Sol-gel-cum-hydrothermal synthesis of mesoporous Co-Fe@Al2O3?MCM-41 for methylene blue remediation

Article abstract of DOI:10.1007/s12039-017-1230-5

A combined sol-gel-cum-hydrothermal method has been employed to synthesize novel monometallic (Mn, Fe, Co) and bimetallic (Co-Fe, Mn-Co, Fe-Mn) nanoparticles loaded onto Al ₂O₃?MCM-41. Powder XRD, N ₂ sorption, field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM) measurements show that the materials possess mesoporosity, high surface area and nanosize. Monometallic Fe, Co and Mn @Al ₂O₃?MCM-41 and bimetallic Co-Fe, Fe-Mn and Mn-Co @Al ₂O₃?MCM-41 materials were tested for methylene blue remediation from aqueous media. In the present study, Co-Fe@Al ₂O₃?MCM-41 was found to be an excellent adsorbent. The adsorption efficiency of Co-Fe@Al ₂O₃?MCM-41 has been studied as a function of adsorbent dose and pH of the solution. Maximum adsorption of methylene blue was obtained at high pH values of the solution. Framework mesoporosity, high surface area, and narrow pore distribution are the key factors for an efficient adsorption of methylene blue on Co-Fe@Al ₂O₃?MCM-41. [Figure not available: see fulltext.]

Full text of DOI:10.1007/s12039-017-1230-5

c
J. Chem. Sci. ꢀ Indian Academy of Sciences.
DOI 10.1007/s12039-017-1230-5
REGULAR ARTICLE
Sol-gel-cum-hydrothermal synthesis of mesoporous
Co-Fe@Al2O3−MCM-41 for methylene blue remediation
AMARESH C PRADHAN∗, ANIMESH PAUL and G RANGA RAO∗
Department of Chemistry, Indian Institute of Technology Madras, Chennai, Tamil Nadu 600 036, India
Email: amaresh32@gmail.com; grrao@iitm.ac.in
MS received 15 October 2016; revised 28 December 2016; accepted 3 January 2017
Abstract. A combined sol-gel-cum-hydrothermal method has been employed to synthesize novel monometal-
lic (Mn, Fe, Co) and bimetallic (Co-Fe, Mn-Co, Fe-Mn) nanoparticles loaded onto Al2O3−MCM-41. Powder
XRD, N2 sorption, field emission scanning electron microscopy (FESEM) and high resolution transmission
electron microscopy (HRTEM) measurements show that the materials possess mesoporosity, high surface area
and nanosize. Monometallic Fe, Co and Mn @Al2O3−MCM-41 and bimetallic Co-Fe, Fe-Mn and Mn-Co
@Al2O3−MCM-41 materials were tested for methylene blue remediation from aqueous media. In the present
study, Co-Fe@Al2O3−MCM-41 was found to be an excellent adsorbent. The adsorption efficiency of Co-
Fe@Al2O3−MCM-41 has been studied as a function of adsorbent dose and pH of the solution. Maximum
adsorption of methylene blue was obtained at high pH values of the solution. Framework mesoporosity, high
surface area, and narrow pore distribution are the key factors for an efficient adsorption of methylene blue on
Co-Fe@Al2O3−MCM-41.
Keywords. Oxides; sol-gel; adsorption; surface properties; composite materials.
1. Introduction
Porous materials such as MCM-41 with high textural
properties such as surface area, narrow pore diameter
and large pore volume are preferred for efficient adsorp-
tion and removal of pollutant molecules.28,29 For exam-
ple, MCM-41 framework with surface area greater than
1000 m2 g−1 and pore diameter of about 2–3 nm can
effectively be used to trap methylene blue molecules
of molecular volume 0.4 nm × 0.61 nm × 1.43 nm.30
Moreover, loading of aluminum into the framework
of MCM-41 leads to isomorphous substitution of alu-
minum for silicon which creates ion exchange sites in
the molecular sieve framework.31 This ion exchange
property within the Al2O3−MCM-41 may aid the
adsorption of methylene blue on the material. In tran-
sition metal oxides, vanadium doped TiO2 and mag-
netite show remarkable enhancement of the adsorption
capacity by an order of magnitude compared to pure
oxides, which significantly promotes the adsorption
and degradation of methylene blue.32 Further, hydro-
gen bonding between the associated hydroxyl groups
on the adsorbent surface with the lone electron pair
on nitrogen and sulphur atoms of aromatic rings
in methylene blue structure can also play a sig-
nificant role in the adsorption of methylene blue.33
Monometallic and bimetallic particles are embedded
in porous frameworks associated with Al2O3–MCM-
41 which are expected to show good dye adsorption
properties.20,21 This is possible because, (i) the pore
Industrial dyes and dye related compounds show adverse
effects on the aquatic life and the ecosystem.1 4 In
general, dyes are categorized as cationic dyes (methy-
lene blue, rhodamine B and 6G, methyl violate, methy-
lene green, Malachite green, cationic red X-GRL),
anionic dyes (methyl orange, eosin Y, methyl red,
acid green 25, Congo red, N719), phenolic compounds
(bromophenol blue, bisphenol A, phenol, 2-chloro-
4-nitrophenol, 4-chloro-2-nitrophenol) and other dye
molecules such as para red (azo dye), alizarin (mor-
dant dye) and indanthrene blue (vat dye). Some of
these dye molecules are considered as contaminants
and their remediation is studied extensively by adsorp-
tion on porous materials,5 12 photocatalytic degradation
using semiconducting oxide materials,13 17 photo-
Fenton oxidation by Fe-based materials,18 21 biologi-
cal degradation22 and degradation by graphene-based
materials.23 27 Among these methods, adsorption pro-
cess is cost-effective and reproducible for the removal
of pollutant molecules.2,18 The major advantage of the
adsorption process is that it does not require any chem-
icals and UV radiation, and hence widely accepted in
water purification industry.
∗For correspondence

Amaresh C Pradhan et al.
2 h (solution A) to obtain Al2O3−MCM-41 with Si/Al ratio
diameter (2–3 nm) in the framework of monometallic
and the bimetallic@Al2O3−MCM-41 is compatible
with molecular diameter of methylene blue, (ii) frame-
work mesoporosity, and (iii) high surface area of mono
and bimetallic@Al2O3-MCM-41.
In the present study, we have explored monometal-
lic Fe, Co and Mn@Al2O3−MCM-41, and bimetallic
Co-Fe, Fe-Mn and Mn-Co@Al2O3−MCM-41 as sta-
ble and active adsorbents for the removal of methy-
lene blue from aqueous solutions. We have loaded
monometallic (Mn, Fe, Co) and bimetallic (Co-Fe, Fe-
Mn, Mn-Co) particles into tailor-made in situ meso-
porous Al2O3−MCM-41. The dye adsorption was
found to be highly efficient on Co-Fe@Al2O3−MCM-
41 under basic conditions.
10. Then 1.0 mmol of FeSO4.7H2O was dissolved in 20 mL
ethanol and 5 mL of oleic acid was added and stirred for
two hours (solution B). Solutions A and B were mixed and
stirred for 2 h. The total mixture was transferred into a stain-
less steel autoclave and put into a furnace for 20 h at 120◦C.
The gel was washed with distilled water and ethanol, and
further dried in an oven at 70◦C for 12 h. The white powder
was calcined at 500◦C at 5 h in air. This material is denoted
as Fe@Al2O3−MCM-41. Similar procedure was adopted to
synthesize Co@Al2O3−MCM-41 and Mn@Al2O3−MCM-
41 samples by taking 1.0 mmol cobalt(II) nitrate hexahy-
drate (Co (NO3)2.6H2O) and 1.0 mmol of manganous acetate
tetrahydrate (C4H6MnO4.4H2O), respectively. The experi-
mental weight of monometallic Fe, Co and Mn is 0.056 g,
0.058 g and 0.055 g in 1 g of Fe@Al2O3−MCM-41, Co@
Al2O3−MCM-41 and Mn@Al2O3−MCM-41, respectively.
For synthesis of bimetallic@Al2O3−MCM-41, 0.5 mmol
of Co (NO3)2.6H2O and 0.5 mmol of FeSO4.7H2O are mixed
in ethanol. The above synthesis procedure was followed to
obtain Co-Fe@Al2O3−MCM-41, Fe-Mn@Al2O3−MCM-
41 and Mn-Co@Al2O3−MCM-41 samples. The experimen-
tal weight of bimetallic Co and Fe is 0.029 g and 0.028 g
in 1 g of Co-Fe@Al2O3−MCM-41 sample. Similar calcu-
lated weight ratio of the two metals was maintained in both
Fe-Mn@Al2O3−MCM-41 and Mn-Co@Al2O3−MCM-41.
2. Experimental
2.1 Preparation of mesoporous Al2O3
Mesoporous Al2O3 was synthesized by sol-gel method.
Cetyltrimethylammonium bromide (CTAB, C19H42NBr,
Aldrich, 99%) was used as structure directing agent and
aluminium isopropoxide (99%, Sigma-Aldrich) as alumina
source. Initially, CTAB was dissolved in water in order to
form micelles. Then, aluminium isopropoxide was added and
stirred for 2 h. The molar ratio of CTAB and aluminium iso-
propoxide was kept at 1:1. Ammonia was added to maintain
the pH of the solution at 10 and the suspension was stirred for
12 h. Final product was filtered, washed with distilled water
and ethanol before drying them at 70◦C for 12 h. The meso-
porous Al2O3 powder was obtained by calcining the material
at 600◦C for 6 h.
2.4 Characterization of materials
The X-ray diffraction patterns (XRD) of the materials were
obtained by employing Bruker AXS D8 Advance diffrac-
tometer and Cu Kα (λ = 0.15408 nm) radiation. A scan rate
of 2◦/min was used to record high angle reflections from 10
to 8◦, and 0.01◦/s scan rate for low angle reflections from 0.5
to 10◦. The specific surface area, pore size and pore volume
were measured by N2 adsorption-desorption method at liquid
nitrogen temperature (−196◦C) using Micromeritics ASAP
2020. The specific surface area and pore size distribution
were estimated based on Brunauer-Emmett-Teller (BET) and
Barrett-Joyner-Halenda (BJH) methods, respectively. For the
field emission scanning electron microscopy (FESEM) anal-
ysis, powder samples were dispersed on a conducting carbon
tape by FEI Quanta 400 instrument. Transmission electron
microscopy (TEM) images were obtained using Philips CM
200 transmission electron microscope with a LaB6 filament
and equipped with an ultrathin objective lens and CCD cam-
era. HRTEM images were recorded by using JEOL 3010
machine. Diffuse reflectance UV-Vis (DRUV-Vis) spectra of
the materials were performed by JASCO V-660 spectropho-
tometer equipped with 60 mm integrating sphere. The mea-
surements were carried out at a bandwidth of 5 nm in the
wavelength range of 200–800 nm at a scanning speed of
2.2 Synthesis of MCM-41
MCM-41 was prepared by sol-gel-cum-hydrothermal method.
2.4 g of CTAB was added to 120 mL water and then, 8 mL
of aqueous NH3 was added into it. Stoichiometric amount of
tetraethyl orthosilicate (TEOS, C8H20O4 Si, Aldrich, 99%)
was added to the solution under vigorous stirring for 1 h. The
gel was transferred into stainless steel autoclave and placed
in a furnace for 20 h at 120◦C. The final product was filtered
and dried at 70◦C for 12 h. The surfactant was removed from
the product by calcining at 550◦C in air for 5 h.
2.3 Fabrication of monometallic and bimetallic@Al2
O3−MCM-41
In a typical synthesis, 2.5 g of CTAB was added to 120 mL of 100 nm/min. The FTIR spectra of the samples were recorded
H2O and stirred for one hour and then 0.377 g of mesoporous with JASCO FTIR-4100 spectrophotometer in the range of
Al2O3 was added to it. The mixture was continuously stirred 400–4000 cm−1 at room temperature using KBr as reference.
by adding 10 mL aqueous NH3 after an hour. Then, 8 mL of The zeta potential of the material was measured by equili-
TEOS silica source was added to the mixture and stirred for brating 5 mg of Co-Fe@Al2O3−MCM-41 adsorbent powder

Sol-gel-cum-hydrothermal synthesis
in 50 mL of 0.01 M KCl solution using Zetasizer Nano ZS
bimetallic@Al2O3−MCM-41 systems. The metal loaded
Al2O3−MCM-41samples are substantially amorphous
in nature and do not show any x-ray reflections of the
respective metal oxide phases. The broad band centred
at 2θ = 22◦ can be assigned to the characteristic refection
from amorphous SiO2 (JCPDS29-0085). The XRD
results indicate that Al2O3−MCM-41 matrix is highly
amorphous in which cluster-like Fe, Co, Mn, Co-Fe,
Mn-Co, Fe-Mn oxide species are embedded.
(Malvern, UK).
2.5 Adsorption procedure
Methylene blue was obtained from Merck, India. A 100 mg/L
stock solution of methylene blue was prepared and suitably
diluted to the required initial concentration. Adsorption stud-
ies were carried out by taking 20 mL of 100 mg/L methy-
lene blue solution and 0.02 g of adsorbent dose at pH = 10.
The solution was taken in a tightly fitted conical flask and
the pH of the solution was adjusted by adding 0.01 M HNO3
and/or ammonia (Merck GR grade). Systronics μ pH sys-
The representative low angle XRD pattern for MCM-
41, Al2O3−MCM-41 and Co-Fe@Al2O3−MCM-41
samples are shown in Figure 2. The three samples exhi-
tem 361 was employed to monitor the pH while stirring. The bited highly intense d100 diffraction peak at low angle
indicating the mesoporous nature.35 It was observed that
adsorption process was completed in 3 h. The solution was
centrifuged and analysed by JASCO V-660 UV-visible spec-
trophotometer. The maximum absorbance of methylene blue
the peak intensity (d100) slightly decreased from MCM-
4 to Al2O3−MCM-41 and extensively decreased from
Al2O3−MCM-41 to Co-Fe@Al2O3−MCM-41. This is
due to the loading of the mesoporous Al2O3 into the
extra-framework of the MCM-41 and loading of the (Co
and Fe) onto the surface of the Al2O3−MCM-41.21 The
other three reflections indexed as d110, d200 and d210 were
comparatively less intense. This suggests the presence
of a periodic hexagonal arrangement of the channel.36
The MCM-41 shows d100, d110, d200 and d210 reflec-
tions, indicating well-ordered hexagonal mesoporous
channel. The (100) and (110) diffraction peaks related
to Al2O3−MCM-41 are intact, indicating that addition
of mesoporous Al2O3 powder into the MCM-41 does
not affect the mesoporosity and periodic hexagonal
arrangement of the channel. This phenomenon is due
to, (i) the isomorphous of substitution of Si4+ by Al3+
occurs at 664 nm. The percentage of methylene blue remain-
C
C0
ing in the solution was calculated by
× 100%, where
C and C are the initial concentration and concentration of
methylene blue after adsorption, respectively.
3. Results and Discussion
3.1 XRD analysis
Figure 1 shows the XRD pattern of mesoporous Al2O3
and monometallic and bimetallic@Al2O3−MCM-41
samples. Mesoporous Al2O3 is crystalline in nature
showing diffraction peaks at (440), (400) and (311)
due to γ -phase.34 However, the diffraction peaks of
γ -Al2O3 phase are very feeble in monometallic and
Figure 1. High angle x-ray diffractorgrams of (a) Al2O3,
(b) MCM-41, (c) Co@Al2O3−MCM-41, (d) Mn@Al2O3−
MCM-41, (e) Fe@Al2O3−MCM-41, (f) Mn-Co@Al2O3−
MCM-41, (g) Fe-Mn@Al2O3−MCM-41, and (h) Co-Fe@Al2
O3−MCM-41 materials.
Figure 2. Low angle x-ray diffractorgrams of (a) MCM-
41, (b) Al2O3−MCM-41 and (C) Co-Fe@Al2O3−MCM-41
materials.

Amaresh C Pradhan et al.
in MCM-41 without affecting its mesoporosity and
periodicity,37 and (ii) the coordination of Al3+ ions with
Si4+ through oxygen leading to extra-framework mod-
ification of MCM-41.21 Loading of Fe and Co onto the
mesoporous Al2O3−MCM-41 leads to the degeneration
of structural order as shown by weak d100 plane and
disappearance of reflections (110), (200) and (210) in
Figure 2c. This is because some Co and Fe particles
tend to block the pores of Al2O3−MCM-41 network.
Similar behaviour can be predicted in all monometallic
and bimetallic@Al2O3−MCM-41 materials.
3.2 N2 sorption studies
The N2 sorption isotherms of the materials are shown
in Figures 3 and 4. All the materials showed type-
IV isotherm with H1 hysteresis. This isotherm repre-
sents the mesoporous behaviour of the material.38 The
adsorption step of MCM-41, Al2O3−MCM-41 material
(Figure 3) centred in the relative pressure (P/P0) region
from 0.1 to 0.5. This phenomenon indicates the pres-
ence of framework-confined mesopores or framework
mesoporosity/intra-particle mesoporosity.39,40 The nature
of sorption step in MCM-41 as well as Al2O3−MCM-41
is tall and sharp which indicates the framework meso-
porosity. The adsorption step of mesoporous Al2O3
meet with desorption curve at relative pressure (P/P0)
in the region of 0.5. This can be treated as a bor-
der line framework mesoposity. The sorption isotherms
of monometallic (Fe, Co, Mn) and bimetallic (Co-Fe,
Fe-Mn, Mn-Co) @Al2O3−MCM-41 systems are pre-
sented in Figure 4. The hysteresis loops for monometal-
lic and bimetallic@Al2O3−MCM-41 samples begin at
a relative pressure of about 0.45, which indicates the
framework mesoporosity.
Figure 4. N2 sorption isotherms of Mn@Al2O3−MCM-
41, Co-Fe@Al2O3−MCM-41, Fe-Mn@Al2O3−MCM-41,
Fe@Al2O3−MCM-41, Mn-Co@Al2O3−MCM-41and Co@
Al2O3−MCM-41 materials.
The pore size distribution curves are shown in
Figure 5. The result shows that mono modal and narrow
mesoporous range between 2–3 nm, except mesoporous
Al2O3 of 3.6 nm. This indicates the presence of frame-
work mesoporosity in MCM-41 and Al2O3−MCM-41,
whereas Al2O3 is attributed to the border line frame-
work mesoporosity. This is because the pore diameter
of Al2O3 is nearer to narrow range (2–3 nm). Figure 6
represents the pore size distribution curves of mono and
bimetallic@Al2O3−MCM-41 materials. These materi-
als are also in similar framework mesoporosity as that
of MCM-41 and Al2O3−MCM-41 materials.
The surface area, pore diameter, pore volume of
samples are summarized in Table 1. These values are
Figure 3. N2 sorption isotherms of Al2O3, MCM-41 and Figure 5. Pore size distributions of Al2O3, MCM-41 and
Al2O3−MCM-41 materials. Al2O3−MCM-41 materials.

Sol-gel-cum-hydrothermal synthesis
obtained from N2 sorption isotherms. The high specific is more effective in the case of bimetallic materials
surface area of Al2O3−MCM-41as compared to MCM- compared to monometallic materials.
41 indicates that the meso-Al2O3 is incorporated into
the extra-framework of the MCM-41. In other words,
the high texture mesoporous Al2O3 has been incorpo-
3.3 FTIR spectral analysis
rated into the extra-framework of MCM-41 by coordi- The FTIR spectra of MCM-41 and mesoporous Al2O3−
nation of Al3+ to Si4+.21 The other factor is mesoporous MCM-41 are shown in the Figure 7. The anti-symmetric
Al2O3 hinders the crystal growth of MCM-41 which Si−O−Si vibration bands of MCM-41 and Al2O3−
aids to increase the surface area of Al2O3−MCM-41. MCM-41 samples are at 1089 and 1082 cm−1, respec-
After loading of monometallic system such as Fe, Co tively.41 This shift is attributed to the incorporation of
and Mn onto the surface of mesoporous Al2O3−MCM- Al2O3 into SiO2 matrix in MCM-41. The increase in the
41, the surface area decreases as compared to pure mean Si−O distances in the walls is caused by the sub-
Al2O3−MCM-41. This is because blocking of the stitution of small size Si4+ (rSi = 40 pm) by the large
4+
mesopore network by the metal. Bimetallic systems, aluminium ion (rAl = 53.5 pm).42 The absorption
3+
Co-Fe, Fe-Mn and Mn-Co incorporated Al2O3−MCM- band at 967 cm−1 (MCM-41) decreases to 961 cm−1
41 materials show much less surface area as compared (Al2O3−MCM-41), which is assigned to the stretch-
to monometallic@Al2O3−MCM-41. The pore blocking ing vibration of unsubstituted −Si−O−Si− and Al2O3-
Figure 6. Pore size distributions of Fe-Mn@Al2O3−
MCM-41, Co-Fe@Al2O3−MCM-41 Fe@Al2O3−MCM-41,
Co@Al2O3−MCM-41, Mn@Al2O3−MCM-41 and Mn-
Co@Al2O3−MCM-41 materials.
Figure 7. FTIR spectra of MCM-41 and Al2O3−MCM-41
samples.
Table 1. Textural properties of Al2O3, MCM-41, Al2O3−MCM-41, monometallic
@Al2O3−MCM-41 and bimetallic@Al2O3−MCM-41 materials measured by
BET method.
Surface area
(m2/g)
Pore volume
(cm3/g)
Samples
Pore diameter (nm)
Al2O3
MCM-41
268
800
870
379
321
308
300
275
265
0.67
1.10
1.78
0.96
0.95
0.94
0.93
0.85
0.79
3.6
2.2
2.1
2.2
2.2
2.2
2.3
2.3
2.3
Al2O3−MCM-41
Fe@Al2O3−MCM-41
Co@Al2O3−MCM-41
Mn@Al2O3−MCM-41
Co-Fe@Al2O3−MCM-41
Mn-Co@Al2O3−MCM-41
Fe-Mn@Al2O3−MCM-41

Amaresh C Pradhan et al.
incorporated −Si−O−Si− (−Si−O−Al−), respectively. of intensity of this band in Figure 8 are attributed
This is generally considered as a proof for the incor- to the loading of mono and bimetallic systems onto
poration of heteroatom into MCM-41.41 The absorption Al2O3−MCM-41 framework.40 The bands observed at
bands at 1057 and 1225 cm−1 are typically from the 796 cm−1 and 460 cm−1 are assigned to the symmet-
asymmetric stretching vibrations of Si–O–Si bridges, ric stretching vibration of T−O−T unit (T= Si, Al,
for both MCM-41 and Al2O3−MCM-41.43 When Al2O3 Fe, Co, Mn, Co-Fe, Fe-Mn and Mn-Co).44 This is also
is incorporated in MCM-41, small shifts are observed an evidence for loading and formation of mono and
in the vibrational bands from 801 to 795 cm−1 and 464 bimetallic oxides within Al2O3−MCM-41 framework.
to 460 cm−1 (Figure 7). These shifts provide evidence The full FTIR spectrum of mesoporous alumina is pre-
for the incorporation of Al2O3 into MCM-41.40
sented in Supplementary Information (Figure S1). The
The FTIR spectra of mono and bimetallic@Al2O3− peak at 1400 cm−1 is due to Al–OH species in the meso-
MCM-41 are presented in the Figure 8. The band porous Al2O3. The shoulder at 909 cm−1 is assigned to
at 1640 cm−1 is attributed to the bending mode of tetrahedral AlO4 units while the peaks in the region
water present in all the samples. The two broad 530–620 cm−1 are identified as octahedral AlO6 unit.34
vibrational bands at 1028 and 1232 cm−1 are due to These peak positions have changed due to the loading
asymmetric stretching vibrations of –Si–O–Si– bridges of metallic species as discussed above.
present in mono and bimetallic@Al2O3−MCM-41
systems.43 Moreover, the −Si–O–Si− vibrational bands
3.4 Microscopy studies
in pure MCM-41 (1089 cm−1) and Al2O3−MCM-41
The FESEM image gives an account of surface mor-
(1082 cm−1) have been shifted to lower values in mono
phology of the materials. The FESEM pictures of the
and bimetallic@Al2O3−MCM-41 systems. This occurs
Co@Al2O3−MCM-41, Fe@Al2O3−MCM-41 and Co-
because there is an increase in mean Si–O distance
Fe@Al2O3−MCM-41 are shown in Figure 9. These
in the walls caused by the loading of metallic ions of
micrographs reveal that the materials have spongy
larger radius. The remnant vibrational band at 975 cm−1
nature consisting of small particles and appear to be
is assigned to the stretching vibration of −Si−O−M
mesoporous in nature.
or M−Si−M (M = Al, Fe, Co, Mn, Co-Fe, Fe-Mn
The energy dispersive X-ray (EDX) spectroscopy
and Mn-Co).44 The Al, Fe, Co, Mn, Co-Fe, Fe-Mn
was used to characterize the surface composition of
and Mn-Co coordinate with Si atom through oxygen
the Co-Fe@Al2O3−MCM-41 (Figure 10(a)). The peak
atom formed oxide composite. The weak vibrational
intensities of elements show that the composite Co-
band at 975 cm−1 in metal loaded systems is the same
Fe@Al2O3−MCM-41 contains high amount of Si and
Al and less amounts of Co and Fe. Figure 10(b) demon-
strates the EDX mapping analysis of Co-Fe@Al2O3−
MCM-41. As seen from Figure 10(b), the high distribution
of Si and Al elements was homogeneous and spread
on the whole surface of the Co-Fe@Al2O3−MCM-41,
indicating that the composite contains high amount of
Si. The less distribution of Al as compared to Si is
also detected which is consistent with the experimen-
tal procedure. In addition, the elements of Co and Fe
are distributed very less as compared to Si and Al,
revealing that percentage of Co and Fe are less in the
composite. The amount of Co and Fe is very less but
they formed respective oxides by combining with oxy-
gen. The formation of metal oxides has been proved
by the presence of O in EDX mapping. Thus, the
EDX spectrum and EDX mapping depict the presence
and distribution of elements in particular surface of
Co-Fe@Al2O3−MCM-41.
as the relatively intense vibrational band at 967 cm−1
in pure MCM-41 (Figure 7). The blue shift and loss
The representative HRTEM micrographs of MCM-
41 and Al2O3–MCM-41 are shown in Figure 11. The
mesoporous silica exhibited highly ordered hexagonal
array of pore structure of typical MCM-41, which is
clearly shown in the Figures 11(a) and (b). The SAED
Figure 8. FTIR spectra. (a) Fe@Al2O3−MCM-41, (b)
Co@Al2O3−MCM-41, (c) Mn@Al2O3−MCM-41, (d) Co-
Fe@Al2O3−MCM-41, (e) Fe-Mn@Al2O3−MCM-41, and
(f) Mn-Co@Al2O3−MCM-41 materials.

Sol-gel-cum-hydrothermal synthesis
Figure 9. FESEM micrographs of (a) Co@Al2O3−MCM-41, (b) Fe@Al2
O3−MCM-41 and (C) Co-Fe@Al2O3−MCM-41 materials.
presence of oleic acid at moderate temperatures.45 The
oleic acid has good ability and higher affinity to bind
with the surface of the metal oxide nanoparticles. The
high binding ability is due to the optimum hydrophilic-
ity and predominant hydrophobicity.46
image (Figure 11(c)) shows the amorphous nature of
MCM-41. The HRTEM micrographs of Al2O3–MCM-
41 also show similar well-ordered hexagonal pores
which are shown in Figure 11(d) and 11(e). The
amorphous nature of Al2O3–MCM-41 is shown in the
SAED image (Figure 11(f)). The in situ incorpora-
tion of Al2O3 into the MCM-41 matrix, did not affect
the orders of hexagonal pores and amorphous nature
of Al2O3–MCM-41. The sustainability of amorphous
nature in Al2O3–MCM-41 is due to the presence of very
less amount of crystalline Al2O3 in highly amorphous
MCM-41 matrix.
The low resolution TEM images of Co@Al2O3−
MCM-41, Fe@Al2O3−MCM-41 and Co- Fe@Al2O3−
MCM-41 are shown in Figures 12(a) to (c). These
pictures confirm that the metal particles in the form of
oxide are well dispersed on Al2O3−MCM-41 matrix.
The metal particles of 4 nm size are seen clearly in the
high resolution TEM image of Co-Fe@Al2O3−MCM-
41 material in Figure 12(d). These particles are in inti-
mate contact with the Al2O3−MCM-41 matrix through
oxygen atoms. The formation of mono and bimetal-
lic nanoparticles into the mesoporous Al2O3−MCM-
41 matrix is due to decomposition metal precursor in
presence of oleic acid at 120◦C. It has been observed
that the nucleation and growth of the metal nanoparti-
cles can occur when metal precursor decomposes in the
3.5 29Si MAS NMR Study
The 29Si MAS NMR spectra of mesoporous materials
such as MCM-41, Al2O3−MCM-41 and Co-Fe@Al2
O3−MCM-41 are shown in Figure 13(a)–(c), respectively.
For pure MCM-41, the broad peak around −110, −100
and −91 ppm attributed to Q4 corresponds to Si (OSi)4,
Q3 corresponds to (SiO)3 Si OH and Q2 corresponds to
(SiO)2 Si (OH)2, respectively. But in Al2O3−MCM-41
(Figure 13(b)) the intense peak is observed having peak
intensity at −106, −97 and −88 which correspond to
Q4, Q3 and Q2, respectively. The downfield shift indi-
cates that the Al atom is coordinated/replaced by the
Si atom in the extra-framework of the MCM-41. The
29Si MAS NMR spectrum of Co-Fe@Al2O3−MCM-
41 is shown in the Figure 13(c). The huge downfield
shift of two peaks are observed at −87 (Q4) and −76
(Q3) which is due to the coordination of Co and Fe
atoms to the Al atom through oxygen or replacement
of Si atoms by Co and Fe atoms. This phenomenon
proves the formation of mono and bimetallic oxides

Amaresh C Pradhan et al.
Figure 10. (a) The energy dispersive X-ray (EDX) spectrum of Co-Fe@Al2O3−MCM-41; (b) EDX
mapping analysis of the Co-Fe@Al2O3−MCM-41.
and combines with Al2O2 and SiO2 (MCM-41) within has equal numbers of positively and negatively charged
composite.
species then the pH at that point is called point of zero
charge (pHpzc).47 Above and below pHpzc, the oxide sur-
face is expected to have net surface charge and promote
adsorption processes. We have studied the effect of pH
on the adsorption activity of Co-Fe@Al2O3−MCM-
41. The adsorption of methylene blue on 0.02 g
of Co-Fe@Al2O3−MCM-41 has been monitored in
dark under different pH conditions. The absorbance
of the methylene blue solution was measured after
3 h of its exposure to Co-Fe@Al2O3−MCM-41 and
shown in Figure 14. It was observed that adsorption
of methylene blue on Co-Fe@Al2O3−MCM-41 is
highly favourable at higher pH values. The most
efficient adsorption occurred at pH = 10 which is
3.6 Adsorption studies
3.6a Effect of pH: The pH is the most important
factor affecting the adsorption process. When the sur-
faces of oxide materials containing under-coordinated
surface ions come in contact with aqueous environ-
ment, their chemical nature strongly depends on the pH
of the aqueous phase. They can undergo surface com-
plexation leading to the formation of chemical bonds
with water molecules and other adsorbate molecules.
The surfaces can undergo protonation and deprotona-
tion in aqueous solutions, affecting the surface charge
which is controlled by the pH of the aqueous solution. due to the surface charge and generation of surface
The surface charge of an oxide material can be positive hydroxyl group in the material. The measured pHpzc
or negative depending on the pH. If the oxide surface value of Co-Fe@Al2O3−MCM-41 sample is 3.0 which

Sol-gel-cum-hydrothermal synthesis
Figure 11. HRTEM images of, (a) honeycomb structure, (b) well-ordered mesoporosity
and (c) SAED pattern of MCM-41; HRTEM images of, (d) mesoporous structure, (e) well-
ordered nature and (f) SAED pattern of Al2O3–MCM-41.
Figure 12. TEM images of, (a) Co@Al2O3−MCM-41, (b) Fe@Al2O3−
MCM-41, (c) Co-Fe@Al2O3−MCM-41, (d) HRTEM image of Co-Fe@Al2
O3−MCM-41 materials.
means the surface is uncharged at pH = 3. Above hydroxyl site of Co-Fe@Al2O3−MCM-41 under-
this pH value, the surface of Co-Fe@Al2O3−MCM- goes protonation/deprotonation.48 So the attraction of
41 is expected to be negatively charged and favour cationic MB molecules towards the negative charge sur-
methylene blue adsorption through coulombic inter- face of Co-Fe@Al2O3−MCM-41 will be more at pH =
actions. The gradual development of negative charges 10. Hence, adsorption of MB is favorable at pH = 10.
at higher pH is due to the generation of the sur- The methylene blue adsorption decreases gradually from
face hydroxyl group. In aqueous solution, the surface pH = 10 to pH = 2. This is attributed to the presence

Amaresh C Pradhan et al.
Figure 13. 29Si MAS NMR spectra of, (a) MCM-41, (b) Al2O3−MCM-41 and (C) Co-Fe@Al2O3− MCM-41.
of excess H+ ions competing with cationic group of
the methylene blue. The percentage of methylene blue
adsorbed on the surface of Co-Fe@Al2O3−MCM-41 as
a function of pH is presented in Supplementary Infor-
mation (Figure S2). The graph shows that the percent-
age of methylene blue adsorbed increases with pH of
the cationic dye solution which correlates well with
negatively charged Co-Fe@Al2O3−MCM-41 material.
As methylene blue (MB) adsorbed efficiently at pH =
10, hence the MB degradation occurred at optimum
condition of pH at 10.
out in darkness for 3 h by stirring and the supernatant
solution was then analysed by UV-Vis spectroscopy.
The UV-Vis absorption spectra of the supernatant solu-
tions after methylene blue adsorption by adsorbent are
presented in Figure 15. The 100 mg/L pure methylene
blue solution shows characteristic absorbance peaks
at 664, 615, 292 and 246 nm. The absorbance of
the methylene blue solution decreases when treated
with different adsorbents under the same experimental
conditions. Methylene blue solution (after adsorption)
shows the least absorbance with Co-Fe@Al2O3−MCM-
41 when compared to other adsorbents. Therefore,
Co-Fe@Al2O3−MCM-41 is a very effective adsor-
bent which can be attributed its high surface area
(300 m2g−1) and compatible nature of Co-Fe@Al2O3−
MCM-41 framework. High surface area of Co-Fe@Al2
O3−MCM-41 material offers more active sites which
results increase of MB adsorption. Further, the load-
ing of Al, Fe and Co during synthesis of Co-Fe@Al2
O3−MCM-41, the Si atoms are coordinated/substituted
3.6b Adsorption on different adsorbents: It has been
observed that the maximum amount of MB adsorp-
tion occurred at pH = 10. Hence, the adsorption of
MB on different adsorbents were carried out at pH =
10. The other optimum parameters such as methylene
blue concentration (100 mg/L) and adsorbent amount
(0.02 g in 20 mL of MB solution) were taken for this
study. The adsorption of methylene blue was carried

Sol-gel-cum-hydrothermal synthesis
Scheme 1. Hydrogen bond formation between Co-Fe@Al2
O3–MCM-41 and methylene blue.
hydroxyl group in metal oxide system.49 It has also
been reported that surface hydroxyl group offers a neg-
atively charged surface.50 Hence, the surface charge
of Co-Fe@Al2O3−MCM-41 may be more negative
Figure 14. UV-Vis absorption spectra showing the influ-
ence of pH on the adsorption of methylene blue on the sur-
face of Co-Fe@Al2O3−MCM-41. The pH of the methylene
blue solution is varied from 2 to 10. The adsorption pro-
cess was carried out for 3 h in dark using 100 mg/L methy- which is due to the coordination of more hydroxyl
lene blue solution and 0.02 g of Co-Fe@Al2O3−MCM-41
groups with different metal centres such as Co, Fe,
Al and Si at pH = 10. The more negative charge
material.
surface of Co-Fe@Al2O3−MCM-41 could more effi-
ciently adsorb MB as compared to other adsorbents.
Moreover, the strong interaction of methylene blue and
Co-Fe@Al2O3−MCM-41 through hydrogen bonding
can also improve the adsorption ability. Furthermore,
the molecular volume of methylene blue is 0.4 nm ×
0.61 nm × 1.43 nm which is compactable with pore
diameter of 2.5 nm and pore volume of 0.9670 cm3 g−1
in Co-Fe@Al2O3−MCM-41. Thus, methylene blue
molecule can be accommodated easily into the frame-
work of Co-Fe@Al2O3−MCM-41.
Although monometallic@Al2O3−MCM-41 materi-
als have high surface area as compared to Co-Fe@Al2
O3−MCM-41, their adsorption capacity of methylene
blue is limited which may be due to the generation of
less hydroxyl group and minimal hydrogen bonding
ability. Among the bimetallic systems, Co-Fe@Al2O3−
Figure 15. UV-Vis spectra of the solutions recorded after
MCM-41 shows higher ability for methylene blue
methylene blue adsorption on different adsorbent materials
adsorption compared to other bimetallic systems which
can be attributed to the differences in surface areas. The
for 3 h in dark at pH=10. The concentration of the methy-
lene blue solution used is 100 mg/L and the amount of adsor-
bent taken for each experiment is 0.02 g. The decrease in adsorption of methylene blue in bimetallic@Al2O3−
the absorbance of solution is a measure of the removal of
methylene blue by adsorption process.
MCM-41 system follows the order, Co-Fe@Al2O3−
MCM-41>Mn-Fe@Al2O3−MCM-41>Co−Mn@Al2
O3−MCM-41. It is to be noted that the surface area of
by Al, Fe and Co through oxygen atom. This pro- mesoporous Al2O3 is nearly similar the surface areas of
cess helps to generate surface hydroxyl groups. The mono and bimetallic@Al2O3–MCM-41 materials and
surface hydroxyl groups of Co-Fe@Al2O3−MCM-41 adsorption capacity is less compared to metal@Al2O3–
may increase the tendency to form hydrogen bonding MCM-41 materials. This is due to the absence of more
with the lone pair electrons of N atom of methylene metal onto the Al2O3–MCM-41 matrix. The absence of
blue, as shown in Scheme 1. It has been noted that metal onto the Al2O3–MCM-41 may not produce more
alkaline medium favours high production of surface surface hydroxyl group like bimetallic systems. This

Amaresh C Pradhan et al.
may also lead to less hydrogen bonding towards N
centre of MB molecule. Hence, presence of metal
onto the surface of Al2O3–MCM-41 matrix has vital
contribution for adsorption of methylene blue.
3.6c Proof of methylene blue adsorption: The FTIR
spectra of pure methylene blue, methylene blue
adsorbed on Co-Fe@Al2O3−MCM-41 and neat Co-
Fe@Al2O3−MCM-41 are shown in the Figures 16(a)–
(c), respectively. For pure methylene blue, two peaks
appear at 2816, 2720 cm−1 which represent the stretch-
ing vibration of −CH− aromatic and –CH3 methyl
groups. The spectra ranging from 1591 to 1363 cm−1,
are assigned to the aromatic ring structures in methy-
lene blue.51 The peak at 1170 cm−1 is related to the
C=C skeleton of the aromatic rings. Figure 16(b)
shows strong signature of methylene blue indicating
the adsorption of methylene blue on the surface of
Co-Fe@Al2O3−MCM-41. The IR spectrum of Co-
Fe@Al2O3−MCM-41 without adsorbed dye molecules
is shown Figure 16(c) for comparison. The Figure 16(d)
shows the adsorption of methylene blue Co-Fe@Al2O3−
MCM-41 leading to colourless solution at pH = 10. It
should be pointed out that removal of methylene blue
can also be promoted by high surface area (300 m2/g),
pore diameter (2.5 nm) and pore volume (0.967 cm3/g)
of Co-Fe@Al2O3−MCM-41 material. The molecu-
lar dimensions of cationic methylene blue (0.4 nm ×
0.61 nm × 1.43 nm) are of the order of pore diame-
ter of Co-Fe@Al2O3−MCM-41 and the molecule can
be accommodated in the pores very well as shown
schematically in Figure 17.
Figure 17. Schematic pathways of methylene blue adsorp-
tion on Co-Fe@Al2O3−MCM-41.
material as a function of amount of adsorbent
(Figure 18). The amount of methylene blue adsorbed
at room temperature has been estimated from UV-Vis
absorption spectra of the solutions. The results show
that maximum methylene blue adsorption occurs on
0.02 g of Co-Fe@Al2O3−MCM-41. Further increase
of adsorbent dose does not have much impact on the
amount of dye adsorbed.
3.6e Recovery and recyclability study of adsor-
bent: It was difficult to recover quantitatively the
adsorbed methylene blue on the surface of Co-Fe@
Al2O3−MCM-41. It has been reported in the Material
Safety Data Sheet (ISO9001:2000 Certified) that the
melting point of methylene blue is 100◦C. The methy-
lene blue will decompose above 100◦C. Methylene blue
is removed from the surface of Co-Fe@Al2O3−MCM-
3.6d Effect of adsorbent dose: We have further stud- 41 by heating at 180◦C for 3 h. The recyclability study
ied the adsorption capacity of Co-Fe@Al2O3−MCM-41 was performed to know the stability of the adsorbent
Figure 16. FTIR spectra of (a) pure methylene blue, (b) methylene blue adsorbed on
Co-Fe@Al2O3−MCM-41 in comparison with (c) Co-Fe@Al2O3−MCM-41 material;
(d) colour change after adsorption of methylene blue dye (100 mg/L) using 0.02 g of
Co-Fe@Al2O3−MCM-41 at pH = 10.

Sol-gel-cum-hydrothermal synthesis
material which was recovered after Run 2. The results
(Figure 19) show that there is marginal decrease in the
adsorption of MB in recovered Co-Fe@Al2O3−MCM-
41 adsorbent. This indicates that there may not be
change of textural properties like surface area, pore
size and pore volume. The textural properties may not
change effictively by heating at 180◦C for 3 h because
the Co-Fe@Al2O3−MCM-41 wass stabilied by calcin-
ing with 600◦C for 6 h at the time of synthesis.
4. Conclusions
In this study, we have highlighted a novel sol-gel-cum-
hydrothermal method to fabricate mesoporous mono
and bimetallic@Al2O3−MCM-41 materials. Oleic acid
acts as a capping agent for the synthesis of mono
and bimetallic oxide nanoparticles onto mesoporous
Al2O3−MCM-41 material. These materials were found
to be very efficient in removing methylene blue from
aqueous solutions at pH = 10. Framework meso-
porosity, high surface area, appropriate pore diam-
eter and presence of metal nanoparticles are the
key factors for high adsorption of methylene blue.
The mesoporous Co-Fe@Al2O3−MCM-41 is identi-
fied as the best adsorbent for methylene blue removal.
Quantitatively, 0.02 g of mesoporous bimetallic Co-
Fe@Al2O3−MCM-41 is sufficient to remove cationic
methylene blue dye (100 mg/L) in 20 mL solution.
Figure 18. Adsorption capacity of Co-Fe@Al2O3−MCM-
41 adsorbent as a function of its amount using 20 mL of
methylene blue solution (100 mg/L) in each experiment.
Co-Fe@Al2O3−MCM-41. The recyclability of Co-Fe
@Al2O3−MCM-41 was investigated after removal of
adsorbed methylene blue on the surface Co-Fe@Al2
O3−MCM-41 (after heating at 180◦C for 3 h). The
adsorption process was performed for three runs. The
Run 1 was performed on the parent material (Co-Fe@
Al2O3−MCM-41) which is showing 100% adsorption
shown in the Figure 19. The Co-Fe@Al2O3−MCM-41
which was used in Run 1 was recovered by removing
the MB at180◦C for 3 h. The recovered Co-Fe@Al2O3−
MCM-41 was used for methylene blue adsorption (Run
2) in similar conditions. Run 3 was performed on the
Supplementary Information (SI)
Additional information pertaining to FTIR spectrum
(Figure S1) and methylene blue adsorbed (%) on Co-
Fe@Al2O3−MCM-41 material (Figure S2) are given in the
Supporting Information, which is available at www.ias.ac.
in/chemsci.
Acknowledgements
Amaresh Chandra Pradhan thanks IIT Madras for Post-
doctoral Fellowship. The instrumental facilities established
under the FIST Scheme of SERC division of DST, Ministry
of Science and Technology, New Delhi, have been very help-
ful to carry out this work. Mr. A. Narayanan and Mrs. S.
Srividya carried out BET and XRD measurements.
References
Figure 19. Recycling studies of methylene blue by using
Co-Fe@Al2O3−MCM-41 as adsorbent. The adsorption pro-
cess is carried out for 3 h in dark using methylene blue solu-
tion (100 mg/L) and 0.02 g of Co-Fe@Al2O3−MCM-41. See
text for details.
1. Tan K B, Vakili M, Horri B A, Poh P E, Abdullah A Z
and Salamatinia B 2015 Adsorption of dyes by nano-
materials: Recent developments and adsorption mecha-
nisms Sep. Purif. Technol. 150 229

Amaresh C Pradhan et al.
2. Dias E M and Petit C 2015 Towards the use of
Enhanced Photocatalytic Properties by Band Alignment
Investigations J. Phys. Chem. C 117 22098
18. Jain A, Lodha S, Punjabi P B, Sharma V K and Ameta S
C 2009 A study of catalytic behaviour of aromatic addi-
tives on the photo–Fenton degradation of phenol red J.
Chem. Sci. 121 1027
19. Tian S, Zhang J, Chen J., Kong L, Lu J, Ding F
and Xiong Y 2013 Fe2(MoO4)3 as an Effective Photo-
Fenton-like Catalyst for the Degradation of Anionic and
Cationic Dyes in a Wide pH Range Ind. Eng. Chem. Res.
52 13333
20. Parida K M and Pradhan A C 2010 Fe/meso-Al2O3:
An Efficient Photo-Fenton Catalyst for the Adsorptive
Degradation of Phenol Ind. Eng. Chem. Res. 49 8310
21. Pradhan A C and Parida K M 2012 Facile synthesis
of mesoporous composite Fe/Al2O3–MCM-41: An effi-
cient adsorbent/catalyst for swift removal of methylene
blue and mixed dyes J. Mater. Chem. 22 7567
22. Hsu C A, Wen T N, Su Y C, Jiang Z B, Chen C W
and Shyur L F 2012 Biological Degradation of Anthro-
quinone and Azo Dyes by a Novel Laccase from Lenti-
nus sp Environ. Sci. Technol. 46 5109
23. Swathi R S and Sebastian K L 2012 Excitation energy
transfer from dye molecules to doped graphene J. Chem.
Sci. 124 233
24. Bi H, Xie X Yin K, Zhou Y, Wan S, He L, Xu F,
Banhart F, Sun L and Ruoff R S 2012 Spongy Graphene
as a Highly Efficient and Recyclable Sorbent for Oils
and Organic Solvents Adv Funct. Mater. 22 4421
25. Ramesha G K, Kumara A V, Muralidhara H B and
Sampath S 2011 Graphene and graphene oxide as effec-
tive adsorbents toward anionic and cationic dyes J.
Colloid Interface Sci. 361 270
26. Chowdhury S and Balasubramanian R 2014 Recent
advances in the use of graphene-family nanoadsorbents
for removal of toxic pollutants from wastewater Adv.
Colloid Interface Sci. 204 35
27. Jiang S -D, Tang G, Ma Y F, Hu Y and Song L
2015 Synthesis of nitrogen-doped graphene−ZnS quan-
tum dots composites with highly efficient visible light
photodegradation Mater. Chem. Phys. 151 34
28. Lam K F, Yeung K L and Mckay G 2007 Selective
mesoporous adsorbents for Cr2O2− and Cu2+ separation
Microporous Mesoporous Mater.7100 191
29. Chen X, Lam K F, Zhang Q, Pan B, Arruebo M and
Yeung K L 2009 Synthesis of Highly Selective Magnetic
Mesoporous Adsorbent J. Phys. Chem. C 113 9804
30. Pelekani C and Snoeyink V L 2000 Competitive adsorp-
tion between atrazine and methylene blue on activated
carbon: The importance of pore size distribution Carbon
38 1423
31. Eftekhari S, Habibi-Yangjeh A and Sohrabnezhad S
2010 Application of AlMCM-41 for competitive adsorp-
tion of methylene blue and Rhodamine B: Thermody-
namic and kinetic studies J. Hazard. Mater. 178 349
32. Nguyen T B Hwang M J and Ryu K–S 2012 High
adsorption capacity of V-doped TiO2 for decolorization
of methylene blue Appl. Surf. Sci. 258 7299
metal–organic frameworks for water reuse: A review of
the recent advances in the field of organic pollutants
removal and degradation and the next steps in the field
J. Mater. Chem. A 3 22484
3. Khin M M, Nair A S, Babu V J, Murugan R and
Ramakrishna S 2012 A review on nanomaterials for
environmental remediation Energy Environ. Sci. 5 8075
4. Yusuf M, Elfghi F M, Zaidi S A, Abdullah E C and
Khan M A 2015 Applications of graphene and its deriva-
tives as an adsorbent for heavy metal and dye removal:
A systematic and comprehensive overview RSC Adv.
5 50392
5. Bonakala S and Balasubramanian S 2015 Modelling
Gas Adsorption in Porous Solids: Roles of Surface
Chemistry and Pore Architecture J. Chem. Sci. 127 1687
6. Huang C–H, Chang K–P, Oua H–D, Chiang Y–C
and Wanga C–F 2011 Adsorption of cationic dyes
onto mesoporous silica Microporous Mesoporous Mater.
141 102
7. Bhaumik A 2002 Mesoporous titanium phosphates and
related molecular sieves: Synthesis, characterization and
applications J. Chem. Sci. 114 451
8. Sui Z–Y, Cui Y, Zhu J–H and Han B–H
2013 Preparation of Three-Dimensional Graphene
Oxide−Polyethylenimine Porous Materials as Dye and
Gas Adsorbents ACS Appl. Mater. Interfaces 5 9172
9. He X, Male K B, Nesterenko P N, Brabazon D, Paull
B and Luong J H T 2013 Adsorption and Desorption
of Methylene Blue on Porous Carbon Monoliths and
Nanocrystalline Cellulose ACS Appl. Mater. Interfaces
5 8796
10. Ma J, Yu F, Zhou L, Jin L, Yang M, Luan J, Tang Y,
Fan H, Yuan Z and Chen J 2012 Enhanced Adsorptive
Removal of Methyl Orange and Methylene Blue from
Aqueous Solution by Alkali-Activated Multiwalled Car-
bon Nanotubes ACS Appl. Mater. Interfaces 4 5749
11. Han B, Zhanga F, Fenga Z, Liub S, Denga S, Wanga
Y and Wanga Y 2014 A designed Mn2O3/MCM-
41 nanoporous composite for methyleneblue and rho-
damine B removal with high efficiency Ceram. Int.
40 8093
12. Yagub M T, Sen T K, Afroze S and Ang H M 2014 Dye
and its removal from aqueous solution by adsorption: A
review Adv. Colloid Interface Sci. 209 172
13. Jyothi D, Deshpande
P
A, Venugopal
B
R,
Chandrasekaran S and Madras G 2012 Transition
metal oxide loaded MCM catalysts for photocatalytic
degradation of dyes J. Chem. Sci. 124 385
14. Merka O, Yarovyi V, Bahnemann D W and Wark
M 2011 pH-Control of the Photocatalytic Degradation
Mechanism of Rhodamine B over Pb3Nb4O13 J. Phys.
Chem. C 115 8014
15. Zhou X, Yang H, Wang C, Mao X, Wang Y, Yang Y and
Liu G 2010 Visible Light Induced Photocatalytic Degra-
dation of Rhodamine B on One-Dimensional Iron Oxide
Particles J. Phys. Chem. C 114 17051
16. Guo B, Shen H, Shu K, Zeng Y and Ning W 2009
The study of the relationship between pore structure and
photocatalysis of mesoporous TiO2 J. Chem. Sci. 121 317
17. Uddin M T, Nicolas Y, Olivier C, Toupance T, Muiller 33. Gutierrez-Alejandre A, Larrubia M A, Ramirez J and
M M, Kleebe H J, Rachut K, Ziegler J, Klein A and
Jaegermann W 2013 Preparation of RuO2/TiO2 Meso-
porous Heterostructures and Rationalization of Their
Busca G 2006 FT-IR evidence of the interaction of ben-
zothiophene with the hydroxyl groups of H-MFI and
H-MOR zeolites Vib. Spectrosc. 41 42

Sol-gel-cum-hydrothermal synthesis
34. Parida K M, Pradhan A C, Das J and Sahu N 2009 43. Selvaraj M, Sinha P K, Lee K, Ahn I, Pandurangan
Synthesis and characterization of nano-sized porous
gamma-alumina by control precipitation method Mater.
Chem. Phys. 113 244
A and Lee T G 2005 Synthesis and characterization
of Mn–MCM-41 and Zr–Mn-MCM-41 Microporous
Mesoporous Mater. 78 139
35. Guthrie C P and Reardon E J 2008 Metastability of 44. Atchudan R, Pandurangan A and Joo J 2013 Synthesis of
MCM-41 and Al-MCM-41 J. Phys. Chem. A 112 3386
36. Konovalova T A, Gao Y, Schad R and Kispert L D 2001
Photooxidation of Carotenoids in Mesoporous MCM-
multilayer graphene balls on mesoporous Co-MCM-41
molecular sieves by chemical vapour deposition method
Microporous Mesoporous Mater. 175 161
41, Ni-MCM-41 and Al-MCM-41 Molecular Sieves J. 45. Moya C, Batlle X and Labarta A 2015 The effect of oleic
Phys. Chem. B 105 7459
37. Li S, Xu Q, Chen J and Guo Y 2008 Study and
acid on the synthesis of Fe3−xO4 nanoparticles over a
wide size range Phys. Chem. Chem. Phys. 17 27373
Characterization of Al-MCM-41 Prepared with the 46. Arulmozhi K T and Mythili N 2013 Studies on the
Assistance of Supercritical CO2 Ind. Eng. Chem. Res.
47 8211
38. Brunaure S, Deming L S, Deming W E and Teller E
chemical synthesis and characterization of lead oxide
nanoparticles with different organic capping agents AIP
Adv. 122122 1
1940 On a Theory of the van der Waals Adsorption of 47. Churchill H, Teng H and Hazen R M 2004 Correla-
Gases J. Am. Chem. Soc. 62 723
39. Tanev P T and Pinnavaia T J 1996 Mesoporous Silica
Molecular Sieves Prepared by Ionic and Neutral Surfac-
tion of pH-dependent surface interaction forces to amino
acid adsorption: Implications for the origin of life Am.
Mineral. 89 1048
tant Templating: A Comparison of Physical Properties 48. Hu Q H, Qiao S Z, Haghseresht F, Wilson M A and Lu
Chem. Mater. 8 2068
40. Goyne K W, Zimmerman A R, Newalkar B L, Komar-
G Q 2006 Adsorption Study for Removal of Basic Red
Dye Using Bentonite Ind. Eng. Chem. Res. 45 733
neni S, Brantley S L and Chorover J 2002 Surface 49. Sengupta A K 2016 In Ion Exchange and Solvent
Charge of Variable Porosity Al2O3(s) and SiO2(s)
Adsorbents J. Porous Mater. 9 243
41. Selvaraj M and Pandurangan A 2004 Compari- 50. Papirer E 2000 In Adsorption on Silica Surfaces (New
Extraction: A Series of Advances (Boca Raton: CRC
Press) vol. 22 p. 178
son of Mesoporous Zn-Al-MCM-41 and Al-MCM-
York: CRC Press) vol. 90 p. 442
41Molecular Sieves in the Production of p-Cymene by 51. Lau Y–Y, Wong Y–S, Teng T–T, Morad N M and
Isopropylation of Toluene Ind. Eng. Chem. Res. 43 2399
42. Greenwood N N and Earnshaw A 1998 In Chemistry of
the Elements (UK: Reed Educational and Professional
Publishing) p.1341
Rafatullah S–A O 2015 Degradation of cationic and
anionic dyes in coagulation–flocculation process using
bi-functionalized silica hybrid with aluminum-ferric as
auxiliary agent RSC Adv. 5 34206