Online version is available on http://research.guilan.ac.ir/csm
CSM
Chemistry of Solid Materials
Vol. 2 No. 1 2014
[Research]
Synthesis and characterization of amine functionalized mesoporous
magnetite nanoparticles having environmental applications
M. Khabazipour
1
, Sh. Shariati*2
1
MSc
Student, Department of Chemistry, Islamic Azad University, Rasht Branch, Rasht,
Iran.
2
Associate Professor, Department of Chemistry, Islamic Azad University, Rasht Branch,
Rasht, Iran.
* Corresponding author’s E-mail: Shariaty@iaurasht.ac.ir
Article history:
(Received: 10 Jun 2014, Revised: 9 Aug 2014, Accepted: 16 Aug 2014)
ABSTRACT
In this study, amino functional groups were chemically bonded to the surface of newly
synthesized KIT-6 mesoporous magnetite nanoparticles (MMNPs) by post-toluene reflux
synthesis method. This method treats calcined mesoporous nanoparticles with the functional
organosilanes. Physical and chemical structures of the synthesized mesoporous magnetite
nanoparticles were characterized by scanning electron microscopy (SEM), powder X-ray
diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and nitrogen adsorption-
desorption isotherms. Finally, the ability of the newly synthesized aminated mesoporous
magnetite nanoparticles as a novel and recoverable sorbent with environmental applications was
examined by studying the removal of dichromate ions from aqueous samples.
Keywords: KIT-6, Mesoporous magnetite nanoparticles, Amine functionalized
1. INTRODUCTION
Various methods for water refinement
have been developed and used.
Adsorption is one of these methods,
which is a fast, inexpensive and widely
applicable technique [1]. Mesoporous
materials are very attractive for
separation and adsorption processes
due to their high specific surface area,
large pore volume, regular structure,
uniform pore size distribution and
relatively high thermal stability [2].
Mesoporous silica materials like
MCM-n, SBA-n and Kit are fairly new
types of material that have pores in the
mesoscopic range of 2–50 nm. The
synthesis of magnetite nanoparticles
coated with mesoporous silica leads to
an improvement in the surface area and
in the textural properties of the
magnetite nanoparticles which in turn,
provides more stable supports for
various organic and inorganic species.
Many efforts have been made to
prepare metal-fill in mesoporous
through post-synthesis grafting
procedures or direct synthesis [3].
However, it is very difficult to
introduce the metal ions into
mesoporous directly due to the facile
dissociation of metal-O-Si bonds under
strong acidic hydrothermal conditions
[4-7]. Most of the works have been
focused on the post-synthesis method.
But the post-synthesis method always
forms metal oxides in the channels or M. Khabazipour, Sh. Shariati /CSM Vol.2 No.1, 2014 pp.11-19
12
external surface of the support, which
would block the channels and not allow
the reactants to access all the reaction
sites in the porous matrix [8-10].
Here, we report a simple and effective
procedure for successful preparation of
mesoprous KIT-6 magnetite nano-
particles with high surface area. For the
surface modification of KIT-6 coated
magnetite with an NH2 linker,
aminopropyltriethoxysilane (APTES)
was used as the surface modification
agent. Surface modification or
functionalization of mesoporous
materials is a great technique for
removal of some organic and inorganic
contaminants [11]. In this context,
aliphatic hydrocarbons [12], phenyl
[13], amine [14], thiol and sulfonic
functionalities have been mainly
studied as surface modifiers. Among
these useful functional groups, amine
groups represent great potential for
metal ion extraction [15], molecular
gates [16], sensors, adsorption [17] and
catalysts [18]. In the present research,
the synthesis of new mesoporous
magnetite nanoparticles with a high
density of amino groups is studied.
This strategy involves Fe3O4
nanoparticle as the magnetic core
coated by SiO2 and after that KIT-6
mesoporous silica as a thin layer to
form a core/shell structure that is
functionalized by amine via post
synthesis method. In this method,
organic functional groups are
covalently attached to the silanol
groups (Si–OH) of the pore surface by
the reaction of the organosilane under
reflux condition in toluene solvent. To
the best of our knowledge, this is the
first report on the synthesis and
application of this newly synthesized
MMNPs.
2. EXPERIMENTAL
2.1. Material
Ferric chloride hexahydrate (FeCl3-
6H2O), ferrous chloride tetrahydrate
(FeCl2.4H2O), sodium hydroxide,
tetraethylorthosilicat (TEOS), 3-
aminopropyltriethoxysilane (H2N-
CH2CH2CH2Si(OC2H5)3, APTES) as
organosilane, potassium dichromate, n-
butanol, p-toluenesulfonic acid,
absolute ethanol and hydrochloric acid
(37 wt %) were purchased with high
purity from Merck (Darmstadt,
Germany). Pluronic P123 (EO20–PO70–
EO20, MW=5800) as a non-ionic
surfactant was prepared from Aldrich
(Milwaukee, WI, USA). All stock and
working solutions were prepared using
doubly distilled water.
2.2. Instrumentation
The crystal phases and crystallinity of
synthesized MMNPs were analyzed on
X-PRTPRO (PANalitical, Netherlands)
X-ray diffraction (XRD) instrument
using Cu Kα radiation source with 2θ
range of 0.5-70o
. To investigate the
chemical structure of synthesized
MMNPs, Shimadzu Fourier transform
infrared spectrophotometer (FT-IR-
470, Japan) in the wave number range
of 400-4000 cm-1
was used. Nitrogen
adsorption-desorption experiments for
determination of surface area and pore
size of the nanoparticles were carried
out at 77 K (Bel, Japan). The size and
morphology of the modified
nanoparticles were observed under a
Philips XL 30 scanning electron
microscope (SEM, Netherlands). For
absorption measurements a Shimadzu
UV-Vis spectrophotometer (3100 pc
series, Japan) was used. pH of solutions
were measured by using a Crison pH
meter (Basic 20, Spanish). For
magnetic separation a strong super
magnet with 1.4 T magnetic field (1 × 3
× 5 cm) were applied.
2.3. Synthesis of silica coated magnetite
nanoparticles (Fe3O4@SiO2 MNPs)
Fe3O4 MNPs were chemically
synthesized with addition of an
aquoues solution of ferous and ferric M. Khabazipour, Sh. Shariati /CSM Vol.2 No.1, 2014 pp.11-19
13
ions (in a 1:2 molar ratio) to amonia
solution with little modification in the
methodology already described in the
literature [19]. Briefly, 10.4 g of
FeCl3.6H2O, 4.0 g of FeCl2.4H2O and
1.7 ml of HCl (12 mol L-1
) were
dissolved in 50 ml of deionized water
in order to prepare stock solution of
ferrous and ferric chloride. This
solution was degassed with purging
nitrogen gas (99%) for 20 min.
Simultaneously, 250 ml of 1.5 mol L-1
ammonia solution was degassed (for
15 min) and heated to 80 o
C in a
reactor. Then, the stock solution was
slowly added to the ammonia solution
using a dropping funnel during 60 min
under nitrogen gas atmosphere and
vigorous stirring (1000 rpm) by
magnetic stirrer. During the whole
process, the solution temperature was
maintained at 80 o
C and nitrogen gas
was purged to remove the dissolved
oxygen. After completion of the
reaction, the obtained Fe3O4 MNPs
were separated from the reaction
medium by a magnet (1.4 Tesla), and
then washed with 500 ml doubly
distilled water four times. Finally, the
obtained Fe3O4 MNPs were dried for
120 min at 90 o
C. Due to instability of
Fe3O4 MNPs under acidic condition
for KIT-6 mesoporous synthesis, a
silica layer was coted on the surface of
synthesized particles. For synthesis of
Fe3O4@SiO2 MNPs, 1.0 g of the
synthesized MNPs were homo-
geneously dispersed in 500 ml of
ethanol containing ammonia (25 ml,
25 wt %), under stirring at 80o
C
followed by dropwise addition of
ethanolic solution of TEOS (10.8
%v/v). After stirring at 80 o
C for 2 h,
the Fe3O4@SiO2 nanoparticles were
obtained and washed several times
with a mixture of water-ethanol (1:1).
Then, the synthesized nanopartices
dried at 100°C for 5 h.
2.4. Synthesis of KIT-6 mesoporous
magnetite nanoparticles (Fe3O4@
SiO2@KIT-6 MMNPs)
The KIT-6 mesoporous silica with
cubic Ia3d symmetry as shell on the
magnetite core was synthesized
according to the method described in
the literature [20]. Typically, 1.25 g of
Pluronic P123 was dissolved in 45 ml
of distilled water. Then, 1 g of
Fe3O4@SiO2 and 2.4 ml of HCl
solution (37 wt %) were added to the
solution under vigorous stirring. After
complete mixing, 1.3 g of n-butanol
(99.4 wt %) was added. Following
further stirring for 1 h, 2.7 g of TEOS
(as silica source) was added
immediately. Subsequently, the mixture
was left stirring at 35°C for 24 h and
transferred into an autoclave, which
was sealed and maintained at 100°C for
another 24 h under static conditions.
The resulting solid product was filtered
and dried at 100°C overnight. After
that, the filtrate was stirred for 1 h in a
mixture of 300 ml EtOH containing 20
ml concentrated HCl (37 wt %). After
ethanol/HCl washing, the final
nanoparticles were filtered, dried at 90
°C and finally calcined at 550 °C for 6
h in air.
2.5. Synthesis of amine functionalized
KIT-6 mesoporous magnetite nano-
particles (Fe3O4@SiO2@KIT-6-NH2 MM
NPs)
Synthesis of amine functionalized
MMNPs was carried out by the post-
synthesis grafting method [21]. A post-
synthesis grafting method is based on
the silylation of surface silanol groups
with organoalkoxysilanes. A detailed
experimental description for synthesis
of Fe3O4@SiO2@KIT-6-NH2 MMNPs
is as follows: 0.5 g of synthesized KIT-
6 mesoporous magnetite was dispersed
in 75 ml of toluene by stirring for 0.5 h
at 50 °C. After that, 3.5 mg of p-
toluenesulfonic acid and 1.0 mmol of M. Khabazipour, Sh. Shariati /CSM Vol.2 No.1, 2014 pp.11-19
14
organosilane (APTES) were added to
the mixture. The mixture was heated up
to 120 °C and stirred for 4 h. After
refluxing for 4 h, the solid product was
filtered and washed with absolute
ethanol several times and was dried at
100 °C for 12 h [21]. Figure 1 (a-d)
shows the colour of synthesized
nanoparticles during different steps.
Fig.1. Samples synthesized: (a) Fe3O4 (b) Fe3O4@SiO2 (c) Fe3O4@SiO2@KIT-6 (d)
Fe3O4@SiO2@KIT-6-NH2
3. RESULTS AND DISCUSSION
3.1. Characterization of the synthesized
MMNPs
IR spectra of Fe3O4@SiO2@KIT-6-
NH2 MMNPs is shown in Figure 2. The
bands at ~557 and 439 cm-1
are
attributed to the Fe-O vibration of
Fe3O4 in tetrahedral and octahedral
sites, respectively. Also, the peak at
~1049 cm-1
is attributed to asymmetric
stretching vibrations of Si-O-Si and
stretching vibration of the N-H
functionalities was observed at 3429
cm-1
.
Fig. 2. FT-IR spectra of Fe3O4@SiO2@KIT-6-NH2 MMNPs
M. Khabazipour, Sh. Shariati /CSM Vol.2 No.1, 2014 pp.11-19
15
Figure 3 shows the XRD patterns of KIT-
6 (A) and Fe3O4@SiO2@KIT-6-NH2 in
low(B) and wide (C) angels. Three peaks
with 2θ at 1, 1.6 and 1.83, indicating well
resolved (211), (220) and (332) peaks
which are typical for cubic order
materials with la3d space group. Other
peaks with 2θ at 26.05, 30.315, 35.66,
43.35, 53.8, 57.3, 62.96 and 71.51
correspond to Fe3O4. As shown in Figure,
the intensities of XRD patterns decrease
and d spacing was shifted to small angle
with the increase of mesopores coating on
the iron oxide core. It seems that absence
of the prominent peaks revealed the
mesostructure would collapse with iron
oxid core, compared to that of the
mesoporous KIT-6.
Fig. 3. (A) X-ray diffraction pattern of KIT-6, (B) Fe3O4@SiO2@KIT-6-NH2 in small angle
and (C) Fe3O4@KIT-6-NH2 in wide angle.
Nitrogen adsorption–desorption iso-
therm of the MMNPs show a
characteristic type IV curve (Figure
4A) with a distinct hysteresis loop in
the p/p0 range of 0.6–0.9, indicating the
presence of a narrow distribution of
mesoporous pore size. The type IV
isotherm (IUPAC classification) is
typical for mesoporous systems. The
typical BJH (Barrett– Joyner–Halenda)
pore size distributions (Figure 4B)
indicates narrow pore size distributions
for samples. A comparison between
the BET and XRD results of the
synthesized sorbent with other reported
mesoporous samples are summarized in
Table 1. The results clearly indicate
that the core/shell structure of MMNPs
has high surface areas, large and
uniform pores. Therefore, it could be
deduced that the pores of the silica
mesoporous shell were remained after
loading on the surface of iron oxide
nanoparticles. M. Khabazipour, Sh. Shariati /CSM Vol.2 No.1, 2014 pp.11-19
16
Fig. 4. (A) Nitrogen adsorption-desorption isotherms measured at 77K; (B) pore size
distribution curves (inset) of core–shell structured synthesized and BET (C) of Fe3O4@SiO2@
KIT-6.
Table 1: A comparison between the BET and XRD results of the synthesized nanoparticles
with other reported mesoporous samples.
Fe3O4@SiO2@
KIT-6
KIT-6- α-Fe2O3
[22]
SPIO@mSiO2
[23]
ASP–Fe3O4@MCFS
[24]
SBET [m2
g-1
] 241.68
148
46
140
ap[m2
g-1
] 224.84 -
- -
Vtotal[cm2
g-1
]
0.583
- - -
Vp[cm2
g-1
]
0.566
0.47
0.0813
0.36
d0(BJH)[nm]
9.25 2.7 7.03 10.3
W (nm)
2.84 - - -
d100/d211 99.20 - - -
BET surface area calculated in the range of relative pressure (p/p0) = 0 - 0.5
do = mean pore dimeter (BJH)
Vtot = total pore volumes measured at (p/p0) =0.98
Vp= mean volume of the pores
ap= surface of pores
d = d-spacing
a = unitcell parameter
w = wall thickness
M. Khabazipour, Sh. Shariati /CSM Vol.2 No.1, 2014 pp.11-19
17
Figure 5 shows the SEM image of the
synthesized Fe3O4@SiO2@KIT-6
nanoparticles. As seen in image, the
morphologies are very uniform and
spherical nanoparticles with diameters
about 17 nm were synthesized.
Fig. 5. SEM micrograph of Fe3O4@SiO2@KIT-6 MMNPs
3.2. Application of synthesized amine
functionalized MMNPs
The newly synthesized amine
functionalized MMNPs were good
sorbents for removal of the anionic
species from aqueous solutions. At
acidic pHs, amino groups have positive
charges and can be linked to anionic
species via electrostatic interaction.
The ability of the aminated mesoporous
magnetite was examined for the
removal of Cr(VI) in hydro-
genchromate (HCrO4
-
) form as model
anionic compound from aqueous
solutions. A solution of 150 mg L-1
Cr(VI) was prepared by dissolving a
known quantity of potassium
dichromate (K2Cr2O7) in double-
distilled water. The equilibrium studies
were systematically carried out in a
batch process, covering various process
parameters. Different species of Cr(VI)
(Cr2O7
2−
, HCrO4
−
, Cr3O10
2−,
Cr4O13
2−
)
coexist at acidic pH condition. At pH
2–3 the predominant Cr(VI) species is
HCrO4
−
, which is favorable adsorbed
since it has a low adsorption free
energy.
2CrO4
2-
+ 2H+
⇌ 2HCrO4
−
⇌
H2O
+ Cr2O7
2-
The maximum Cr(VI) adsorption
capacity, calculated via absorption
spectrophotometry measurements, was
obtained as 185.18 mg g-1
at the
optimal conditions (Sample volume: 75
ml, pH=2, contact time: 15 min,
MMNPs dose: 1 g L-1
). Cr(VI) ions
were desorbed with alkali solutions.
The obtained magnetite was reused for
the Cr(VI) adsorption for 4 cycles with
Cr(VI) removal efficiency higher than
90%. A comparison between the newly
synthesized MMNPs with the other
reported sorbents for removal of Cr(VI)
pollutant was summarized in Table 2.
According to results, very good
sorption capacity was achieved in a
relatively shorter time that confirm the
potential of these nanoparticles for
Cr(VI) removal.
M. Khabazipour, Sh. Shariati /CSM Vol.2 No.1, 2014 pp.11-19
18
Table 2. A comparision between the apllicability of proposed sorbent with other reported
sorbents in Cr(VI) removal.
Adsorbents pH
Contact
Time
(h)
Dose of
Adsorbent
(g L-1)
Adsorption
Capacity
(mg g-1)
References
NH2 functionalized KIT-6 mesoporous
magnetite
2 0.25 1 185.2 This
Work
Activated carbon-based iron containing
adsorbents
2 48 0.6 68.49 [25]
Hevea Brasilinesis sawdust activated carbon
2 5 0.1 44.05 [26]
Modified, cationic surfactant spent mushroom
3.39 1.15
5
43.86
[27]
Chemically activated Neem Sawdust
4 3 6 24.63
[28]
Peanut shell
4 6 0.4
4.32
[29]
Oxidized activated carbon from peanut shell
2 24 0.1
14.54
[30]
Poly- (methyl acrylate) fuctionalized guar
gum
1 24 4 29.67
[31]
Mesopore of Activated Carbon
3 48 2
53.8
[32]
Immobilized mycelia in carboxy methyl-
cellulose (CMC) of Lentinus sajor-caju
2 2 25 32.2
[33]
4. CONCLUSION
In this study, well-ordered amine
functionalized KIT-6 mesoporous
magnetite nanoparticles were chemi-
cally synthesized. The resultant
materials showed good crystallographic
order and large uniform pore size.
Surface functionalization of
synthesized MMNPs with amino
groups produces good properties to
sorbent for magnetically removal of
anionic species as well as for solid
phase extraction of trace amounts of
analytes and induces optimum
interaction between sorbent and
adsorbate. The proposed regenarable
nanoparticles are synthesized easily
and separated via magnet. Due to their
very high surface areas, high sorption
capacity can be achieved in short
exposure times. These nanoparticles are
useful for the design of an
economically treatment process for
removal of anionic pollutants.
Acknowledgement
Financial support by Rasht Branch,
Islamic Azad University Grant No.
4..5830 is gratefully acknowledged.
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