Cyclic ligand functionalized mesoporous silica (SBA-15) for selective adsorption of Co2+ion from artificial seawater

Article abstract of DOI:10.1166/jnn.2014.9957

Hard donor atoms (N and O) containing macrocyclic ligand was synthesized and further functionalized with mesoporous SBA-15 materials by chemical modification method. The modification was achieved by the immobilization of 3-chloropropyltriethoxysilane (ClP

Full text of DOI:10.1166/jnn.2014.9957

Article
Journal of
Nanoscience and Nanotechnology
Vol. 14, 8891–8897, 2014
Copyright © 2014 American Scientific Publishers
All rights reserved
Printed in the United States of America
www.aspbs.com/jnn
Cyclic Ligand Functionalized Mesoporous Silica
SBA-15) for Selective Adsorption of Co2
Ion from Artificial Seawater
+
(
1
1
2
1ꢀ∗
Madhappan Santha Moorthy , Sung Soo Park , M. Selvaraj , and Chang-Sik Ha
1Department of Polymer Science and Engineering, Pusan National University, Busan 609-735, Republic of Korea
School of Chemical and Biomolecular Engineering, Pusan National University, Busan 609-735, Republic of Korea
2
Hard donor atoms (N and O) containing macrocyclic ligand was synthesized and further function-
alized with mesoporous SBA-15 materials by chemical modification method. The modification was
achieved by the immobilization of 3-chloropropyltriethoxysilane (ClPTES) onto mesoporous silica sur-
face followed by post grafting route. The resulting material (Py-Cy-SBA-15) has been characterized
by low angle X-ray diffraction (XRD), nitrogen adsorption–desorption isotherm, Fourier-transform
2
9
13
infrared (FT-IR) spectroscopy, Si and C CP MAS NMR spectroscopic analyses, Thermogravimet-
ric analysis (TGA) and elemental analysis. The long range orders of the materials were identified
by transmission electron microscopy (TEM). The functionalized material was employed to the heavy
2
+
2+
2+
2+
+
2+
metal ions adsorption from aqueous solution containing Cu , Co , Zn , Cd and Cr . The pre-
Delivered by Publishing Technology to: Rice University
2
pared hybrid material showed high selectivity and adsorption capacity for Co ion at pH 8.0.
IP: 184.98.40.176 On: Thu, 10 Dec 2015 12:01:18
Copyright: American Scientific Publishers
Keywords: Cyclic Ligand, Mesoporous Materials, Heavy Metal Ions, Selective Adsorption, Metal
Coordination.
1
. INTRODUCTION
of new type of adsorbent materials are currently being
1
1
12
In recent years the heavy metal contamination in the envi-
ronmental water bodies is considerably increasing due to
effluent discharging from various industries such as elec-
troplating, mining, painting units containing heavy metal
explored, including activated carbon, chelating resins,
1
3
14
bisorbents, and mesoporous silica materials. At present,
searching for novel adsorbents for heavy metal adsorption
with high removal efficiency with selectivity and low cost
become the main interest in the research on the adsorp-
tion of heavy metal ions. Organically synthesized chelating
ligand containing N, S and O donor atoms is of a spe-
cial interest because of the variety of ways in which they
are bonded to metal ions. A vast number of adsorbents
exist with various types of ligand that deals with metal
1
ions at high concentrations. Also, water pollution includes
insecticides, volatile organic compounds, chemical wastes
and pollutants from live stock operations. Even though
some of these metals in trace are recognized as nutri-
ents required for animal and plant life, they are usually
toxic at higher levels. The heavy metals include essential
elements like iron and cobalt as well as toxic elements
like cadmium, lead, copper and mercury. Recently great
attention has been paid to the removal of heavy met-
als from the aqueous solution. Conventional method for
1
5–18
adsorption.
Specific sorbents comprising of a ligand
2
ꢀ3
that can interact with the metal ion of interest and a solid
support have been of our research interest since meso-
1
9ꢀ20
porous silica materials
including SBA-15 received a
4
the heavy metal removal includes ion exchange, mem-
brane separation, solvent extraction, precipitation and
adsorption.
great interest as a solid support due to their large sur-
face area, well defined pore size, excellent mechanical and
chemical stability and easiness to modify.
5
6ꢀ7
8
9
ꢀ10
Among these methods, adsorption is gen-
erally preferred for the removal of heavy metal ions
because of the availability of various adsorbents, high effi-
ciency, easy handling and cost effectiveness. A variety
In the present work, we have tried to develop chelating
ligands containing more numbers of chelating sites for the
assembly of basic functional groups and utilize them to
modify SBA-15 to apply for heavy metal ions adsorp-
tion and synthesized ligands showing significantly high
∗
Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2014, Vol. 14, No. 11
1533-4880/2014/14/8891/007
doi:10.1166/jnn.2014.9957
8891

Cyclic Ligand Functionalized Mesoporous Silica (SBA-15) for Selective Adsorption of Co2 Ion
+
Moorthy et al.
adsorption selectivity due to the presence of lone pair
electrons from hard donor atoms (N and O) and the macro-
cyclic ligand having five coordination sites in the single
molecule which makes a selective coordination with a spe-
cific metal ion.
2
2
. EXPERIMENTAL DETAILS
.1. Materials and Reagents
Poly(ethylene glycol)-block-poly(propylene glycol)-block-
(
poly ethylene)glycol (Pluronic P123) (M = 5800)
,
w
tetraethyl orthosilicate (TEOS, 98%), 3-chloropropyltri-
ethoxysilane (ClPTES, 95%) and salicylaldehyde, 2,6-di-
aminopyridine were purchased from Aldrich chemicals
and used as received. Standard stock solution of all
metals was prepared by dissolving salts form of metal
nitrates in water. Artificial seawater was used in the
preparation of standard stock solutions of metals. The
general composition of the artificial seawater is as
follows: NaCl-41.5%, MgCl -2.5%, CaCl -0.8%, KCl-
2
2
Scheme 1. (a) Synthesis of Py-Cy derivative and (b) functionalization
of Py-Cy ligand onto SBA-15 surface.
0
0
.9%, NaHCO -0.23%, KBr-0.08%, H BO -0.04%, SrCl -
3 3 3 2
.007%, NH Cl-0.01%, NaF-0.07%, NaSiO -0.002% and
4
3
FePO -0.0005%.
4
dried ovenight. The C N bond was reduced to C N by
2
.2. Synthesis of Organic Ligand Precursor
NaBH (Scheme 1(a)). The final product was labeled as
Py-Cy-ligand. Yield: 0.35 g (54%). H NMR (DMSO, ꢁ
4
1
Synthesis of macrocyclic pyridine ligand precursor was
carried out by two steps as following;
ppm): ꢁ 1.5 (s, 4 H), ꢁ 2.0 (s, 1 H), ꢁ 2.8 (s, 1 H),
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1
3
ꢁ
7.2 (t, 2 H), ꢁ 7.5–8.0 (mt, 4 H). C NMR (DMSO, ꢁ
IP: 184.98.40.176 On: Thu, 10 Dec 2015 12:01:18
2
.2.1. Synthesis of 1,6-Bis(2-Formyl CP oh pe yn ry i lg) h Et :t hA amn ee rican S cp i pe mn t) i :f i ꢁc 6P 8u . 0b l (i sC hHe
2
r Cs H ), ꢁ 189.4 (C
2
Npy), ꢁ 113.0–160.8
(aromatic).
The macrocyclic ligand was prepared according to the
published procedure with slight modification.21ꢀ22 In the
first step, salicylaldehyde (6.0 g, 50 mmol) was dissolved
in 50 ml of DMF and K CO (3.2 g, 20 mmol) was
2.3. Preparation of Mesoporous Silica
SBA-15 Adsorbent
2
3
added. To this, 1,2-dibromoethane (5.2 g, 30 mmol) in
5 ml DMF was added dropwise to the reaction mix-
Mesoporous silica SBA-15 was prepared using Pluronic
P123 triblock copolymer as a surfactant template and
1
2
3
ture. The resultant yellow solution was kept under stir-
TEOS as a silica source in acidic conditions. In a typ-
ical synthesis, 4 g of triblock copolymer was dissolved
in 125 g of de-ionized water and 20 g of con. HCl was
ꢀ
ring at 150–155 C for 5 h at room temperature for
5
h (Scheme 1(a)). Then, 200 ml of distilled water was
added and the mixture was kept in a refrigerator. After
h, the precipitate was filtered and washed with 500 ml
ꢀ
added under stirring at ambient temperature (25–30 C)
1
for 1 h. 8.5 g of TEOS was added to the homogeneous
ꢀ
water. Then, the obtained precipitate was recrystallized by
surfactant solution and the mixture was stirred at 35 C
1
ethanol. Yield: 8.7 g, (67%). H NMR (CDCl , ꢁ ppm):
for 24 h. Then, it was allowed to stand for crystallization
3
ꢀ
ꢁ
1
2.2 (s, 4 H), ꢁ 7.2 (d, 1 H), ꢁ 7.5 (t, 2 H), ꢁ 7.8 (d,
under static hydrothermal conditions at 100 C for 24 h
1
3
H), ꢁ 10.3 (s, 2 H). C NMR (CDCl , ꢁ ppm): ꢁ 68.7
in a Teflon-lined autoclave reactor. The crystallized prod-
uct was filtered, washed with water and dried. Finally, the
3
(
CH CH ), ꢁ 187.5 (CHO), ꢁ 113–161.5 (aromatic).
2 2
ꢀ
occluded template was removed by calcination at 550 C.
2
.2.2. Synthesis of Cyclized Compound
In the second step, the cyclized compound was prepared
using the first step product as a starting material. A solu-
tion of 2,6-diaminopyridine (1.2 g, 11 mmol) in methanol
2.4. Immobilization of SBA-15 with Py-Cy-Ligand
Immobilization of Py-Cy-ligand onto SBA-15 was carried
out using a post grafting method as following steps;
In a typical procedure, approximately 2.0 g of SBA-
(30 ml) was slowly added to the reaction flask contain-
ꢀ
ing 1,6-bis(2-formyl phenyl)ethane (0.65 g, 2.0 mmol)
in methanol (40 ml). After the the addition was com-
pleted, stirring was continued for further 6 h. A yellow
precipitate was filtered and washed with methanol and
15 material was pre-treated at 140 C for 3 h and then
immersed into 50 ml toluene and 10 ml (0.05 M) of
ClPTES in a 250 ml flask. Then, the reaction mixture was
ꢀ
kept for reflux at 80 C for 24 h under nitrogen atmosphere.
8
892
J. Nanosci. Nanotechnol. 14, 8891–8897, 2014

Moorthy et al.
Cyclic Ligand Functionalized Mesoporous Silica (SBA-15) for Selective Adsorption of Co2 Ion
+
Upon completion, the solid product was filtered, washed
with 100 ml ethanol, and dried in oven at 60 C for 6 h
to obtained a triethoxysilylpropylchloride functionalized
SBA-15 materials (ClPTES-SBA-15) (Scheme 1(b)).
Series II CHN Elemental analyzer. Quantitative determina-
tion of metal ions was performed by ICP-AES (ACTIVA,
JY HORIVA, Japan).
ꢀ
3
. RESULTS AND DISCUSSION
2
.4.1. Immobilization of Py-Cy-Ligand with SBA-15
3.1. Adsorbent Characterization
Chemically synthesized Py-Cy-ligand (0.5 g, 1.78 mmol)
was added to ClPTES-SBA-15 (1.0 g) in chloroform
Figure 1 shows the XRD patterns of the SBA-15 and the
Py-Cy ligand functionalized SBA-15 samples. All the sam-
ples show a well ordered hexagonal structure represent-
ing that the ligand modification process does not affect
the mesostructural order of the materials. The XRD pat-
terns show two well resolved peaks (110) and (200) in the
(60 ml) in the presence of triethyamine base to scav-
enge the HCl generated by the derivitazation reaction
(Scheme 1(b)). The resultant pale yellow solid was filtered
ꢀ
off, washed with chloroform and dried at 60 C under
vacuum and stored under inert atmosphere. The obtained
product is labeled as Py-Cy-SBA-15.
ꢀ ꢀ
ꢈ range between 1.6 and 2.1 , and the d-spacing val-
2
ues for the two peaks were 54.6 and 48.1 Å, respectively.
No obvious changes in the XRD patterns were observed
after ligand functionalization. This indicates that the ligand
modification did not affect the structure of the materials.
Figure 2(A) shows the nitrogen adsorption–desorption
isotherms for SBA-15 and Py-Cy-SBA-15 materials.
The isotherm curves belong to type IV pattern and have
an H1 hysteresis loops that is representative for the class
of mesoporous materials. The inflection position in the lig-
and functionalized SBA-15 shifted slightly towards lower
relative pressure and the volume of nitrogen adsorbed was
decreased with ligand modification, which indicates the
reduction of pore size. Table I shows the structural param-
2
.5. Determination of Metal Adsorption Capacity
Approximately 250 mg adsorbent sample of Py-Cy-SBA-
5 was suspended in 5 ml of metal solution from stock
1
−
3
(
1 × 10 M) was stirred (300 rpm) for 12 h. Then,
the adsorbent was separated by filtration and the filtrate
was collected and analyzed for metal ion concentration
by Inductively Coupled Plasma Atomic Emission Spec-
troscopy (ICP-AES) analysis.
The heavy metal adsorption process was carried out at
pH 8.0. The amounts of each metal ion adsorbed by Py-
Cy-SBA-15 were calculated as below,
ꢂC −D Ce li ꢃv Ve red by Publishing Technology to: Rice University
0
e
qe =
eters, such as BET surface area, total pore volume and
IP: 184.98.40.176 On: Thu, 10 Dec 2015 12:01:18
W ×metal atomic weight
pore diameter for SBA-15 and Py-Cy-SBA-15. BET sur-
face area, pore volume and pore diameter was decreased
after surface modification and ligand functionalization pro-
cess (Table I). These changes can be attributed to the pres-
ence of pendant groups on the mesoporous SBA-15 surface
that partially blocks the adsorption of nitrogen molecules.
The surface functionalization of SBA-15 also results in
the shrinkage of the BJH pore diameter (Table I), which
was ascribed to the lining of pore wall with the organic
functional groups (Fig. 2(B)).
Copyright: American Scientific Publishers
−
1
where q is the adsorption capacity (mmol g ) of the
adsorbent at equilibrium; C and C are the initial and
equilibrium concentrations of solution (ml) and W is the
mass of the gram adsorbent used (g).
e
0
e
2
.6. Characterization
X-ray diffraction (XRD) measurements were performed by
using a Bruker AXS using Cu Kꢄ radiation (ꢅ = 1ꢆ5418 Å)
ꢀ
at 40 kV and 40 mA in the 2 theta range of 1.2–10 . Trans-
mission electron microscopy (TEM) images were obtained
with a JEOL 2010 electron microscope with an acceleration
voltage of 200 kV. The BET (Brunauer–Emmett–Teller)
method was used to calculate the specific surface area. The
pore size distribution curve was obtained from an analysis
of the adsorption branch using the Barett–Joyner–Halenda
(
BJH) method. Before the measurement the sample were
ꢀ
13
degassed at 120 C for 2 hrs in vaccuo. C cross polariza-
2
9
tion (CP) and Si MAS NMR spectra were obtained with
a Bruker DSX 400 spectrometer with a 4 mm of Zirconia
rotor spinning at 6 kHz (resonance frequencies of 79.5 and
2
9
13
1
00.6 MHz for Si MAS and C CP MAS NMR, respec-
ꢀ
tively; 90 pulse width of 5 ꢇs, contact time 2 ms, recycle
2
9
13
delay 3 s for both Si MAS and C CP MAS NMR).
Thermogravimetric analysis (TGA) was performed with a
Perkin-Elmer Pyris Diamond TG instrument at a heating
ꢀ
−1
rate of 10 C min in air. Elemental analysis (% C, % N,
O and % S) was performed at the Perkin Elmer 2400
%
Figure 1. XRD patterns of (a) SBA-15 (b) Py-Cy-SBA-15.
J. Nanosci. Nanotechnol. 14, 8891–8897, 2014
8893

Cyclic Ligand Functionalized Mesoporous Silica (SBA-15) for Selective Adsorption of Co2 Ion
+
Moorthy et al.
Figure 3. TEM images of Py-Cy-SBA-15 taken at (100) (a) and (110)
direction (b).
functionalized SBA-15. The alkyl group resonance sig-
nals are assigned as (1), (2) and (3) appearing at 18.8,
32.0 and 45.2 ppm, respectively. The aromatic carbon res-
onance signals arise at 160.0 and 210.3 ppm, assigned to
the phenyl and pyridine groups that are labeled (5), (6)
3
0
and (7) present in the ligand. These results confirm the
successful modification of SBA-15 by Py-Cy ligand. The
quantity of the ligand molecules attached to the SBA-15
surface (L = 1ꢆ80 mmol/g) was calculated from the per-
0
centage of nitrogen in the functionalized mesoporous sil-
ica, as estimated by elemental analysis (Table I), using the
following expression:
%
of N ×10
L =
0
Nitrogen atomic weight
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The molar ratio of C/N was calculated from the ele-
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Figure 2. (A) Nitrogen adsorption–desorption isotherms and (B) Pore
size distribution profiles of (a) SBA-15 and (b) Py-Cy-SBA-15.
mental analysis of the Py-Cy-SBA-15 indicates a 2:1 stoi-
chiometry between the silanol groups on the silica surface
Copyright: American Scientific Publishers
and the ligand. The result confirms a high efficiency in the
functionalization of the SBA-15 surface.
The TEM image in Figure 3(a) revealed the well order
hexagonal pore arrangement in the (100) direction. The
TEM image in Figure 3(b) also displayed the pore arrange-
ment parallel to each other in the (100) or (010) directions,
clearly indicating that the ligand modification process did
not affect the long-range order of the mesoporous adsor-
bents. Figure 4(a) shows the Si MAS NMR data and the
two groups of singals appeared on the spectrum indicat-
ing the presence of both the inorganic and organic silane
2
9
4
3
functionalities in the materials. The Q (−110 ppm), Q
2
(
−101 ppm) and Q (−87 ppm) peaks represent the fully
and partially condensed inorganic silica source, while the
3
2
T
(−67 ppm) and T (−49 ppm) peaks are assigned
to the terminal and cross-linked organosilane function-
alities in the pore surface. Figure 4(b) shows 13C CP
MAS NMR spectra in the solid state for the Py-Cy ligand
Table I. Textural properties of SBA-15 and Py-Cy-SBA-15 adsorbents.
Specific
surface
area (m /g)
Total pore Average
Py-Cy
ligand
volume
pore
2
3
a
a
Material
(cm /g)
size (Å) (mmol/g) C/N
SBA-15
Py-Cy-SBA-15
750
330
0.92
0.58
39.9
35.4
–
1.8
–
3.5
Figure 4. Solid-state (a) 29Si and (b) 13C CP MAS NMR spectra of
Py-Cy-SBA-15.
a
Note: Elemental analysis.
8
894
J. Nanosci. Nanotechnol. 14, 8891–8897, 2014

Moorthy et al.
Cyclic Ligand Functionalized Mesoporous Silica (SBA-15) for Selective Adsorption of Co2 Ion
+
2
+
2+
Figure 7. Amounts of adsorption of heavy metal ions (Cu , Co ,
Zn , Cd
adsorption.
2
+
2+
2+
and Cr ) on Py-Cy-SBA-15 at pH 8 after 12 h of
Figure 5. Thermogravimetric curve of Py-Cy-SBA-15.
Thermogravimetric analysis of Py-Cy-SBA-15 was per-
formed (Fig. 5). The stepwise weight loss of the adsor-
bent indicates that the adsorbent contains various chemical
compositions obtained from each step of the modification.
The Py-Cy ligand modified adsorbent shows the initial
3.2.1. Effect of pH of the Adsorption Medium
Solution pH is one of the important parameters that influ-
ence the adsorption of metal ions from aqueous solution,
since it affects the solubility of metal ions and the ligand
functionality. To measure the pH effect on heavy metal
ion adsorption, pH was selected at pH 4, 6 and 8. The
metal adsorption profiles (Fig. 6(a)) show the metal ion
adsorption varied depending on the pH of the adsorption
ꢀ
weight loss 2 wt% of physisorbed water at 100 C. In the
second step, decomposition of the organic ligand resulted
ꢀ
in the weight loss of 10.6 wt% at 200–550 C. This major
weight loss was mainly attributed to the degradation of
Py-Cy ligand molecule present in the SBA-15 materials.
Delivered by Publishing Tech nm oe l do i gu ym t. o T: hRe i ce ef fi Uc i ne ni vc ey r so if t ym etal ion adsorption is lower at
The degradation of the silica ne It Pw :o 1r k8 4o. c9 c8u . r4r 0e d. 1 7b e6 t wO ene :nThu, 10 Dec 2015 12:01:18
lower pH. In contrast, the metal uptake efficiency increased
51–800 C, leading to a weight loss Co fo 7p y wr i tg%h .t : American Scientific Publishers
ꢀ
5
with the increase of the medium pH. At pH 8, func-
tionalized material showed equilibrium degree of adsorp-
2
+
3
.2. Adsorption of Heavy Metal Ions
tion. Co ion showed the higher amount of adsorption
at pH 8 than the competitive metal ions. The optimum
The adsorption capacities of heavy metal ions from aque-
ous solutions were measured to determine the capability
of functionalized ligand molecules present in the meso-
porous adsorbents. Targeted heavy metal ions including
2
+
pH for Co ion adsorption ranged from 5 to 8. At low
pH, it is expected that the coordination sites of the ligand
undergo protonation to varying degree in the adsorption
medium. Due to the protonation of the ligand, a competi-
tion existing between protons and heavy metal ions causes
a decreased complexation ability of metal ions with ligand
2
+
2+
2+
2+
2+
Co , Cu , Zn , Cd and Cr were utilized to study
the effect of various parameters towards the adsorption,
and the selectivity of the heavy metal ions by Py-Cy func-
tionalized SBA-15 was also determined.
1
7ꢀ24
molecules.
Figure 6. Effects of pH (a) and time (b) on the adsorption of Cu2 , Co , Zn , Cd and Cr ions.
+
2+
2+
2+
2+
J. Nanosci. Nanotechnol. 14, 8891–8897, 2014
8895

Cyclic Ligand Functionalized Mesoporous Silica (SBA-15) for Selective Adsorption of Co2 Ion
+
Moorthy et al.
Figure 8. Effects of ionic strength (a) and metal ion concentration (b)on the adsorption of Co2 ion.
+
3
.2.2. Effect of Time on Heavy Metal Adsorption
adsorption of Co2 ion was not significant in the forma-
+
tion of selective coordination of Co ion with the Py-Cy
ligand.
2
+
The adsorption efficiency of ligand increased with respect
to the contact time before equilibrium is reached at 25 C.
ꢀ
2
+
Figure 6(b) revealed that the Co ion adsorption effi-
ciency increased gradually up to 90% and reached equilib-
rium when the contact time was increased 30 min to 4 h.
Similarly, the adsorption rate of other metal ions such as
Cu , Zn , Cd and Cr also shows various percentage
of adsorption. The adsorption almost reached equilibration,
when the adsorption time reaches at 2 h. This indicates
that the heavy metal ion adsorption takes place on the
Py-Cy-SBA-15 as fast adsorption at the initial stage fol-
lowed by the slow adsorption in which the metal cations
diffuse into the SBA-15 adsorbents and coordinate with
functionalized ligand molecules. The adsorption amounts
3.2.4. Effect of Initial Metal Ion Concentration
The metal ion uptake mechanism mainly depends on the
initial metal ion concentration in the aqueous medium.
At low concentration, the metal ions are adsorbed by spe-
cific functional groups present in the adsorbent materials
whereas an increasing the metal concentration cause lower
adsorption, due to the saturation of the adsorption sites
resulting in the equilibration between metal ions and bind-
2
+
2+
2+
2+
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Copyright: American Scientific Publishers
29
2+
ing sites. Figure 8(b) shows Co ion adsorption, where
a decreased rate of adsorption was observed from 98% (for
2+
2+
Co = 100 mg/L) to 78% (for Co = 1000 mg/L).
2
+
2+
2+
2+
2+
of Co , Cu , Zn , Cd and Cr after 12 h of adsorp-
−
2
−2
tion were 29ꢆ8×10 mmol/g, 13ꢆ0×10 mmol/g, 10ꢆ4×
−
2
−2
−2
4. CONCLUSIONS
Py-Cy ligand functionalized mesoporous silica SBA-15
material was synthesized by post grafting method. The pre-
1
0
mmol/g, 6ꢆ3×10 mmol/g and 6ꢆ2×10 mmol/g,
respectively, for the Py-Cy ligand functionalized SBA-15,
as shown in Figure 7. The difference in the amount of
adsorption of various heavy metal ions in the same adsor-
bents mainly depends on the ionic radii, electronegativity
of the donor atoms and coordination tendency and geom-
pared material was characterized by XRD, N adsorption
2
2
9
13
desorption, Si and C CP MAS and TGA analysis. The
adsorption capacity and selectivity of the modified materi-
als was tested with various heavy metal ions from artificial
seawater solution at pH 8. Py-Cy-SBA-15 showed a selec-
2
5–27
etry of the ligand-metal complex.
2
+
tivity and higher adsorption capacity towards Co ion
3
.2.3. Effect of Ionic Strength of Metal Ion Solution
−
2
(
29ꢆ8×10 mmol/g) than the competitive metal ions such
Ionic strength of the adsorption medium may be an
important factor that influences aqueous phase equilibrium
between heavy metal ions and adsorbent materials. In gen-
eral, the rate of adsorption decreases with increasing ionic
strength of the adsorption media which can attribute to the
2+ −2 2+ −2
as Cu (13ꢆ0×10 mmol/g), Zn (10ꢆ4×10 mmol/g),
2
+
−2
2+
−2
Cd (6ꢆ3×10 mmol/g) and Cr (6ꢆ2×10 mmol/g).
The selectivity is mainly due to the ionic radii of metal
ions, electronegativity of donor atoms and the coopera-
tive effect of nucleophilic pyridine and electron rich nitro-
gen and oxygen donating sites existing in the ligand,
which makes a more preferable octahedral coordination
with cobalt ions than the other competitive metal ions.
2
8
presence of coordination sites of different affinities. NaCl
is one of the major compositions in the artificial seawater.
The effect of ionic strength on the adsorption efficiency
of Co2 ion was investigated. The result (Fig. 8(a)) indi-
+
cates that the ionic strength at higher concentration (1.0 M)
marginally affected on the adsorption of Co2 ion onto the
+
Acknowledgments: The work was supported by the
Py-Cy-SBA-15. The effect of an excess of NaCl on the
National Research Foundation of Korea (NRF) Grant
8
896
J. Nanosci. Nanotechnol. 14, 8891–8897, 2014

Moorthy et al.
Cyclic Ligand Functionalized Mesoporous Silica (SBA-15) for Selective Adsorption of Co2 Ion
+
funded by the Ministry of Science, ICT, and Future
Planning, Korea {Pioneer Research Center Program
13. S. Zakhama, H. Dhaouadi, and F. M. Henni, Bioresource Technol.
02, 786 (2011).
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52, 690 (2008).
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Delivered by Publishing Technology to: Rice University
IP: 184.98.40.176 On: Thu, 10 Dec 2015 12:01:18
Received: 8 April 2013. Accepted: 2 December 2013.
Copyright: American Scientific Publishers
J. Nanosci. Nanotechnol. 14, 8891–8897, 2014
8897