Vol.2, No.5, 469-475 (2010) Natural Science
Copyright © 2010 SciRes. OPEN ACCESS
Extraction, identification and adsorption-kinetic studies
of a natural color component from G. sepium
Konaghatta Narayanachar Vinod1, Puttaswamy1*, Kurikempanadoddi Ninge Gowda2,
Rajagopal Sudhakar2
1Department of Post-Graduate studies in Chemistry, Central College Campus, Bangalore University, Bangalore, India;
*Corresponding Author: pswamy_chem@yahoo.com
2Department of Apparel Technology and Management, Central College Campus, Bangalore University, Bangalore, India;
Received 24 December 2009; revised 25 January 2010; accepted 23 February 2010.
The use of synthetic dyes causes environmental
pollution as majority of these dyes are toxic and
non-biodegradable. Natural dyes on the other
hand have proved to be eco-friendly, biodegra-
dable and highly compatible with the environ-
ment. Consequently, dyes derived from natural
sources have emerged as important alternatives
to synthetic dyes. In the present work, the major
color component isolated from the pods of G.
sepium plant is morin, which is a flavonoid
moiety. The dyeing behaviour of this component
on silk yarn was investigated. Mordanting stu-
dies have indicated that the post-mordanting
method was found to be a better method com-
pared to pre-mordanting. Variation of pH on dye
extract pointed out that the maximum absorb-
ance was at pH 4 and hence all the dyeing
studies have been carried out at that pH. Ther-
modynamic parameters were determined by
studying the dyeing process at different tem-
peratures. Heat of dyeing was positive which
indicated the dyeing process was endothermic.
The adsorption process of morin on silk was
tested with Langmuir, Freundlich and Tempkin-
Pyzhev isotherm models. The adsorption proc-
ess followed both the Langmuir and Freund-
lich isotherms. The value of regression coeffi-
cient, however, indicated that the Langmuir
isotherm was a better fit than the Freundlich
isotherm. These results signified that the adsor-
ption of morin on silk yarn was homogeneous in
nature with the formation of a monolayer. Hence,
the dye obtained from the pods of G. sepium
plant may be an alternative source to synthetic
dye for the dyeing of silk as well as other textile
Keywords: G. Sepium; Morin; Adsorption-Kinetics;
The use of synthetic dyes causes environmental pollu-
tion as majority of these dyes are toxic and non-biode-
gradable. For this reason, there is a revival of interest in
the non-toxic and eco-friendly natural dyes. Nature pro-
vides a wealth of plants which yield color for the pur-
pose of dyeing, many have been used since antiquity
[1-4]. Natural dyes exhibit better biodegradability com-
pared to their synthetic counterparts and generally have a
higher compatibility with the environment. There are
several reports in the literature pertaining to the applica-
tion of natural colorants and evaluation of their dyeing
properties on various fibers [5-8], but a very few reports
are available on their kinetic and adsorption aspects
[9-11]. G. sepium, is an important member of the family
Fabaceae, which is widely naturalized in the tropical
Americas, Caribbean, Africa, Asia, and the Pacific Is-
lands. Since this tree possesses high nitrogen-fixing
properties and also the leaves can be used for mulch and
green manure, which makes it highly suitable in agro-
forestry systems. G. sepium is a small, thornless, semi-
deciduous tree, which yields flattened pods, 10-15 cm
long, containing three to eight seeds. The abundantly
available pods, unless otherwise used go as natural
Keeping this in view and also due to our continued
interest in the identification of colorant from natural
plants, a major color component from the pods of G.
sepium plant was identified. The present research was
performed with the following objectives: 1) To extract
and isolate the main color component from the pods of G.
sepium plant, 2) To explore the dyeing properties of the
color component on silk, 3) To study adsorption iso-
therms of the color component on silk and 4) To evaluate
the thermodynamic parameters of the dyeing process
through kinetic studies.
K. N. Vinod et al. / Natural Science 2 (2010) 469-475
Copyright © 2010 SciRes. OPEN ACCESS
2.1. Materials
The pods of G. Sepium were collected from the south-
eastern region, Shimoga, India. The pods were washed
well with tap water and dried under laboratory condi-
tions. The dried pods were then finely ground to powder.
Raw silk yarn of 40 denier was scoured with 2 g dm-3
non-ionic detergent and 1 g dm-3 sodium carbonate at
90℃ for 1 h, and rinsed with water and dried under la-
boratory conditions.
2.2. Isolation
The air dried powder of G. Sepium pod (550 g) was ex-
tracted with 90% methanol (3 × 250 ml) at room tem-
perature using a soxhlet apparatus and the procedure was
repeated till the color from the extract was negligible.
The extracts were combined, concentrated under reduced
pressure and the residue was successively extracted with
pet. ether, chloroform and ethyl acetate. The ethyl ace-
tate soluble fraction was concentrated under reduced
pressure and was chromatographically separated over
silica gel (60-120 mesh) using methanol as eluent. The
fractions obtained were combined according to TLC
(silica gel, CHCl3-MeOH-H2O, 80:18:2) in increasing
order of polarity to yield two fractions. Solvent was
evaporated from the first fraction (major) to get yellow
colored amorphous compound and it was used for fur-
ther studies.
2.3. Mordanting
Pre-and post-mordantings were carried out on silk using
2, 4 and 6% tannic acid and alum (Al(NH4) (SO4)2.
12H2O) as mordants, separately. Mordanting was carried
out for 30 min at 70 and the silk was then rinsed with
tap water and dried.
2.4. Dyeing
Open bath beaker dyeing machine equipped with pro-
grammable control of temperature and time was used to
carry out all dyeing studies. The silk yarn was dyed with
4% dye solution at pH 4 with M: L ratio of 1 : 20. The
dyeing was started at 40 and the temperature was
gradually raised to 90 in 20 min and the dyeing proc-
ess was continued for 45 min. After dyeing, samples
were removed from dyeing machine and soaped at 60
for 10 min. Further, the samples were rinsed with tap
water and dried. In case of post-mordanting samples,
soaping was done after mordanting.
2.5. Characterization
IR spectrum of the major color component was recorded
on a Perkin-Elmer 298 grating IR Spectrophotometer.
The NMR spectrum of the compound was recorded on the
Brucker 400 NMR spectrophotometer. The mass spectrum
was recorded on an Esquire 3000 plus spectrometer.
2.6. Absorbance and Color Strength
The dye solutions (1-5%) of the extract were prepared
with M: L ratio of 1 : 20. The absorbance of the dye so-
lutions was recorded prior and after the dyeing process
using UV-Vis spectrophotometer. The dye exhaustion
was calculated using the equation, % Exhaustion =
[(Cg-Ct)/Cg] × 100, where Cg is the concentration of dye
offered and Ct is the concentration of residual dye in the
spent liquor.
The surface reflectance and colorimetric data (CIE L*
a* b* C h) for the dyed samples were obtained by Gretag
Macbath Color Eye 7000A spectrophotometer. The spec-
trophotometer was interfaced to a PC under illuminant
D65 with a 100 standard observer. Surface color strength
(K/S) was calculated from the surface reflectance values
using the Kubelka-Munk equation [12]: K/S = (1-R)2/2R,
where R is the reflectance, K is the absorption coeffi-
cient and S is the light scattering coefficient. A higher
K/S value signifies better dye receptivity of the sub-
strates. The wash fastness of the dyeing was tested using
ISO method 105-C10-A(1)-2006 and crocking fastness
was assessed using AATCC Test Method 8-1996. Color
fastness to light was evaluated as per AATCC Test
Method 16-2004 option 5.
2.7. Kinetic Studies
Kinetic studies were investigated with aqueous solution
of the dye extract 0.5 g dm-3 (without any further purifi-
cation) prepared in an acetate buffer of pH 4. The dyeing
was carried out with M:L ratio of 1:20 at 50. Known
volume (5 ml each) of the dye-bath solution was pipetted
into a cuvette at regular intervals of time and absorbance
measurements were made at its λmax 580 nm (Figure 1).
The absorbance readings of Do and Dt at the beginning
and at any time interval during the dyeing process,
400 450 500 550 600 650 700 750 800 850
Wavelength in nm
pH 4pH 7pH 9
Figure 1. Visible Spectra of G. sepium in aqueous solution at
different pH.
K. N. Vinod et al. / Natural Science 2 (2010) 469-475
Copyright © 2010 SciRes. OPEN ACCESS
respectively, were recorded. Plots of log (Do /Dt) versus
time were made to evaluate first-order rate constants (k/
s-1). The experiment was repeated at 60, 70 and 800C and
the dye uptake rate was calculated at each temperature.
The energy of activation and other thermodynamic pa-
rameters were deduced.
2.8. Adsorption Isotherms
The adsorption isotherm indicates how the adsorption
molecules distribute between the adsorbate and adsorb-
ent when the adsorption process reaches an equilibrium
state. The amount of dye adsorbed at equilibrium qe
(mg/g) was calculated by the following mass balance
equation [13]:
MCCVq eie /)(  (1)
where V is the volume of solution used in the adsorption
experiment, Ci and Ce are the initial and equilibrium
concentrations of the dye (mg dm-3), respectively, and M
is the mass of silk (g).
In the present case, the adsorption isotherm study was
carried out on Langmuir, Freundlich and Tempkin-py-
zhev isotherms. The applicability of the isotherm equa-
tion was compared by judging the value of regression
coefficients (r). The equilibrium adsorption isotherm is
fundamental in describing the interaction between ad-
sorbent and adsorbate, and is also important in the de-
sign of an adsorption system. A basic assumption of
Langmuir theory is that in which the sorption takes place
at specific homogeneous sites within the adsorbent. It is
then also assumed that once a dye molecule occupies a
site, no further adsorption can take place at that site.
Theoretically, a saturation value is reached beyond
which no further sorption can take place. The Langmuir
isotherm [14] was applied for adsorption equilibrium
and represented as:
e (2)
where Ce = Concentration of adsorbent (mg dm-3) at
equilibrium; qe = Amount of dye adsorbed at equilibrium
(mg/g); Qo = A constant (mg/g) which signifies the prac-
tical limiting adsorption capacity when the surface is
fully covered with dye molecules and it aids in the com-
parison of adsorption performance and b = Langmuir
constant related to the affinity of the binding sites (cm-3
Freundlich isotherm model assumes heterogeneous
surface energies, in which the energy term in Langmuir
equation varies as a function of the surface coverage.
The well known logarithmic form of Freundlich model
[15] is given by the following equation:
Kq e
loglog  (3)
where Kf and 1/n = Freundlich constant related to ad-
sorption capacity and adsorption intensity respectively
obtained from the plot. In general, as the Kf value in-
creases the adsorption capacity of the adsorbent for the
given adsorbate increases. 1/n is the heterogeneity factor,
if n is close to unity, the surface heterogeneity could be
assumed to be less significant and as n approaches 10,
the impact of surface heterogeneity becomes more sig-
nificant [16].
Tempkin and Pyzhev [17] considered the effects of
indirect adsorbate-adsorbent interactions on the adsorp-
tion isotherms. As a result, the heat of adsorption of all
the molecules on the adsorbent surface layer would de-
crease linearly. The Tempkin isotherm can be expressed
in its linear form as:
ee CBABq lnln
where B and A are the Tempkin constants and can be
determined by a plot of qe versus ln Ce. The constant B is
related to heats of adsorption and A is the equilibrium
binding constant.
3.1. Characterization of Major Color
Morin (2', 3, 4', 5, 7-Pentahydroxyflavone) [18-20] was
isolated from the pods of G. sepium as the major color
component and it was confirmed by IR, 1H-NMR,
13C-NMR and Mass spectral studies.
3.2. Effect of Dye Concentration and Color
Table 1 revealed that the absorption of dye increased
with increase in dye concentration (1-5%) and the maxi-
mum dye uptake was observed at 4% concentration. The
values of K/S also increased with the increase in dye
concentration (Table 1). Further, it was noticed that the
K/S value was higher at 4% dye concentration, indicat-
ing deeper shades at higher concentrations. Therefore,
4% dye concentration was fixed as optimal concentra-
tion for further dyeing process.
Table 1. Absorbance (%) and K/S values of different dye con-
centrations at 360 nm.
Dye oncentration
(%) Absorbance Dye uptake
(%) K/S
Before dyeing after dyeing
1 0.130.10 23.0 4.14
2 0.270.19 29.6 4.28
3 0.470.31 34.0 4.43
4 0.610.33 45.9 4.50
5 0.840.55 34.5 4.45
K. N. Vinod et al. / Natural Science 2 (2010) 469-475
Copyright © 2010 SciRes. OPEN ACCESS
3.3. Effect of Mordanting
The K/S values of the mordanted samples were better
compared to that of the un-mordanted samples (Table 2).
The K/S values and the fastness properties (Table 3) of
the post-mordanted samples were better compared to
pre-mordant samples. Tannic acid was found to be a bet-
ter mordant with deeper shades and fastness ratings as
compared to alum in pre-mordanting. But in case of
post-mordanting, both the mordants showed comparable
K/S values. All the color co-ordinates were positive and
hence the dyed samples were located in the yellow-red
quadrant of the color-space diagram.
3.4. Effect of pH on Dye Extract
The visible spectrum of the dye extract at different pH (4,
7 and 9) is illustrated in Figure 1. The λmax of the dye
extract remained the same with varying pH. The ab-
sorbance of the dye extract increased with an increase in
pH, which may be due to the high solubility of phenolic
groups in the alkaline pH.
3.5. Kinetic Studies
From the linear plot log k/ versus 1/T (r = 0.9979), the
energy of activation (Ea) was found to be 61.2 kJ mol-1.
Further, thermodynamic parameters such as ΔH, ΔG,
Table 2. Color co-ordinates and K/S values of the dyed silk samples.
Method Mordants K/S L* a* b* C h
Nil 4.50 63.1 15.1 17.3 23.0 48.9
Alum (2%) 4.61 69.7 11.5 14.1 18.2 50.5
Alum (4%) 4.63 69.7 11.7 13.8 18.1 49.5
Alum (6%) 4.73 69.9 11.8 13.9 18.2 49.6
Tannic acid (2%) 5.22 75.2 9.85 12.0 15.5 50.7
Tannic acid (4%) 5.27 74.3 10.1 12.8 16.3 51.6
Tannic acid (6%) 5.37 74.9 9.41 12.7 15.8 53.5
Alum (2%) 5.76 62.5 12.9 23.5 26.9 61.1
Alum (4%) 5.55 63.1 13.2 22.8 26.3 59.9
Alum (6%) 5.44 62.8 13.2 22.9 26.5 60.1
Tannic acid (2%) 5.66 68.1 12.7 17.4 21.6 53.7
Tannic acid (4%) 5.57 68.7 12.4 17.5 21.5 54.5
Tannic acid (6%) 5.30 66.2 13.2 19.9 23.9 56.3
L*- Lightness, a* - (+ ve- red, - ve- blue), b* - (+ ve- yellow, - ve- green), C-Chroma and h-Hue.
Table 3. Results derived from fastness properties of dyed silk samples.
Mordants light fastness crocking fastness wash fastness
wet dry
Nil 2 4 4-5 3-4
Alum (2%) 2 4-5 4-5 4
Alum (4%) 2-3 4-5 5 4-5
Alum (6%) 2-3 4-5 5 5
Tannic acid (2%) 2-3 4-5 5 4-5
Tannic acid (4%) 2-3 5 5 5
Tannic acid (6%) 3 5 5 5
Alum (2%) 2 4-5 4-5 4
Alum (4%) 2 4-5 4-5 4
Alum (6%) 2-3 4-5 5 4-5
Tannic acid (2%) 2 4-5 4-5 4
Tannic acid (4%) 2-3 5 5 4-5
Tannic acid (6%) 2-3 5 5 5
K. N. Vinod et al. / Natural Science 2 (2010) 469-475
Copyright © 2010 SciRes. OPEN ACCESS
ΔS and log A were calculated and recorded in Table 4.
The high positive value of the standard free energy (ΔG)
indicates the spontaneous and strong adsorption of dye
molecules on the surface of silk. The enthalpy of dyeing
or heat of dyeing (ΔH) was positive indicating that the
dyeing process is endothermic in nature. Further, large
negative entropy (ΔS) indicates that the dye molecules
are more systematically arranged on the surface of silk
3.6. Adsorption Isotherms
The experimental adsorption data were analyzed using
Langmuir, Freundlich and Tempkin and Pyzhev isotherm
models. The Langmuir constants Qo and b were deduced
from the intercept and slope of the plot 1/qe versus 1/Ce.
The plot was linear with a regression value of r = 0.9987
(Figure 2). The value of Qo was found to be 142 mg/g,
signifies the amount of dye required to form a complete
mono layer at equilibrium. The value of Langmuir con-
stant b = 1.97 cm3/mg, which relates with the binding
energy of dye molecules on silk. Further, the essential
characteristics of the Langmuir isotherm can be ex-
pressed in terms of a dimensionless constant separation
factor for equilibrium parameter, RL [21-23]:
1 (5)
where Co is the initial concentration of dye (mg/dm3)
and b is the Langmuir constant (mL/mg). The value of
RL indicates the type of isotherm to be either irreversible
(RL= 0), favorable (0 < RL< 1), linear (RL = 1) or unfa-
vorable (RL > 1). In the present study, the value of RL
was found to be 0.835, indicating that Langmiur adsorp-
tion isotherm to be a favorable process.
A plot of log qe versus log Ce was a straight line with a
regression coefficient of 0.9975 (Figure 3) for Freun-
dlich adsorption isotherm. The values of Kf and 1/n,
were calculated from the intercept and slope of such a
plot and were found to be 2.50 and 0.84, respectively.
The value of 1/n indicates that the adsorption process is
homogeneous, as the value is very close to unity.
Further, Tempkin and pyzhev model was also consid-
ered to correlate the experimental data. The plot of qe
versus log Ce was curvilinear with regression coefficient
r = 0.9560 (Figure 4).
The linear regression coefficient was normally used to
decide the most fitted isotherm in adsorption process. As
seen from Table 5, the Langmuir model yielded some-
what better fit (r = 0.9987) than the other models fitted.
The results demonstrated the formation of homogeneous
monolayer. Further, the value of 1/n (0.84) in Freundlich
isotherm model also supports the formation of monolayer.
The major coloring component obtained from the pods
of the G. sepium was identified as morin, a flavonoid.
The dyeing behaviour of this component on silk yarn
was investigated. Mordanting studies have indicated that
the post-mordanting method was found to be a better
method compared to pre-mordanting. For dyeing of silk,
heat of dyeing (H) was positive which indicates endo-
thermic nature of the process. The negative value of S
indicates a more ordered adsorption of color component
on silk. The high positive value of free energy change
signifies that the color component has stronger affinity
Table 4. Kinetic and thermodynamic parameters for the dyeing
of coloring matter on to silk yarn.
Temperature (0C) 104 k/ (s-1)
50 2.64
60 4.79
70 9.25
80 18.4
Ea (kJ mol-1) 61.2
ΔH (kJ mol-1) 58.4
ΔG (kJ mol-1) 103
ΔS (JK-1 mol-1) -133
log A 6.32
Table 5. Isotherm constants for silk dyeing with pods of G.
sepium extract.
Langmuir isotherm constants
Qo (mg/g) 142
b (mL/mg) 1.97
r 0.9987
Freundlich isotherm constants
Kf (mg/g) 2.50
1/n 0.843
r 0.9975
Tempkin and Pyzhev isotherm constants
B (mg/g) 3.43
A (mL/mg) 1.46
r 0.9560
Figure 2. Langmiur isotherm plot at pH 4 for dyeing silk
with color component of G. sepium at 80.
K. N. Vinod et al. / Natural Science 2 (2010) 469-475
Copyright © 2010 SciRes. OPEN ACCESS
Figure 3. Freundlich isotherm plot at pH 4 for dyeing silk
with color component of G. sepium at 80.
0.6 0.70.8 0.911.11.2 1.31.4
2 + log Ce
Figure 4. Tempkin and Pyzhev isotherm plot at pH 4 for
dyeing silk with color component of G. sepium at 80.
towards silk. The adsorption isotherm of morin on silk
was carried out using different models: Langmuir,
Freundlich and Tempkin-Pyzhev models. The adsorption
of morin on silk fitted well to the Langmuir and Freun-
dlich isotherm. However, Langmuir model was found to
be better fit, and suggesting the formation of homoge-
neous monolayer on silk.
One of the authors (K.N.V.) is grateful to Bangalore University, Ban-
galore for awarding the Research Fellowship under the Interdiscipli-
nary Collaborative Research Project.
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