determined from the slope of the plots qt against t 1/2 , Figure 9 showed a linear relationship after certain time but they do not pass through origin. This is due to boundary layer effect. The larger the intercept, the greater the contribution of surface sorption in rate determining step. The intercepts and Ki values of plots qt against t 1/2 increases with increase the initial concentration of dye, Table (2). Initial portion is attributed to the liquid film mass transfer and linear portion to the intra particle diffusion. Previous studies showed the same features of the plot which characterize different steps of adsorption process (Zaksu, et al. 2005). The linearized form of Elovich kinetic equation is presented as qt =1/ β [ln(αβ)] + ln t /β (6) Where α is the initial adsorption rate (mg /g /min), β is the desorption constant (g mg–1) during any experiment. Constants α and β are the calculated, from the intercept and slope of plot qt against ln t. Figure 10. This Elovich kinetic model gave quiet satisfactory results for TTBP. Table 2. Initial rate of adsorption was found to increased and desorption constant decreased with increase in dye concentration.

Figure 9 : Intra particle diffusion plot of effect of initial dye concentration and contact time on adsorption of MB onto TTBP.

Figure 10: Elovich plot of effect of initial dye concentration and contact time on adsorption of MB on TTBP.


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Table 1: Effect of initial dye concentration and contact time on adsorption of MB Initial MB Conc. (mg/l) 100 150 200 250 300 350 400

Pseudo first order model

Pseudo second order model

K1 h q e(the) qe(exp) K2 qe(the) 2 R (min (mg/g (mg/g) (mg/g) (g/mg/min) (mg/g) 1 ) .min) 0.025 100 250 99.4 0.0714 7.362 0.995 99.4 0.036 166.667 944.013 145.2 0.129 7.499 0.894 145.2 0.025 200 1000 189.8 0.1313 19.055 0.922 189.8

q e(exp) (mg/g)

229.5 0.0507 27.164 0.903 229.5 268 0.1028 34.514 0.973 268 300 0.1128 30.832 0.974 300

0.008

0.0622 29.376 0.955

325

325

250

R 2

500

1 1 1 1

0.009

333.333 999.998

1

0.009

333.333 999.998

1

0.009

333.333 999.998

1

Table 2: Effect of initial dye concentration and contact time on adsorption of MB on TTBP

Initial MB Conc. (mg/l)

Intra particle diffusion model

Natarajan and Khalaf model

Elovich Model

K (min 1 )

Bhattacharya and Venkobachar model K (min R 2 1 )

Ki (mg/g/min 1/2 )

R

α

100

0.937

0.906

1.9

150

0.875

0.513 2.305 0.441 0.669 0.046 0.613 0.129 0.894

200

1.825

0.648 4.733 0.217 0.798 0.046 0.766 0.131 0.922

250

3.993

0.848 8.124 0.128 0.909 0.021

300

3.363

0.79

350

2.967

0.766 7.422 0.138 0.889 0.012 0.842 0.113 0.974

400

4.14

0.887 10.147 0.102 0.97 0.007 0.839 0.062 0.955

2

β

2

R

R 2

0.537 0.723 0.055 0.984 0.069 0.961

0.85

0.069 0.961

8.414 0.123 0.899 0.016 0.868 0.108 0.973

3.3 Adsorption isotherms The Freundlich equation was employed for the adsorption of MB onto the adsorbent. The isotherm was represented by log qe = log Kf + 1/n log Ce

(7)


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Where qe is amount of MB adsorbed at equilibrium (mg g1), Ce is the equilibrium concentration of MB in solution (mg l1), Kf and n are constant incorporating factors affecting the adsorption capacity and intensity of adsorption respectively. The plots of log qe against log Ce showed good linearity (R2 = 0.903 to 0.998) indicating the adsorption of MB obeys the Freundlich adsorption isotherm, Figure 11. The values of Kf and n given in the Table (3). Values of n between 2 to 3 indicates an effective adsorption (Potgeiter, et al., 2005) while higher values of Kf represents an easy uptake of adsorbate from the solution (Mahvi, et al., 2004). The Langmuir isotherm was represented by the following equation Ce / qe = 1/ (qm b) + Ce /qm (8) Where qm is monolayer (maximum) adsorption capacity (mg g1) and b is Langmuir constant related to energy of adsorption (1/mg). A linear plots of Ce / qe against Ce suggest the applicability of the Langmuir isotherms Figures 12 (R2= 0.986 to 0.989). The values of qm and b were determined slop and intercepts of the plots, Table (3). The essential features of the Langmuir isotherm can be expressed in terms of dimensionless constant separation factor, RL, which is defined by the following relation given by Hall, et al., 1966 RL = 1/ (1+bCo)

(9)

Where Co is initial MB concentration (mg l1). The nature of adsorption if, RL > 1= Unfavourable,

RL = 1 Linear,

RL = 0Irreversible , 0 2, RL = 0.015 to 0.3289 ) confirmed that the adsorption of MB on TTBP was favourable. 3. Langmuir and Freundlich isotherm models and Lagergen pseudo second order model were found to be best fitting isotherm and kinetic models. 4. The values amount of MB adsorbed per unit mass of TTBP obtained by Lagergen pseudo second order model, qe(the) were in consistent with the experimental values, qe(exp) .indicate chemisorptions playing role in rate determining step. 5. Intra particle diffusion model showed boundary layer effect and larger intercepts indicates contribution of surface adsorption was high in rate controlling step. 6. Adsorption was found to increase on increasing pH, temperature, agitation speed and decreasing particle size. 7. Thermodynamic analysis showed that adsorption of MB on TTBP was: · favourable and spontaneous (negative values of ∆G, 4.882 to 12.1 KJ mole · Endothermic (positive values of ∆H, 9.827 to 12.72 KJ mole1) · Physisorption ( small ∆H