Adsorption study of some sulphanilic azo dyes on charcoal

Article abstract of DOI:10.1155/2011/487287

Studies on the removal of two dyes (sulphanilic azo antipyrine and sulphanilic azo imidazole) from aqueous solution by adsorption on charcoal as an adsorbent were carried out. A series of experiments were under taken in a batch adsorption technique to access the effect of the process variables i.e. contact time, initial dye concentration, initial pH, adsorbent dose and temperature. Adsorbent dosage (0.1 g) higher value for both dyes. The equilibrium in the solution was observed within (35 min) of two sulphanilic dyes on charcoal. The equilibrium isotherms for both dyes were determined to describe the adsorption process. The results showed that the equilibrium data was fitted by of the Freundlich isotherms on charcoal surface. The result obtained shows that the adsorption isotherm for both dyes on charcoal was according to Giles classification. The thermodynamic factors such as δH, δG and δS were calculated.

Full text of DOI:10.1155/2011/487287

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
2011, 8(2), 739-747
http://www.e-journals.net
Adsorption Study of Some
Sulphanilic Azo Dyes on Charcoal
H. J. MOHAMMED*, B. J. KADHIM§ and ASEEL SH. MOHAMMED
Dept of Basic Science, College of Dentistry, Kufa University, Iraq
§Dept of Food Science, College of Agriculture, Kufa University, Iraq
ibrahiem_af@yahoo.com
Received 29 March 2010; Accepted 23 July 2010
Abstract: Studies on the removal of two dyes (sulphanilic azo antipyrine and
sulphanilic azo imidazole) from aqueous solution by adsorption on charcoal as
an adsorbent were carried out. A series of experiments were under taken in a
batch adsorption technique to access the effect of the process variables i.e.
contact time, initial dye concentration, initial pH, adsorbent dose and
temperature. Adsorbent dosage (0.1 g) higher value for both dyes. The
equilibrium in the solution was observed within (35 min) of two sulphanilic
dyes on charcoal. The equilibrium isotherms for both dyes were determined to
describe the adsorption process. The results showed that the equilibrium data
was fitted by of the Freundlich isotherms on charcoal surface. The result
obtained shows that the adsorption isotherm for both dyes on charcoal was
according to Giles classification. The thermodynamic factors such as ∆Η, ∆G
and ∆S were calculated.
Keywords: Charcoal, Adsorption, Organic dyes, Sulphanilic azo dye.
Introduction
Charcoal is often used as an adsorbent for the removal of a different of organic dyes because
it is highly inert and thermally stable, it can also be used at different hydrogen function
range1. Activated carbon is the most commonly used adsorbent, although other materials
such as activated clay, wood and types of cellulose have also been studied2,7. Some of azo
compounds are stable and do not suffer biodegradation and those including metals are toxic.
Consequently it is important to remove these pollutants from the wastewaters before their
final disposal8,9. Adsorption methods have been reported as an effective process to remove
organic dyes from wastewaters. The widely used adsorbent for industrial residue is activated
carbon10,11. Many methods including coagulation precipitation, filtration and oxidation have
been used for the treatment of dye-containing effluents12,13. These methods are costly and
can not be used effectively to treat the wide range of dye wastewaters when compared with

740
H. J. MOHAMMED et al.
adsorption processes. The aim of this study was to determine the adsorption capacity of
charcoal in aqueous organic dyes varying with process factors including initial dye
concentration, contact time, initial pH, adsorbent dose and temperature.
Experimental
All spectral and absorbance measurements were carried out on APEL - PD - 303 UV visible
recording spectrophotometer. Shaking inductor GCA/precision scientific Chicago, U.S.A
and Maga fuge 1.0 Herouse centrifuge were used .A digital pH meter Hanna was used. The
charcoal sample used as adsorbent was supplied from India where as the sulphanilic azo
imidazol and sulphanilic azo antipyrine were prepared according to the equations by
Hussain14 (Scheme 1).
0-5 C
0-5 C
HCl
HO3S
NH2
HO3S
N
NCl
HO3S
NH3Cl
NaNO2
dizonium salt
Sulphanilic acid
H
N
H
N
0-5 C
HO3S
N
NCl
+
N
N
SO3H
NaOH
N
N
Sulphanilic azo imidazole
dye (A)
CH3
CH3
H3C
H3C
N
N
0-5 C
NaOH
H2N
N
N
N
SO3H
HO3S
N
NCl
+
N
H2N
O
O
Sulphanilic azo antipyrine
dye (B)
Scheme 1. Preparation of dyes
Table 1. Structures, molecular weights and wavelengths of the dyes
Molar
Name
Chemical structure
mass
λmax / nm
H
Sulphanilic
azo imidazole
(A)
N
252
386
410
N
N
SO3H
N
CH3
H3C
N
Sulphanilic
azo antipyrine
(B)
N
N
N
SO3H
370
H3C
O
General procedure for isotherms
Portions of dye (A or B) solution, 15 mL of known initial concentration (10 - 100 ppm) and
varied amounts of charcoal (0.02 - 0.12 g) were poured into volumetric flask. Analytical
determination of sulpanilic azo imidazol or sulpanilic azo antipyrine in solutions after
equilibrium (35 min at 25 ºC) were performed by means of a APEl-PD 303
spectrophotometer . Optical densities were determined at 410 nm for dye A and at 370 for

Adsorption Study of Some Sulphanilic Azo Dyes on Charcoal
741
dye B (Figure 1 & 2) which corresponds to the maximum absorption peak of dye A and B.
From the difference between initial concentration and equilibrium, the amounts of dye A
and B adsorbed were calculated by the following relation:
(Co −Ce)Vsol
(1)
Qe =
M
Where, Qe amount of dye adsorbed (mg.g-1), Co and Ce are the initial and equilibrium
concentration (mg. L-1) respectively. M is the adsorbent dosage (in g), Vsol is the solution volume (in
mL). The adsorption capacity was determined with the effect of contact time, initial concentration
of dye A and B, pH, temperature and agitation rate. The equilibrium concentration, adsorption
capacity at equilibrium was determined to fit in the adsorption isotherms.
Calibration graphs of two dyes
In to a series of ten calibrated flask, different volumes of dye A and B working solution
(100 mg.mL-1) were transferred to cover the range of the calibration curve. Linear
calibration graphs of two dyes were obtained, that obeyed Beer’s law over the concentration
range of (10 - 100 ppm) with correlation coefficient 0.9981, 0.9889 and an intercept of 0.2,
0.53 for dye A and B respectively.
nm
Figure 1. Spectrum of sulphanilic azo imidazole dye A
nm
Figure 2. Spectrum of sulphanilic azo antipyrine dye B

742
H. J. MOHAMMED et al.
Results and Discussion
Adsorption isotherms
The Freundlich models are the most frequently employed models. The Freundlich isotherms
have been widely adopted to characterize the adsorption capacity of dyes pollutant using
different adsorbent by fitting the adsorption data (Figure 3).
8
7
6
5
Dye A
Dye B
4
3
2
1
0
0
10
20
30
40
50
60
70
Ce
Figure 3. Adsorption isotherms of dye A and B at pH 12 and 2 respectively
The Freundlich isotherms have the general from such as:
½
Qe =KfCe
(2)
(3)
This equation can be modified as:
Co −Ce
Qe =
= Kf Ce1/ 2
M
Where, Kf and 1/n are Freundlich constants related to adsorption capacity and adsorption
intensity, respectively, of the sorbent. The values of Kf and 1/n can be obtained from the
intercept and slope respectively of the linear plot of experimental data of log Qe versus log
Ce (Table 2 Figure 4&5).
Table 2. Frundlich constant for two dyes in aqueous solution using charcoal as an adsorbent
Frundlich constant
Adsorbent
n
log Kf
R
dye A
dye B
1.08
1.00
0.06
0.9601
0.9669
0.15
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
r = 0.9601
1
1.1
1.2
1.3
1.4
log Ce
1.5
1.6
1.7
1.8
Figure 4. Freundlich isotherm of dye A with charcoal at pH 12

Adsorption Study of Some Sulphanilic Azo Dyes on Charcoal
743
0.9
r = 0.9669
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
2
0
0.2 0.4 0.6 0.8
1
1.2 1.4 1.6 1.8
log Ce
Figure 5. Freundlich isotherm of dye B with charcoal at pH 2
log Qe = log Kf + 1/n log Ce
(4)
The values showed that the equilibrium data for two dyes fitted well to the Freundlich
isotherms in the studied concentration ranges. Based on the correlation coefficients (r) the
equilibrium data was fitted in the isotherms Freundlich equations (Table 2).
Many authors have used these isotherm to evaluate the adsorption capacity by different
adsorbent with different dyes15,16. The results showed that the adsorption of dye A and B on
charcoal was found to be effective at pH 12 and 2 respectively. The Freundlich equations
were used to study data concerning the dependence of the adsorption of two dyes on
charcoal at pH 12 and 2.
The adsorption constants evaluated from the isotherms with correlation coefficient are
(Table 2) very high, regression coefficient (0.9601, 0.9669) was found for dye A and B
respectively. The regression values showed that the equilibrium data for dyes fitted well to
the Freundlich isotherm in the studied concentration ranges.
Effect of pH
In order to study the hydrogen ion concentration (pH) on sulphanilic azo imidazole and
sulphanilic azo antipyrine by adsorbent charcoal, dyes solutions were prepared in the range of
10-100 ppm and adjusted to different pH values (2, 4, 7, 9 and 12) using 0.1 N of HCl and
0.1 N of NaOH . The results are shown in Figure 6 & 7. It is clear that the amount of dyes
removed at various pH. pH 12 produces a large adsorbed quantity for dye A, whereas pH 2
produces a large adsorbed quantity for dye B. It is clear that, the lower pH value (Figure 6)
explained on the basis of formation of a positively charged surface on charcoal.
16
14
12
10
pH 2
pH 4
8
6
4
2
0
pH 7
pH 9
pH 12
0
10
20
30
40
Ce, mg/L
50
60
70
Figure 6. Removal of colour from aqueous solution of sulphanilic azo antipyrine at various pH

744
H. J. MOHAMMED et al.
At solution pH acidic, the removal capacity was expected to decrease, as the adsorbent
was positively charged and the dye molecules were neutral charged Figure 7.
12
10
8
pH 2
pH 4
pH 7
pH 9
pH 12
6
4
2
0
0
10
20
30
40
Ce, mg/L
50
60
70
Figure 7. Removal of colour from aqueous solution of sulphanilic azo imidazole at
various pH
Contact time
The influence of the contact time on the adsorption capacity of two dyes by adsorbent charcoal
was conducted through batch experiments to achieve the equilibrium as shown in Figure 8.
0.6
0.5
0.4
B
0.3
A
0.2
0.1
0
0
5
10
15
20
25
Time
30
35
40
45
50
55
Figure 8. Adsorption capacity against contact time of dyes A and B with charcoal
The results indicated that the high affinity between the sorbent surface and the reactive
dye molecules the dye molecule favorably adsorb on the carbon surface with low
competition from water molecule
Adsorbent dosage
In order to study the effect of adsorbent dosage on dyes removal as the adsorption capacity
with fixed initial concentration of type of dye, pH, temperature ,agitation rate and charcoal
as an adsorbent. Different weight of dosage was used (0.02, 0.03, 0.05, 0.07, 0.09, 0.10 and
0.12 g). The maximum removal of dyes was observed with the dosage more than 0.09 g and
0.1 g used for all subsequence experiments.

Adsorption Study of Some Sulphanilic Azo Dyes on Charcoal
745
Effect of temperatures
Adsorption isotherms were taken for the dyes in the temperature range of 298 to 313 K. The
results are shown in Figure 9 & 10. The thermodynamic parameters ln K, ∆G, ∆S and ∆H
were computed.
8
7
6
5
298 K
303 K
308 K
313 K
4
3
2
1
0
0
10
20
30
40
50
60
70
Ce, mg/L
Figure 9. Effect of temperature on the adsorption capacity of dye A with charcoal at pH 12
8
7
6
5
298 K
303 K
308 K
313 K
4
3
2
1
0
0
10
20
30
40
50
60
70
Ce, mg/L
Figure 10. Effect of temperature on the adsorption capacity of dye B with charcoal at pH 2
The free energy change (∆G) was calculated from the relation18
∆G = - RT ln K
(5)
Enthalpy change (∆H) was computed from the following (Van Hoff–Arrhenius equation19).
- ∆H
(6)
(7)
log Xm =
+ con
2.303RT
And the entropy was calculated from the equation20
∆G = ∆ H - T ∆ S
The thermodynamic factors evaluated from isotherms are shown in Table 3.
Table 3. Thermodynamic values of sulphanilic dyes in aqueous solution using charcoal as
an adsorbent
Dyes
A
∆H, kJ.mol-1
-4.94
-7.41
∆G, kJ.mol-1
5.196
5.70
∆S, J.mol-1
-0.034
-0.043
B
The up take of two dyes decreases with an increasing temperature up to 40 °C. The
results indicated that the adsorption process is endothermic in nature21,22. Many variables
such as the molecular volume of the dyes, its planarity and its ability to bind to the
adsorbent, among others, can affect the degree of adsorption.

746
H. J. MOHAMMED et al.
The two temperatures was the favorite for adsorption of sulphanilic azo dyes on
charcoal due to the thickness of the boundary layer decrease with the increase in
solution temperature. Therefore, the increasing tendency of dyes to escape from the
solid phase to the liquid phase, as a result of increase in kinetic energy of the adsorbent
species at high temperature23
.
More dye B is adsorbed on charcoal than dye A dye. This difference is most related to
the higher affinity of the dye B on the charcoal surface. Also this may be due to a tendency
for the dye A molecule to escape from the solid phase of charcoal to the liquid phase of dye
with an increase in temperature of the solution24 Figure 11 & 12.
0.83
r = 0.9897
0.82
0.81
0.8
0.79
0.78
0.77
0.76
3.18
3.2
3.22
3.24
3.26
3.28
3.3
3.32
3.34
3.36
1000/T (K)
Figure 11. Relationship between the log Xm and 1/T of dye A with charcoal as an adsorbent
0.79
r = 0.9555
0.78
0.77
0.76
0.75
0.74
0.73
0.72
0.71
0.7
0.69
3.16
3.18
3.2
3.22
3.24
3.26
3.28
3.3
3.32
3.34
3.36
1000/T (K)
Figure 12. Relationship between the log Xm and 1/T of dye B with charcoal as an adsorbent
The apparent adsorption enthalpy is -4.49 kcal /mol for the sulphanilic azo imidazole
dye and - 7.41 kcal /mol for sulphanilic azo antipyrine. The low value of adsorption enthalpy
indicates a physical adsorption17.

Adsorption Study of Some Sulphanilic Azo Dyes on Charcoal
747
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