Indian Journal of Chemical Technology Vol. 19, September 2012, pp. 311-321

Adsorption of basic dyes from synthetic textile effluent by activated carbon

prepared from Thevetia peruviana

J Raffiea Baseri1,*, P N Palanisamy2 & P Siva Kumar3 1 Department of Chemistry, Al-Ameen Engineering College, Erode 638 104, India

2 Department of Chemistry, Kongu Engineering College, Perundurai, Erode 638 052, India 3Department of Chemistry, Arignar Anna Government Arts College, Namakkal 637 002, India

Received 4 August 2011; accepted 25 January 2012

The adsorption capacity of activated carbon obtained from Thevetia peruviana for three basic dyes, namely Malachite Green, Crystal Violet and Rhodamine–B, available in synthetic textile effluents has been studied. The percentage removal of Malachite Green, Crystal Violet, and Rhodamine–B on to the activated carbon decreases from 98.46 to 89.80, from 97.83 to 88.66 and from 97.33 to 87.12 respectively with the increase in initial dye concentration from 25 mg/L to 100 mg/L at 30ºC. The removal data have been analyzed using Langmuir, Freundlich, Temkin and D-R isotherm models at various temperatures varying from 30 ºC to 45 ºC. The positive value of enthalpy indicates that the adsorption of basic dyes on to activated carbon is endothermic, which is further supported by the increase in adsorption rate of dyes with the increase in temperature from 30 ºC to 45 ºC. It is found that an activated carbon prepared by the chemical impregnation of Thevetia

peruviana with H3PO4 acid can be used as the best adsorbent for the removal of basic dyes from synthetic textile effluents.

Keywords: Activated carbon, Adsorption isotherm, Crystal violet, Effluent treatment, H3PO4 acid, Malachite Green,

Rhodamine–B, Kinetic models, Thevetia peruviana

Water pollution is mainly due to the discharge of untreated or partially treated waste water from many

industries on land or in water bodies1. The anaerobic

decomposition of the dyes and incomplete bacterial degradation produce toxic amines which are harmful

to the environment2. Adsorption is one of the

best conventional waste water treatment methods compared to other treatment methods such as

coagulation, flocculation3, reverse osmosis, ozonation

4,

electrochemical techniques5 and fungal decolorisation.

Activated carbon is the most popular and widely used adsorbent because of high adsorption efficiency

for the organic compound. But the commercially

available activated carbon is very expensive and has problems of regeneration. Hence, production of low

cost and effective adsorbents is still a field of interest

and research is continuing in this area. Coir pith6,

coconut shell7, peanut hull

8, rice husk

9, saw dust

10,

corn cob11

have been used as low cost natural

adsorbents.

The extent of adsorption depends on the porosity and surface area of the adsorbent. The porous

structure plays a major role in the increase of adsorption rate. Activated carbon is produced by

a process of carbonization followed by activation.

The carbonization process converts the organic material to primary carbon, whereas the activation

process removes the decomposition products

deposited in the pores and makes the activated carbon porous in nature.

The objective of this research work is to study the

adsorption kinetics and thermodynamics of cationic (basic) dyes namely Malachite Green, Crystal Violet

and Rhodamine–B by the activated carbon prepared

from Thevetia peruviana (TPAC). Activated carbon was prepared from the plant Thevetia peruviana by

the carbonization process followed by chemical

impregnation with phosphoric acid. The adsorption data are also analyzed by kinetic models and isotherm

models.

Experimental Procedure

Preparation of adsorbent from Thevetia peruviana

Thevetia peruviana is abundantly available tree through out India, which has no economical

importance. The bark of this tree was cut into small

—————— *Corresponding author. E-mail: raffiea2010@gmail.com

INDIAN J. CHEM. TECHNOL, SEPTEMBER 2012

312

pieces of 2 - 3 cm size and then dried in sunlight

for 10 days. The dried material was soaked in

a boiling solution of 10 % H3PO4 for 1 h and kept at room temperature for 24 h. After that, the wood

material was separated, air dried and carbonized in

muffle furnace at 400°C. The carbonized material

was powdered and activated in a muffle furnace at 800°C for a period of 10 min. Then the material was

washed with plenty of water to remove residual

acid, dried, sieved to a desired particle size and stored in a tight lid container for further adsorption

studies. The characteristics of the activated carbon

are studied as per the standard procedures12,13

and are

given in Table 1.

Preparation of synthetic solutions of dyes

Basic dyes, Malachite Green (Basic Green 4), Crystal Violet (Basic Violet 3) and Rhodamine–B

(Basic Violet 10) were used. All the chemicals

were of high purity, commercially available AR grade. The properties of the selected dyes are given

in Table 2 and their structures are shown in Fig.1.

A stock solution of 1000 mg/L was prepared by

dissolving 1000 mg of dye in one litre of double distilled water. The experimental solutions were

obtained by diluting the dye stock solutions

in accurate proportions to different initial concentrations. For simplification, Malachite Green,

Crystal Violet and Rhodamine–B are noted as BG4,

BV3 and BV10 respectively.

Table 1—Physico – chemical characteristics of TPAC

Property Value

pH 6.68

Moisture content,% 12.2

Bulk density, g/mL 0.41

Porosity,% 55.43

Methylene Blue number, mg/g 420

Iodine number, mg/g 825

Table 2—Details of selected dyes

Dyes Mol. formula

Mol. weight

Wavelength λmax, nm

C.I. No.

Malachite Green

(BG4) C23 H25 N2 Cl 364.93 616.8 42000

Crystal Violet (BV3) C25 H30 N3 Cl 407.99 540 42555

Rhodamine-B (BV10) C28 H31 N2 O3.Cl 479.01 555 45170

Adsorption experiment

The adsorption experiments were carried out by

agitating 100 mg adsorbent with 200 mL of dye

solutions (25 - 100 mg/L) at 150 rpm on an orbital

shaker (REMI make). The mixture was withdrawn at specified intervals, centrifuged using electrical

centrifuge (Universal make) at 5000 rpm for 20 min

and unadsorbed supernatant liquid was analyzed for the residual dye concentration using Elico make

UV Spectrophotometer (CI 73) at a wavelength

corresponding to the λmax of each dye. The effect of pH was studied by adjusting the pH (2 – 12) of the

adsorptive solutions using dilute HCl and NaOH solutions. The effect of temperature was studied

using four different temperatures (30, 35, 40 & 45°C).

Fig. 1—Molecular structures of basic dyes

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All experiments were carried out in duplicate and

the mean values are reported, where the maximum

deviation was within 4%. The effects of each parameter (initial dye

concentration, pH, agitation time) were evaluated in

an experiment by varying that parameter, while

keeping the other parameters as constant. The amount of dye on TPAC adsorbent was calculated using the

following equation:

M

CCq e

t

)( 0 −= V … (1)

where qt (mg/g) is the amount of dye adsorbed at

time t ; C0 and Ce (mg/L) , the concentrations of dye at initial and equilibrium respectively; V and M ,

the volume of the solution (litre) and the mass (g) of

dry adsorbent used respectively. Desorption studies

Desorption studies were carried out to analyse

the mechanism of adsorption and recovery of the

adsorbate and adsorbent. The regeneration of the

adsorbent may make the treatment process economical. The supernatant was separated after

centrifugation and the adsorbent was separated and

allowed to agitate with 100 mL of distilled water at different pH (2 – 11) above the equilibrium time of

adsorption. The desorbed dye solution was separated

by centrifugation and estimated as given in the adsorption studies

14.

Results and Discussion

Characterization studies

The characteristic of carbon prepared from

Thevetia peruviana is presented in Table 1. The

surface morphology of TPAC was visualized via scanning electron microscope (SEM) (Make-Jeol,

Model 6390LA) at × 500 magnification. Examination

of SEM micrographs of the TPAC particles shows rough areas on the surface of the carbon (Fig. 2). The

characteristics of TPAC (Table 1) show that TPAC

has high porosity and iodine number value.

Effect of agitation time and initial dye concentration

The adsorption curves for the uptake of dyes BG4,

BV3 and BV10 onto TPAC are single, smooth and continuous till the saturation of dye on the carbon

surface. It is observed that the maximum amount

of dye adsorption occurs within the contact time of 30 min and it reaches equilibrium at 90 min. After

that no significant change is observed in the extent of

adsorption. The uptake of dye varies from 49.23 mg/g

to 179.59 mg/g for BG4, from 48.91 mg/g to 177.32 mg/g for BV3 and from 48.67 mg/g to 174.23 mg/g

for BV10 respectively while increasing the initial dye

concentration from 25 mg/L to 100 mg/L. This is due

to the fact that with the increase in dye concentration, the presence of dye molecules near the adsorbent

also increases. Similar behaviors are reported for

the adsorption of basic dye, methylene blue onto activated carbon prepared from oil palm empty fruit

bunch15

and for the removal of some basic dyes by

adsorption on akash kinari coal16

.

Effect of pH

The pH is the important factor which controls the adsorption process especially for cationic dyes

17.

The percentage of dye adsorption increases with the

increase in pH from 2 to 4 and remains constant

thereafter. Figure 3 shows the effect of pH for the adsorption of BG4, BV3 and BV10 dyes on to TPAC

over a pH range of 2 - 11. In the acidic range 2 - 4,

the dye becomes protonated and the electrostatic repulsion between the positive surface charges of

adsorbent increases. So that the adsorption rate

is decreased in the lower pH. When the pH is increased, the electrostatic attaraction increases and

the adsorption rate gets increased.

Kinetics of adsorption

Adsorption kinetics is used to investigate the

mechanism and the rate controlling steps of

adsorption. The mechanism of adsorption involves the chemical reaction of functional groups present

on the surface of the adsorbent and the adsorbate,

Fig. 2—SEM photograph of TPAC

INDIAN J. CHEM. TECHNOL, SEPTEMBER 2012

314

Fig. 3—Influence of pH on adsorption of BG4, BV3 and BV10 dyes onto TPAC at 30°C (initial dye concentration 50 mg/L and agitation time 180 min)

temperature and pH. In the literature, several models have been applied to know the order of adsorbent-

adsorbate interactions and the rate of adsorption of the

dyes. In this present study, the following four kinetic

models are applied for the experimental data.

Pseudo first - order kinetic model

This model assumes that the rate of change of solute uptake with time is directly proportional to difference in saturation concentration and the amount of solid uptake with time

18. The rate constant of

adsorption is expressed as a first – order rate expression, as shown below:

)(1 te

t qqkdt

dq−= … (2)

where qt and qe are the amount of dye adsorbed

(mg/g) at contact time t (min) and at equilibrium; and k1, the pseudo first-order rate constant (min

-1). After

integrating with the boundary conditions at initial

time (t = 0), qt = 0 and at any time (t >0), amount of

dye adsorbed is qt and by rearranging Eq. (2), the rate law for a pseudo- first-order reaction becomes:

log tk

qqqete

303.2log)( 1−=− … (3)

The plot of log (qe-qt) versus t should give a

straight line with slope of –k1/2.303 and intercept log qe which allows calculation of adsorption rate

constant k1 and equilibrium adsorption capacity

qe. Calculated values of k1 and qe are summarized for the adsorption of BG4, BV3 and BV10 dyes on TPAC

(i) with different initial dye concentrations at 30°C

and (ii) with different temperatures at initial dye

concentration of 50 mg/L in Tables 3 and 4. It is

observed that the experimental data does not fit a straight line. Similar results are found in preparation

and utilization of Kapok Hull carbon for the removal

of Rhodamine-B from aqueous solution19

. The pseudo

first-order kinetic model of Lagergren does not fit well with the experimental data over the whole range

of initial concentrations studied.

Pseudo second-order kinetic model

The pseudo second-order kinetic equation is expressed as

eet q

t

qkq

t+=

2

2

1 … (4)

where k2 is the rate constant of pseudo second –order

adsorption (g/mg min); and qe, the equilibrium

adsorption capacity (mg/g)20

.

The initial adsorption rate h (mg/g min) is expressed as

h =2

2 eqk … (5)

Figure 4 shows the pseudo second-order plots for the adsorption of BG4, BV3 and BV10 dyes by TPAC at various initial dye concentrations and 30°C. When the pseudo second-order kinetic is applicable, the plot of t/qt against t should give a linear relationship from which k2 and qe can be determined respectively from the intercept and slope of the plot.

The correlation coefficient values are higher than the values of pseudo first-order model. Further, the rate constant, k2 decreases with the increase in initial dye concentration. It is observed from Tables 3 and 4 that the adsorption of BG4, BV3 and BV10 dyes onto TPAC fits to the pseudo second-order kinetic model.

Elovich model

The Elovich equation is generally expressed as

tqe

dt

dqβα −= … (6)

On integrating this equation for the boundary conditions, it gives

qt = tln1

)ln(1

βαβ

β+ … (7)

where α is the initial adsorption rate (mg/g min); and β, the desorption constant which is related to the extent of surface coverage and the activation energy for chemisorption (g/mg).

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If the adsorption of BG4, BV3 and BV10 dyes on

TPAC fits to the Elovich model, a plot of qt versus

ln t should give a linear relationship with a slope of (1/β) and an intercept of 1/β ln (αβ). The results of

Elovich plot for the adsorption of BG4, BV3 and BV10

dyes on TPAC at various initial concentrations and

at various temperatures are given in Tables 3 and 4. The correlation coefficient values show that the

Elovich model does not fit for the adsorption of basic

dyes onto TPAC. The Elovich equation is mainly applicable for chemisorption kinetics

21. It indicates

that the adsorptions of these basic dyes on TPAC are

physisorption at various initial dye concentrations and

also at various temperatures.

Intra particle diffusion model

Since the pseudo first-order and the pseudo second-

order models could not identify the diffusion

mechanism through the pores present in the surface of

adsorbent, the kinetic results are further analyzed by using the intraparticle diffusion model. Adsorption is

a multi-step process involving transport of the solute

molecules from the aqueous phase to the surface of the solid particulates followed by diffusion into the

interior of the pores. Assuming that the rate is

controlled by pore and intra particle diffusion, the

amount adsorbed (qt) is proportional to the t 2/1 , as shown below:

2/1tkq idt = + I … (8)

where qt is the amount of dye adsorbed (mg/g) at time

t (min); and I is the intercept (mg/g). kid and I values

are obtained from the slopes and intercepts of the linear plot.

Figure 5 represents the plot of qt versus t1/2

for adsorption of BG4, BV3 and BV10 onto TPAC

for the initial dye concentration of 25 – 100 mg/L.

It seems that the plots are non-linear for all the concentrations but careful observations shows the

data points can be represented by double linear.

In first straight line, the sudden increase in slope

signifies that the dye molecules are transported to the external surface of the adsorbent through film

diffusion. Intra-particle diffusion of dye molecules

through pore is represented by second straight line. The linear portion does not pass through the origin

which concludes that the pore diffusion is the only

rate determining step and not the film diffusion22

. The values of kid and r

2 for the adsorption of BG4,

BV3 and BV10 dyes on TPAC at various initial

concentrations and at various temperatures are given

in Tables 3 and 4. Similar results were also obtained for the adsorption of the Crystal Violet and Methyl

Orange onto skin almond waste23

.

Adsorption isotherm

Adsorption isotherm indicates the relationship

between the adsorbate in the liquid phase and the adsorbate adsorbed on the surface of the adsorbent

under equilibrium at constant temperature24

.

Adsorption isotherms are important to describe the interaction of adsorbate molecules with adsorbent

surface. In this study, Langmuir, Freundlich, Temkin

and Dubinin – Raduskevich isotherms have been

employed for the treatment of the equilibrium

Fig. 4—Pseudo second-order plots for adsorption of BG4, BV3 and BV10 dyes onto TPAC at 30° C (adsorbent dosage 100mg and pH 8.9)

BASERI et al.: ADSORPTION OF BASIC DYES FROM SYNTHETIC TEXTILE EFFLUENT

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adsorption data. The applicability of the isotherm

equation is compared by judging the correlation

coefficient r2.

Langmuir isotherm

The Langmuir adsorption isotherm is the best known linear model for monolayer adsorption on the

homogeneous surface and most frequently utilized to

determine the adsorption parameters. Langmuir model is represented by the following equations:

Non-linear form

eL

eo

eL

eL

eCb

bCQ

Cb

CKq

+=

+=

11 … (9)

Linearized form

e

oLoe

e CQbQq

C

+=

11 … (10)

where qe is the amount adsorbed at equilibrium (mg/g); Qo, the monolayer adsorption capacity

(mg/g); Ce, the equilibrium concentration of adsorbate

(mg/L); and bL, the Langmuir constant related to

energy of adsorption. Figure 6 shows a linearized plot of Ce/qe against

Ce. Values of Qo and bL are given in Table 5.

The Langmuir adsorption capacities vary from 133.63 mg/g to 158.73 mg/g for BG4, from

129.87 mg/g to 156.25 mg/g for BV3 and from

120.48 mg/g to 136.99 mg/g for BV10 dyes respectively onto TPAC with the increase in

temperature from 30º C to 45º C. This indicates the

adsorption at high operating temperature. Similar

values are already reported for the removal of basic and acidic dyes by the low cost adsorbent

25. From the

values, it is concluded that the maximum adsorption

corresponds to a saturated mono layer of dye molecules on the adsorbent surface with constant

energy and there is no transmission of dye molecules

on the adsorbent surface. The Langmuir isotherm fits

quite well with the experimental data with good correlation coefficient (Table 5).

The separation factor RL is calculated by the

following equation to confirm the favorability of the adsorption process:

RL = 1/ (1+ bL.C0) … (11)

where bL is the Langmuir constant; and C0, the initial

concentration of dye (mg/L). The values of RL are

found to be between 0 and 1 and confirm that the

adsorption process is favorable.

Freundlich isotherm

The Freundlich equation is an empirical relationship describing the sorption of solutes from

a liquid to a solid surface. Freundlich model is

expressed as

n

efe Ckq /1= … (12)

where Kf is the measure of adsorption capacity; and n,

the adsorption intensity. Linear form of Freundlich

equation is

efeC

nkq log

1loglog += … (13)

Fig. 5—Intraparticle diffusion plots for adsorption of BG4, BV3 and BV10 dyes onto TPAC at 30° C (adsorbent dosage 100mg and pH 8.9)

INDIAN J. CHEM. TECHNOL, SEPTEMBER 2012

318

A plot of log qe versus log Ce gives a linear

line with a slope of 1/n and intercept of log kf

(Table 5). From the experimental data, kf values increase with increasing temperature for basic

dyes, implying that the adsorption process may

be endothermic in nature. Values n>1 represent a favorable adsorption condition. The correlation

coefficient values are poor compared to the

Langmuir isotherm model.

Fig. 6—Langmuir adsorption isotherm plots for adsorption of

BG4, BV3 and BV10 dyes onto TPAC (adsorbent dosage 100mg, pH 8.9 and agitation time 120 min)

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Temkin isotherm

Temkin isotherm equation is based on the

assumption that adsorption takes place through the

characterization of uniform distribution in binding

energies up to a certain level and the sorption energy decreases linearly as the coverage of adsorbent

increases26

.

The linear form of Temkin equation is

e

T

T

T

e Cb

RTa

b

RTq lnln += … (14)

where bT is the Temkin constant related to heat of sorption (J/mg); aT, the Temkin isotherm constant;

R, the gas constant with the value of 8.314(J/mol/K);

and T, the absolute temperature in Kelvin. The values of the constants aT and bT are calculated

from the intercept and slope of the plot qe versus ln Ce.

The correlation coefficient values are very poor (Table 5). This shows that Temkin model does not fit

with the experimental data. Dubinin – Raduskevich (D- R) isotherm

The D-R isotherm describes the adsorption on a

single uniform pore. Dubinin-Raduskevich isotherm is generally expressed as follows

27:

2.

εB

De eqq−= … (15)

The linear form of D-R isotherm equation is represented as

2lnln εBqq De −= … (16)

)1

1ln(eC

RT +=ε … (17)

where qD is the theoretical saturation capacity (mol/g);

B, a constant related to the mean free energy of adsorption per mole of the adsorbate (mol

2/ J

2); ε, the

Polanyi potential; Ce, the equilibrium concentration

of adsorbate in solution (mol/L); R (J/mol/K), the gas constant; and T(K), the absolute temperature. The

D-R constants qD and B are calculated from the linear

plots of ln qe versus ε2 and are given in Table 5.

The constant B gives an idea about the mean free energy E (kJ/mol) of adsorption per molecule of

the adsorbate when it is transferred to the surface of

the solid from infinity in the solution and can be calculated using the following relationship

28:

E = 1/ (2B) 1/2

… (18)

It is observed29

that the adsorption is physisorption if

the energy of activation is in the range of 5 – 40 kJ/ mol

and chemisorption if the energy of activation is 40- 800 kJ/mol. From Table 5, it can be predicted that

the adsorptions of BG4, BV3 and BV10 by TPAC are

physisorption in nature. D-R isotherm is not able to

describe the experimental data properly because of the poor linear correlation coefficient as shown in Table 5

for the adsorption of three basic dyes onto TPAC at

different temperatures. Thermodynamics of adsorption and effect of temperature

The experiments were carried out at four different

temperatures (30, 35, 40 and 45°C) to observe the

effect of temperature on the adsorption of BG 4, BV3 and BV10 dyes respectively on the activated carbon

of Thevetia peruviana. It has been observed that the

percentage removal of BG4, BV3 and BV10 by TPAC increases from 95.74% to 98.94% for BG4,

from 95.45% to 98.70% for BV3 and from 94.64% to

98.21% respectively while increasing the temperature.

This indicates that the sorption of basic dyes on to

TPAC is endothermic in nature.

Thermodynamic parameters provide in-depth

information of inherent energetic changes associated

with adsorption; therefore, these parameters should be accurately evaluated. Langmuir isotherm equation is

applied to calculate the thermodynamic parameters as

follows:

ln k L = TR

H

R

S 1°∆−

°∆ … (19)

where kL is the Langmuir equilibrium constant; °∆H

and °∆S , the standard enthalpy and entropy changes

of adsorption respectively.

Thermodynamic parameters, like °∆H , °∆S and

°∆G were determined from the slope and intercept of

Van’t Hoff’s plot of ln kL versus 1/T. Table 6 shows

the thermodynamic parameters °∆H , °∆S and °∆G

for the removal of BG4, BV3 and BV10 by TPAC

respectively. The °∆G values are found to be

negative at all tested temperatures (30 - 45°C),

indicating that the adsorptions of BG4, BV3 and BV10 dyes onto TPAC are spontaneous

and thermodynamically favorable. The positive

°∆H values indicate that the adsorptions of BG4,

BV3 and BV10 dyes onto TPAC are endothermic process, which is supported by the increase in

adsorption of the dye with the increase in temperature.

INDIAN J. CHEM. TECHNOL, SEPTEMBER 2012

320

Table 7—Activation energies from Arrehenius plots for the

adsorption of BG4, BV3 and BV10 dyes onto TPAC

Dyes Ea, kJ/mol

BG4 15.73

BV3 15.52

BV10 21.37

Furthermore, the positive °∆S indicates that the

degrees of freedom increase at the solid – liquid

interface during adsorption of these basic dyes onto

TPAC. Generally, °∆G for physisorption is between

-20 kJ/mol and 0 kJ/mol and for chemisorption it is between -80 kJ/mol and -400 kJ/mol

30. The

∆G° values for BG4, BV3 and BV10 dyes are given in Table 6. This confirms that the adsorption

of basic dyes onto TPAC is physisorption in nature.

The pseudo second-order rate constant k2 of the

dye adsorption is expressed as a function of temperature by Arrhenius relationship using the

following equation:

RT

EAkn a−= ln1 2 … (20)

The value of Ea can be calculated from the slope

of a plot of ln k2 versus 1/T. The magnitudes of

activation energy give an idea about the type of adsorption which is already reported in literature

29.

The values of activation energy (Ea) for the basic dyes

BG4, BV3 and BV10 are given in Table 7. From the

Ea values, it is confirmed that the adsorptions of these dyes on TPAC are physisorption process.

Desorption studies

The desorption of dyes by mineral acids and alkaline medium indicates that the dyes are adsorbed

onto the activated carbon by physisorption. Maximum

desorptions of 41.5% for BG4, 38.6% for BV3 and

37.9 % for BV10 dyes respectively are reported at a pH range of 2 - 5. There is no change in desorption

after pH 5 for all the three basic dyes.

Conclusion

It is found that low cost activated carbon can be prepared from the wood of Thevetia peruviana for the adsorption of basic dyes namely Malachite Green [BG4], Crystal Violet [BV3] and Rhodamine–B [BV10] from its aqueous solution. The physico- chemical characteristics and surface morphology of the activated carbon are determined. The adsorbed amount of BG4, BV3 and BV10 increases from 49.23 mg/g to 179.59 mg/g, from 48.91 mg/g to

177.32 mg /g and from 48.67 mg/g to 174.23 mg/g respectively while increasing the initial dye concentration. The adsorption of the basic dyes increases with the increase in temperature indicating that the adsorption is endothermic in nature. Kinetic studies show that the adsorption of these basic dyes follows pseudo second-order model with multi-step intra-particle diffusion model. The data obtained from adsorption isotherms are well fitted with Langmuir model which suggests the monolayer coverage of the three basic dyes on surfaces of TPAC. The negative °∆G values obtained from

Van’t Hoff plots confirm that the adsorptions of three basic dyes are spontaneous in nature. The positive

°∆H values for the adsorption of BG4, BV3 and BV10 onto TPAC suggest that the adsorptions of basic dyes on TPAC are endothermic in nature.

Acknowledgement

The authors (PNP and PSK) gratefully acknowledge the financial support provided by the

University Grants Commission (UGC), New Delhi

under the major research project scheme to carryout

this research project.

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Table 6—Thermo dynamical parameters from Van’t Hoff plots for the adsorption of BG4, BV3 and BV10 dyes onto TPAC

Temperature BG4 BV3 BV10

ºC

∆Hº kJ/mol

∆Sº kJ/K/mol

∆Gº kJ/mol

∆Hº kJ/mol

∆Sº kJ/K/mol

∆Gº kJ/mol

∆Hº kJ/mol

∆Sº kJ/K/mol

∆Gº kJ/mol

30 60.762 - -9.3522 61.127 - -7.654 73.016 - -7.8547

35 60.762 - -10.5092 61.127 - -8.789 73.016 - -9.1892

40 60.762 - -11.6662 61.127 - -9.924 73.016 - -10.5237

45 60.762 0.2314 -12.8232 61.127 0.227 -11.059 73.016 0.2669 -11.8582

BASERI et al.: ADSORPTION OF BASIC DYES FROM SYNTHETIC TEXTILE EFFLUENT

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