Journal of Analytical Sciences, Methods and Instrumentation, 2012, 2, 60-67 Published Online June 2012 (
Selective Separation and Analysis of Pb(II) Using a New
Surface Imprinted Multi-Walled Carbon Nanotubes
Combined with AAS
Haisheng Zhang1, Weiping Zhou2, Hongqing Wang1*, Yuyuan Wang1, Fangfang He1, Zhiqiang Cheng1,
Honglin Li1, Jinhui Tang1
1School of Chemistry and Chemical Engineering, University of South China, Hengyang, China; 2College of Mathematics and Physi-
cal, University of South China, Hengyang, China.
Email: *
Received March 2nd, 2012; revised March 20th, 2012; accepted April 10th, 2012
A new surface ion-imprinted Multi-walled carbon nanotubes (MCNTs), which was 6,6’-((1E,1’E)-(pyridine-2,6-diyl-
bis(azanylyl))bis(methanylylidene))bis(2-allyl-phenol) and Pb(II) complex as functional monomer and template ion was
presented for extracting and enrichment traces of Pb(II) ion. Parameters affecting the recovery of Pb(II) have been in-
vestigated in detail. The novel IMCNTs display high afnity, specicity, and selectivity for Pb(II) with a maximum
uptake capacity of 115.5 mg·g–1 at pH 4.0. Meanwhile, only 11 mins was enough for extracting 98.5% Pb(II) for the
IMCNTs. No signicant loss in adsorption capacity is observed when the IMCNTs are reused for eleven times. Separa-
tion and preconcentration with IMCNTs particles results in a limit of detection of 0.47 μg·L–1 (3σ) and RSD (n = 8) of
1.16% by using atomic absorption spectrophotometer (AAS).
Keywords: Lead Determination; Ion Imprinted Particles; Carbon Nanotube; Selective Recognition
1. Introduction
Soil and water pollution, caused by toxic heavy metals, is
a major environmental concern [1]. Among toxic heavy
elements, lead is one of the commonest for animals and
humans, even at lower concentrations [2,3]. Unlike organic
compounds, lead is non-biodegradable and accumulative
through its interaction with inorganic and organic materials,
including adsorption, formation of complexes and chemical
combinations etc. [4]. Consequently, the development of
reliable methods for the removal and determination of lead
from environment is of particular significance [5,6].
However, for conventional techniques, determining lead is
very difficult due to its low concentrations in environmental
samples and matrix interference. Thus, an effective
enrichment and separation process is usually necessary
prior to determination.
In recent years, Surface imprinting technique (SIT) has
become a powerful method for high selectivity adsorption
of target metal ions [7]. It is exible, economical, environ-
mental-friendly, highly selective, speedy, simple, rich in
accessible sites, safe, easily automatic, and quick in mass
transfer and binding kinetics [8-10]. The particularly
promising applications of SIT are trace enrichment and
trace separation [8-12]. SIT is mainly based on the utiliza-
tion of inorganic and organic solid sorbents which possess
a stable and insoluble porous matrix having suitable
active groups (typically organic groups) to interact with
metal ions. Silica gel [13,14] and MCNTs [15] are ideal
supports for organic groups. There are some reports
about the enrichment and separation of Pb(II), using SIT
with silica gel as the support [2,3,6]. However, there is
few report on the synthesis of IMCNTs for Pb(II) extrac-
The classical preparation procedure of ion-imprinted
polymer is collecting template molecule, functional
monomer and cross-linker together to compounding. But
the template molecule with functional monomer often
isn’t monogamous combination in ion-imprinted polymer.
The coordination effect between metal ion and ligand is
forceful, combination quickly, steady, convenient [16]. So,
the coordination effect between metal ion and ligand is a
top choice in SIT progress. The kinds of o-Hydroxyphenol
Schiff base chemical compound have very well coordi-
nation capability with metal ions [17,18]. In order to
increase relative selectivity of absorbent for Pb(II), a
novel complex of 6,6’-((1E,1’E)-(pyridine-2,6-diylbis
*Corresponding author.
Copyright © 2012 SciRes. JASMI
Selective Separation and Analysis of Pb(II) Using a New Surface Imprinted Multi-Walled Carbon
Nanotubes Combined with AAS
ABMBAPOL) with Pb(II) was synthesized as functional
monomer and template molecule of ion-imprinted polymer
in this study. Meanwhile, a new surface-grafted Pb(II)-
imprinted carbon nanotubes sorbent was presented.
Parameters affecting the separation and pre-concentration
of Pb(II) from aqueous solution were also discussed.
Finally, a new method for determining traces of Pb(II)
was developed.
2. Materials and Methods
2.1. Reagents and Chemicals
Analytical and spectral grade chemicals and doubly dis-
tilled water (DDW) were used throughout the experi-
ments. 0.1 M HNO3 or 0.1 M NH3·H2O were utilized for
adjusting pH of solutions. Standard solutions (1.0
mg· mL –1) of Pb(II), Cd(II), Cu(II) and Ni(II), containing
1.0% HNO3, were prepared by dissolving corresponding
amounts of nitrate salts in DDW.
3-Allylsalicylaldehyde, 2,6-Diaminopyridine, Acrolein,
and 2,2’-azobisisobutyronitrile (AIBN) (98%) were offered
by Aladdin. 3-Aminopropy ltrimethoxysilane (APS) and
ethylene glycol dimethacrylate (EGDMA) were pur-
chased from Golden Dragon Industrial (HK) Co., Ltd.
MCNTs was supplied by Shenzhen Nanotech Port Co.
Ltd. Lead standard liquid (GBW08619) was supplied by
National Institute of Metrology. Other chemicals were
purchased from J&K scientific LTD.
2.2. Apparatus
Scanning Electron Microscope (SEM, JEOL JSM 6700 F)
was used to study the morphology and shape of the
MCNTs. A Perkin-Elmer Lambda 45 AAS spectrometer
was used for determining concentrations of metal ions.
IR Spectra (4000 - 400 cm–1) in KBr pellets were re-
corded using IR Prestige-21 from Shimadzu. 1H-NMR
spectra were taken on a Varian XL-300 Spectrometer
with TMS as the internal reference and CD3COCD3 as
the solvents. A pHs-3 C digital pH meter was used for
measuring pH.
2.3. Preparation of Samples
Natural water samples were taken locally. River water
came from Xiangjiang River, Hengyang, China. The Tap
water was collected from our laboratory. The waste water
was obtained from lead-zinc mine of Songbai, Hengyang,
China. Before filled with the water samples, polyethylene
bottles were cleaned with detergent, water, diluted nitric
acid and DDW in sequence. All water samples were
filtered through a 0.45 μm membrane filter and adjusted
to pH 4 with the diluted HNO3 and NH3·H2O.
2.4. Preparation of IMCNTs and Non-IMCNTs
2.4.1. Synthesis of
The functional monomer was prepared as the literature
[19]. Firstly, 100 mL methanol (MeOH) and 3-Allyl-
salicylaldehyde (2.97 g) were added to a three-neck flask
one after another. Then, 2,6-Diaminopyridine (1.00 g) in
60 mL MeOH was added dropwise to the above solution
under stirring at room temperature. After being continu-
ously stirred for 2 h at room temperature, many yellow
solids were obtained by filter. Recrystallization of the
yellow compound with CH2Cl2 and n-hexane (2:1), gave
2.38 g yellow crystals.
Yield: 2.38 g (60%), mp: 162.1˚C - 162.8˚C, 1H-NMR:
(CD3COCD3, d ppm), δ: 3.48 (d, 4H, CH2), 5.04 - 5.14
(m, 4H, CH2), 6.04 - 6.09 (m, 2H, CH), 6.96 - 8.08 (m,
9H, Ar), 9.70 (s, 2H, CH). FT-IR (KBr, cm–1) γ: 3633.89
(O-H); 3045.60 (C-H of Ar-C-H); 2938.10, 2870.67(C-H);
1683.74 (C=N); 1662.32 (C=C); 1608.04 (C=N, pyri-
dine); 1487.56, 1450.21 (Ar-C=C).
2.4.2. Synthesis of MCNTs Functionalized by
MCNTs were first hydroxylated according to literature
[20]. Then, they were functionalized with amino to pre-
pare MCNTs-NH2 as described in literature [21]. The
typical process was as following. Under stirring, 4 ml of
3-aminopropyltriethoxysilane was added to the mixture
of MCNTs-OH (4.01 g) and dry-toluene (100 ml). After
the reactions proceeded for 24 h at room temperature, the
MCNTs-NH2 was obtained by centrifugation, followed
by redispersion in methanol and centrifugation for three
2.4.3. Synthesis of Vinyl-Group-Functionalized
Under stirring, 4 mL acrolein (dissolved in 10 mL MeOH)
was added dropwise to a solution of MCNTs-NH2 (1.90
g) and MeOH (90 mL). After reacting for 3 h at room
temperature, the reaction solution was centrifugated, re-
sulting in the solid nanoparticles Vinyl-Group-Function-
alized MCNTs (MCNTs-CH=CH2, 1.99 g) which was
then washed with MeOH/DDW/DMF (1:1:1 in volume).
2.4.4. Synthesis of IMCNTs and Non-IMCNTs [22]
The synthesis process of IMCNTs, whose surface was
grafted by Pb(II)-imprinted group, is presented as
Scheme 1. Firstly, 0.76 g (CH3COO)2Pb·3H2O was dis-
solved in 25 mL MeOH. Then, this solution was slowly
added to a glass reactor containing the functional mono-
mer (PDABMBAPOL, 1.59 g) in DMF (25 mL) under
Copyright © 2012 SciRes. JASMI
Selective Separation and Analysis of Pb(II) Using a New Surface Imprinted Multi-Walled Carbon
Nanotubes Combined with AAS
Copyright © 2012 SciRes. JASMI
in the filtrate were directly determined by AAS. The ad-
sorbing IMCNTs were eluted with 10 mL HCl (6 M)
solution, and the concentrations of the metal ions in the
eluent were also determined by AAS. Unless otherwise
stated, each measured value is mean to three replicates.
Pb(II)-IMCNTs-elute was used to denote these MCNTs
stirring. After the mixture was stirred for 3 h at room
temperature, MCNTs-CH=CH2 (2.01 g), AIBN (0.10 g)
and EGDMA (4 mL) were added. Then, nitrogen was
bubbled in to drive away oxygen in the reactor for 25
mins. After being kept stirred for 24 h at 60˚C under ni-
trogen atmosphere, the mixture was natually cooled
down to room temperature and ltered. The products
obtained were washed with MeOH/DDW/DMF (1:1:1 in
volume), and then treated with 6 M HCl solution for 12 h
to remove Pb(II) imprinted in IMCNTs. The nal prod-
ucts were cleaned with DDW for several times until
acid-free, and then dried under vacuum at 70˚C for 48 h.
Non-IMCNTs were prepared similarly in the absence of
2.5.2. Parameters
The amount of Pb(II) adsorbed on the MCNTs (Q), the
distribution ratio (Kd), the selectivity coefcient (k) and
the relative selectivity coefcient (k') were calculated
using the following equations, respectively:
2.5. Enrichment of Pb(II)
2.5.1. Batch Process
The pH values of Pb(II) standard and sample solution
were adjusted to the desired with 0.1 mol·L1 HNO3 or
0.1 mol·L1 NH3·H2O, and the volume was adjusted as
desired with DDW. After that, 30 mg of IMCNTs or
Non-IMCNTs were added, and the mixed solution was
shaken vigorously for 30 mins. Thereafter, the solution
was centrifuged, and the concentrations of the metal ions
Scheme 1. Preparation of IMCNTS and Non-IMCNTS.
Selective Separation and Analysis of Pb(II) Using a New Surface Imprinted Multi-Walled Carbon
Nanotubes Combined with AAS
where 0 and 0 are the initial and equilibrium con-
centrations of metal ions (mg·mL1), respectively. W is
the mass of Pb(II)-ion-imprinted or non-imprinted carbon
nanotube (g) and V is the volume of metal ion solution
(mL). X is the interfering ion. dPb
sent the distribution ratios of Pb(II) and Cd(II), Cu(II),
MCNTs and k
IMCNTs represent the selectivity
factor of imprinted sorbent and non-imprinted sorbent,
3. Results and Discussion
3.1. Characterization
FT-IR spectra was used to confirm functional groups on
the IMCNTs (Figure 1). Compared with the original
MCNTs, the IMCNTs, whether adsorbing Pb(II) or not,
or being eluted, presented -C=N- bond locating around
1681.75 - 1724.29 cm1, and -OH bond around 3650 cm1
[15,18,23,24]. These phenomena demonstrated that the
functional groups had been grafted onto the surface of
IMCNTs. With Non-IMCNTs and Pb(II)-IMCNTs-elute
(curve b and d), there were almost no difference between
their FT-IR spectra, demonstrating Pb(II) was removed
from the IMCNTs completely. However, for Pb(II)-
IMCNTs saturated, it wasn’t the case. The characteristic
absorption peak of -C=N- groups shifted from 1681.75
cm1 (curve b, d) to 1724.29 cm1 (curve c), suggesting
the PbII ions had been imprinted on IMCNTs. In
curves b, c and d, the absorption peak at 3650 cm1, was
attributed to γ O-H. This suggested that -OH had not
been coordinated with Pb(II).
The surface morphologies of MCNTs and Pb(II)-im-
printed functionalized MCNTs were shown in Figure 2.
Apparently, the surface of MCNTs was smooth. On the
contrary, the IMCNTs appear porous, rough, irregular
and agglomerative.
Figure 1. FT-IR spectra of MCNTs (a), Non-IMCNTS (b),
IMCNTs saturated with Pb(II) (c) and Pb(II)-IMCNTs-
elute (d).
3.2. Effect of pH
The effect of pH on Pb(II) uptake was investigated using
batch process. Because of the hydrolysis of Pb(II) ion in
strong alkali solution, all the experiments were carried
out under pH lower than 7.0. Figure 3 showed that the
adsorption of lead was strongly affected by pH of the
solution. The enrichment efficiency of lead was very low
at pH below 2, because the protonation made the bonding
capability of adsorbent decrease. From pH 2.0 to 4.0, the
adsorption efficiency increased sharply with increasing
pH. The recoveries of Pb(II) were 95.6% - 97.5% with in
the pH range of 4.0 - 6.0. Here, pH 4.0 was a relatively
optimal condition for adsorbing Pb(II), and subsequent
experiments were made at pH 4.0.
3.3. Kinetic Experiment
Uptake kinetics of Pb(II) on the IMCNTs were investi-
gated using batch process. After adjusted pH to 4.0, Pb(II)
aqueous solution (25 mL, 10 μg·mL1) was mixed with
30 mg IMCNTs. During the process of absorbing, Pb(II)
Figure 2. SEM images of MCNTs (a) and IMCNTS (b).
Copyright © 2012 SciRes. JASMI
Selective Separation and Analysis of Pb(II) Using a New Surface Imprinted Multi-Walled Carbon
Nanotubes Combined with AAS
concentration in the suspension was determined every 3
min. Figure 4 showed that only 11 mins. was enough for
extracting 98.5% Pb(II) of the solution and plateau val-
ues were gradually attained within 17 mins, owing to the
high complexation rate between Pb(II) ions and func-
tional ligand of IMCNTs.
3.4. Static Adsorption Capacity
Adsorption capacity of the IMCNTs and Non-IMCNTs
was investigated using batch experiments. The concen-
tration of Pb(II) ion in the initial solution ranged from 20
to 180 μg·mL1. Figure 5 showed that the adsorption
amount increased with increasing the initial concentra-
tion of Pb(II). When the initial concentration of Pb(II)
was large enough, a plateau began. The maximum Pb(II)
adsorption capacity of the IMCNTs was 115.5 mg·g1,
much higher than that of Non-IMCNTs (84.4 mg·g1).
Figure 3. Effect of pH on sorbent of Pb(II); other conditions:
Sorbent 30 mg, Pb(II) 10 μg·mL1, V 25 mL, T 298 K.
Figure 4. Effect of equilibrium time on sorbent of Pb(II), C0
10 μg·mL1.
Figure 5. Effect of Pb(II) initial concentration on the ad-
sorption quantity of IMCNTS and Non-IMCNTS. Other
conditions: Sorbent 30 mg, V 25 mL, pH 4.0, T 298 K.
3.5. Thermodynamics of Adsorption
The effect of temperature on the adsorption equilibrium
of Pb(II) ion was analyzed for IMCNTs in the tempera-
ture range from 298.15 to 318.15 K. Thermodynamic
parameters such as standard Gibbs free energy change
, kJ·mol1), enthalpy change (
, kJ·mol1), and
entropy change (S
, kJ·(mol·K)1) were calculated us-
ing the following equations:
 K (5)
  (6)
ln SH
 (7)
where K is equilibrium constant (as
C and
C are the equilibrium concentration of Pb(II) on ad-
sorbent and in the solution, respectively), T is absolute
temperature (K), and R is the gas constant (R = 8.314
The plot of ln
against 1T is shown in Figure 6.
According to Equation (7), the slope and intercept of the
straight line in Figure 6 corresponds to
 and
respectively. Therefore,
and S
calculated to be 70.12 kJ·mol1 and 0.27 kJ·(mol·K)1,
respectively. By Equation (5), at various tem-
perature was calculated as 10.37 kJ·mol1 (298.15 K),
11.72 kJ·mol1 (303.15 K), 13.07 kJ·mol1 (308.15 K),
14.42 kJ·mol1 (313.15 K), and 15.77 kJ·mol1
(318.15 K). The positive
indicates the endother-
mic character of the adsorption process, however, the
negative G
reveals the adsorption spontaneous na-
ture of Pb(II). The positive represents a chaos in-
crease in the adsorption process.
Copyright © 2012 SciRes. JASMI
Selective Separation and Analysis of Pb(II) Using a New Surface Imprinted Multi-Walled Carbon
Nanotubes Combined with AAS
Figure 6. Effect of temperature on sorbent of Pb(II) on
IMCNTS. Pb(II) 10 μg·mL1, V 25 mL, pH 4.0.
3.6. Cycling and Reproducibility of
Pb(II)-IMCNTs, were subjected to adsorption-desorption
cycles in a batch process to test their reproducibility and
cycling behavior. 6 M HCl (10 mL) acted as a desorption
agent. The recycled Pb(II)-IMCNTs presented a recovery
not less than 95% at the 10th cycle, suggesting an ad-
sorption capacity loss only by about 4%. Therefore, it
can be concluded that the IMCNTs can be used repeat-
edly without compromising their adsorption capacities,
3.7. Selectivity of the IMCNTs
The selectivity of an imprinted material for a given ion
plays the key role in its practical use. This paper has es-
timated the selectivity of the imprinted MCNTs for Pb(II)
relative to Cd(II), Cu(II) and Ni(II), separately. Each
metal ion in its solution had the concentration of 10
μg·mL1. As shown in Table 1, with IMCNTs, the rela-
tive selectivity coefficients () of Pb(II)/Cd(II), Pb(II)/
Cu(II) and Pb(II)/Ni(II), were 21.6, 5.5 and 22, respec-
tively, greater than one, indicating IMCNTs displayed
higher selectivity for Pb(II) relative to Cd(II), Cu(II) and
Ni(II). Therefore, the above IMCNTs could be applied to
selectively separating Pb(II) from the solution containing
Cd(II), Cu(II) and Ni(II). Two possible factors contri-
buted to the higher selectivity for Pb(II) in the presence
of the above competitive ions. One was the holes size
selectivity. The size of Pb(II) ion cut out for the cavity of
the IMCNTs. The other was the coordination geometry
selectivity. IMCNTs could provide ligand groups with
preferred selectivity for Pb(II) ions.
3.8. Accuracy and Precision of the Analytical
The accuracy and precision of the analytical method
were evaluated by repeating the experiment for eight
times under the optimal experimental conditions. The
results indicated that the precision of the method, evalu-
ated as the relative standard deviation (RSD, n = 8), was
1.16%. The limit of detection (LOD), calculated based on
the three times of the blank standard deviation of eight
runs the blank solution, was 0.47 μg·L1. This indicated
that the method had good precision for the analysis of
trace Pb(II).
3.9. Application of the Proposed Method
The accuracy of the method was evaluated by determin-
ing the amount of Pb2+ ions in the certified reference
material and three environmental water samples (River
water, Tap water, Waste water). For water samples, the
standard addition method was adopted. From Table 2, it
could be seen that the estimated values agreed well with
the certified values. The recoveries of Pb(II) ions were in
Table 1. Competitive sorption of Pb(II) and metal ions on
IMCNTs and NIMCNTs at pH 4.0.
Mixture of ions
(10 μg·mL1, 250 mL)
(mL·g1) kIMCNTs kNIMCNTs k'
Pb(II)/Cd(II) 1658.3/64 21.7/18.1 25.9 1.2 21.6
Pb(II)/Cu(II) 1646/71 33/7.9 23.2 4.2 5.5
Pb(II)/Ni(II) 1613/6720.1/18.7 24.1 1.1 22
Table 2. Determination of Pb(II) in environmental water
Sample Pb(II) added
Pb(II) founded
0 BQLb
5.0a 4.85 ± 0.02 97.0
10.0a 9.75 ± 0.03 97.5
0 0.59 ± 0.01 -
5.0 5.76 ± 0.06 103.0 River water
10.0 10.57 ± 0.12 99.8
0 BQLb -
5.0 4.98 ± 0.07 99.6 Tap water
10.0 10.01 ± 0.11 100.1
0 1.17 ± 0.02 -
5.0 6.24 ± 0.08 101.1 Waste water
10.0 11.08 ± 0.14 99.2
aReference value. The certified sample solution was accurately diluted to 5
and 10 μg·L1, respectively; bBelow the quantification limit.
Copyright © 2012 SciRes. JASMI
Selective Separation and Analysis of Pb(II) Using a New Surface Imprinted Multi-Walled Carbon
Nanotubes Combined with AAS
Copyright © 2012 SciRes. JASMI
Table 3. Comparisons of maximum adsorption capacity, analytical precision and accuracy of different SPE materials for
pre-concentration of Pb(II).
SPE material coupled with
analytical technique
The maximum adsorption
capacity (mg·g1)
(%) Ref.
P2AT modified MWCNTs/AAS 186.4 1 3.2 [25]
PANI modified MWCNTs/UV 22.2 ND ND [26]
Column SPE on MWCNTs/AAS ND* 8.0 <2.5 [27]
IDA modified MWCNTs/ICP-MS 8.98 0.00070 1.0 [28]
IMCNTs/AAS 115.5 0.47 1.16 Present work
*ND: not detected.
the range of 97.0% - 103.0%. The comparisons of maxi-
mum adsorption capacity, analytical precision and accu-
racy of different SPE materials for Pb(II) was given in
Tables 3. As could be seen, the present analytical
method was comparable with that obtained by other re-
ported different SPE materials in recent years. These
results clearly demonstrated that the IMCNTs prepared
were highly efficient, suitable and satisfactory for ex-
tracting and determining Pb(II) ions.
4. Conclusion
The newly IMCNTs was synthesized using a complex of
PDABMBAPOL with Pb(II) as functional monomer and
template ion. The IMCNTs exhibited high affinity, selec-
tivity and fast kinetics for Pb(II) ions. Under optimal
conditions, the maximum adsorption quantity of IMCNTs
was 115.5 mg·g1 much higher than that of Non-
IMCNTs (84.4 mg·g1). The presence of other metal ions
such as Cd(II), Cu(II), or Ni(II) did not affect IMCNTs
selectivity for Pb(II). Separation and pre-concentration
by solidphase extraction with IMCNTs particles results
in a limit of detection of 0.47 μg·L1 (3σ) and RSD (n =
8) of 1.16% by using AAS. In addition, the IMCNTs
prepared had high reproducibility and were efficient,
sensitive and reliable for the enrichment and determina-
tion of trace lead.
5. Acknowledgements
This research was supported by the National Natural
Science Foundation of China (No. 11175080) and by the
Nature Science Fund of the Hunan Province (No.
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