The results of this study clearly
demonstrate that MSCG can be easily
prepared by the exposure of SCG, a waste
material from the coffee industry, to the
water-based ferrofluid, leading to the fact
that the magnetic material can be easily
separated from the suspensions by a
permanent magnetic. The effects such as
pH, contact time, dosages of the adsorbent,
initial MB concentration on the MB
adsorption onto MSCG have been
investigated. The estimated maximum
adsorption capacity of the MSCG from
Langmuir isotherm modes was 30.7 mg.g–1
at pH 7, the temperature of 25oC, the
contact time of 60 min and the agitated rate
of 150 rpm. These results make the MSCG
highly suitable as a new low-cost adsorbent
for the large-scale removal of pollutants
from wastewaters
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Tạp chí phân tích Hóa, Lý và Sinh học - Tập 20, số 3/2015
THE STUDY ON THE ADSORPTION OF METHYLENE BLUE (MB) ONTO
MAGNETICALLY MODIFIED SPENT COFFEE GROUNDS (MSCG)
Đến tòa soạn 16 - 6 - 2015
Bùi Xuân Vững, Ngô Văn Thông
Chemistry Department, Danang Education University
TÓM TẮT
NGHIÊN CỨU HẤP PHỤ THUỐC NHUỘM METHYLEN XANH
BẰNG VẬT LIỆU BÃ CÀ PHÊ TỪ TÍNH
Bài báo này trình bày kết quả nghiên cứu về khả năng hấp phụ methylene xanh của bã cà phê
có từ tính. Vật liệu hấp phụ này nhận được từ việc cho bã cà phê sau khi chiết bằng nước
nóng tiếp xúc với dung dịch nano oxit sắt từ Fe3O4. Thành phần vật liệu đã được kiểm tra
bằng các phân tích SEM và nhiễu xạ tia X. Các yếu tô ảnh hưởng đến sự hấp phụ của
methylene xanh lên vật liệu này như thời gian cân bằng hấp phụ, nhiệt độ, pH và nồng độ ban
đầu của methylene blue đã được khảo sát. Các số liệu cân bằng hấp phụ được đánh giá bằng
phương trình Langmuir. Kết quả cho thấy ở pH 8 và tại nhiệt độ phòng, thời gian cân bằng
hấp phụ khoảng 60 phút và dung lượng cực đại hấp phụ là 30.67 mg.g-1. Vật liệu sau khi hấp
phụ được thu hồi dễ dàng từ dung dịch nước bởi một nam châm vĩnh cửu. Các kết quả thu
được đã chứng minh cho khả năng sử dụng bã cà phê được từ tính hóa để loại bỏ các thuốc
nhuộm trong nước thải.
1. INTRODUCTION
One of the most effective physical
processes for the removal of pollutants
from wastewater is adsorption [1]. The
adsorbent widely used in industrial
applications is activated charcoal due to its
excellent adsorption capacity. However,
this adsorbent has high costs and difficult
generation [2]. That is the reason why there
have been a lot of efforts, in recent times, to
produce low-cost adsorbents replacing
activated charcoal.
Spent coffee grounds (SCG) are the main
waste discharged with a very large amount
from the production of instant coffee by
thermal water extraction from roasted
coffee bean. The main composition of this
waste is polysaccharides such as cellulose
and galactomannans that are insoluble
solids during the extraction process [3].
371
SCG can be used as compost and feedstock,
yet most of them are burned as a waste,
which leads to the production of CO2, the
green house gas [4]. Clearly, it is necessary
to find out the way of reusing this waste for
more useful purposes. In recent times, spent
coffee grounds have been used as an
adsorbent for removal of lead [5],
chromium [6] and other heavy metal ions
[7-9].
Magnetic separation is a promising
technique for adsorption of target
compounds from difficult-to-handle
samples. Magnetic modification of
inexpensive adsorbents and carriers can
lead to materials suitable for large-scale
biotechnology and environmental
applications [10]. MSCG were prepared as
a possible inexpensive adsorbent and its
potential for the adsorption to remove
organic dyes from aqueous solutions.
In the current work, we have investigated
the adsorption of MB, a common cationic
dye, onto MSCG prepared by contacting
the material with a ferrofluid containing
magnetite nanoparticles.
2. EXPERIMENTAL
2.1. Material and experimental methods
Raw spent coffee grounds obtained from a
coffee shop in Danang city. Ferrous
chloride (FeCl2·4H2O), ferric chloride
(FeCl3·6H2O), Acid perchloric (70 wt.% in
water), hydrogen chloride, sodium
hydroxide, methyl alcohol and MB were
purchased from China. All other chemicals
were of analytical grade.
2.2 Preparation of adsorbent
The raw spent coffee grounds were washed
with hot water until the washing solution
was colorless so that soluble and coloured
compounds were completely removed. The
solid was then dried at 60 °C for 24 h.
Lastly, the resulting spent coffee grounds
were ground, sieved to < 0.5 mm and stored
at room temperature in the dark until use.
2.3 Preparation of magnetically modified
spent coffee grounds
The preparation of aqueous ferrofluid was
based on the procedure reported by Berger
et al.[11] with some modifications.
Magnetite (Fe3O4) nanoparticles were first
produced by combining 4 mL of 1M FeCl3
solution and 4 mL of 0.5 M FeCl2 and then
adding very slowly 150 mL of aqueous 0.1
M ammonia solution whilst stirring. After
the addition was complete, stop stirring.
The black precipitate were magnetically
decanted by a strong magnet and rinsed
several times with distilled water to remove
water-soluble impurities. Finally, the solid
was resuspended in 2M perchloric acid
solution. For preparation of the
magnetically modified material, 5.00 g of
the spent coffee grounds were suspended in
40 mL methanol with 5 mL of the
ferrofluid. The suspension was stirred for 1
h at room temperature. Then, the
magnetically modified spent coffee grounds
were repeatedly washed with methanol and
air dried.
2.4 Characterization of prepared MSCG
MSCG samples were sent to Institute of
Materials Science belonged to Vietnam
Academy of Science and Technology for
analysis. The morphological analysis of
SCGs samples was performed by a
scanning electron microscope (SEM S-
4800, Hitachi, Japan). X-ray diffraction
372
(XRD) analysis was carried out with a
Siemens D5000 diffractometer (Siemens,
Germany) using Cu Kα radiation at λ =
1.54056 Å. Diffraction patterns were
recorded from 20° to 90° 2θ at a scan rate
of 1°.min−1.
2.5 Adsorption Experiments
Adsorption experiments were performed in
batch mode. MSCG and the dye solution
were initially loaded into glass flasks,
which were stirred with agitation rate of
150 rpm at determined temperature for the
required time. After that, the adsorbent was
separated from the heterogeneous mixture
using a permanent magnet and then the
solution was analyzed for dye
concentration. The concentration of MB
was determined spectrophotometrically at
665 nm [14], using UV–VIS LAMBDA
spectrometer (USA).
In the current work, the adsorption of MB
onto the MSCG as a function of pH, contact
time, temperature in equilibrium and initial
MB concentration was investigated.
The effect of pH was conducted by mixing
0.1 g of the adsorbent with 30 mL of 50
mg/L MB solution at temperature of 25oC,
magnetically stirring the mixture with 150
rpm for 01 h. The pH value, ranging
between 4 and 9, was kept constant
throughout the adsorption process by
micro-additions of HNO3 (0.01 mol/L) or
NaOH (0.01 mol/L).
To determine the effect of the mass of
adsorbent, experiments were carried out
varying the dosage (0.05–0.5 g of the
MSCG/30 mL of 50 mg.L-1MB solution)
and keeping constant all the other
parameters: pH free; 25 °C; 150 rpm; 1 h.
All parameters of experiments to determine
the effect of contact time were kept
constant: dosage (0.1g of the MSCG/30 mL
of 50 mg.L-1MB solution); pH free; 25 °C;
150 rpm. After the time interval of 10
minutes, the remaining concentration of
MB in the solution was
spectrophotometrically determined until the
total adsorption time was 90 mimutes.
Similarly, the effect of temperature in
equilibrium was investigated when
temperature was changed in the range from
25 oC to 60 oC.
The effect of initial MB concentration on
equilibrium was observed by mixing 0.1 g
of the MSCG with 30 mL of dye solutions
of different initial MB concentrations (10–
60 mg/L).The suspensions were stirred for
01 h at pH free in water bath at 25 °C
(agitation rate = 150 rpm). The equilibrium
data were analyzed by the Langmuir and
the Freundlich models.
3. RESULTS AND DISCUSSION
3.1. Characterization of the MSCG
3.1.1. SEM analysis
Figure 1 shows the SEM images of the
SCG (left) and the prepared MSCG (right).
As can be seen from these SEM
micrographs, the SCG has porous structures
and many cavities, which allow adsorbing
Fe3O4 nano particles in the
ferrofluid. A little bit of differences in
surface morphology were observed
between untreated and magnetically
modified SCG supporting the fact that the
deposition of Fe3O4 nano particles onto the
surfaces of the MSCG took place.
373
Figure 1: Scanning Electron Micrograph of the SCG (left) and the prepared MSCG (right).
3.1.2. X-ray diffraction analysis
Figure 2: XRD pattern of the MSCG with the characteristic peaks of magnetite
The XRD pattern of the prepared
magnetically modified SCG was presented
in Figure 2. We can see from this figure the
five characteristic peaks at 2θ = 29.9°,
35.6°, 42.8°, 53.2° and 56.9° correspond to
the planes (220), (311), (400), (422) and
(511) of magnetite (Fe3O4). This
demonstrates that the magnetic particles are
deposited on the surface of the SCG when
we made the exposure of the SCG to the
water-based ferrofluid leading to the
formation of the magnetic adsorbent. The
average size of magnetite crystallites was
estimated from the strongest diffraction
peak (at 2θ = 35.6°) by the Scherrer
equation:
0.89
.
D
B cos
where D is the average crystallite size, λ is
the wavelength of Cu Kα radiation =
1,54056Å , β is the full-width at half
maximum of the peak and θ is the Bragg
diffraction angle. The average size D = 4.15
nm. Figure 3 shows the images of the
prepared magnetically modified SCG and
the separation of this material from the
suspensions by a permanent magnet.
374
Figure 3: The prepared MSCG (left) and the separation of the MSCG
by a permanent magnet (right)
3.2. Adsorption Experiments
3.2.1. Effect of pH
The effect of pH on the adsorption of MB
onto the magnetic SCG is presented in
Figure 4. In general, the higher dye uptakes
were showed in basic pH-region. MB is a
potent cationic dye and at basic pH values,
the surface of the magnetic adsorbent can
be easily charged negatively due to the
excess of OH- groups in the solution.
Therefore, the negatively charged adsorbent
can be easily charged negatively due to the
excess of OH- groups in the sites of the
adsorbent can interact with the positive
amino groups of MB, forming a strong
bond between adsorbent and dye.
At pH> 8, more than 95% of MB adsorbed
onto the adsorbent.
Figure 4: Effect of pH on the adsorption
3.2.2. Effect of contact time
Figure 5 shows the effect of contact time on
MB adsorption with the magnetic
adsorbent. It can be seen from the figure
that the adsorption was rapid at the initial
20 minutes stage of the contact, but it
gradually slowed down until the
equilibrium at about 60 minutes. The fast
adsorption at the initial stage can be
explained by the fact that a large number of
surface sites were available for adsorption.
When time lapsed away, the remaining
surface sites were difficult to be occupied
because the repulsion between
the solute molecules of the solid and bulk
phases made it take long time to reach
equilibrium [12].
375
Figure 5: Effect of the contact time
3.2.3. Effect of the dosage of adsorbent
Figure 6 illustrates data from the MB
adsorption onto the prepared magnetic
material by varying the dosage of
adsorbent. It is obvious that increasing the
adsorbent’s dosage, adsorption efficiency is
higher. For the dosage 0.5g/30 mL of 50
ppm MB, the adsorption efficiency is
nearly 100%.
Figure 6: Effect of the dosage
3.2.4. Effect of the initial MB
concentration- Isotherms
The equilibrium data were analyzed by the
Langmuir and the Freundlich models:
max
1/n
e f e
. (2)
1 .
K . 3
e
e
e
bCq q
bC
q C
Equation (2) and (3) can be rearranged to
obtain respectively the linear forms as
follows:
max max
1 (4)
.
loglog log (5)
e e
e
e
e f
C C
q q b q
Cq K
n
where Ce and qe are the equilibrium
concentrations in the liquid and solid
phases, qmax is the maximum adsorption
capacity, b is the Langmuir equilibrium
constant, and Kf and n are the Freundlich
constants.
As can be seen from Figure 7, the
Langmuir model provided a more accurate
376
description of the adsorption process. The
maximum adsorption capacity (qmax) of MB
on the magnetic material estimated from
linear Langmuir isotherm equation (4) is
30.7 mg.g–1 at pH 7. An examination of the
literature reveals that the adsorption
capacity of the MSCG for MB is smaller
activated charcoal (150 mg.g-1) [12] but
significantly higher than some low-cost
adsorbents such as pine sawdust (16.75
mg.g–1), sugar extracted spent rice biomass
(8.13 mg.g–1), wheat shells (21.50 mg.g–
1),[13]. The Freundlich constants drawn
from fitting equilibrium isotherm data
according to equation (5) are n = 1.42 and
Kf = 8.31.
Figure 7: Langmuir adsorption isotherm data (left)
and linear Langmuir isotherm form (right)
4. CONCLUSIONS
The results of this study clearly
demonstrate that MSCG can be easily
prepared by the exposure of SCG, a waste
material from the coffee industry, to the
water-based ferrofluid, leading to the fact
that the magnetic material can be easily
separated from the suspensions by a
permanent magnetic. The effects such as
pH, contact time, dosages of the adsorbent,
initial MB concentration on the MB
adsorption onto MSCG have been
investigated. The estimated maximum
adsorption capacity of the MSCG from
Langmuir isotherm modes was 30.7 mg.g–1
at pH 7, the temperature of 25oC, the
contact time of 60 min and the agitated rate
of 150 rpm. These results make the MSCG
highly suitable as a new low-cost adsorbent
for the large-scale removal of pollutants
from wastewaters.
REFERENCES
[1] Dabrowski A., (2001). Adsorption, from
theory to practice. Adv. Colloid Int. Sci.,
93, 135–224.
[2] San M.G., Lambert S.D., Graham N.J.,
(2001). The regeneration of field-spent
granular-activated carbons. Water Res.,
35, 2740–2748.
[3] Jooste T., Garcia-Aparicio M.P.,
Brienzo M., Van Zyl W.H., Görgens J.F.,
(2013). Enzymatic hydrolysis of spent
coffee ground. Appl Biochem Biotechnol,
169(8):2248-62.
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[4] Silva M.A., Nebra S.A., Silva M.J.M.,
Sanchez C.G., (1998). The use of biomass
residues in the Brazilian soluble coffee
industry. Bio-mass Bioenerg, 14:457–467.
[5] Tokimoto T., Kawasaki N., Nakamura
T., Akutagawa J., Tanada S., (2005).
Removal of lead ions in drinking water by
coffee grounds as vegetable biomass. J
Colloid Interface Sci., 281:56–61.
[6] Fiol N., Escudero C., Villaescusa I.,
(2008). Re-use of exhausted ground coffee
waste for Cr(VI) sorption. Sep Sci
Technol., 43:582–596.
[7] Djati Utomo H., Hunter K.A., (2006).
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[8] Djati Utomo H., Hunter K.A., (2006).
Adsorption of divalent copper, zinc,
cadmium and lead ions from aqueous
solution by wastetea and coffee adsorbents.
Environ Technol., 27:25–32.
[9]. Yasuda M., Sonda T., Hasegawa N.,
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metals with fresh and used coffee grounds.
J Home Econ Jpn, 54:827–832.
10 Safarik I., Horska K., Svobodova B.,
Safarikova M., (2012). Magnetically
modified spent coffee grounds for dyes
removal. Eur Food Res Technol., 234:345–
350.
[11] Berger P., Adelman N.B., Beckman
K.J., Campbell D.J., Ellis A.B., Lisensky
G.C., (1999). Preparation and properties of
an aqueous ferrofluid. J. Chem. Educ., 76,
943–948.
[12] Ahmad, M.A.; Rahman, N.K., (2011).
Equilibrium, kinetics and thermodynamic of
Remazol Brilliant Orange 3R dye
adsorption on coffee husk-based activated
carbon. Chem. Eng. J., 170, 154–161.
[13] Mohammed M.A., Shitu A. and
Ibrahim A., (2014). Removal of Methylene
Blue Using Low Cost Adsorbent: A Review.
Research Journal of Chemical Sciences,
Vol. 4(1), 91-102.
14 Zuorro A., Battista A.D., Lavecchia
R., (2013). Magnetically Modified Coffee
Silverskin for the Removal of Xenobiotics
from Wastewater; Chemical engineering
transactions, Vol. 35, 1375-1380.
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