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Journal of Scientific & Industrial Research
J SCI IND RES VOL 72 JULY 2013
Vol. 72, July 2013, pp. 428-434
Biosorption of methylene blue on chemically modified Chaetophora
Elegans algae by carboxylic acids
Farah Mikati and Mouhiaddine El Jamal*
Chemistry Department, Faculty of Sciences (I), Lebanese University, El Hadath, Lebanon
Received 20 July 2012; revised 28 December 2012; accepted 02 April 2013
Chemical modification of Chaetophora Elegans algae with carboxylic acids were undertaken in order to improve the methylene
blue adsorption. The modified algae with 1 M acetic and formic acid showed an increase in the maximum uptake, but the modified
algae with 1M oxalic acid showed an important decrease in the uptake from 143 mg g-1 to 20 mg g-1. The type and concentration
of acid used in the chemical modification (0.1 M -1 M) is the major parameter affecting the maximum uptake. The carboxylic acids
having more than one –COOH lead to cross-linking effect and so to decrease in qmax. Langmuir-Freundlich isotherm model fitted
better the isotherm adsorption data for modified and unmodified algae. Pseudo second order model was well in line with the
experimental data. The adsorption rate constant (K2) is higher for modified algae with acetic acid than that of raw algae. The
maximum uptake is independent of isotherm adsorption temperature in the range studied.
Keywords: Modified algae, acetic acid, formic acid, oxalic acid, methylene blue, isotherm adsorption, kinetic.
Introduction
The extensive use of dyes poses pollution problems.
They reduce light penetration and photosynthesis; in
addition, some dyes are carcinogenic1. Several methods
exist for reducing the color in textile effluent streams:
adsorption, oxidation–ozonation, biological treatment,
coagulation–flocculation and membrane processes. The
adsorption process is one of the most effective and
attractive processes for wastewaters tr eatment.
Adsorption using activated carbon is certainly one of the
most suitable techniques for treating wastewater
containing toxic pollutants; however, it is not economical
due to its expensive cost 2-4 . Therefore, research is
directed toward the development of low-cost adsorbents
alternative to activated carbon. In the past years, many
low cost materials have been tested for the removal of
dyes and transition metals5-12.The sorption capacities of
a raw biosorbents are generally low, but chemical
modification can improve it31. The chemical treatment
increases the number of the active sites or replaces the
existing sites by more attractive ones. Many chemical
reagents, organic or inorganic are used for this purpose.
The reagents used for this modification are citric
acid13-19, HCl20- 21, oxalic acid22, tartaric acid23, NaOH24,
KMnO425, formaldehyde26, 27, CaCl2 21, 26, 28, methanol27, 29, 30.
Citric acid is the mostly reagent used since it
introduces carboxylate group at the surface of the
biomass13, 14, but sometimes the chemical modification
has a negative effect on the uptake, due to decrease in
the available number of active sites: increase in crosslinking degree leads to accessibility problem to the active
sites15, 19. Previous work, in our laboratory, showed a
dramatic decrease in MB uptake after chemical treatment
of Chaetophora Elegans alga with citric acid31 . The
uptake decreased with the increase in citric acid
concentration used. Similar results are obtained after
treatment of the brown macroalga, S. marginatum with
several organic compounds such as formic acid, methanol,
and formaldehyde30. The authors explained the decrease
as a result of blocking carboxyl, hydroxyl and amine
groups. To understand better the cross-linking effect
observed with citric acid (with 3 -COOH) on the uptake
of methylene blue (MB), a chemical modification with
similar car boxylic acids such as acetic acid
(CH3-COOH), formic acid (H-COOH) and oxalic acid
(HCOO-COOH) is undertaken.
Materials and Methods
Dye Solution Preparation.
*Author for correspondence
E-mail: [email protected]
Methylene blue was purchased from Sigma
(C.I. 52015, 82 %). Stock aqueous solution of the dye
MIKATI & JAMAL: BIOSORPTION OF METHYLENE BLUE ON C E ALGAE
(500 mg L-1) was prepared, without further purification,
and then eight working solutions were prepared by dilution
in order to draw the adsorption isotherm.
Surface Modification
The chemical modification was carried out with
different carboxylic acids, different acid concentrations,
and temperature of the chemical reaction. The acids used
for this purpose were acetic, formic and oxalic acid. The
concentrations of the acid were 0.1, 0.5 and 1 M. The
chemical reaction between the acid and the raw algae
(RG) in the water bath shaker was 25, 40, 50 and 60 oC.
Chaetophora elegans algae (collected in June 2010,
and prepared as described in a previous work32 was mixed
with acid solution at a ratio of 5.0 g biomass to 50 mL of
a selected acid concentration and stirred for 4 h at a
selected water bath temperature. The acid/biomass was
then heated at 110 oC for 4 h, afterward; the dried powder
was washed and filtered several times with distilled water
(~ 500 ml) until the pH and color of drain water became
neutral and clear respectively. The washed biomass was
finally dried in an oven at 110 oC for 4 h. Three samples
of raw algae were treated in the same manner at 40, 50
and 60 oC by replacing the acid solution with distilled
water in order to use them as references. The biomass
weight loss was determined after each treatment. For
simplicity the samples treated with oxalic acid are called
aOX b, where a represents the concentration of the acid
used and b the temperature of the water bath. The
abbreviation aFO b and aAC b are used for the samples
treated with formic and acetic acid.
Batch Mode Adsorption Studies
Batch adsorption experiments were conducted to
evaluate the MB adsorption capacities of the raw and
modified algae. The different parameters affecting the
adsorption such as pH, mass of algae, equilibrium time,
are already determined in a previous work33. 0.1 g of
modified biomass was added to 100 ml plastic erlnmeyer,
containing 50 mL of MB solutions of different
concentration and agitated in the water bath shaker at
200 rpm at 25±1 oC for 3h 30 min, which was sufficient
to attain equilibrium. Several initial MB concentrations
(Co: 62.5, 125, 150, 250, 300, 350, 400, 450 and 500 mg L-1)
were used in order to draw the adsorption isotherm and
deduce qmax. After equilibrium being attained, the samples
were centrifuged and the remaining concentrations (Ce)
in the supernatant solutions were analyzed at 666 nm,
lmax of MB, using a double beam UV – Visible
429
spectrophotometer (Specord 200, Analytical Jena).
Isotherm experiments were carried out in duplicate. For
the kinetic study, several samples were prepared in the
same conditions (0.1 g of biomass, 50 mL of MB of fixed
concentration). Then 2 ml was withdrawn at a selected
time in order to determine the adsorption rate constant
and the order of adsorption.
Characterization of the Modified Algae
The raw and the modified algae were characterized
by FTIR (spectrophotometer Thermo, Nicolet IR 200,
dilution with KBr) to know the functional groups that
might intervene in the adsorption process. XR diffraction
is carried out with D8 Focus Bruker (Cu K a 1.54 Ao at
50 KV) to observe any change in the modified biomass
with respect to raw algae.
Results and Discussion
FTIR and XR Diffraction Analysis
The IR spectrum of raw algae (RG) displays a
number of absorption peaks: at 3350 cm-1 (-OH or –
NH2), 2915 cm-1 (-CH or COOH), 1620 cm-1 (>C=O)
and 1060 cm-1 (C-O or >S=O) (Fig.1a) 31, 33.
Effervescence is observed immediately after addition
of acid to raw algae, but it is stronger with formic acid.
Chemical reaction occurred between the acid and the
carbonate already presents in the protective wall of algae,
leading to the formation of CO2 and a dramatic decrease
in algae weight. The weight loss is more affected by the
acid concentration used and by its nature rather than by
the temperature of the chemical treatment: ~ 20 %,
~ 40% and ~ 60 % with 0.1 M, 0.5 M and 1 M of acid
(formic or acetic) respectively. A decrease in the amount
of biomass was found by Lodeiro et al., after treatment
by HCl/ HCOH34. The authors explained the decrease
by the replacement of Ca2+, and Mg2+ bound to active
sites by H+. The IR spectrum of modified algae with
acetic acid is similar to that of raw algae with few
differences decrease in the strong peak at 1430 cm-1
and in the peak at 866 cm-1 . These two peaks are
characteristic bands of carbonate. The decrease in the
peak’s intensities and in the weight of algae after chemical
treatment is proportional to acid concentration used. So
the chemical modification with acetic acid decreases the
amount of carbonate in the raw biomass and let the algae
more pure. Thermal analysis (TG-DSC) on Carolina algae
showed a sharp decrease at 786 o C (endothermic)
attributed to the conversion of CaCO3 to CaO (s) and
CO 2(g)26 .
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J SCI IND RES VOL 72 JULY 2013
12 0
120
T %
10 0
100
80
80
1AC 60
1 FO 40
I%
RG
60
60
0 .1 F O 60
RG
0 .5 F O 60
40
40
20
0
4 00
20
0
900
140 0
1 90 0
24 00
2 900
-1
W avenu m be r (cm )
3 40 0
39 00
10
15
20
25
2 q?
30
35
40
Fig. 1(a)—IR spectra of raw algae and of modified algae with formic acid treated at 60 oC.
Fig. 1(b)—XR diffraction spectra of raw algae (RG) and of modified algae with acetic and formic acid.
After treatment with formic acid, the broad band at
3350 cm-1 is divided into several bands and the intensity
of the band at 1400 cm-1 is function of the formic acid
concentration used Fig. 1(a).The crystalline state of raw
algae is good as shown by its XR diffraction spectrum.
The XR diffraction spectra of algae before and after
treatment with acetic and formic acid are different with
respect to the peaks’ intensities Fig. 1(b). The three peaks
at 2 q :14.64, 17.1, and 22.92 became more intense, and
the intense peak in RG at 29.54 remained the intense
one after treatment (100 %). The IR spectrum and the
XR diffraction spectrum of algae after treatment with
acetic acid are similar to those obtained with HCl31. The
IR spectrum of algae after treatment with oxalic acid is
different from that of raw algae: the broad band of OH
at 3365 cm-1 is divided into several bands (OH of COOH
and OH of alcohol). The intensity of the band at 2914
cm-1 which corresponds to COOH increases dramatically.
New bands appeared at 1615 and 1336 cm-1, which can
be assigned to C=O stretching vibration of COOH and
COO- indicating the introduction of a new COOH sites15.
Other bands appeared also for wavenumber < 900 cm-1.
The same behavior is observed with the other treated
samples (0.1 M and 0.5 M), but it is more pronounced
with 1 M of oxalic acid. The IR spectrum of algae after
treatment with oxalic acid is similar to that obtained with
citric acid31.
The XR diffraction spectra of algae before and after
treatment with oxalic acid are very different. For
example, the sample 1OX 25 showed the appearance of
new intense peaks (2 q : 14.9, 15.22, 24.38 and 30.1) and
the disappearance of that at 29.52 (100 % in the raw
algae). We thought that an important chemical reaction
occurred between the raw algae and oxalic acid.
Isotherm Modeling Analysis
Several isotherm models are used to find the
relationship between qe and Ce .The experimental data
related to the adsorption of MB molecules onto the algal
biomass at 25 o C were fitted using Langmuir 35,33 ,
Freundlic36,33 , Temkin37,33 , and combined LangmuirFreundlich equations38,33. In this study, the theoretically
predicted isotherm data were determined using a nonlinear regression analysis via the Origin 7 software.
Raw Algae
The experimental isotherm adsorption data of raw
algae fitted better Langmiur-Freundlich isotherm than
the other models listed above. The untreated raw algae
and the treated with distilled water at 40, 50 and 62 oC
showed an average of qmax equal to 143 ± 5 mg g-1. The
raw biomass (organic compounds) looses its adsorption
property with storage time. In a previous work, the
maximum uptake of MB onto fresh collected algae was
much higher (300 mg g-1)33. The decrease in qmax is related
to deterioration of the external surface. According to
the IR spectrum of raw algae and the effect of initial pH
on the adsorption of crystal violet32 and methylene blue33,
it is seemed that the functional groups –COOH are
responsible of this adsorption.
Modified Algae with Formic and Acetic Acids
The formic and acetic modified algae showed an
increase in the qmax. The increase in the maximum uptake
is more related to acid concentration than to the reaction
temperature (Fig. 2a and 2b). The maximum uptake
passed from 143 mg g-1 (for RG) to 297 and 254 mg g-1
for 1FO 25 and 1AC 25 respectively. In general the algae
treated with formic acid have qmax higher than those
431
MIKATI & JAMAL: BIOSORPTION OF METHYLENE BLUE ON C E ALGAE
0.1M F O
350
0.5M F O
1M FO
300
300
0.1M AC
0.5 M AC
1 M AC
250
200
-1
q (mg g )
-1
q (mg g )
250
200
150
150
100
100
50
50
0
0.1M F O
0.5M F O
1M F O
25 oC
40 oC
60 oC
159
223
297
152
220
310
149
219
300
0
0.1M AC
0.5 M AC
1 M AC
25 oC
40 oC
60 oC
161
193
254
170
185
250
174
180
240
T ( o C)
o
T ( C)
Fig. 2(a)—Effect of formic acid concentration and temperature, used in the chemical modification of algae on the maximum uptake
according to non linear Langmuir- Freundlich model. (0.1g of algae, T: 24 oC, pH: 6)
Fig. 2(b)—Effect of acetic acid concentration and temperature, used in the chemical modification of algae on the maximum uptake
according to non linear Langmuir- Freundlich model. (0.1 g of algae, T: 24 oC, pH: 6)
300
250
was the case with Sargassum muticum biomass treated
with acetone (elimination of lipid)21.
1AC 60
1 FO 60
Modified Algae with Oxalic Acid
q raw
-1
q (mg g )
200
1OX 60
150
100
50
0
0
20
40
60
Ce (mg L-1)
80
100
Fig. 3—Isotherm adsorption of several modified algae (0.1 g of
algae, T: 24 oC, pH: 6).
obtained with acetic acid. The difference in the uptake
between the raw algae and the treated algae is
manifested for high initial MB concentration ([MB]o >
150 mg L-1 ). The remained concentration of MB in
contact with 500 mg L-1 of MB is 10.8 mg L-1 for 1FO
25 and 19.4 for 1AC 25 against 144.4 mg L-1 for the raw
algae (RG). The increase in the uptake of RG after
treatment with formic acid is similar to that treated with
HCl (320 mg g-1)31. Qmax increases with the increase in
acid strength (Acetic acid < Formic acid < HCl), in other
way it is related to the ability of the acid the remove
carbonate from the raw algae. The increase in the uptake,
is not always related to the cross-linking between the
algae and the chemical reagent, but sometimes it is related
to a change in the chemical composition of the algae as
Concerning, the isotherm adsorption of modified algae
with oxalic acid, Langmiur - Freundlich model remained
the best model. All the samples showed a decrease in
the uptake (Fig. 3). The lowest qmax (20 mg g-1) is obtained
with 1 M of oxalic acid (1OX 60). The concentration of
oxalic acid is the important factor which governs the
decrease in the uptake. The decrease in qmax may be due
to increase in the cross-linking degree which would
hamper the adsorption of MB15 . Similar results are
obtained with citric acid31. It seems that in our case the
chemical modification with high concentration of
carboxylic acid having more than 1 -COOH such as
oxalic acid and citric acid leads to increase in the crosslinking degree, preventing the MB adsorption. As the
cross-linking degree decreased with the decrease in acid
concentration, the modified algae with 0.1 M citric or
oxalic acid have approximately the same qmax as RG.
The increase in the uptake with acid such as HCl31,
acetic acid and formic acid is explained in majority by
the elimination of a high percent of carbonate already
present in the protective cell walls of algae (proved by
effervescence effect). In the case of oxalic acid, in
addition to the elimination of a part of carbonate, there is
also cross-linking effect causing steric hindrance and
make against the adsorption of basic dyes.
432
J SCI IND RES VOL 72 JULY 2013
Table 1—Pseudo first and pseudo second order adsorption kinetic parameters at 24 oC and error estimation deduced at different initial
dye concentrations for 1AC 25 and raw algae (values between ())
[MB] o
(mg L-1)
62.5
100
150
qe calc.
(mg g-1)
29.9
(28.5)
48.15
(47.0)
72.1
(72.3)
Pseudo-first order (Non linear)
K1
R2
-1
(min )
2.5
0.995
(1.52)
(0.98)
2.47
0.994
(1.4)
(0.983)
2.03
0.994
(0.79)
(0.993)
χ2
qe
(mg g-1)
30.5
(29.7)
49.0
(48.0)
73.80
(73.80)
0.46
(1.79)
1.56
(3.93)
3.78
(3)
Pseudo-second order (Non linear)
K2
R2
-1
-1
(g mg .min )
0.293
1
(0.111)
0.998
0.174
0.999
(0.077)
(0.995)
0.078
1
(0.024)
(0.999)
χ2
0.06
(0.2)
0.30
(1.11)
0.19
(0.31)
Table 2—The activation kinetic parameters for modified algae with 1M acetic acid (1AC 25) and raw algae (values between ())
[MB]o(mg L-1)
62.5
100
Ea (kJ.mol-1)
23.9 (48.6)
6.7 (48)
DH# (kJ.mol-1)
21.36 (46)
4.2 (46.1)
Kinetic Study
The modified algae with acetic acid were selected
for the kinetic study. Non-linear regression method has
been used to predict the best sorption kinetic model
(Lagergren first order and pseudo-second order) and also
to obtain reliable kinetic parameters33, 39, 40. For initial
MB concentrations (60 mg L-1 - 150 mg L-1), the uptake
of modified algae with acetic acid and the raw algae as
a function of time is quite similar Table 1. The adsorption
rate of both kinds of algae is very fast in the first five
minutes, then decreases to become negligible after 30 min.
The dynamic sorption behavior of MB onto
Chaetophora elagans’ surface under several initial dye
concentrations was monitored and modeled. The related
kinetic parameters and error derivation values are
presented in Table 1. The first and the second adsorption
models can be used to interpret the results, but according
to R2 values, the pseudo-second order model fit better
the kinetic data. In this range of initial MB concentrations
the maximum uptake increased linearly (R2:1), but the
rate constant K 2 decreased linearly with [MB] o
(R2: 0.978).
Effect of Temperature
The activation parameters associated with the
adsorption of 62.5 and 100 mg L-1 MB onto 1AC 25 are
calculated as follow: plot of ln K2 vs. 1/T gives the value
of the activation energy (Ea), according to Arrhenius
equation. The DH# and DS# value can be calculated from
Eyring equation31.The rate constant K2 increased with
the increase in temperature for the acetic acid modified
DS# (kJ.mol-1.K-1)
-0.19 (-0.11)
-0.25(-0.12)
DG#298 (kJ.mol-1)
78 (78.8)
78.7(81.9)
algae and for unmodified algae. The rate constants k2
obtained with 1AC 25 are higher than those obtained
with the unmodified algae in the range of temperature
studied (25 oC-35 oC). The kinetics parameters are listed
in Table 2. The activation energies for modified algae
are less than those of raw algae, but the free energies
are approximately the same Table 2.
Conclusions
Chemical modification of Chaetophora Elegans algae
with acetic and formic acids showed an increase in the
maximum uptake. The increase is proportional to acid
concentration used. Modified algae with 1 M of acetic
and formic acids gave the best uptake (qmax increased
from 143 mg g-1 to 254 and 297 mg g-1 at 24 o C
respectively). The modified algae with oxalic acid showed
an important decrease in the uptake. The decrease in
qmax is inversely proportional to oxalic acid concentration
used. Modified algae with 1 M oxalic acid gave the worst
uptake (qmax decreased from 143 mg g-1 to 20 mg g-1).
Acid concentration used in the chemical modification is
the major parameter affecting the maximum uptake. The
decrease is related to increase in the cross-linking degree.
It seems that the carboxylic acids having more than one
–COOH lead to cross-linking effect. The temperature
of the chemical modification has a small effect on the
uptake (25 oC – 60 oC). Langmuir-Freundlich isotherm
model fitted better the isotherm adsorption data for all
samples studied. Pseudo second order model was well
in line with the experimental data. The adsorption rate
constants (K2) are higher for modified algae with acetic
MIKATI & JAMAL: BIOSORPTION OF METHYLENE BLUE ON C E ALGAE
acid than those of raw algae. The activation
thermodynamic parameters Ea, DH#, DS# and DG# were
calculated. The equilibtium uptake is independent of
isotherm adsorption temperature in the range studied
(25oC – 35oC).
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