Selective solid-phase extraction of Cu2+ by a novel Cu(II)-imprinted silica gel

Article abstract of DOI:10.1002/jccs.201200581

A new Cu(II)-imprinted salen functionalized silica gel adsorbent was synthesized by surface imprinting technique and was employed as a selective solid phase extraction material for Cu²⁺ removal from aqueous solutions. The samples were characterized by FT-IR, ¹HNMR, ¹³CNMR, CHNS and DTG techniques. The BET surface area of the silica gel was also determined. The adsorbent was then used for removal of Cu ²⁺ from aqueous solutions under different experimental conditions. It was concluded that the synthesized imprinted silica gel had higher selectivity and capacity compared to the non-imprinted silica gel and themaximal adsorption capacity of 67.3 and 56.5 mg.g^-1 was obtained respectively for ion-imprinted and non-imprinted adsorbents. The relative selectivity factor (β) of 50.32 and 31.94 was obtained respectively for Cu²⁺/ Ni²⁺ and Cu²⁺/Zn²⁺ pairs. The dynamic adsorption capacity of the imprinted adsorbent was close to the static adsorption capacity due to the fast kinetic of adsorption. Furthermore, the ion-imprinted adsorbent was recovered and repeatedly used and satisfactory adsorption capacity with acceptable precision was obtained. Each experiment was repeated at least for three times and the mean and the standard deviation for each measurement were calculated. The applicability of the method was examined for Zayandehrood water as real sample. Acceptabe standard deviation was obtained.

Full text of DOI:10.1002/jccs.201200581

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Selective Solid-phase Extraction of Cu2+ by a Novel Cu(II)-imprinted Silica Gel
Hossein Faghihiana,* and Khadijeh Asgharib
aDepartment of Chemistry, Shahreza Branch, Islamic Azad University, 86145-311, Iran
bYoung Researchers Club, Shahreza Branch, Islamic Azad University, Shahreza, Iran
(Received: Nov. 4, 2012; Accepted: Jul. 19, 2013; Published Online: ??; DOI: 10.1002/jccs.201200581)
A new Cu(II)-imprinted salen functionalized silica gel adsorbent was synthesized by surface imprinting
technique and was employed as a selective solid phase extraction material for Cu2+ removal from aqueous
solutions. The samples were characterized by FT-IR, 1HNMR, 13CNMR, CHNS and DTG techniques. The
BET surface area of the silica gel was also determined. The adsorbent was then used for removal of Cu2+
from aqueous solutions under different experimental conditions. It was concluded that the synthesized im-
printed silica gel had higher selectivity and capacity compared to the non-imprinted silica gel and the max-
imal adsorption capacity of 67.3 and 56.5 mg.g-1 was obtained respectively for ion-imprinted and non-im-
printed adsorbents. The relative selectivity factor (b) of 50.32 and 31.94 was obtained respectively for
Cu2+/Ni2+ and Cu2+/Zn2+ pairs. The dynamic adsorption capacity of the imprinted adsorbent was close to
the static adsorption capacity due to the fast kinetic of adsorption. Furthermore, the ion-imprinted adsor-
bent was recovered and repeatedly used and satisfactory adsorption capacity with acceptable precision
was obtained. Each experiment was repeated at least for three times and the mean and the standard devia-
tion for each measurement were calculated. The applicability of the method was examined for Zayandehrood
water as real sample. Acceptabe standard deviation was obtained.
Keywords: Surface imprinting; Salen-functionalized; Copper; Solid-phase extraction.
INTRODUCTION
As the result of industrial activities development, the
amounts of high purity organic solvents some of which are
harmful to health and cause environmental problems.4
Solid-Phase Extraction (SPE) is widely used as a powerful
and fast emerging sample preparation technique for separa-
tion or enrichment of selected analytes. SPE is based on the
distribution of analyte between an aqueous solution and ad-
sorbent by mechanisms such as adsorption, co-precipita-
tion, complex formation and other chemical reactions.
Comparing with the traditional enrichment procedure such
as liquid-liquid extraction, SPE is considered to be superior
due to its simplicity, rapidity, environmental and economi-
cal friendly, minimal cost owning to low consumption of
reagents, absence of emulsion, flexibility, ease of automa-
tion, safety with respect to hazardous materials and the
ability to combine with different modern detection tech-
nique.5 The choice of adsorbent is a key point in SPE, be-
cause it can control the analytical parameters such as selec-
tivity, affinity, and capacity. An efficient adsorbing mate-
rial should possess a stable and insoluble porous matrix
having suitable active groups that interact with selected
metal ions. Silica gel is an ideal support for organic groups,
because it is thermally, mechanically and chemically stable
and non-swelling material.6 However, the basic disadvan-
tage of these adsorbents is the lack of metal selectivity
amount of transition metals released into the environment
has increased continuously. It has been proved that large
amounts of many heavy metals such as copper, zinc, lead,
cadmium and mercury seriously affect environment health
because of their toxicity, accumulation in the food chain
and persistence in nature. Since copper and its compounds
are widely used as chemical materials in modern society,
they are widespread in natural waters and soils. Several in-
dustries, for example, dyeing, paper, petroleum, copper/
brass plating and copper-ammonium rayon, release unde-
sired amounts of Cu2+ into the environment. High Cu con-
centration in soils causes delay in flowering and fruiting
and low seed set.1,2 It is also toxic to fish life even at low
concentrations. Copper contaminant in soil and water sys-
tem can eventually impact human health through the food
chain. The health impact includes hepatic, cirrhosis, ane-
mia, unusual symptoms of the nervous system and vascular
sclerosis.3 Consequently, development of reliable methods
for removal and determination of copper in real samples is
of particular significance. Traditional separation methods
for metal ions are liquid-liquid extraction, co-precipitation
and ion-exchange. These methods often require large
* Corresponding author. Tel: +983213213098; Fax: +983213213098; Email: faghihian@iaush.ac.ir
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Article
Faghihian and Asghari
which leads to other species interfering with the target
metal ion. Moreover, matrix of environmental samples is
too complex and separation of trace elements in compli-
cated matrix is interfered by other species. So the selective
separation of cations is of great significance. Ion-imprint-
ing, is an effective technique for recognition of template
metals. In recent years, a lot of ion-imprinted polymer
(IIPs) have been prepared and used for selective solid
phase extraction and enrichment of metal ions.7,8 However,
with the usage of ion-imprinted polymers, the kinetics of
the adsorption and desorption is unfavorable.9-11 This may
be interpreted that the templates and functionality are to-
tally embedded in the polymer matrix. So the mass transfer
is slow. Surface imprinting technique, to brief, is localizing
of binding sites to the surface of high accessibility. Ion-im-
printed adsorbents prepared by this technique show many
advantages including high selectivity, more accessible
sites, fast mass transfer and fast binding kinetics. There-
fore, intensive researches have been performed in recent
years. Wang et. al prepared an ion-imprinted thiol function-
alized silica gel sorbent for selective separation of mercury
ions.12 Hu and coworkers prepared Cr(III)-imprinted silica
gel and the material was successfully applied to the specia-
tion of trace chromium in environmental samples.13 Pd-im-
printed functionalized silica gel showed high selectivity for
palladium(II) preconcentration.14 Chang et al synthesized a
surface imprinted amino-functionalized silica gel material
for selective solid-phase extraction of Zr(IV).15 Surface
imprinting technique was also used for selective separation
of Cu2+. The synthesize of a Cu(II)-imprinted sorbent by
surface imprinting and functionalizing by N-[3-(trimeth-
oxysilyl)propyl] ethylenediamine (TPED) on silica gel sur-
face has been reported.16 Gue and coworkers synthesized a
new Cu(II) ion-imprinted diethylenetriamine (DETA)
modified silica gel sorbent by surface imprinting tech-
nique.17 The choice of a complexing ligand is of great im-
portance here, as it directly influences selectivity of the ad-
sorbent. Effectiveness of a surface imprinted adsorbent in
rebinding metal ions has been attributed to the complexa-
tion chemistry between the ligand which supported onto
the silica-gel surface and the target ion. Also the coordina-
tion geometry and the coordination number of a metal ion
together with the charge and the size of the target ion play
an important role in obtaining selectivity. Schiff bases may
be perspective complexing ligand for ion-imprinting pur-
poses due to their complexing abilities toward heavy
metals. They have been applied as modifying agents for
adsorption of various metal ions.18-23 In this study a new
Cu(II)-imprinted silica-gel was synthesized by function-
alization of silica gel surface by salen-Cu complex the ion
imprinted adsorbent was used for removal of Cu2+ from
aqueous solutions and the effect of imprinting process on
the selectivity of the adsorbent was examined.
EXPERIMENTAL SECTION
Chemicals and reagents
Cu(OAC)2.H2O, Ni(NO3)2.6H2O, Zn(NO3)2.4H2O, 4-hy-
droxysalicylaldehyde, 1,2-diamino ethane, silica gel (5-40 µm
particle size, and 3-chloropropyltrimethoxysilane were received
from Merck. All solvents; such as methanol, ethanol, toluene, di-
ethyl ether and chloroform were purchased from Merck. For prep-
aration of the solutions double distilled water was used.
Apparatus and instruments
FT-IR spectra (4000-400 cm-1) were recorded on FT-IR,
Perkin Elmer 65, using KBr pellets. A PG instrument Ltd, T70
UV-Vis spectrometer was used to provide the UV-Vis spectra of
the synthesized ligand and complex. A 3505 Jenway digital pH
meter was used for the pH adjustments. A flame atomic adsorp-
tion spectrometer (A. Analyst 300 Perkin Elmer flame) was used
for determining the concentration of Cu(II), Ni(II) and Zn(II).
Hollow cathode lamps were used as the radiation sources at 324.8
(Cu), 232.0 (Ni) and 213.9 nm (Zn). TG-DTG measurements
were performed on a Setaram TG-DSC thermal analyzer. A
13CNMR spectrometer (Bruker DPX400 13CNMR) was used to
prepare the 13CNMR spectrum of the synthesized ligand. The
1
1HNMR Spectrumeter (Bruker HNMR 100 MHz) was used to
obtain the 1HNMR of the synthesized ligand. ElementarVarioEl
III (CHNS) analyzer was used to examine the elemental composi-
tion of the synthesized ligand and complex. The specific surface
area of the silica gel was determined by the Brunauer-Emmett-
Teller (BET) method by using a Quantachrome apparatus.
Activation of silica gel
Silica gel is an amorphous inorganic polymer having
siloxane groups (Si-O-Si) in the bulk and silanol groups (Si-OH)
on its surface. The silanol groups facilitate the introduction of the
organic groups which covalently bind to the silica surface. Com-
mercial silica gel contains a low concentration of surface silanol
groups suitable for modification. Silica gel surface was activated
before modification to increase the surface silanol groups and re-
moval any adsorbed impurities. Hydrochloric acid was used for
the activation of silica gel. To activate the silica gel surface, 5.000
g of silica gel was mixed with 50 mL of 6 M hydrochloric acid.
The mixture was refluxed for 8 hours. The solid was filtered and
thoroughly washed with doubly distilled water. Activated silica
2
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Selective Solid-phase Extraction of Cu2+ by a Novel
Table 1. Cu content of each solid product
gel was dried at 110 °C for 6 hours. The specific surface area of
the silica gel was determined by N2 adsorption. to be 450 m2.g-1.
Preparation of chlorofunctionalized silica gel
Amount of complex
(mmol)
Cu content (mg/g) Cu content (meq/g)
To prepare the chlorofunctionalized silica gel 5.000 g of ac-
tivated silica gel was dispersed into dry toluene (50 mL) and then
10 mL 3-chloro propyltrimethoxysilane (CPTS) was added in one
portion. The mixture was refluxed for overnight under nitrogen
atmosphere. The product was filtered off, washed with dry tolu-
ene, ethanol and diethyl ether respectively and dried under vac-
uum at 70 °C for 6 hours.24
1
4
6
8
40.01
90.28
106.82
110.05
1.26
2.91
3.36
3.37
diethyl ether, and then dried at 50 °C for 6 hours. The un-reacted
complex was extracted by soxhelet (in toluene) for 8 hours. The
covalently anchorage of the complex to the silica-gel surface was
confirmed by wet and thermal analyses. Different amount of com-
plex was immobilized on silica gel surface, in order to investigate
its optimal quantity. The Cu content of the solid product which
was determined by FAAS, represents the amount of complex sup-
ported on silica gel surface. This also shows the maximum acces-
sible adsorption capacity of the synthesized adsorbent. Table 1
shows the Cu content of the products.
Preparation of N,N¢-bis(4-hydroxysalicylidene)ethyl-
ene-1,2-diamine; H2[(OH)2-salen]
The stoichiometric amount of 4-hydroxysalicylaldehyde
(0.02 mol, 2.760 g) dissolved in methanol (25 mL) was added
drop-by-drop to 0.01 mol, 0.6 g of 1,2-diaminoethane solution
dissolved in 25 mL methanol. The mixture was refluxed for 4
hours and a bright yellow precipitate of symmetrical Schiff base
ligand; H2[(OH)2-salen]; was obtained. The yellow precipitate
was separated by filtration, washed with cold methanol and dried.
It was then re-crystallized from methanol to remove the unreacted
materials. The Schiff base ligand was characterized by CHN anal-
ysis, UV-vis spectroscopy, FT-IR spectroscopy and 1H and
13CNMR spectroscopy.25 Anal. Calculated for Schiff base ligand:
C, 63.99; H, 5.37; N, 9.33; found: C, 63.69; H, 5.53; N, 9.64.
Synthesis of [Cu((OH)2-salen)]
According to this data, 6 mmol of complex was selected as
the optimal amount of Cu-complex for the synthesis process. The
elution of copper ions acting as a template in the salen-
functionalized silica gel was examined by different solvent; in-
cluding NH3, EDTA and HNO3. 0.1 mol. L-1 nitric acid was the
most effective eluent. At the second step, 0.200 g of silica gel sup-
ported by [Cu((OH)2-salen)] was shaken with 0.1 mol.L-1 HNO3
for 4 hours to remove metal ions and leave Cu(II)-imprinted silica
gel adsorbent. The solid product was filtered under reduced pres-
sure and washed with 0.1 mol.L-1 HNO3 and doubly distilled wa-
ter respectively. The Cu(II)-imprinted silica gel adsorbent was
characterized by FT-IR spectroscopy and thermal analysis. The
same procedure was repeated for preparation of non-imprinted
silica gel but H2[(OH)2-salen] was used instead of [Cu((OH)2-
salen)]. In each preparation about 1.5 g of the adsorbent was ob-
tained. Since we needed more than 30 g of material, the procedure
was repeated more than 20 times and the products were character-
ized according to the same procedures.
Aflask containing a stirred suspension of copper(II) acetate
mono hydrate (3.192 g, 0.016 mol) in methanol (100 mL) was
warmed to 50 °C. Then N,N¢-bis(4-hydroxysalicylidene)ethyl-
ene-1,2-diamine; H2[(OH)2-salen], (4.800 g, 0.016 mol) was added
in one portion, and the resulting brown suspension was then
refluxed for 8 hours. The mixture was cooled and filtered under
reduced pressure. The collected solid was washed with diethyl
ether and dried in air to give brown crystalline [Cu((OH)2-salen)]
which was purified by re-crystallization from chloroform. This
Schiff base complex was characterized by CHN analysis, UV-vis
spectroscopy, FT-IR spectroscopy.26 Anal. Calculated for
[Cu((OH)2-salen)]: C, 52.83; H, 4.43; N, 7.70; found: C, 52.36; H,
4.38; N, 7.61.
Static adsorption expriments
To perform the static adsorption, 0.200 g portion of
Cu(II)-imprinted or non-imprinted adsorbent was transferred into
a polyethylene bottle previously cleaned with detergent and dou-
bly distilled water. Then 20 mL of standard solution of Cu2+ was
added and the pH was adjusted with HCl and NaOH. The mixture
was shaken for 5 min. The solid was separated by filtration and
centrifugation. The concentration of the metal ion, in the initial
and the final solutions was directly determined by FAAS and the
adsorption capacity was measured.
Preparation of Cu(II)-imprinted and non-imprinted
silica gel adsorbents
At the first step, to anchor the copper(II) complex onto the
silica gel surface, 2.190 g (0.006 mol) of synthesized copper(II)
salen complex was dispersed in dry toluene (50 mL) and warmed
to 60 °C with continuous stirring. Then 1.000 g of chloro-
functionalized silica gel was added in one portion. The mixture
was refluxed under nitrogen atmosphere for overnight. The re-
sulting product was filtered, washed with dry toluene, ethanol and
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Article
Faghihian and Asghari
Effect of pH
tronic spectrum of the ligand exhibits two bands at 280 and
310 nm which could be respectively assigned to intra
ligand s®s* and p®p* transitions. All these bands
shifted to higher wavelength, indicating the restructuring
of the ligand after coordination with the metal ion.
In order to investigate the effect of the pH on Cu2+ adsorp-
tion, according to the static procedure, 0.200 g of Cu(II)-im-
printed or non-imprinted adsorbent was equilibrated with 20 mL
of Cu2+ solution (1000 ppm) at different pH. The mixture was fil-
tered and the concentration of Cu2+ in the filtrate was determined.
Effect of contact time
The electronic spectrum of this kind of Schiff base,
which are widely used as chelating agents, are relevant due
to the possibility of finding them in the solid state and/or in
solution as keto-amine or phenol-imine tautomer. In the
solid state salicylaldimine Schiff bases tend to form
(N…H-O) or (N-H…O) types of hydrogen binding, re-
spectively. In many cases in solution, both types of hydro-
gen bonds have been observed indicating phenol-imine,
O-H…N, keto-amine, O…H-N, tautomerism. Polar sol-
vents such as EtOH, favor the formation of the keto-amine.
The interaction of enol-imine with a hydrogen bond form-
ing solvent would presumably reduce the O-H bond
strength and facilitate proton transfer to the nitrogen center.
Thus, the band in 385 nm is assigned to n®p* transition of
keto-amine tautomeric structure of ligand. Addition to
these bands, the electronic spectra of complex contain a
weak broad band in the 560 nm which assigned to d®d
transition of the metal ion. Appearance of a weak band due
to charge transfer transition, underneath of n®p* transition
(as a shoulder at 360 nm) in the electronic spectrum of the
complex, makes this band broad.27,28
0.200 g portion of Cu(II)-imprinted or non-imprinted ad-
sorbent was equilibrated with 20 mL of Cu2+ solution (1000 ppm)
at optimized pH of 5 for different contact time. After separation
the concentration of Cu2+ in the filtrate was determined.
Selectivity
In order to determine the selectivity of the method, the solu-
tions containing known concentration of Cu2+ and competitive
ions were prepared. The solutions were equilibrated with 0.200 g
portion of Cu(II)-imprinted or non-imprinted adsorbent for 5 min.
The mixture was filtered and the concentration of Cu2+ was deter-
mined in the filtrate. Five real samples from different location of
Zayandehrood river were taken and 20 mL of each sample was
mixed with 0.200 g of the Cu(II)-imprinted sorbent. After
equlibration, the adsorbent was separated and the adsorbed metal
ions were eluted with 0.1 M HNO3. The concentration of Cu2+ was
measured by Flame Atomic Adsorption Spectrometer.
Reusability of the adsorbent
To test the reusability of the imprinted adsorbent, it was
subjected to eight adsorption-elution cycles. Adsorption cycles
were adjusted at optimized conditions and the elution operations
were carried out by shaking 0.200 g portion of the adsorbent with
25 mL of 0.1 mol.L-1 HNO3 for 4 hours. At the end of each cycle
the amount of Cu2+ was measured in the eluted solution.
Dynamic adsorption procedure
1H and 13CNMR Spectra
The 1H and 13CNMR spectra of the ligand have been
recorded in DMSO-d6 as solvent (Fig. S2 and S3). It is im-
portant to emphasize the 1HNMR resonance of the ortho
OH group at 13.7 ppm is attributed to the presence of inter
molecular hydrogen bounding. The singlet at 9.9 ppm can
be assigned to the para OH proton. The single-proton reso-
nance in the 1HNMR spectrum of the ligand near 8.3 ppm
has been assigned to the azomethine group proton. The
multiples at 6.1-7.1 ppm can be attributed to the protons of
the aromatic ring. In addition, the CH2 groups are observed
at 3.7 ppm. The 13CNMR spectral data of the ligand con-
A glass column (50 mm in length and 7 mm in inner diame-
ter) was cleaned with detergent and doubly distilled water. 500
mg portion of Cu(II)-imprinted adsorbent in water was trans-
ferred into the column. A small amount of glass wool was placed
at both ends of the column to prevent loss of the adsorbent parti-
cles during sample loading. Before use, the column was washed
successively with doubly distilled water. Asolution containing 20
mg.L-1 of Cu2+ was allowed to pass through the column. The sam-
ple flow rate was adjusted at 0.1 mL.min-1 and each 10 mL of the
effluent was collected for determination the Cu+2 concentration.
1
firms the results of the HNMR spectrum. The greatest
downfield peak in 168 ppm, is likely to arise from the
HC=N. The peak in 157.1 ppm is due to carbon atoms
which are attached to the hydroxyl groups. The signal at
56.1 can be attributed to the carbon atoms of the CH2
groups.29,30
RESULTS AND DISCUSSION
Characterization
UV-Vis spectra
FT-IR
UV-Vis spectra of the synthesized ligand and the
complex have been prepared in ethanol (Fig. S1). Elec-
The FT-IR spectrum of H2[(OH)2-salen] and [Cu-
((OH)2-salen)] are shown in Fig. S4. The band appeared at
4
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Selective Solid-phase Extraction of Cu2+ by a Novel
3400-3600 cm-1 is assigned to uO-H stretching. The band at
2751 cm-1 is assigned to OH group (ortho position) associ-
ated inter-molecularly with the nitrogen atom of CH=N
group. This band disappeared in the FT-IR spectrum of the
complex. The sharp strong band observed at 1642 cm-1 in
ligand spectrum is assigned to the azomethine group vibra-
tion. This band is slightly shifted to lower frequencies in
the complex indicating that the imine nitrogen atom is co-
ordinated to the Cu2+ ion. In the spectrum of the complex,
the medium or weak bands observed at 564 and 473 cm-1
can be respectively attributed to (Cu-O) and (Cu-N) mods.
FT-IR spectrum of the activated silica gel includes the
bands at 1099 and 956 cm-1 which indicated respectively
Si-O-Si and Si-OH stretching vibrations. The most infor-
mative spectroscopic data to elucidate anchoring of
H2[(OH)2-salen] and [Cu((OH)2-salen)] on the silica gel
surface obtained from the comparison of the set of FT-IR
spectra including activated silica gel (SG), SG-H2[(OH)2-
salen] and SG-[Cu((OH)2-salen)], imprinted and non-im-
printed silica gel adsorbent31,32 (Fig. S5).
sorption by Cu(II)-imprinted and non-imprinted silica gel
adsorbent was tested (Fig. 2). At low pH ranges due to the
protonation of the active sites, the Cu2+ adsorption is low-
ered. The maximal complex formation was observed at pH
5. Considering the ksp of Cu(OH)2 (4.8 × 10-20), the solu-
bility of Cu2+ at pH = 5 was 4.8 × 10-2 M (3050 ppm), while
at pH = 6 it reduced to 4.8 × 10-4 M (30.50 ppm). The opti-
mized concentration was 1000 ppm, therefore, the pH
above 5 could not be used.
Kinetic of the reaction
Figure 3 shows that an equilibrium time of about 5
min was required for complete adsorption process. As the
time of 50% adsorption (t1/2) was less than 1 min. It means
that the sorption rate is very fast. This kind of fast kinetic
adsorption is due to accessibility of active sites on the sur-
face of the adsorbent.34
Static adsorption capacity of Cu(II)-imprinted and
non-imprinted adsorbent
The adsorption capacity is an important factor be-
cause it determines how much adsorbent is required to
Thermal analysis
TG and DTG curves of imprinted and non-imprinted
silica gel adsorbent are shown in Fig. 1. The weight loss oc-
curred in temperature range of 225-227 °C reflects the sur-
face grown salen groups. This could confirm the covalent
anchoring of functional group on silica gel surface. That
one in temperature range of 88-90 °C corresponds to the
loss of humidity.
Batch adsorption experiments
Effect of pH
Complex formation between salen immobilized on
the silica-gel surface and copper ions was expected to be
pH dependent. For this reason pH influence on the Cu2+ ad-
Fig. 2. Effect of pH on sorption of the Cu(II) by Cu(II)-
imprinted and non-imprinted silica gel.
Fig. 3. Effect of stirring time on the Cu(II) sorption by
Cu(II)-imprinted and non-imprinted silica gel.
Fig. 1. TG-DTG curves of Cu(II)-imprinted (a) and
Non-imprinted silica gel (b).
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Article
Faghihian and Asghari
Table 2. Tolerance limits (ppm)
quantitatively extract the analyte from a given solution. As
can be seen from Figure 4, the amount of Cu2+ ions ad-
sorbed per unit mass of ion-imprinted or non-imprinted ad-
sorbent increased till plateau values were obtained. The
static adsorption capacity of the Cu(II)-imprinted and
non-imprinted silica gel for Cu2+ sorption were calculated
67.3 mg.g-1 and 56.5 mg.g-1, respectively. Wu et al. used
imprinted silica gel modified by N-[3-(trimethoxy-silyl)-
propyl]ethylenediamine (TPED) for removal of Cu2+ from
aqueous solutions. Their reported adsorption capacity was
higher than the value of this work, but the selectivity was
lower.16 Gue et al also use diethylenetriamine imprinted sil-
ica for Cu2+ adsorption. The adsorption capacity of 41.1
mg.g-1 and selectivity coefficient of 411 was reported.17
The reported adsorption capacity of different imprinted
material used for adsorption of a variety of cations was al-
ways lower than the value obtained in this work.18-47 Fur-
thermore the Cu(II)-imprinted silica gel prepared in this
work showed faster adsorption kinetic and higher selectiv-
ity value for the studied cations.
Cu(II)-imprinted
Non-imprinted
adsorbent
Metal ion
adsorbent
Ni(II)
Zn(II)
10100
8000
180
120
Adsorption capacity, distribution ratio, the selectivity
factor of Cu+2 with respect to Ni+2 and Zn+2 and the relative
selectivity factor were calculated by following equations.35
(C0 -Ce )V
Q =
D =
(1)
(2)
(3)
(4)
W
Q
Ce
aCu DCu
=
M
DM
aI
b =
aN
where Q represents the adsorption capacity (mg.g-1), C0
and Ce represent the initial and equilibrium concentration
of metal ion respectively (mg.L-1), W is the mass of the ad-
sorbent (g), and V is the volume of metal ion solution (L),
DCu and DM represent the distribution ratios of Cu+2 and
Ni+2 or Zn+2 (mL.g-1), aCu(II)/M(II) is the selectivity coeffi-
cient with respect to competitive ion, aI and aN represent
the selectivity factor of Cu(II)-imprinted and non-im-
printed salen-functionalized silica gel adsorbent respec-
tively. The calculated D values for Cu2+ is high, while sig-
nificantly lower for Ni2+ and Zn2+. The b values for Ni+2
and Zn+2 are 50.32 and 31.94 respectively which are greater
than one (Table 3). This means that Cu(II)-imprinted adsor-
bent has higher selectivity for Cu+2 adsorption than non-
imprinted one.36 Thus Cu(II)-imprinted adsorbent can be
used for removal of Cu2+ in the presence of high concentra-
tions of Zn+2 and Ni+2.
Selectivity of the Cu(II)-imprinted adsorbent
The Zn2+ and Ni2+ ions were chosen as the competi-
tive species because these ions have similar charge, ionic
radius and properties. Additionally they exist in real and
environmental samples together. Tolerance limit of Cu(II)-
imprinted and non-imprinted adsorbent are listed in Table
2. The tolerance limit is defined as the ion concentration
causing a relative error ³5% in adsorption of Cu+2. The tol-
erance limits of the investigated competitive ions of non-
imprinted adsorbent are 55 and 65 fold of Cu(II)-imprinted
one (Table 2).
There are two possible factors for the selectivity of
Cu(II)-imprinted salen functionalized silica gel adsorbent.
Table 3. Selectivity of Cu+2 ions on imprinted and non-imprinted
silica gel sorbent
b c
a
b
Competitive ion
aI
aN
Ni(II)
Zn(II)
566.53
350.49
11.26
10.97
50.32
31.94
a: selectivity factor of Cu(II)-imprinted silica gel adsorbent
b: selectivity factor of non-imprinted silica gel adsorbent
c: the relative selectivity factor (aI/aN)
Fig. 4. The effect of Cu(II) initial concentration on ad-
sorption capacity.
6
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© 2013 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J. Chin. Chem. Soc. 2013, 60, 000-000

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Selective Solid-phase Extraction of Cu2+ by a Novel
Table 4. Ionic radii of Zn2+, Ni2+ and Cu2+
Table 5. Cu2+ concentration and standard deviations of real
samples
Cation
Radius (pm)
Cu(II) concentration
(ppm)
Standard deviation
(ppm)
Cu2+
Zn2+
Ni2+
73
74
69
Region
ZamanKhan
Zarinshahr
Ziyar
Ejieh
Varzaneh
67.28
342.50
78.30
29.39
35.73
2.08
2.94
2.08
1.89
1.94
One is the functional group inherent selectivity; salen
ligand has good affinity toward Cu2+.
The second is the coordination-geometry selectivity
that means the Cu(II)-imprinted adsorbent can provide the
ligand groups in a suitable way required for coordination of
Cu2+ ion.37 The selectivity factor of Cu(II)-imprinted ad-
sorbent with respect to Ni2+ were higher than Zn2+. This is
attributed to similarity of the ionic radius of Zn2+ and Cu2+
which intensified the interfering effect of Zn2+ (Table 4).
The applicability of the method for real samples was
successfully examined for analysis of cooper in aqueous
solutions taken from different location of Zayandehrood
river (Table 5). In Zarinshahr sample due to the presence of
many industrial factories including Isfahan Steel Factory,
higher concentation of the Cu2+ was observed. The stan-
dard deviation between 1.84-2.94 was obtained which was
acceptable for the method.
Table 6. Extraction recyclability through eight adsorption/elution
cycles
Adsorption
capacity
Recovered
capacity
(mg.g-1)
Standard
deviation of
Adsorption
recycle
(mg.g-1)
capacity (mg.g-1)
1
2
3
4
5
6
7
8
67.28
64.01
63.94
62.69
60.72
59.06
54.16
53.82
100.0
95.2
95.0
93.2
90.2
87.8
80.5
80.0
1.08
0.94
1.08
1.09
0.99
0.89
0.95
0.94
pacity is more significant than the dynamic capacity. The
breakthrough capacity was calculated with the assumption
that the breakthrough occurred at Ce/Ci = 0.01. It was 60.2
mg.g-1 of dry functionalized silica gel and very close to
static adsorption capacity as a result of fast kinetic of ad-
sorption.38,39
Precision of the method
Under the optimized conditions, twelve replicate
samples were examined by static method. The mean quan-
tity of adsorbed Cu2+ was 67.28 mg.g-1. The relative stan-
dard deviation of the adsorption capacity was 1.56% which
indicated that the method had good precision.
Reusability of the adsorbent
CONCLUSION
Adsorption capacity of the Cu(II)-imprinted silica gel
was determined for eight consecutive recycling. The de-
crease on the adsorption capacity was attributed to the sep-
aration of loosely bonded ligands but the ligands which are
covalently anchored to the surface were not separated,
hence the capacity remained constant after seventh regen-
eration cycle. The variation in adsorption capacity within 8
adsorption-desorption cycles are displayed in Figure 5.
These results showed that the synthesized Cu(II)-im-
printed adsorbent can be used repeatedly with satisfactory
adsorption capacity (Table 6).
In this research, a new adsorbent for selective adsorp-
Dynamic adsorption capacity of Cu(II)-imprinted ad-
sorbent
Figure 6 shows the breakthrough carve of the Cu(II)-
imprinted adsorbent. The calculated total dynamic capacity
was 65.4 mg.g-1. For column operation, breakthrough ca-
Fig. 5. Variation of adsorption capacity of the ion-im-
printed sorbent within eight adsorption/desorp-
tion cycles.
J. Chin. Chem. Soc. 2013, 60, 000-000
© 2013 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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7

Article
Faghihian and Asghari
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