Indian Journal of Chemistry
Vol. 39A, June 2000, pp. 611-617
Adsorption of methylene blue on cellulose from its own solution and
its mixture with methyl orange
Debashish Palit & Satya P Moulik*t
Centre for Surface Science, Department of Chemistry, Jadavpur University, Calcutta 700032, India
Received 22 March /999; revised 20 October /999
The adsorption behaviour of the cationic dye, methylene blue (MB) from its own solution and from its mixture with an
anionic dye, methyl orange (MO) on cellulose has been investigated. The effects of temperature and KCl on the adsorption
process have been examined. The anionic dye, MO neither individually nor in mixed condition adsorbs on the negatively
charged cellulose surface under the studied conditions of temperature and ionic strength. The dye MB alone and from its
mixture with MO adsorbs on the cellulose surface, the former shows lower extent of adsorption than the latter. At a temperature >303 K, the mixed dyes MB and MO undergo complexation. The results have been analysed in the light of the adsorption isotherms of Freundlich, Frumkin and Langmuir and related adsorption thermodynamics.
The adsorption of solutes on solid surfaces offers the
basis for the understanding of heterogeneous catalysis, chromatographic separation, dyeing of textiles
and clarification of effluent, etc 1• 2 . As an adsorbent,
cellulose is employed for the treatment of textile mill
waste water to remove dyes or pigments 3 ; this most
abundant polymer is used as a raw material for many
products in paper and textile industries and its derivatives find new applications in the pharmaceutical
industry in drug delivery devices 4 . The dyeing of
cellulose and cellulosic materials is also of great interest in textile and paper industries . The investigation of dye adsorption on such materials is of fundamental importance for the understanding of the dyeing mechanism in the production of textile materials .
The adsorption of dyes on charged solids is an associated field of stud/. In this direction, the adsorption
of dyes on charged solids, for example, cationic dyes
(including azo dyes) on alkaline chromatographic
alumina, crystal violet on hydrou s ferric oxides, anionic dye, new coccine acid red # 18 onto sludge particulate, etc. can be mentioned 6-9 . Davidson has
worked on the adsorption of methylene blue on oxycellulose prepared by the action of alkaline hypobromite on cotton; the dye has a high affinity for the carboxyl group of the polymers 10 •
Although adsorption of a single component, for
tE-Mail: [email protected]
example, a dye on different adsorbents has been
studied in plenty, such a process for mixed dyes has
11
been rarely examined •
The objective of the present research is to understand how ionic dyes when mixed behave in terms of
adsorption onto negatively charged cellulose surface
under different environmental conditions . The pair of
dyes considered for the work are the cationic dye,
methylene blue and the anionic dye, methyl orange.
The results of study are expected to offer an understanding of the basics of the dye adsorption in combination.
Materials and Methods
The cationic dye, methylene blue (3,9-bisdimethylaminophenazothionium chloride) was a G.R. product
of E. Merck, Germany and was used as received. The
anionic dye, methyl orange (Na salt of 4, [4(dimethylamino)phenylazo]benzenesulphonic
acid)
was a product of Reanal , Budapest and was used after
repeated (three times) crystallization from ethanolwater mixture (I: I v/v) . The purified sample was
dried at 353 K for 24 h to remove moi sture.
The cellulose used was prepared from straw. The
straw was cut down to small pieces and soaked in
water for seventy two hours . It was then treated with
lime and alkali for twenty four hours whence it became free of lignin. It was thoroughly washed with
di stilled water and the ~lightly yellowish material was
612
INDIAN J CHEM, SEC. A, JUNE 2000
then bleached with H202 and dried in an oven at 353
K. The dried material was then pulverised to convert
it into powder.
A Shimadzu UV -vis spectrophotometer ( 160A)
was employed for spectral measurements using silica
cells of path lengths 1 em. Doubly distilled conductivity water was used for solution preparation. All
measurements were taken at constant temperature
with a thermostatic arrangement with a temperature
fluctuation of ± 0.1 o.
Stock solutions of the dyes (MB and MO) and
electrolyte (KCI) were prepared in doubly distilled
conductivity wat and stored in thoroughly cleaned,
steamed coming v umetric flasks and diluted as required. In the adsorption xperiment, weighed quantity of the cellulose (0.2 g) was taken in a series of
standard-joint pyrex glass stoppered bottles (25 rnl),
to each of which was added 20 rnl of the dye solution
with varying initial concentration (Ci) . The bottles
were covered with black marble paper to protect
them from light and were shaken in a horizontal
shaker for 2 h, and then placed in a thermostated water bath at the desired temperature for 20 h with occassional shaking. The system was observed to reach
the adsorption equilibrium after 12-14 h but was allowed 20 h time to ensure the completion of the process. After the equilibrium, 5 ml aliquots were withdrawn from the bottles, centrifuged and 3 rnl of each
solution was used for spectrophotometric estimation.
4r---------------------------~~-.
'e
The amount of dye adsorbed was calculated from the
difference in the initial concentration (C) and the
equilibrium concentration (Ce) measured spectrophotometrically. The position of the maximum absorbances (Amax) of the MB and MO solutions were
664 nm and 460 nm respectively. The concentrations
of the experimental solutions were observed to obey
the Beer-Lambert's law with molar extinction coeffi4
cients, 6.25xl04 and 2:38xl0 dm 3 mor 1cm· 1 at 303 K
for MB and MO respectively.
Results and Discussion
Adsorption of M B on cellulose
The adsorption isotherms of various classes of
compounds in different surface~ have been classified
according to their shapes. In the literature, four types
of isotherms have been reported 12 , i.e., (i) the Langmuir type (L) with an initial concavity to the concentration axis, (ii) the S-type with an initial convexity to
the concentration axis, (iii) the H-type resulting from
extremely strong adsorption and having an intercept
on the ordinate and (iv) the C-type having an initial
linear portion. The adsorption isotherms of the dye
MB on cellulose at different temperature are represented in Fig. I. The curves are Langmuirian or Ltype. The change in temperature has no effect on the
shape of the isotherm. It is apparent from Fig. 1 that
the adsorption of MB on cellulose shows fairly strong
affinity. The interaction between cellulose surface
and MB is primarily electrostatic in nature (the dye is
cationic and the adsorbent is negative). The adsorption process of MB on cellulose is exothermic; it decreases with increasing temperature. This is the expected and normally observed feature.
3
3
7
1
01
J
0
E
.......
e
'
~
"'~
'e01
2
2
0
E
.......
e
'
)(
<D
9
0
2
0
4
6
10 . Ce/mol lit-
1
Fig. !-Adsorption isotherm for MB-cellulose system in aqueous
medium at different temperatures [curve I, 303 K ; curve 2, 313
K ].
4
12
8
6
20
16
10 . Ce/mollit-
24
1
Fig. 2-Adsorption isotherm for MB-cellulose system in aqueous
KCI medium at 303 K [curves I, 2, 3 & 4 stand for 0.0 I , 0.05, 0.1
& 0.3 M KCI].
613
PALIT eta/. : ADSORPTION OF METHYLENE BLUE ON CELLULOSE
The adsorption process is retarded by the presence
of salt, KCl (Fig. 2). The increase in salt (ionic
strength) decreases the attractive interaction between
the cationic dye and the negative (-COOH) cellulose
sites. The adsorption process is, therefore, not preferred. The retardation of adsorption of dyes and
polymer on solid surfaces in salt environment has
been reported in the past 13· 14 .
Adsorption of MB-MO mixtures on cellulose
The adsorption of MO alone on cellulose has been
found to be absent (Fig. 3). The anionic dye, MO
does not prefer the negative surface of cellulose. In
combination with MO, the adsorption of MB has decreased at lower temperature of 303 K. At temperatures 308 and 313 K, the adsorption is greater than
that of pure MB . Increase of temperature has induced
increasing adsorption (Fig. 4 ). Esumi et al. 15 have
found that polystyrene sulphonate (PSS) forms complexes with ionic surfactants viz, sodium dodecyl sulphate (SDS) and hexadecyltrimethyl ammonium chloride (HT AC) in solution and consequently the adsorption of PSS on alumina gets enhanced. Like pure
MB, the adsorption of MB from the MB-MO mixture
also decreases in presence of KCI.
It may be mentioned that although most of the
curves in Fig. 4 as well as in Figs I and 2 are of
Langmuirian type, on the lower side of concentration
(in some of them), the curves appear like S-shaped for
deviations due to experimental errors.
Spectral features of MB-MO mixtures
The decrease in MB absorption in presence of MO
in solution as well as its increased adsorption with
increasing temperature are unusual features. Complex
formation between the two dyes in solution is envisaged. In Fig. 5, spectra of the individual dyes and
their mixtures under different conditions are presented. The decreasing absorbance of MB and that of
MO particularly at higher temperature is evidenced.
The two dyes undergo interaction and complex formation when heated for 20 h at 313 and 321 K
showing changes in their spectra. The absorbance of
MB is moderately reduced but that of MO suffers
4
2
6
8
6
10 .Ce/ mot l it-•
10
Fig. 4--Adsorption isotherm for MB-MO (I: I) - cellulose system
in aqueous medium at different temperatures [curve I , 31 3 K ;
curve 2, 308 K ; curve 3, 303 K].
2-0 0 . - - --
-
-
-
-
-
-
- -- --
-
-
"c
u
.
0
0
0
Ill
0
<(
"c0v
..
.D
0
Ill
.D
...
700
BOO
Wa v e l e ngt h (n m )
Fi g. 3-Spectra of pure MB and MO and their I : I mi xture befo re
and after adsorption on cellulose at 31 3 K [curve I , pure MB ;
curve 2, MB-MO mi xture ( 1: I) ; cut·.·-! 3, MB -MO mi xture aft er
adso rpt ion ; curve 4, MB after adso rpti on ; curve 5, pure MO ;
cu rve 6, pure MO afte r adso rpt ion ].
soo
Wa ve l e n gth ( nm)
Fig. 5-Spectra of MB and MB -MO mixture (I: I) at 3 13 K
[curve I, pure [MB] = 30 ~ ; cur ve 2, MB -MO eac h of concentratio n 30 J.lM ; cu rve 3, [MO] = 30 J.lM] .
614
INDIAN J CHEM, SEC. A, JUNE 2000
striking reduction and it may also disappear. The absorption maximum of MB , however, remains unchanged. The formed complex (optically clear with
respect to MO) is adsorbed more on cellulose compared to MB. The complex formation, however, is
tentati vely proposed: isolation and characterization of
the product is required for th e elucidation of its behaviour. It can be mentioned that at higher concentration , precipitation from the oppositely charged mixed
dye solution of MB and MO has been observed.
Quantifi cation of the adsorption results
Attempts have been made to analyze the adsorption
results in the light of Freundl ich, Frumkin and Lang.
.
I
mUir equattons at constant temperature .
Freundlich equation
log (x/m) = log k + ( 1/n) log Ce
... (l)
where k and n are constants (n> 1) and x/m and Ce are
the mole of the dye adsorbed per g of the adsorbent
and the equilibrium concentration of the dye in mol
dm-3 respectively .
where v = log [8-( 1-8) Ce] ' e = xlxm. where X = the
mole of dye adsorbed at equilibrium and Xm = the
monolayer dye adsorption density (mol g·1) and a
and ~ are constants ; the other term Ce is already defined .
Langmuir equation
.. . (3)
1
where k is the constant of equilibrium for the adsorption and desorption processes, and the other
terms have been already defined .
Graphical plotting of the results in the form of log
(x/m) against log Ce for equation 1, V against e for
equation 2 and rn/x against 1/Ce for equation 3 can
yield the parameters of the equations 1,2 and 3. Representative plots are depicted in Figs 6-8 . The results
are presented in Tables 1, 2 and 3.
The adsorption results obey the Freundlich equa-
-5 -4
Frumkin equation
V
= log(~ /55 .55) +2a8/2 .303
. .. (2)
Frumkin Isotherm
-5 -6
-5~------------------------~
-5 -8
Freundlich Isotherm
-6-0
J)
,......
-6-2
E
~ -6
o;
0
-6 -4
-6-6
-7 L_______________J__ __
-6
_ __ _ _ __
___J_4
-5
-6-8
o.o
0 -4
0 -6
o.s
v
log Ce
Fig. 6-Plot of log (x/m) vs log Cc according to Freund lich Isotherm fo r MB-cellulose system in KCI medium at 303 K [Lines 14 stand for 0.01 , 0.05, 0. 1 and 0.3M KCI res pect ive ly].
0 -2
e
Fig. 7-Pl ot of vs V acco rding to Frumkin Isotherm for MBMO ( I: I) - cellulose system in aqueous medium at di fferent temperatures [Lines 1-3 represent 303, 308 and 3 13 K respectively].
615
PALIT et al.: ADSORPTION OF METHYLENE BLUE ON CELLULOSE
Table 2-Results of Frumkin plot for the adsorption• of MB and
MB :MO on cellulose under different conditions
a
I
0
E
E
01
........
6
~
4
E
System
Medium
Temp,K
a
~ xl0·6
MB
Aqueous
303
3 13
303
1.87
3.07
3.26
3.51
3.16
2.64
2.31
2.30
0.86
2.02
1.65
2.19
3.33
2.29
9.0
3.76
7.32
16.00
26.60
39.30
7.16
~
It>
MB:MO(I : I)
(1 :2)
(2: I)
MB :MO(I :l)
'2
0
4
2
16
a
6
5 1
.( /Ce)/lit
10
mol-
Table !-Results of Freundlich plot for the adsorption• of pure
MB and MB :MO on cellulose under different conditions.
System
Medium
Temp, K
n
k X 10"6
MB
Aqueous
303
313
303
2.56
5.00
1.72
1.72
1.72
1.72
1.75
1.75
1.29
2.12
2.04
0.78
2.41
1.32
0.83
1.82
2.88
2.63
4.57
1.32
2.51
1.41
0.79
0.71
3.9
0.69
O.OIM KCI
MB :MO(I : I)
MB:M0(1:2)
(2: I)
0.05MKCI
O. IMKCI
0.3MKCI
0.005MKCI
0.05&0 .1M KCI
Aqueous
0.005MKCI
0.05MKCI
O.IOMKCI
1
Fig. 8- Plot of mix vs liCe according to reciprocal Langmuir plot
for MB-MO (I : I) - cellulose system in aqueous medium at differ~
ent temperatures [Lines 1-3 represent 303, 308 and 313 K respectively].
303
308
313
303
•tn the calculation of the extents of adsorption, due consideration
to the dependence of the extinction coefficient on temperature
particularly owing to the complex formation between MB and
MO has been given.
tion reasonably well. Then and k values of equation 1
are presented in Table l . Except for two cases, the n
values are nearly two; the k values vary in a reasonable range. The variation in the adjustable parameters
suggests variation in the surface or the binding sites
on the biopolymer (cellulose) for associating the dye
MB. The temperature and salt dependencies are involved factors in the process.
The Frumkin plots are linear. The a and ~ values
O.OIMKCI
0.05MKCI
O.IMKCI
0.3MKCI
Aqueous
303
308
313
303
303
10.10
26.00
7.85
8.22
11.10
15.70
31.20
•same conditions as in Table I
Table 3-Results of Langmuir plot for the adsorption• of pure
MB and MB :MO mixtures on cellulose under different conditions
System
MB
Medium
Aqueous
MB:MO(I:l)
0.05MKCI
O.IMKCI
Aqueous
l'
0.005MKCI
MB:M0(1 :2)
MB:M0(2:1)
0.05MKCI
O. IMKCI
Aqueous
..
Temp, K
303
313
303
303
303
308
313
303
303
303
303
303
Kxl0·5
2.13
1.20
0.31
0.23
0.19
1.78
2.27
3.00
1.25
0.39
0.39
1.27
•same conditions as in Table I.
are obtained from the linear least squares analysis.
They, under different environmental conditions, are
broadly of equal ma~itudes. The ~ increases with
salt (KCI) concentration. The temperature has sizeable effects on both a and ~ for the adsorption of
pure MB on cellulose; fo r MB :MO(I : 1) mixture, the
effects are mild.
The Langmuir plots and results (Table 3) reveal
that for pure MB, the adsorption decreases with tem1
1
perature and hence k also decreases . The k values
also decrease with increasing salt concentration (Fig.
9), for salt lowers the favourable electrostatic interaction between the dye and the cellulose. This is also
corroborated by the MB :MO ( 1: 1) mixture. The
formed MB-MO complex at temperature greater than
303 K is favourably adsorbed on the cellulose with
616
INDIAN J CHEM, SEC. A, Jlfl\:!3 2000
2.--------------------------y~
langmuir Isotherm
Langmuir or the Freundlich equation . An indirect
correlation is anticipated.
Like many adsorbent/adsorbate systems, the adsorption of MB on cellulose is an exothermic process.
The standard enthalpy change of adsorption has been
calculated from the integrated van't Hoff equation, In
k'
X
'
E
MI~"
= constant - ~.
The enthalpy value obtained
is -45.2 kJmor' and corresponding standard free energy and entropy changes calculated at 303 K from
<D
0
the relations !:::..dad = - RTin k and f1Siad = (t:Jfad !:::..dad)fT are -30.9 kJmor' and -47 J mor'K' respectively. The negative D.ftad suggests that the MEcellulose product is organized.
The mixed system of MB and MO has shown increased adsorption w.ith temperature. The standard
endothermic enthalpy of adsorption for the I: I ratio
has been also derived from the van't Hoff equation .
The enthalpy ~alue obtained is 38.2 kJmor' and the
corresponding standard free energy and entropy
changes of adsorption at 303 K are -30.5 kJmor' and
226 JK 1mor' respectively. The endotherrnicity of the
adsorption process has been attributed to hydrophobic
association of the MB-MO combine wi th the cellulose leading to loosening of the biopolymer configuration producing positive entropy change. Similar
reports of endothermic enthalpy change are also
16
found in recent literature on the adsorption of bile
salts on graphite in aqueous medium.
1
2
-51
10(/ce) /lit mol
-1
Fig. 9-Plot of rn/x vs liCe according to reciprocal Langmuir plot
for pure MB-cellulose system in aqueous KCI medium at 303 K
[Lines 1-4 represent 0.3, 0. 1, 0.05 and 0.0 1 M KCl respecti vely].
increasing temperature. There is no apparent preference for the adsorption of MB at constant temperature
(303 K) in presence of MO at different molar ratios.
The specific surface area (S) of the cellulose sample was estimated from the Xm value realised from the
intercept of the reciprocal Langmu ir plot (equation 3).
The value of Xm obtained was 5x10·6 mol g- 1 for all
the cases.
S
= Xm Ncr
... (4)
where S = the specific surface area (m 2/g) ; Xm = the
monolayer dye adsorption density (mol/g) ; N = the
23
Avogadro's number (6.023xl0 molecules/mol); cr =
the area occupied by a single dye molecule (m 2/molecule).
Taking cr = 120 A2 from a literature report', a value
of 3.6 m2g-1 has been obtained for S.
It is observed that the equations of Freundlich,
Frumkin and Langmuir are applicable to the adsorption of MB alone and in mixtures with MO on cellulose in aqueous and salt solutions. The derived parameters are, therefore, useful to characterize the adsorption process. Since the adsorption results fit in
the three equations, ex istence of a common basis for
them is apparent. In the moderate range of concentration the Langmuir equation can transform into the
Freundlich equation. Apparently, the Frumkin equation does not show a direct correlation with either the
Conclusions
The following conclusions can be drawn from the
results:
The dye MB adsorbs on cellulose at ambient
I.
temperature whereas MO does not. At temperature above 303 K, MB and MO interact whereby
the adsorption of MB in the complexed form increases.
2. The adsorption process under different conditions of temperature and MB/MO ratio is reduced in presence. of KCI.
3.
The adsorption results under different environmental conditions of temperature and salt obey
the equations of Freundlich, Frumkin and
Langmuir.
4.
While pure MB is adsorbed on cellulose with
negative enthalpy change, the mixture of MB
and MO is adsorbed with positive enthalpy
change indicating interplay of hydrophobic mteraction.
PALIT ·et al.: ADSORPTION OF METHYLENE BLUE ON CELLULOSE
Acknowledgement
We thank Dr. D. P. Khan of Baruipur, Calcutta
with appreciation for preparing the cellulose sample
and gifting it to us. Financial support from the Jawaharlal Nehru Memorial Fund, New Delhi to carry out
the work is thankfully acknowledged .
6
7
8
9
I0
II
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