Ion-imprinted polymer for selective separation of Cerium (III) ions from rare earth mixture

Article abstract of DOI:10.1166/jnn.2019.16538

Ion-imprinting polymers (IIPs) materials draw the great recognition because of the powerful selectivity to the desired metal ions. Therefore, the ion-imprinting polymer (Ce-IIP) was prepared by using cerium metal with amidoxime ligand as the complexing agent, in addition ethylene glycol dimethacrylate (EGDMA) and 2,2-azobisisobutyronitrile (AIBN) are crosslinking agent and free radical initiator, respectively. Aqueous HCl was applied to leach the cerium ions from the imprinted polymer for the creation of cavities of template, which is utilized for further cerium ions adsorption with high selectivity. The Ce-IIP was characterized by using ICP-MS, FE-SEM and also solid state analysis by UV-vis NIR spectroscopy. FT-IR study confirmed the complexation of the Ce-IIP was successful. The optimum pH was found to be 6 and the highest adsorption capacity was estimated about 145 mg g^-1. Thus, the prepared Ce-IIP gave very good selectivity to cerium ions in the presence of lanthanide ions and also Ce-IIP can be reused 10 times without a substantial loss in adsorption capacity.

Full text of DOI:10.1166/jnn.2019.16538

Article
Journal of
Nanoscience and Nanotechnology
Vol. 19, 5796–5802, 2019
Copyright © 2019 American Scientific Publishers
All rights reserved
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Printed in the United States of America
Ion-Imprinted Polymer for Selective Separation of
Cerium(III) Ions from Rare Earth Mixture
Md Lutfor Rahman1ꢀ∗, Perng Yang Puah1, Mohd Sani Sarjadi1, Sazmal Effendi Arshad1,
Baba Musta1, and Shaheen M. Sarkar2
1Faculty of Science and Natural Resources, Universiti Malaysia Sabah, 88400 Kota Kinabalu, Sabah, Malaysia
2Institute Bernal Institute, Department of Chemical Sciences, University of Limerick, Castletroy, Limerick, V-94, Ireland
Ion-imprinting polymers (IIPs) materials draw the great recognition because of the powerful selec-
tivity to the desired metal ions. Therefore, the ion-imprinting polymer (Ce-IIP) was prepared by
using cerium metal with amidoxime ligand as the complexing agent, in addition ethylene glycol
dimethacrylate (EGDMA) and 2,2-azobisisobutyronitrile (AIBN) are crosslinking agent and free rad-
ical initiator, respectively. Aqueous HCl was applied to leach the cerium ions from the imprinted
polymer for the creation of cavities of template, which is utilized for further cerium ions adsorption
with high selectivity. The Ce-IIP was characterized by using ICP-MS, FE-SEM and also solid state
analysis by UV-vis NIR spectroscopy. FT-IR study confirmed the complexation of the Ce-IIP was
successful. The optimum pH was found to be 6 and the highest adsorption capacity was estimated
about 145 mg g−1. Thus, the prepared Ce-IIP gave very good selectivity to cerium ions in the
IP: 5.101.217.114 On: Fri, 10 May 2019 10:27:36
presence of lanthanide ions and also Ce-IIP can be reused 10 times without a substantial loss in
Copyright: American Scientific Publishers
adsorption capacity.
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Keywords: Ion-Imprinting Polymers, Rare Earth Metals, Selectivity, Adsorption.
1. INTRODUCTION
extraction, catalysis, design of sensor, protein separation,
as receptor, antibody and also in one of the most impor-
tant application which is in wastewater treatment.4 Poly-
meric nature of MIPs is being used in a wide range of
applications. However, identification and selective recog-
nition of metal ions remain challenging for MIPs in a large
range of analytical applications.1–4 Ion-imprinting tech-
nology (IIT) has been used to prepare the ion-imprinted
polymers (IIPs) for the sorption of metal ions with high
selectivity.3 The IIPs are prepared using an ion as a tem-
plate to form a cross-linked material with stable and robust
properties. Guo et al.5 reported neodymium ion-imprinted
polymer (Nd3+-IIP) material display adsorption capacity
of 35.18 mg g−1 towards neodymium ions and having
the large selectivity coefficient (over 110) for neodymium
ions from the mixture of lanthanide ions (La, Ce, Pr and
Sm).
Molecular imprinting technology (MIT) is a unique tech-
nique for the synthesis of molecularly imprinted poly-
mers (MIPs). MIT used to the concept of molecular lock
pair with molecular key, which is enable to the binding
sites of MIPs paired to the template compounds based on
size, shape, and functional groups.1 Many researches have
reported the MIT technique to prepare new pattern of MIPs
for versatile applications, such as chromatographic sepa-
ration, sensor devices, catalysis and in vitro diagnostic.1
Molecular imprinting technology allows us to synthesize
the compounds with high specificity and selectivity recep-
tor sites to the target molecule. The molecular imprinted
polymers (MIPs) are very specific in identified the size,
shape, and functional group of the template.2 This tech-
nology has been applied in numerous fields of pharma-
ceutical, biotechnology, biochemistry, chemistry and many
more.3 In many years back until now, molecular imprinting
has become a well-known method used in the solid-phase
Rare earth elements (REEs) exhibit outstanding physi-
cal and chemical nature and have been marked as impor-
tant material resources for many high-tech applications.6–16
However, the separation of REEs from fission prod-
ucts or aqueous media has become a challenging task.5
∗Author to whom correspondence should be addressed.
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Rahman et al.
Ion-Imprinted Polymer for Selective Separation of Cerium(III) Ions from Rare Earth Mixture
Some metals-imprinted polymers have been developed for
REEs separation.17–20 Thus, europium(III)-imprinted poly-
mer nanoparticles were synthesized by using suspension
polymerization.21 A new Nd(III)-imprinted polymer with
selectivity towards Nd3+ in aqueous solutions that contains
various lanthanide ions (Ce(III), La(III) and Eu(III) ions)
were also reported recently by Ibrahim et al.22 The maxi-
mum binding capacity was reported to 14.6 mg Nd3+ g−1
and Nd(III) binding with Nd-imprinted polymer was dou-
ble as compared to non-imprinted polymer.22 Yan et al.23
used SBA-15 mesopores microreactor as a support for syn-
thesizing a Ce(III) ion-imprinted polymer (Ce-IIP) grafted
on Fe3O4 nanoparticles. The purification of these elements
is attained considerable attention with the increasing need
for high-purity rare earth elements.23 Therefore, a new
material is always needed to develop and defeat the con-
straint of the separation and purification of rare earth
metals.
2.3. 4-(allyloxy)Benzonitrile (1)
4-Bromobenzonitrile, 5.0 g (17.7 mmol) was transferred to
the round bottom flask (100 mL) and fitted with condenser.
Dry acetone (55 mL) was poured into the flask to allow the
starting material is fully dissolved with slow heat. Then
allyl alcohol, 1.39 g (24 mmol) and potassium carbon-
ate 3.31 g (24 mmol) were added to the mixture. Further
catalytic amount of potassium iodide was added into the
reaction. The reaction was reflux for overnight. The crude
mixture was poured into the 100 mL ice-cooled water
and dilute HCl was added for neutralization of the mix-
ture. The product was extracted with dichloromethane and
the solvent eliminated by rotatory evaporator. The crude
intermediate was purified with column chromatography by
ethyl acetate and hexane (1:4) as eluent. The solvent was
removed by rotatory evaporator and finally compound was
recrystallized from ethanol to yield 66% as white solid 1.
IR, ꢀmax/cm−1 2926, 2754 (CH2ꢁ, 2244 (CN), 1600, 1501
(C C), 1250, 1145 (CO), 1044 (CH). ꢂH (500 MHz;
CDCl3; Me4Si) 7.38 (d, 2H, J = 8.1 Hz, ArH), 7.00 (d,
2H, J = 8.6 Hz, ArH), 5.88 (m, 1H, CH), 5.24–5.26 (dd,
2H, J = 16.5 Hz, CH2ꢁ, 4.60 (t, 2H, J = 6.6 Hz, OCH2ꢁ.
ꢂC (150 MHz; CDCl3; Me4Si) 72.1, 105.1, 115.3, 115.9,
116.5, 133.1, 133.9, 165.0.
Thus, a new method known as ion imprinted polymers
(IIPs) are interested in scientific community due to its
capability to remove the desired metals effectively and
selectively. Amidoxime is a known ligand easily complex
form with transition metals, lanthanides and actinides ele-
ments. In this study, we have used cerium ions as the tem-
plate molecule and the amidoxime as the functional ligand.
We are focusing on rebinding of the cerium ions to the
template to find the selectivity of the templates towards
2.4. 4-(allyloxy)-Nꢀ-Hydroxybenzamidine (2)
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the metal. The Ce-IIP polymer was used for extraction of
Copyright: American Scientific Publishers
solved into 50 mL of ethanol:water (4:1) mixture. Sodium
target cerium ions real conditions.
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hydroxide (50%) solution was poured into the mixture
at cool condition until the pH 10.5 and NaCl precipita-
tion was occurred in this condition. The precipitated NaCl
was removed by filtration. Then 3.0 g (18.8 mmol) of
4-(allyloxy)benzonitrile was added to the hydroxylamine
solution and the reaction was reflux for 6 hrs. Then the
mixture was acidified with dilute HCl until pH 4. The pre-
cipitate product obtained by filtration and the crude prod-
uct was purified by recrystallization from ethanol to yield
75% of pale yellow solid 2. IR, ꢀmax/cm−1 3410 (OH),
3320 (NH2ꢁ 2929, 2750 (CH2ꢁ, 1600, 1508 (C C), 1250,
1142 (CO), 1047 (CH). ꢂH (500 MHz; CDCl3; Me4Si)
7.50 (d, 2H, J = 8.1 Hz, ArH), 6.98 (d, 2H, J = 8.4 Hz,
ArH), 5.89 (m, 1H, CH), 5.24–5.25 (dd, 2H, J = 16.6 Hz,
CH2ꢁ, 4.61 (t, 2H, J = 6.7 Hz, OCH2ꢁ, 2.10 (d, 2H, NH2ꢁ,
2.0 (s, 1H, OH). ꢂC (150 MHz; CDCl3; Me4Si) 72.0,
114.5, 116.6, 121.2, 127.8, 133.6, 162.2, 164.0.
2. EXPERIMENTAL DETAILS
2.1. Materials
Allyl bromide (Merck), 4-bromobenzonitrile (Sigma-
Aldrich), hydroxylamine hydrochloride (Merck), EGDMA
(Aldrich) and chloride form of rare earth such
as cerium(III), europium(III), gadolinium(III), neo-
dymium(III), praseodymium(III), samarium(III) from
Sigma-Aldrich were used as received. Eethylene glycol-
dimehylacrylate (EGDMA), 2,2-azobisisobutyronitrile
(AIBN) (Aldrich) were used as received.
2.2. Instruments
The characterization of Ce-IIP was carried out by using
several instruments. The structure of the intermediate and
IIP were determined by spectroscopic method. Perkin
Elmer (670) FT-IR spectrometer was used to record the
IR spectra. Bruker (DMX500) spectrometer was used to
record the proton NMR and carbon-13 NMR spectra.
JEOL (JSM-7800F) was used to obtain FE-SEM for the
morphology study of amidoxime and Ce-IIP. The solid
state UV-Vis NIR spectrophotometer (UV-2600 Shimadzu)
was used to determine the absorbance of complex and
Ce-IIP. Concentrations of metal ions were determined by
ICP-MS (Agilent 7500 series).
2.5. Preparation of Cerium-Complex (3)
The cerium-complex 3 was prepared with equivalent molar
solution of cerium chloride (1.0 mmol) and 1.0 mmol of
amidoxime functional ligand 2, were dissolved into 10 mL
of DMF solvent with stirring for 2 h. The brown colour
complex was produced with cerium ions and amidoxime
ligand, which was confirmed with the spectrophotometric
(UV-vis NIR) technique.
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Ion-Imprinted Polymer for Selective Separation of Cerium(III) Ions from Rare Earth Mixture
Rahman et al.
2.6. Preparation of Amidoxime Ligand-Based Cerium
Ion Imprinted Polymer (4)
ICP-MS. The Kd is the distribution ratio (mL g−1ꢁ of met-
als between the Ce-IIP and aqueous solution calculated by
Eq. (3).
The free radical polymerization technique was used to pre-
pare the Ce-IIP from the amidoxime ligand-based cerium
complex. A solution of complex 3 (10 mL DMF from pre-
vious section) was placed into a polymerization reaction
tubes, and the N2 gas was purged for 20 min to remove its
molecular oxygen. Then, EGDMA (10.0 mmol) and AIBN
(20 mg in 1 mL DMF) poured into the reaction. Again,
the N2 gas was purged into reaction for 20 min. Then, the
ꢀ
ꢁ
Ci −Cf
V
Kd =
(3)
Cf
m
Here, k is the selectivity coefficients for specific rare
earth metal relative to other rare earth ions in the solution
and k can be defined by the Eq. (4).
3+
KdLn
KdM
ꢀ
kLn3+
=
(4)
/Mn+
n+
reaction tube sealed and heated in a water bath at 60 C
for 48 h to complete the polymerization of 4. The cerium-
imprinted polymer was precipitated in methanol and ppt.
was washed 3 times with methanol. The product Ce-IIP (4)
3+
n+
where KdLn and KdM are the distribution ratios of spe-
cific rare earth metal and other rare earth metal ions,
respectively.
ꢀ
was dried at 50 C for overnight. After imprinting, the
template as the Ce3+ ions was leached with 50 mL of 2 M
HCl for 3 h duration. Thus, the imprinted cavity polymer
as IIP (5) was prepared and used to further adsorption
study.
2.9. Desorption Experiment
The desorption of the lanthanide metals on the imprinting
polymer (Ce-IIP) were performed by batch experiments:
As such cerium ions was pre-concentrated onto imprinted
polymer material (IIP) and eluted by 50 mL of 2 M HCl
solution with 3 h agitation. The suspension was filtered
and then eluent solutions with cerium ions were extracted
from the Ce-IIP. Then resulted cerium contents in the solu-
tions are determined by ICP-MS. The percentage of metals
adsorbed by IIP was estimated using the Eq. (1).
2.7. Complex Adsorption Study
The adsorption study on the cerium ions imprinted cav-
ity polymers (5) in aqueous solutions was carried out by
batch experiments: Exactly, 20 mL of cerium(III) chlo-
ride solution (50 mg L−1ꢁ was added to the amidoxime-
based imprinted polymer 5 (100 mg) at various pH 2–9.
The mixture in the plastic viol stirred for 2 h by a small
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magnetic bar. The solid was then removed and the resul-
Copyright: American Scientific Publishers
3. RESULTS AND DISCUSSION
tant solution was diluted with deionized water. The total
cerium contents in the solutions were determined by ICP-
MS. The adsorption of metals on the IIP was calculated
by the general Eq. (1), it was expressed as percentage of
metal extraction, where Ci is the initial metal concentration
(mg L−1ꢁ and Cf is the metal concentration after extraction
(mg L−1ꢁ.
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3.1. Synthesis
The 4-(allyloxy)benzonitrile (1) was synthesized from
the etherification reaction of 4-bromobenzonitrile and
allyl alcohol in presence of potassium carbonate as
base with catalytic amount of potassium chloride. Fur-
ther, 4-(allyloxy)-Nꢁ-hydroxybenzamidine (2) containing
amidoxime ligand was prepared from 1 under reflux
with hydroxylamine hydroxide at pH 10.5. Then cerium-
complex (3) was produced by compound 2 with DMF
as porogen solvent. The dark-brown complex was formed
as the cerium-IIP nanoparticles, which is converted into
imprinted polymer (Ce-IIP) using free radical polymer-
ization method. In the polymerization procedure, solu-
tion complexꢀof 3 with a cross-linker agent EGDMA was
stirred at 60 C for 48 h in presence of free radical initia-
tor (AIBN). The polymer was precipitate in methanol and
the Ce-IIP 4 was yielded. The imprinted ion (i.e., Ce3+
ion) was leached for cavity formation 5 in the Ce-IIP by
2 M HCl solution. Thus cerium was adsorbed further for
reusability study (Scheme 1).
Ci−Cf
Extraction ꢃ%ꢁ =
×100
(1)
Ci
Here, Q is the sorption capacity (mg g−1ꢁ of the
imprinted metals was determined by Eq. (2), various conc.
rare earth metals were utilized e.g., 10, 20, 30, 40 and
50 mg L−1. Here, V is the volume of the solution and m
is the mass of imprinted polymer materials (IIP in mg).
Ci −Cf
Q =
×V
(2)
m
2.8. Adsorption Selectivity Study
The competitive sorption studies were performed for the
recognition and selectivity of 5. Six mixed lanthanide
(Ce, Pr, Nd, Sm, Eu and Gd) solutions (e.g., 20 mL of
50 mg L−1ꢁ were added into the IIP 5 (100 mg) at pH 6.
The mixtures were poured into the plastic viols and stirred
for 2 h by a magnetic bar. All mixtures were filtered and
the rare earth metals in each solution were determined by
3.2. Characterization Studies
3.2.1. FT-IR Spectra
FT-IR spectra of the amidoxime and Ce-IIP were deter-
mined using KBr pellet as shown in Figure 1. The charac-
teristic peaks for the amidoxime compound 2 exhibits two
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Rahman et al.
Ion-Imprinted Polymer for Selective Separation of Cerium(III) Ions from Rare Earth Mixture
IP: 5.101.217.114 On: Fri, 10 May 2019 10:27:36
Scheme 1. Synthesis of amidoxime ligand based cerium ion imprinted polymer.
Copyright: American Scientific Publishers
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Ce-IIP 4 (Fig. 1(b)), a broad absorption band was present
peaks at 3201 and 3401 cm−1 for NH2 and OH stretching
bands, respectively (Fig. 1(a)). The compound 2 also
show other characteristic bands at 2867 and 2908 cm−1
for CH str. (alkane), 1651 cm−1 for C N str. (ami-
doxime), 1611 for C C str. (alkene), 1567 and 1410 for
C–C str. (aromatic), 1518 for N–H bend, 1396 for CH
bend, 1214 for C–O str., 1110 for C–N str., 1053 for
C–O str., 960 for C–H bend (alkene), 846 for N–H wag.
(amine), 755 cm−1 for C–H bend (alkene). In case of
at 3440 cm−1 assigned to O–H stretching band, which is
shifted from the 3401 cm−1 due to coordination bonding
with cerium ions, in addition 1635 cm−1 also shifted from
amidoxime 1651 cm−1 due to coordination with cerium
ions. Additional stretching bands for aromatic and CH are
retains for Ce-IIP. A cross-linking agent EGDMA hav-
ing an ester functional group, which was appeared at
1721 cm−1 of C O for Ce-IIP, which confirmed the for-
mation of polymer complex as shown in Figure 1(b). Gen-
erally, IR spectra can be used for the proof of functional
groups in the materials.
3.2.2. FE-SEM Analysis
Scanning electron microscopy study was carried out to
find the morphological properties. The synthesized com-
pounds were evaluated by field emission scanning electron
microscopy (FE-SEM) to investigate the surface morpho-
logical properties. It shows very clearly the morphological
difference between the functional monomer as the ami-
doxime 2 and the polymers 4 and 5. The FE-SEM images
were presented in Figures 2(a)–(c). The micrographs under
the magnifications 30,000 clearly showed the crystalline
surface of amidoxime compound 2 with some agglom-
erations of crystalline surface (Fig. 2(a)). The surface
morphology of the Ce-IIP 4 shows unsmooth spherical
Figure 1. FT-IR spectra of (a) amidoxime ligand 2, (b) Ce-IIP of 4
materials.
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Ion-Imprinted Polymer for Selective Separation of Cerium(III) Ions from Rare Earth Mixture
3.2.3. UV-Vis Absorption Study
Rahman et al.
(a)
(b)
(c)
The Ce-IIP compound 4 showed stable physical and chem-
ical properties of cerium ions as shown in Figure 3 (orange
line). The reflectance spectra of Ce-IIP (4) was observed to
dissimilar from non-imprinted amidoxime (2) as shown in
Figure 3 (pink line). Thus, a broad peak at around 718 nm
observed for Ce-IIP (yellow line), whereas the amidoxime
did not exhibits any peak around 650–900 nm, because
no complex formation with compound 2 (pink line). The
reflectance spectra of the Ce-IIP showed the new peak
at approximately 718 nm due to the cerium ions, which
proof the charge transfer (ꢄ–ꢄ for Ce ions) complex was
observed which is strong evidence for the coordination-
bonding occurred in the complex.
3.3. Sorption/Desorption Studies
3.3.1. The Effect of pH
The perfect eluent and retained cerium metal were con-
sidered for sorption/desorption studies. The Ce3+ ion was
removed from Ce-IIP (4) with 2 M HCl as aqueous solu-
tions. Thus, the bounded cerium ions was fully desorbed
by 50 mL of 2 M HCl solution to obtained the recovery
of 99% for cerium ion as estimated from the Eq. (1) as
shown in Figure 4. This solution may exhibit polar char-
acter, which electrostatically disorder the binding interac-
tion between cerium ions and the IIPs.8 The coordination
spheres of cerium ions is disordered and cerium ions lib-
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erated from Ce3+ templates into the desorption agent as
Copyright: American Scientific Publishers
aqueous HCl solution. The binding properties of metal ions
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are greatly pH dependent and binding event is described
in the literature.17–23 The concentration of soluble metal
species are actively influences the precipitation of the met-
als in the absence of complexing agents. The more general
batch adsorption procedure was used to find the effect of
pH on the uptake of cerium ions.
Exactly 20 mL solutions containing 50 mg L−1 of
cerium ions at various pH (2–9) were considered accord-
ing to the reported procedure.22 Figure 4 shows that the
effect of pH on the extraction (%) of Ce3+ ions of IIP5.
Figure 4 also shows that the adsorption of Ce3+ ions is
increases with the increasing of pH at 6. At the higher
pH beyond 7, precipitation of cerium ions was occurred,
Figure 2. FE-SEM image of (a) amidoxime ligand (2), (b) Ce-IIP (4)
and (c) IIP materials.
shape with variable size due to the compound is poly-
meric nature in structurally. Thus, Ce-IIP compound 4 pos-
sesses distinct morphology compared to organic ligand of
amidoxime compound 2. In case of cerium leached IIP
compound 5 shows very similar morphology of Ce-IIP
compound 4.
Figure 3. UV-vis absorption spectra of amidoxime ligand 2 (pink
colour) and Ce-IIP 4 given in the figure yellow line.
5800
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Rahman et al.
Ion-Imprinted Polymer for Selective Separation of Cerium(III) Ions from Rare Earth Mixture
160
140
120
100
80
100
80
60
60
40
20
40
0
2
3
4
5
6
7
8
9
10
20
30
40
50
pH
Initial Metal Conc., Ci (mg L–1
)
Figure 4. Extraction of cerium metal as a function of various pH
solution.
Figure 5. Effect of the cerium ions concentration on the adsorption of
cerium metal by using IIP 5.
whereas the protonation of the binding sites of Ce-IIP was
increases at lower pH decreases adsorption value. Conse-
quently, either Ce3+ with amidoxime complex is not stable
at low pH or the aggressive binding of proton and Ce3+
ions by the ligands at lower pH values is reduced the per-
formance of extraction.23
Thus, the imprinting procedure plays an important role in
the absorption behavior of the Ce-IIP polymer.
3.3.3. Selectivity Study
To find the selectivity of the Ce-IIP to the metal ions, a
series of batch adsorption experiments is performed with
the Ce-IIP and pairs of Ce3+ and coexisting cations (some
rare earth metals cations) were extracted by 100 mg of
Ce-IIP at pH 6. On the other hand, IIP 5 and pairs of
Ce3+ with selected cations are also used for extracted the
same amount (100 mg) of IIP 5 at pH 6. Simultaneously
adsorption property of cerium ions with some cations for
IIP particles in their mixture was evaluated under optimum
conditions. Thus, the distribution ratios (Kdꢁ and selectiv-
ity coefficients (k) for Cu2+ ions relative to foreign cations
were estimated by the Eqs. (3) and (4), respectively. The
results for Kd and k are presented in Table I.
3.3.2. Adsorption Capacity
The adsorption of cerium ion was performed with a
fixed amount of Ce-IIP using a batch adsorption method.
Adsorption capacity of the IIP (5) was calculated to be
145 mg g−1 for Ce at pH 6 by using Eq. (2). As we
observed in this study, the absorption capacity of the
IP: 5.101.217.114 On: Fri, 10 May 2019 10:27:36
Copyright: American Scientific Publishers
Ce-IIP materials is depending on the molar mass of rare
earth metals.
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Obviously ion imprinted polymers exhibit absorptive
property as compare with other absorbent and extrac-
tion capacity usually expressed as metal ions adsorbed
per gram of IIP 5. The optimum pH 6 was chosen to
find the adsorption properties at various concentrations of
cerium ions in solutions. The adsorption capacity (Q) is
defined with metals adsorbed per gram of the IIPs and
Q is the important parameter to determine the efficiency
of the IIP 5.22 The more general batch adsorption method
was used to find the maximum adsorption values of Ce3+
on IIP. Thus, 100 mg of IIP 5 was equilibrated with
50 mL of cerium solutions with various concentrations
(10–50 mg L−1ꢁ at optimum pH 6. Generally, the precipi-
tation of Ce3+ ions at pH 6 does not occur with this limit
of cerium concentration. The adsorption behaviour of IIP
with these parameters is given in Figure 5.
The competitive adsorption property of IIP 5 for Ce3+
ions is higher than Ce-IIP-polymer beads due to the nature
of ligand atoms accepted electron form cerium ion. How-
ever, IIP polymer shows for the competitive adsorption
capacity. Table I can be used to compare the selectivity
results, which clearly given the scenario of ion-imprinted
effect. In this study, the imprinted polymer was pro-
duced with cerium metal ions complex as the template,
so three-dimensional cavities is formed by cerium leach-
ing with HCl and IPs are more selective for correspond-
ing cerium ions with amidoxime ligand. In principle, the
Table I. Distribution ratio (Kdꢁ and selectivity coefficient (k) values of
specific Ce-IIP and different lanthanide cations.
The maximum Q for the cerium ions on the IIP 5 was
calculated to be 145 mg g−1 at pH 6 by using Eq. (2),
which was presented in the extraction efficiency. The
adsorption of Ce3+ ions is expressed as per unit mass of
the IIP, and Q was increased linearly with the increasing of
Cation
Kd mLg−1
K
Ce3+
Pr3+
Nd3+
Sm3+
Eu3+
Gd3+
La3+
310ꢅ5
16ꢅ1
15ꢅ5
14ꢅ2
18ꢅ2
15ꢅ5
16ꢅ1
18.1
22.3
24.3
19.0
22.3
21.4
concentration of cerium ions in solution up to 50 mg L−1
.
The adsorption value was lower with the initial concen-
tration of the Ce3+ ions as usual, which represents unsat-
uration of the active cavities on the IIP by cerium ions.
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Ion-Imprinted Polymer for Selective Separation of Cerium(III) Ions from Rare Earth Mixture
Rahman et al.
cavities produces with a specific shape and size of the
template of the imprinted polymer allows to accommodate
the corresponding metals ions. The proposed ion-imprinted
polymer showed a high selectivity to the cerium ions and
a substantial difference of the binding capacity of the Ce3+
ions and competitor metal ions. It was observed that the
prepared Ce-IIP can be utilized as a selective adsorbent for
extraction of cerium ions in the presence of other rare earth
metal cations in the various real and synthetic medium.
In this study, the competitive adsorption capacity of
the desired cerium ions using the amidoxime-based IIP is
higher due to the nature of ligand atoms accepted elec-
tron form lanthanide ions (Table I). The selectivity results
show that ion-imprinting effect is attractive by comparing
the Table I. The cerium ion complex as the template was
prepared in the imprinted polymer with three-dimensional
void of cavities formed in the IIP. The cavities act as
specific holes of cerium ions in the imprinted polymer,
which allows selective adsorption of target cerium ions.
By considering the high selectivity coefficient obtained by
the amidoxime-based IIP materials and a significant differ-
ence between the binding of the cerium ions and competi-
tor ions to the imprinted sorbent. Therefore, the prepared
amidoxime-based IIP can be utilized as a selective adsor-
bent for extraction and separation of cerium ions in the
presence of other rare earth metals.
absorption capacity is decreased about 8% after 10 times
using the proposed Ce-IIP.
4. CONCLUSION
In this report, the Ce-IIP was prepared by the cerium ions
as rare earth metals and complexing agent as amidoxime
ligand with EGDMA as cross-linking agent and AIBN as
an initiator. Certainly, the rare earth template is removed
by leaching with HCl solution for further adsorption of
rare earth metals. The sorption capacity (Q) of Ce-IIP is
found to be 145 mg g−1 at pH 6. The imprinting polymers
exhibit higher affinity towards selective rare earth ions over
other competitor rare earth ions. The Ce-IIP are repeatedly
used and regenerated for 10 times without any significant
loss in its original strength of recognition and separation
performances.
Acknowledgments: This research work was supported
by the Universiti Malaysia Sabah (SBK0260-ST-2016).
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Received: 28 June 2018. Accepted: 12 August 2018.
5802
J. Nanosci. Nanotechnol. 19, 5796–5802, 2019