Synthesis of Fe (Co or Ni) loaded mesoporous carbon composites and their adsorption behaviors for methyl orange

Article abstract of DOI:10.1166/jnn.2017.13820

Mesoporous carbon (CMK-3) was synthesized by hard template method using SBA-15 as template and sucrose as carbon source. The magnetic mesoporous carbon materials (Fe/CMK-3, Co/CMK-3, Ni/CMK-3) were prepared by a simple impregnation method. The samples were characterized by XRD, SEM, TEM, N₂ physical adsorption, and the adsorption process was investigated by varying the contact time, temperature, pH, adsorbent dose and initial dye concentration. The results showed that the maximum adsorption capacity of methyl orange (MO) on the Fe/CMK-3, Co/CMK-3 and Ni/CMK-3 were 187, 157 and 166 mg · g^-1, respectively. The equilibrium data were described using the Langmuir and Freundlich isotherms. It was found that the equilibrium data were best represented by the Langmuir isotherm model. The experimental data were fitted well by the pseudo-second-order kinetic model. Thermodynamic analysis revealed that the adsorption was an exothermic and spontaneous process. The negative eliv ΔS^θ suggested decreasing in randomness of adsorbent species. The adsorbents are easy to be recycled in the magntic field.

Full text of DOI:10.1166/jnn.2017.13820

Article
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Nanoscience and Nanotechnology
Vol. 17, 5261–5270, 2017
Copyright © 2017 American Scientific Publishers
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Synthesis of Fe (Co or Ni) Loaded Mesoporous
Carbon Composites and Their Adsorption
Behaviors for Methyl Orange
Tingshun Jiang∗, Weibing Fang, Qian Zhao, Wangping Liu, Haibo Zhao, and Shukun Le
School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, Jiangsu, China
Mesoporous carbon (CMK-3) was synthesized by hard template method using SBA-15 as template
and sucrose as carbon source. The magnetic mesoporous carbon materials (Fe/CMK-3, Co/CMK-3,
Ni/CMK-3) were prepared by a simple impregnation method. The samples were characterized by
XRD, SEM, TEM, N2 physical adsorption, and the adsorption process was investigated by varying
the contact time, temperature, pH, adsorbent dose and initial dye concentration. The results showed
that the maximum adsorption capacity of methyl orange (MO) on the Fe/CMK-3, Co/CMK-3 and
Ni/CMK-3 were 187, 157 and 166 mg·g−1, respectively. The equilibrium data were described using
the Langmuir and Freundlich isotherms. It was found that the equilibrium data were best represented
by the Langmuir isotherm model. The experimental data were fitted well by the pseudo-second-order
kinetic model. Thermodynamic analysis revealed that the adsorption was an exothermic and spon-
ꢁ
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taneous process. The negative ꢀS suggested decreasing in randomness of adsorbent species.
Copyright: American Scientific Publishers
The adsorbents are easy to be recycled in the magntic field.
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Keywords: Mesoporous Carbon, Magnetic Mesoporous Carbon Composite, Adsorption
Behavior, Methyl Orange.
1. INTRODUCTION
Activated carbon is one of most efficient adsorbent for
dye removal and decoloration because of its large specific
surface area and pore volume, strong adsorption power,
chemical inertness, and good stability.16ꢀ17 Activated car-
bon has been a dominant adsorbent in the liquid-phase
adsorption, especially in wastewater treatment. In prin-
ciple, the prominent adsorption performance of activated
carbon for organic pollutant was attributed to its abundant
pore structure and large specific surface area. However,
the previous researches showed that micropores (<2 nm)
were dominant in common activated carbons, so that bulky
molecules or macromolecules cannot easily penetrate into
the micropores and adsorb onto them. Therefore, the per-
formance of common activated carbon in bulky molecules
adsorption is rather constrained due to the microporous
nature of activated carbon.18ꢀ19 Mesoporous materials pos-
sessed unique structures, high surface areas, and large
and tunable pore channels,20–24 showing remarkable advan-
tages in adsorption, separation, catalysis, electrodes and
in particular for the bulky molecular adsorption. Zhuang
et al. reported that the adsorption amount for the bulky
dye is almost twice that of the activated carbon in which
mesopores contribute almost 100% to the total surface
At present, a great deal of colored wastewaters are gen-
erated by both dye manufacturing process and dye con-
suming industries such as the textile, leather, paper and
plastics industries.1–4 Therefore, people pay much atten-
tion to the treatment of dye wastewater because of its high
toxicity. It is essential to remove dyes from colored efflu-
ents before being discharged to aqueous environment. To
date, several methods have been developed to treat the
wastewater such as photodegradation,5 adsorption,6 mem-
brane technology,7 chemical coagulation,8 and biological
degradation.9 Among all the above-mentioned technolo-
gies, physical adsorption has been proposed to be one of
the most efficient and applicable approaches in terms its
simplicity, ease of operation, no generation of by-products
and low sensitivity.10–15 In recent years, researchers pay
more and more attention to developing highly effective
adsorbents, and many unconventional adsorbents, such as
natural materials, biological materials, agricultural and
industrial wastes were selected to remove the dye of
wastewater.
∗Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2017, Vol. 17, No. 8
1533-4880/2017/17/5261/010
doi:10.1166/jnn.2017.13820
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Synthesis of Fe (Co or Ni) Loaded Mesoporous Carbon Composites and Their Adsorption Behaviors for MO
Jiang et al.
area and volume.18 Yuan et al. prepared ordered meso-
porous carbon with varying pore sizes using silica SBA-15
as hard template and investigated the adsorption behav-
ior of bulky molecules of nonylphenol ethoxylate, and the
results indicated that the surface area of the pores larger
than 1.5 nm is a crucial factor to the adsorption capac-
ity of nonylphenol ethoxylate, whereas the most probable
pore diameter of ordered mesoporous carbon is crucial
to the adsorption rate of nonylphenol ethoxylate.19 Qin
et al. studied the adsorption behavior of four anionic dyes
on ammonium-functionalized MCM-41 and the results
demonstrated the adsorbent has a high affinity to four types
of anionic dyes.25 Yan et al. exhibited that the mesoporous
carbon prepared using furfural as carbon source, zeolite
as template has a high adsorption capacity for methy-
lene blue.26 Above-mentioaned studies demonstrated that
mesoporous carbon possessed unique structures, tunable
pore channels and uniform pore sizes, showing advan-
tages in adsorption and separation in particular for the
large-molecule-involved processes. Nevertheless, most of
the adsorbents have been limited because of difficulty to
separate from solution and the need for regeneration.27
Moreover, the conventional approach normally involves a
filtration or centrifugation procedure, which is very com-
plex. Therefore, it is very necessary to find an alternate
cheap and separable adsorbent. Recently, magnetic sep-
aration as a promising strategy has been paid more and
and Ni(NO3ꢁ2 · 6H2O, were purchased from Sinopharm
Chemical Reagent Co., Ltd. All the chemicals used in our
work were of analytical grade without further purification.
Deionized water was used in all experiments.
2.2. Sample Preparation
The template SBA-15 was synthesized by a hydrothermal
method according to previous report.31 Briefly, 2 g of P123
was dispersed in to 60 mL of distilled water. After stirring
for 3 h, a clear solution was obtained. Then, 10 mL of
HCl (37%) was adꢀded into the solution with stirring for
another 2 h at 35 C, and the mixed solution was ultra-
sonically dispersed untill the above mixed solution was
dissolve fully. After that, 4.5 mL of TEOS was added to
ꢀ
the solution with stirring at 35 C for 24 h. The mixture
ꢀ
was crystallizated at 100 C for 48 h, and the obtained
solid product was filtrated, washed and dried at 100 C.
ꢀ
ꢀ
The dried sample was heated to 550 C at a heating rate
of 2ꢀ/min and calcined at 550 C in air for 6 h to remove
ꢀ
the template, denoted as SBA-15.
The synthesis of CMK-3 was carried out in accordance
with the literature via a two-step method using SBA-15
as template, sucrose as carbon source.32 1 g of SBA-15
powder was mixed with an aqueous solution consisting of
1.25 g sucrose, 0.14 g of H2SO4 and 5.0 g of deionized
H2O. The resulting mixture was placed into an oven for
ꢀ
ꢀ
6 h at 100 C and then the oven was heated to 160 C
and kept the temperature for 6 h. The obtained dark brown
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more attention due to the fact that it can be easily sep-
28
Copyright: American Scientific Publishers
arated for regeneration under an applied magnetic-field.
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sample was milled. Subsequently, 0.75 g of sucrose, 0.1 g
of H2SO4 and 5.0 g of deionized H2O were added into
the milled sample with stirring uniformly. After the above
same heating treatment, the resultant sample was placed in
a tubular furnace and the tubular furnace was heated from
On the other hand, magnetically separable mesoporous
carbon composites have received much attention due to
the combined functionalities of mesoporous carbon and
magnetic nanoparticles which endow them with impor-
tant applications in catalyst support, separation technology
and adsorption of biomolecules.29 Wang et al. and Tian
et al. synthesized FeNi magnetic mesoporous carbon mate-
rials via the hard-template method and soft-template route,
respectively.28ꢀ30 Up to date, there is still little literature
reported the application of magnetic mesoporous carbon
in adsorption and desorption field.
ꢀ
ꢀ
room temperature to 900 C at a heating rate of 5 C/min
in a flow of N2 and kept at the temperature for 3 h.
To remove the silica template, the carbonized composite
obtained after pyrolysis was washed with 5 wt.% hydroflu-
oric acid. The resulting sample was filtered, washed with
ꢀ
deionized water and dried at 120 C, denoted as CMK-3.
The Fe/CMK-3 composite was prepared by a simple
impregnation method. Typically, 1 mmol Fe(NO3ꢁ3 ·9H2O
and the desired amount of PVP were dissolved in 100 mL
ethanol, and then 300 mg mesoporous carbon CMK-3
was added into above solution. The black mixture was
obtained after ultrasound a certain time and magnetic stir-
ring for 24 h at room temperature. Then the mixture was
transferred to a microwave chemical reactor and stirred
In this work, the synthesis of the magnetic mesoporous
carbon composite (Fe/CMK-3, Co/CMK-3, Ni/CMK-3)
was carried out by a simple impregnation method with the
assistance of microwave. The effect of important parame-
ters like the contact time, temperature, pH, adsorbent dose
and initial dye concentration on the removal of methyl
orange were studied. Also, the adsorption isotherms, kinet-
ics, thermodynamics were investigated.
ꢀ
under the condition of 400 W, 55–60 C. The final prod-
ꢀ
uct was dried in an oven at 60 C and grinded to powder.
2. EXPERIMENTAL DETAILS
2.1. Materials and Reagents
Finally, the magnetic mesoporous carbon Fe/CMK-3 was
ꢀ
obtained by calcinating at 900 C for 4 h with the pro-
tection of N2 in a tubular furnace. In addition, Co/CMK-3
and Ni/CMK-3 were prepared as the same method above-
mentioned using Co (NO3ꢁ2 ·6H2O and Ni (NO3ꢁ2 ·6H2O
instead of Fe (NO3ꢁ3 ·9H2O, respectively.
Triblock copolymer P123 (Mw = 5,800, EO20-PO70-
EO20ꢁ were purchased from Sigma-Aldrich Chemical Co.,
Tetraethyl orthosilicate (TEOS), sucrose, HCl, H2SO4,
HNO3, NaOH, ethanol, Fe(NO3ꢁ3 ·9H2O, Co(NO3ꢁ2 ·6H2O
5262
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Jiang et al.
Synthesis of Fe (Co or Ni) Loaded Mesoporous Carbon Composites and Their Adsorption Behaviors for MO
2.3. Characterization
X-ray diffraction (XRD) analysis employed a Rigaku
D/MAX 2500PC powder XRD instrument with Cu Kꢂ
radiation (ꢃ = 0.15418 nm) under 40 kV and 100 mA
with the 2ꢄ ranging from 10ꢀ to 80ꢀ (Rigaku, Japan).
The specific surface areas and pore sizes of the samples
were determined by using a NOVA2000e analytical system
made by Quantachrome Corporation (USA). Transmission
electron microscopy (TEM) images were obtained using a
TENCNAI–12 transmission electron microscopy (Phillips,
Japan). The morphologies and microstructures character-
ization of the samples were performed on a JSM-6480
scanning electron microscopy (SEM). The energy disper-
sive spectrometer analyses (EDS) of the samples were also
performed during the SEM measurements. UV-vis diffuse
reflectance spectra of the samples were measured using
a UV-vis spectrophotometer (UV-3100, Shimadzu, Japan).
BaSO4 was used as a reflectance standard.
(d)
(c)
(b)
(a)
70
10
20
30
40
50
60
80
2 Theta (degree)
Figure 1. XRD patterns of the samples: (a) CMK-3; (b) Fe/CMK-3;
(c) Co/CMK-3; (d) Ni/CMK-3.
and a less intense peak at 43.5ꢀ, which can be indexed as
(002) and (101) peaks of a graphitic carbon structure.5 As
demonstrated in Figure 1(b), Fe/CMK-3 composite showed
the characteristic peaks located at 2ꢄ = 44.7ꢀ and 65.0ꢀ
can be respectively indexed to the (110) and (200) reflec-
tions of symmetric metal Fe according to the JCDS files
no. 87-0712. And, the characteristic peaks of iron oxide
Fe3O4 (JCPDS 88-0866) were detected around at 2ꢄ =
2.4. Adsorption Experiment
To study the effect of important parameters like the con-
tact time, temperature, pH, adsorbent dose and initial
dye concentration on the adsorptive removal of methyl
orange, batch experiments were conducted. Batch adsorp-
tion experiments were carried out by adding a fixed
amount of magnetic mesoporous carbon (20 mg) into
100 mL conical flasks containing 50 mL of different ini-
tial methyl orange concentrations (10–100 mg·L−1ꢁ. Then
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35.5ꢀ and 62.6ꢀ, corresponding to the indices of (311)
Copyright: American Scientific Publishers
and (440) planes, respectively. The characteristic peaks of
the mixture was oscillated fully at a constant speed for
1 h at different temperatures (25–80 ꢀC). 5 mL of mixture
solution was withdrawn from the conical flasks at predeter-
mined time intervals and separated the adsorbent, and the
obtained supernatants were measured using a spectropho-
tometer at wavelength 464.0 nm.
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metal Co (JCPDS 88-2325) appeared at 2ꢄ = 45.9ꢀ, 53.5ꢀ
and 79.1ꢀ, assigning to its (111), (200) and (220) planes,
respectively. However, its characteristic peaks shifted to
the left and located at 2ꢄ = 44.2ꢀ, 51.5ꢀ and 75.9ꢀ as
shown in Figure 1(c). In addition, the characteristic peak
located at 2ꢄ = 36.5ꢀ can be indexed to cobalt oxide CoO
(JCPDS 75-393), corresponding to the indices of (111)
plane. The diffraction peaks in Figure 1(d) located at 2ꢄ =
44.5ꢀ, 51.8ꢀ and 76.4ꢀ can be perfectly indexed to face-
centered cubic Ni (JCPDS 65-2865), attributing to (111),
(200) and (220) planes. Particularly, a clear diffraction
peak at around 26ꢀ which is indexed to the (002) reflection
for graphitic carbon in the XRD patterns of Fe/CMK-3,
Co/CMK-3 and Ni/CMK-3 samples,33 indicating that the
nanosized transition metals such as Fe, Co, Ni could accel-
erate the development of graphitic structure of carbon
when they were heat-treated together with carbon materi-
als in inert gas atmosphere.30
The decolorization rate of methyl orange was calculated
using the following formula:
D = ꢅ1 −A/A0ꢁ×100%
(1)
where A0 and A stand for the absorbance of methyl orange
before and after the adsorption, respectively. Besides, the
equilibrium adsorption capacities (qeꢁ were determined
and according to the following formula:
qe = ꢅC0 −CeꢁV /m
(2)
where C0 is the initial concentration, Ce is the equilib-
rium concentration of methyl orange in solution, V is the
volume of the solution and m is the mass of the adsorbent.
3.2. SEM Analysis
The surface morphologies of CMK-3, Fe/CMK-3,
Co/CMK-3 and Ni/CMK-3 are shown in Figure 2. It is
observed that the surface of CMK-3 is non-uniform
and rough with short rod-like structure. For Fe/CMK-3,
Co/CMK-3 and Ni/CMK-3 composites, there is no obvi-
ous effect on the morphology of CMK-3 after the
3. RESULTS AND DISCUSSION
3.1. XRD Analysis
The phase structures of samples were examined by XRD,
as shown in Figure 1. Figure 1(a) exhibited the XRD pat-
tern of CMK-3 along with a strong peak located at 24.0ꢀ
J. Nanosci. Nanotechnol. 17, 5261–5270, 2017
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Synthesis of Fe (Co or Ni) Loaded Mesoporous Carbon Composites and Their Adsorption Behaviors for MO
Jiang et al.
adsorption
desorption
(a) :Fe/CMK-3
(b) :Co/CMK-3
(c) :Ni/CMK-3
(d):CMK-3
(d)
(c)
(b)
(a)
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure(p/p0)
Figure 2. SEM images of samples: (a) CMK-3; (b) Fe/CMK-3;
(c) Co/CMK-3; (d) Ni/CMK-3.
Figure 4. N2 adsorption–desorption isotherms of the samples:
(a) Fe/CMK-3; (b) Co/CMK-3; (c) Ni/CMK-3; (d) CMK-3.
introduction of Fe, Co and Ni nanoparticles. Observation
carefully, some small particles can be found on the sur-
face of Fe/CMK-3, Co/CMK-3 and Ni/CMK-3 compos-
ites. In order to further confirm the existence of Fe, Co and
Ni, the areas of Fe/CMK-3, Co/CMK-3 and Ni/CMK-3
samples with Fe, Co and Ni were selected respectively for
EDS (Fig. 3). According to Figure 3, signals correspond-
ing to Fe, Co and Ni were detected in the area with Fe,
Co and Ni deposited, respectively.
The specific surface area calculated by Brunauer-
Emmett-Teller (BET) method and the pore size and
pore volume calculated by Barrett-Joyner-Halenda (BJH)
method are summarized in Table I. From the Table I,
we noted that the surface areas of the resulting magnetic
mesoporous carbon supported by Fe, Co, Ni particles have
some degree of decline compared with the CMK-3, but
little change in pore size.
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3.3. Results of Nitrogen Physical Adsorption
3.4. Adsorption Capacity
The N2 adsorption–desorption isotherms and the pore size
distributions curves of as-prepared mesoporous carbon
CMK-3 and magnetic mesoporous carbon are shown in
Figures 4 and 5, respectively. As shown in Figure 4(d), the
N2 adsorption–desorption isotherm of the CMK-3 sample
exhibited a typical type IV isotherm with hysteresis loop
caused by capillary condensation in mesoporores, indi-
cating of mesoporous materials. Also, we found that the
isotherms of all composites are similar to that of CMK-3
sample. On the other hand, it is noted from Figure 5 that
the narrow and sharp peaks can be observed in an average
pore size range of 3.3–3.9 nm, which is agreement with
the data listed in Table I.
20 mg CMK-3, Fe/CMK-3, Co/CMK-3 and Ni/CMK-3
were added to a series of 50 mL methyl orange solution
with 40 mg·L−1 of initial concentration, and oscillated for
ꢀ
1 h at 25 C, respectively. Figure 6 presented the effect of
different adsorbents on the decolorization rate of methyl
orange for different contact times. As shown in Figure 6,
the decolorization rate of methyl orange was drastically
increased in 30 min. Then, it remained constant with
increasing of contact time from 30 to 60 min. Thus, 60 min
was considered as equilibrium time where the amount of
adsorbed methyl orange molecules onto adsorbent is in a
dynamic balance with the desorbed molecules from the
surface of adsorbent.6 Further, the decolorization rate of
Figure 3. EDS spectra of samples: (a) Fe/CMK-3; (b) Co/CMK-3; (c) Ni/CMK-3.
5264
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Jiang et al.
Synthesis of Fe (Co or Ni) Loaded Mesoporous Carbon Composites and Their Adsorption Behaviors for MO
Fe/CMK–3
100
Co/CMK–3
Ni/CMK–3
CMK–3
80
CMK–3
Fe/CMK–3
Ni/CMK–3
Co/CMK–3
60
40
20
0
(a)
(b)
(c)
(d)
0
10
20
30
40
50
60
0
5
10
15
20
25
30
t/min
Pore size (nm)
Figure 6. The effect of contact time on methyl orange decoloration.
Figure 5. The BJH pore-size distribution curves of the samples:
(a) CMK-3; (b) Fe/CMK-3; (c) Co/CMK-3; (d) Ni/CMK-3.
from 3 to 12. As shown in Figure 8, there is no obvious
change for the decoloration rate of methyl orange in pH
range of 3–8 and the decoloration rate of methyl orange
on magnetic mesoporous carbon composite is over 98%.
The decoloration rate of methyl orange decreased when
pH value increased from 8 to 12, but the decoloration
rate of methyl orange still maintained at above 95%. In
consideration of environmental reason, pH value of 7 was
chosen for subsequent experiments. Anionic dyes such
as methyl orange have negative charge caused by pres-
ence of SO−3 groups.6ꢀ25ꢀ34 Increasing initial pH resulted in
increasing the amount of hydroxide ions (OH−ꢁ competing
with methyl orange molecules as anionic dye for occupy-
ing adsorption sites of the mesoporous carbon,35ꢀ36 while
decreasing initial pH led to the protonation of the surface
of mesoporous carbon which is favored for sequestering
anionic dyes.37
methyl orange on magnetic mesoporous carbon compos-
ite is better than that of the CMK-3. This may be due
to the introduction of Fe, Co, Ni nanoparticles promoting
the graphitization transition of mesoporous carbon.30 As a
result, the internal pore structure of CMK-3 was changed,
and the proportion of microporous was greatly decreased
and the mesoporous mainly existed in the pore structure of
magnetic mesoporous carbon composites. Therefore, the
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methyl orange molecules can be efficiently transmitted and
Copyright: American Scientific Publishers
quickly adsorbed by the magnetic mesoporous carbon.
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Figure 7 illustrated the effect of different adsorbents
on methyl orange decolorization rate at different temper-
atures. Of which, 20 mg of magnetic mesoporous car-
bon (Fe/CMK-3, Co/CMK-3 and Ni/CMK-3) was added to
50 mL of 40 mg·L−1 methyl orange solution, respectively.
ꢀ
The experiments were carried out for 1 h at 25–80 C.
As shown in Figure 7, the adsorption capacity decreased
slightly with the increase in temperature from 25 to 80 ꢀC,
suggesting that adsorption of methyl orange on mag-
netic mesoporous carbon composite was an exothermic
adsorption.
The effect of different adsorbent doses on methyl orange
adsorption was investigated and the results are shown
100
The effect of initial pH on the decoloration rate of
methyl orange on magnetic mesoporous carbon compos-
ite was shown in Figure 8. 20 mg of magnetic meso-
porous carbon was added into 50 mL of 40 mg·L−1 methyl
95
ꢀ
orange solution with stirring at 25 C for 1 h in a con-
ical flask. The methyl orange solution pH was adjusted
90
using 0.1 mol · L−1 NaOH or 0.1 mol · L−1 HCl solution
Table I. Surface areas (SBETꢁ, pore sizes and pore volumes of the
samples.
85
Fe/CMK–3
Co/CMK–3
Ni/CMK–3
sample
SBET (m2 ·g−1
ꢁ
Pore size (nm) Pore volume (cm3 ·g−1
)
80
CMK-3
1362ꢆ0
534ꢆ4
588ꢆ9
566ꢆ0
3.4
3.9
3.4
3.8
0.970
0.606
0.574
0.671
20
30
40
50
60
70
80
Fe/CMK-3
Co/CMK-3
Ni/CMK-3
Temperature (ºC)
Figure 7. The effect of temperature on methyl orange decoloration.
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Synthesis of Fe (Co or Ni) Loaded Mesoporous Carbon Composites and Their Adsorption Behaviors for MO
Jiang et al.
100
kept constant. Figure 10 plotted the adsorption amount
of magnetic mesoporous carbon versus the equilibrium
concentration of methyl orange solution. The equilib-
rium adsorption capacity was gradually increased with
the increasing of methyl orange equilibrium concentra-
tion. The maximum equilibrium adsorption capacities for
Fe/CMK-3, Co/CMK-3 and Ni/CMK-3 were 187, 157 and
166 mg ·L−1, respectively.
95
90
85
80
The experimental data were fitted to the Langmuir and
Freundlich equations and the constant parameters of the
isotherm equations were calculated. The Langmuir and
Freundlich models were expressed by the equations.
Fe/CMK–3
Co/CMK–3
Ni/CMK–3
Ce
qe
1 Ce
Q0b Q0
Langmuir model:
=
+
(3)
2
4
6
8
10
12
pH
1
Freundlich model: ln qe = ln KF + ln Ce
(4)
Figure 8. The effect of pH on methyl orange decoloration.
n
Where Ce (mg · L−1ꢁ is the equilibrium concentration
of methyl orange in solution, qe (mg · g−1ꢁ is the adsorp-
tion capacity at equilibrium, Q0 (mg·g−1ꢁ is the maximum
adsorption capacity, b (L·mg−1ꢁ is the constant, related to
the free energy of adsorption, KF (L·g−1ꢁ and 1/n are the
Freundlich constants.
in Figure 9. The adsorption capacities of methyl orange
appeared a significant increasing trend with the increase of
adsorbent doses in the range of 5–20 mg. It is well known
that an increase in adsorbent dose increases the availabil-
ity of adsorption sites for the interaction of the dye with
the composite surface. However, the adsorption capacities
almost unchanged when the adsorbent dose in the range
of 20–35 mg. This may be due to the adsorption reached
equilibrium when the adsorbent is 20 mg.
The linearized Langmuir and Freundlich plots are given
in Figures 11(a and b), the slopes of the linearized
Langmuir and Freundlich plots were used to calculate
the adsorption constants presented in Table II. The value
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of correlation coefficient for Langmuir equation (R2 =
Copyright: American Scientific Publishers
3.5. Adsorption Isotherm
0.9991, 0.9999 and 0.9956) are much higher than Fre-
undlich (R2 = 0.7515, 0.6663 and 0.8381), suggesting that
equilibrium data are well described by Langmuir isotherm,
and the adsorption behavior belonged to monolayer.
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Equilibrium adsorption isotherm studies were carried out
to determine the adsorption capacity and equilibrium con-
stant for methyl orange on magnetic mesoporous car-
bon. 20 mg magnetic mesoporous carbon was added
into 50 mL of methyl orange solution with different
initial concentrations from 10 to100 mg · L−1 with stir-
ring for 1 h at room temperature and the pH of 7 was
3.6. Adsorption Kinetics
The pseudo-first-order kinetic and pseudo-second-order
kinetic models were applied to determine the kinetics of
200
160
120
80
100
80
60
40
20
Fe/CMK–3
Co/CMK–3
Ni/CMK–3
Fe/CMK–3
Co/CMK–3
Ni/CMK–3
40
0
–5
0
5
10
15
20
25
30
35
0
5
10
15
20
25
30
35
40
Ce (mg/L)
dose (mg)
Figure 9. The effect of adsorbent dose on methyl orange decoloration
(T = 298 K; contact time = 1 h; [MO]initial = 40 mg/L; pH = 7).
Figure 10. Adsorption isotherms of methyl orange onto different
adsorbents.
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Jiang et al.
Synthesis of Fe (Co or Ni) Loaded Mesoporous Carbon Composites and Their Adsorption Behaviors for MO
Where qe (mg · g−1ꢁ is the adsorption capacity at equi-
0.24
0.20
0.16
0.12
0.08
0.04
a
Fe/CMK–3
Co/CMK–3
Ni/CMK–3
librium, qt (mg · g−1ꢁ is the amount of methyl orange
adsorbed at any time t. k1 (min−1ꢁ and k2 (g ·mg−1 ·min−1
ꢁ
are the adsorption rate constant of pseudo-first-order
and pseudo-second-order models, respectively. The linear
plots of lnꢅqe − qtꢁ versus t for the pseudo-first-order
model and t/qt versus t for the pseudo-second-order
model for methyl orange adsorption on the three mag-
netic mesoporous carbon composites are presented in
Figures 12(a and b). The values of qe, k1 and k2 were
calculated and the results are shown in Table III.
0.00
0
As show in Table III, the values of correlation coef-
ficient for pseudo-second-order are relatively higher than
those for pseudo-first-order kinetic model. Additionally,
experimental qe values are very close to the calculated
qe values for pseudo-second-order kinetic model. These
results implied that the adsorption of MO could be best
described by the pseudo-second order model.
5
10
15
20
25
30
35
Ce(mg/L)
(a) Langmuir isotherm
5.5
5.0
4.5
4.0
3.5
b
4
a
3
Fe/CMK–3
Co/CMK–3
Ni/CMK–3
2
1
Fe/CMK–3
0
IP: 5.101.219.21 On: Sun, 23 Dec 2018 14:41:30
Co/CMK–3
CopyriNgih/CtM: KA–m3 erican Scientific Publishers
Delivered by Inge–n1ta
3.0
–5
–4
–3
–2
–1
0
1
2
3
4
lnCe
(b) Freundlich isotherm
–2
–3
Figure 11. Adsorption isotherms: (a) Langmuir; (b) Freundlich.
0
10
20
30
40
50
60
t/(min)
(a) pseudo-first-order kinetic model
methyl orange adsorption on magnetic mesoporous carbon.
Equations of pseudo-first-order kinetic and pseudo-second-
order kinetic can be expressed as:
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Fe/CMK–3
Co/CMK–3
Ni/CMK–3
b
pseudo-first-order kinetic model:
lnꢅqe −qtꢁ = ln qe −k1t
pseudo-second-order kinetic model:
(5)
(6)
t
1
t
=
+
k2qe2 qe
qt
Table II. Adsorption isotherm parameters of methyl orange adsorption.
Langmuir
Freundlich
0
10
20
30
40
50
60
Adsorbents
Fe/CMK-3
Co/CMK-3 11ꢆ96
Ni/CMK-3 2ꢆ55
b
Q0 (mg/g)
R2
KF
n
R2
t /min
(b) pseudo-second-order kinetic model
2ꢆ11
191.2
157.5
170.4
0.9991
0.9999 106ꢆ51 5.11
0.9956
95ꢆ85 3.23
0.7515
0.6663
Figure 12. Kinetics models: (a) pseudo-first-order model; (b) pseudo-
94ꢆ67 2.76 0.8381
second-order model.
J. Nanosci. Nanotechnol. 17, 5261–5270, 2017
5267

Synthesis of Fe (Co or Ni) Loaded Mesoporous Carbon Composites and Their Adsorption Behaviors for MO
Jiang et al.
Table III. Kinetic parameters for methyl orange adsorption on three magnetic mesoporous carbon composites.
First-order rate kinetic constants
Second-order rate kinetic constants
Adsorbents
Qe (mg·g−1
ꢁ
K1 (min−1
ꢁ
R2
qe (mg·g−1
ꢁ
K2 (g·mg−1 ·min−1
ꢁ
qeꢀ real (mg·g−1
ꢁ
R2
Fe/CMK-3
Co/CMK-3
Ni/CMK-3
35ꢆ71
0ꢆ8928
25ꢆ96
0.09842
0.03198
0.11853
0.9693
0.4002
0.8486
102ꢆ35
99ꢆ90
102ꢆ15
0ꢆ00535
0ꢆ2626
0ꢆ00596
98.78
99.72
98.59
0.9995
0.9999
0.9992
3.7. Adsorption Thermodynamics
The values of ꢇHꢈ and ꢇSꢈ can be calculated by the
Van’t Hoff equation from the slope and intercept of the
linear plot of lnK versus 1/T (Fig. 13) and the results
are listed in Table IV. As shown in Table IV, the negative
value of ꢇHꢈ indicated the exothermic nature of adsorp-
tion process of methyl orange onto magnetic mesoporous
carbon, the negative value of ꢇGꢈ confirmed the spon-
taneity of adsorption process, the negative value of ꢇSꢈ
revealed the decrease in randomness at the solid/solution
interface during the adsorption process.
Thermodynamic parameters like standard Gibbs free
energy change ꢇGꢈ (KJ · moL−1ꢁ, enthalpy change ꢇHꢈ
(KJ·moL−1ꢁ, and entropy change ꢇSꢈ (KJ·moL−1ꢁ were
estimated to evaluate the feasibility of the adsorption pro-
cess by the following equations:
ꢇGꢈ = −RT ln Kꢈ
Kꢈ = Ca/Ce
(7)
(8)
ln Kꢈ = ꢇHꢈ/RT +ꢇSꢈ/R
(9)
ꢇGꢈ = ꢇHꢈ −TꢇSꢈ
(10)
3.8. Regeneration Test
It is well known that the recycling and regeneration of
adsorbent is vital in practical application. Thus, the regen-
eration test was carried out using thermal and desorption
regeneration. 50 mL of 40 mg/L methyl orange solution,
20 mg adsorbent (Co/CMK-3), pH value of 7 and con-
tact time of 1 h at room temperature were used as selec-
Where R (8.314 J · mol−1 · K−1ꢁ is the thermodynamic
constant; Ce (mg·L−1ꢁ is the equilibrium concentration of
methyl orange in solution; Ca (mg · L−1ꢁ is the amount
adsorbed on adsorbent at equilibrium. The following lin-
earized equations were obtained by plotting “ln Kꢈ versus
to 1/T .”
tive parameters to perform a two-stage regeneration test.
IP: 5.101.219.21 On: Sun, 23 Dec 2018 14:41:30
Thermal regeneration was done by heating the spent adsor-
Copyright: American Scientific Publishers
For Fe/CMK-3: ln Kꢈ = 4109ꢆ0/T −9ꢆ04145
ꢀ
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bent in a tube furnace with a nitrogen flow at 300 C
for 2 h, the black bar in Figure 14 showed the results
of thermal regeneration test. On the other hand, the spent
adsorbent placed in distilled water with stirring until the
solution became transparent, and the red bar in Figure 14
represented the desorption regeneration experiment results.
Clearly, regeneration after thermal treatment showed bet-
ter reusability as compared to desorption treatment, the
calcined Co/CMK-3 adsorbent exhibited high stability in
six consecutive adsorption cycles, the removal efficiency
was still up 76.9%, which was much higher than that of
desorption treatment. It may be due to the methyl orange
molecules adsorbed on Co/CMK-3 were removed during
calcination treatment, and the adsorption active sites were
released. However, the methyl orange molecules adsorbed
on Co/CMK-3 cannot be removed completely using des-
orption treatment, and the adsorption active sites reduced
gradually.
ꢅR2 = 0ꢆ9583ꢁ
For Co/CMK-3: ln Kꢈ = 8344ꢆ2/T −21ꢆ2737
ꢅR2 = 0ꢆ9625ꢁ
For Ni/CMK-3: ln Kꢈ = 4623ꢆ0/T −10ꢆ5994
ꢅR2 = 0ꢆ9888ꢁ
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
Table IV. Thermodynamic parameters of methyl orange on three mag-
netic mesoporous carbon.
Fe/CMK–3
Co/CMK–3
Ni/CMK–3
T
ꢇGꢈ
ꢇHꢈ
ꢇSꢈ
Adsorbents
(K)
(KJ·moL−1
−10ꢆ91
−16ꢆ17
−11ꢆ66
ꢁ
(KJ·moL−1
−34ꢆ16
−69ꢆ37
−38ꢆ44
ꢁ
(J·moL−1 ·K−1
ꢁ
0.0028
0.0030
0.0032
1/T(K–1
)
Fe/CMK-3
Co/CMK-3
Ni/CMK-3
303
303
303
−75ꢆ17
−176ꢆ87
−88ꢆ12
Figure 13. ln K versus 1/T plot of methyl orange adsorption on mag-
netic mesoporous carbon.
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Jiang et al.
Synthesis of Fe (Co or Ni) Loaded Mesoporous Carbon Composites and Their Adsorption Behaviors for MO
areas and pore volumes of Fe/CMK-3, Co/CMK-3,
thermal treatment
desorption treatment
100
80
60
40
20
0
Ni/CMK-3 were 534.4, 588.9, 566.0 m2g−1and 0.606,
0.574, 0.671 cm3g−1, respectively. The decoloration of
methyl orange was effected by different adsorption param-
eters. When 20 mg adsorbent was added into 50 mL of
40 mg ·L−1 methyl orange solution with the pH of 7, and
then vibration adsorption for 1 h at 25 ꢀC, the decoloration
rate of CMK-3, Fe/CMK-3, Co/CMK-3 and Ni/CMK-3
were 94.55%, 98.92%, 99.72% and 98.60%, respectively.
It was found that the equilibrium data were best rep-
resented by the Langmuir isotherm model. The experi-
mental data fitted well the pseudo-second-order kinetic
model. Thermodynamic data of standard enthalpy change
(ꢇHꢈ < 0), entropy change (ꢇSꢈ < 0) and Gibbs free
1st run
2nd run
3rd run
4th run
5th run
6th run
energy (ꢇGꢈ < 0) were calculated, indicating the adsorp-
tion was an exothermic, decreasing in randomness of
adsorbent species and spontaneous process.
Figure 14. The regeneration experiments of methyl orange adsorption
on Co/CMK-3.
Acknowledgment: Financial support from Project sup-
ported by the National Natural Science Foundation of
China (51572115) and Project supported by the Grad-
uate Science Research Innovation Program Foundation
of the Jiangsu Higher Education Institution of China
(KYLX15_1040) are gratefully acknowledged.
Figure 15. Magnetic separation images of Co/CMK-3. (a) The initial
state of Co/CMK-3 sample dispersed into MO; (b) after adsorption for
a period of time; (c) magnetic separation after adsorption equilibrum;
(d) after removing the magnet.
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