Synthesis and characterization of amine functionalized mesoporous magnetite nanoparticles having environmental applications

 
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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