A highly selective colorimetric chemosensor for detecting the respective amounts of iron(II) and iron(III) ions in water

Article abstract of DOI:10.1039/b701201m

A novel colorimetric chemosensor containing terpyridine was synthesized. It showed high selectivity and sensitivity for Fe(ii) and Fe(iii) ions in neutral aqueous solution in the presence of other metal ions such as Cd²⁺, Cr³⁺, Zn

Full text of DOI:10.1039/b701201m

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A highly selective colorimetric chemosensor for detecting the respective
amounts of iron(II) and iron(III) ions in water
Zuo-Qin Liang, Cai-Xia Wang, Jia-Xiang Yang,* Hong-Wen Gao,b
a
a
abc
a
c
c
Yu-Peng Tian, Xu-Tang Tao and Min-Hua Jiang
Received (in Montpellier, France) 25th January 2007, Accepted 13th March 2007
First published as an Advance Article on the web 29th March 2007
DOI: 10.1039/b701201m
A novel colorimetric chemosensor containing terpyridine was synthesized. It showed high
selectivity and sensitivity for Fe(II) and Fe(III) ions in neutral aqueous solution in the presence of
2
+
3+
2+
2+
2+
2+
2+
+
2+
2+
other metal ions such as Cd , Cr , Zn , Co , Ni , Cu , Pb , Na , Ca , Mg , K
+
+
2+
3+
and Ag . Upon the addition of Fe or Fe , the sensor displayed a unique new peak around
67 nm in its absorption spectra, and the color of the solution changed from light yellow to light
5
magenta. In particular, the respective amounts of Fe(II) and Fe(III) ions in the solution can be
detected using the light-absorption ratio variation approach (LARVA).
Introduction
spectra. Here, we report on the synthesis and the sensing
application of 3-{4-[2-(4-dibutylaminophenyl)vinyl]phenyl}-1-
The development of chemosensors for metal ions occurred
1
early, but the design of fluorescent and chromogenic chemo-
0
0
00
0
(
4-[2,2 :6 ,2 ]terpyridin-4 -yl-benzyl)-3H-imidazol-1-ium bromide
4
ꢁ1
ꢁ1
4
(
TBIB) (e275 nm = 3.80 ꢀ 10 M cm , e318 nm = 1.50 ꢀ 10
sensors for the detection of low concentrations of metal ions is
2
still an active area of research. This is because chemosensors
ꢁ1 ꢁ1 4 ꢁ1 ꢁ1
M
cm and e
solution. The terpyridine ligand showed high sensitivity and
= 1.46 ꢀ 10 M cm ) in aqueous
3
66 nm
not only possess simplicity and high sensitivity, but are cap-
able of specific recognition of particular ions in the presence of
3
related ones. Fe ion is the most abundant transition-metal ion
2+
3+
selectivity for Fe
and Fe
over other cations in aqueous
solution. In its absorption spectra, a new band appeared at 567
3+
2+
nm only in the presence of Fe or Fe , and the color of the
solution changed from light yellow to light magenta (Fig. 1).
2+
in humans and other mammals, and it plays important roles in
5
4
various biological systems. It has been studied with methods
In addition, we can determine the respective amounts of Fe
such as atomic absorption spectrometry, spectrophotometry,
and so on. These methods can only detect the total amount of
Fe(II + III) or a certain valence iron. In recent years, Meier
et al. and Kimura et al. both described a terpyridine-based
3+
and Fe
in the solution using the light-absorption ratio
12
variation approach (LARVA).
6
chemosensor to recognize Fe(II). Nevertheless, their sensors
Results and discussion
were not selective for a special metal ion. The properties of a
sensor in aqueous solution are very important for compounds
7
intended for application in living systems. Lately we have
The chromophore of the chemosensor was based on a do-
nor–p–acceptor system. This could display a strong color
development as well as great absorbance. This feature could
make it possible for the chemosensor to be a colorimetric one.
The amino group conjugated to the phenyl ring was the
electron donor and the two butyl groups introduced were to
enhance the electron-donating ability of the nitrogen atom.
The imidazolium salt was the electron acceptor, and made
TBIB possess some solubility in aqueous solution. The syn-
thetic strategy and the structure of the resulting product are
depicted in Scheme 1. 4-(4-(1H-Imidazol-1-yl)styryl)-N,N-
developed a sensor for anionic surfactants in water, which has
been applied to the analysis of water samples with satisfactory
8
results, but most of the studies have been concerned with non-
9
aqueous solutions of ions. In addition, colorimetric sensors
are useful to develop simple-to-use, naked eye diagnostic
1
0
tools. Therefore, our target is to design a highly selective
colorimetric sensor in aqueous solution, which can discrimi-
nate between Fe(II) and Fe(III).
Terpyridine ligands themselves have generally not been used
for sensors, due to possessing an excellent ability to coordinate
with a large variety of transition metal ions with high binding
1
1
constants. But we found that iron terpyridine complexes
generally show a band in the visible region in absorption
a
Department of Chemistry, Anhui University, Hefei 230039, People’s
Republic of China. E-mail: jxyang@ahu.edu.cn
Key Laboratory of Yangtze Water Environment of Ministry of
b
Fig. 1 Color changes observed for TBIB in water upon addition of
Education, College of Environmental Science and Engineering,
Tongji University, Shanghai 200092, People’s Republic of China
State Key Laboratory of Crystal Materials, Shandong University,
2
+
2+
cations. From left to right: 1: none; 2: Co ; 3: Ni ; 4: Ag ; 5: Fe
+
2+
3
+
+
2+
or Fe . Upon the respective addition of Na , Ca , Mg , K
2+
+
,
c
2+
3+
2+
2+
2+
Cd , Cr , Cu , Pb , Zn , the color is similar to 3.
Jinan 250100, People’s Republic of China
9
06 | New J. Chem., 2007, 31, 906–910
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Scheme 1 Synthesis of TBIB (7).
dibutylbenzenamine 5 was prepared from 4-imidazol-1-yl-
benzaldehyde 1 and phosphonium salt 4 by the Wittig reac-
The selective and sensitive signal response of TBIB toward
2
+
3+
Fe
ion and Fe
ion was preserved in absorption. All
0
00
0
0
00
tion. 4 -(4 -Bromomethylphenyl)-2,2 :6 ,2 -terpyridine 6 was
titration experiments were performed in aqueous solution
around pH 6.0. As shown in Figs. 3 and 4, the addition of
8
prepared according to the literature. Finally, 5 and 6 in 1,4-
2
+
3+
dioxane were stirred at 100 1C for three days to give the final
product 7 (TBIB).
low concentration of Fe
or Fe
ion to the solution of
TBIB led to a sharp new band at 567 nm (eFe(tpy) 22 + = 1.84 ꢀ
4
ꢁ1
ꢁ1
4
ꢁ1
ꢁ1
The influence of pH on the absorbance of TBIB was
determined in aqueous solution as shown in Fig. 2. The
absorbance of TBIB at 567 nm remained unaffected by varying
pH. The ratios of absorbance at 318 nm and 366 nm were
almost a constant minimal value in the pH range 6.28 to 4.46,
and then rapidly increased from pH 4.46 to pH 2.20. This
change may be caused by the protonation of the pyridyl
nitrogen.
10 M cm ; eFe(tpy) 32 + = 1.98 ꢀ 10 M cm ), which was
6a
caused by the metal-to-ligand-charge-transfer (MLCT).
+
With the increasing concentration of Fe
+
new peak gradually rose until a mole ratio (TBIB/Fe ) of
2 : 1 was reached. The relationship between TBIB concentra-
2
ion, the sharp
2
2
2
+
tion and the formation of the Fe(tpy)
complex is shown in
the inset in Fig. 3. From the inset we also found the absorption
at 567 nm showed a linear increase and a sharp endpoint at
2
+
TBIB/Fe
ratio of 2 : 1 as the concentration of TBIB
increased. The two experiments indicate that there is no
2
+
2+
to Fe(tpy) in the experimental
dissociation from Fe(tpy)
2
3
+
process. The binding mode of the terpyridine unit for Fe
2
was similar to that of Fe(tpy)2 as shown in Fig. 4. Interest-
+
2
ingly, with the increasing concentration of Fe from 0 to 50.0
+
ꢁ
1
2+
mg L in the solution, the bands of the Fe(tpy)2 at 318 nm
and 366 nm rose simultaneously, and the absorbance ratio
A
318 nm/A366 nm didn’t change. However, the band of the
3
+
Fe(tpy)
2
rose at 318 nm, and descended at 366 nm. As a
3
+
result, the absorbance ratio A318 nm/A366 nm of the Fe(tpy)
2
3
+
solutions increased rapidly with the increase of Fe concen-
tration. Based on these characteristics, the LARVA has been
3
applied to the determination of Fe , and its main equations
+
1
2
Fig. 2 Influence of pH on the absorbance of TBIB in aqueous
are given as eqns (2) and (3). The symbol DA
difference of absorbance ratios between the MLn and L
r
is the
solution.
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3+
Fig. 5 Standard curves for the determination of Fe
(1) and the
2
+
3+
total amount of Fe and Fe (2).
ꢁ5
Fig. 3 Changes in absorption spectra of TBIB (1 ꢀ 10 M) on the
2
+
2+
addition of Fe in aqueous solution (pH = 6.0). The Fe concen-
where p is the sensitivity factor and the inverse reverse ratio of
12d
ꢁ1
tration is 0, 20.0, 30.0, 50.0 mg L , respectively. The inset shows the
relationship between TBIB concentration and the absorbance of
C
L0
,
and q is the linear regression intercept, which often
approaches 0. The less L is added, the higher the analytical
sensitivity obtained. However, too low a value of L can cause a
considerable error of measurement because of the instrument
background noise. From the absorption spectra of the
TBIB–Fe(III) reaction as shown in Fig. 4, 318 and 366 nm
2
+
2+
Fe(tpy)
2
solution at 567 nm. The concentration of Fe
is 3.5 ꢀ
ꢁ
6
10
5
M in the solution. The concentration of TBIB is 0, 2.0, 3.0, 4.0,
ꢁ6
.0, 6.0, 7.0, 8.0 ꢀ 10 M, respectively.
0
0
solutions. CM0 is the initial concentration of M. Both p and q
are constants when the reaction and measurement conditions
were selected as the work wavelengths. Thus, DA
calculated by the relation:
r
may be
L
L
are selected. The symbols Al1, Al2, Al1 and Al2
0
3
A318 nm
A366 nm
A
18 nm
DAr ¼
ꢁ
ð4Þ
ꢁ
1
0
ꢁ1
0
ð1Þ
ð2Þ
A
366 nm
M0
3
+
where
where A318 nm and A366 nm are the absorbances of Fe(tpy)2
solution measured at 318 nm and 366 nm against water.
0
L
l2
L
Al2
A
A
0
2+
A
318 nm and A366 nm are the absorbances of Fe(tpy)
2
DAr ¼ Ar ꢁ Ar0 ¼
ꢁ
Al1
l1
solution or the TBIB solution measured at 318 nm and 366
nm against water. The linear regression curves from a series of
standard Fe(II, III) solutions are shown in Fig. 5, where curve 1
are the absorbances of MLn and L solutions, respectively
measured at wavelengths l and l against water. However,
3+
1
2
is used for the determination of the amount of Fe and curve
if CM0 is low enough, eqn (1) may be simplified into:
2+
3+
for the detection of the total amount of Fe and Fe by
2
2
+
3+
and Fe(tpy)2
using the absorbances of Fe(tpy)2
at 567 nm.
DAr ¼ pCM0 þ q
ð3Þ
To further investigate the selectivity and sensitivity of the
described sensory system for metal ions, a series of coloring
experiments were performed in water. The addition of other
2
+
3+
2+
2+
2+
2+
metal ions such as Cd , Cr , Ni , Zn , Cu , Pb
,
2
+
+
2+
2+
+
Co , Na , Ca , Mg and K did not produce significant
changes in the UV/Vis spectra at 567 nm in aqueous solution.
+
Only upon addition of Ag did the system display a new band
(
Fig. 6(b)) at 450 nm. Fortunately, in the competition experi-
+
ments Ag merely showed a little interference. The competi-
ꢁ5
tion experiments were conducted in the presence of 5 ꢀ 10
g
ꢁ
1
2+
ꢁ4
ꢁ1
3+
2+
3+
L
Fe and 2 ꢀ 10 g L Fe mixed with Cd , Cr
,
2+
2
+
2+
2+
2+
+
2+
+
2+
Ni , Zn , Cu , Pb , Ag , Co , Na , Ca , Mg
+
and K in the TBIB solution. The experimental results are
listed in Table 1. The results indicate that the terpyridine
2
+
3+
ligand has a high selectivity for Fe
and Fe
over other
metal ions. In the competition experiments, both Mg(II) and
Ca(II) appear in error over 10% only when their mole con-
centrations are more than 200 times that of Fe(II). Besides,
Co(II), Ag(I) and Cu(II) caused over 10% of error, resulting
from their competition coordination with TBIB. However,
their amounts should be less than such addition amounts in
physiological studies. We estimated that the errors caused by
Co(II), Ag(I) and Cu(II) would be less than 10% in
ꢁ
5
Fig. 4 Changes in absorption spectra of TBIB (1 ꢀ 10 M) on the
3+
3+
addition of Fe in aqueous solution (pH = 6.0). The Fe concen-
ꢁ1
tration is 20.0, 30.0, 50.0, 70.0, 100.0, 150.0, 200.0, 250.0, 300.0 mg L
respectively. The inset shows the relationship between TBIB concen-
,
3+
2
tration and the absorbance of Fe(tpy)
ꢁ6
solution at 567 nm. The
3+
concentration of Fe is 3.5 ꢀ 10 M in the solution. The concen-
ꢁ6
tration of TBIB is 0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0 ꢀ 10 M,
respectively.
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08 | New J. Chem., 2007, 31, 906–910
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Experimental
Syntheses
1
The resulting compounds were characterized by H and
13
C
NMR spectrometry using a Bruker Avance 300 MHz or 400
MHz spectrometer. Electrospray mass spectra (ESI-MS) were
recorded on an ABI API 4000 mass spectrograph. Melting
points were measured with a Mettler Toledo FP62 instrument.
Elemental analyses were performed on an Elementar Vario
EL-III instrument. IR spectra were recorded on a Nicolet
FT-IR-170SX infrared spectrometer. All chemicals were pur-
chased from Aldrich, Acros or Shanghai Reagent Institute and
the solvents were purified according to conventional methods
before use.
+
Fig. 6 UV/Vis absorption of TBIB in the presence of Ag and Zn
2+
in water. [TBIB] = 1 ꢀ 10 M, [Ag ] = 5 ꢀ 10ꢁ6 M, [Zn ] =
ꢁ5
+
2+
4-Imidazol-1-yl-benzaldehyde 1. 4-Fluorobenzaldehyde (25.0
ꢁ
6
3
.67 ꢀ 10 M.
g, 0.200 mol), imidazole (20.4 g, 0.300 mol) and anhydrous
2 3
K CO (40.0 g) were mixed in DMF (300 mL), and then
several drops of catalytic reagent Aliquat 336 were added. The
mixture was refluxed for 24 h at 100 1C. Half of the solvent
was removed under low pressure. After the mixture returned
to room temperature, it was poured into ice water and left
Table 1 The effect of foreign ions in the solutions and error shown
1
Error , %
a
2
Error , %
a
Ion added
Added, mg/10 mL
overnight. After filtration, the light yellow product (31.6 g,
1
Fe(II)
Fe(III)
Cd(II)
Cr(III)
Zn(II)
Co(II)
Ni(II)
Mg(II)
Ca(II)
Cu(II)
Pb(II)
Na(I)
K(I)
0.50
2.00
2.00
4.00
1.17
2.00
4.00
44.0
72.0
0.700
38.0
41.4
69.7
1.93
8.62
3.68
yield 92.0%) was obtained. H NMR (CDCl , 400 MHz) d:
3
4.20
5.04
ꢁ4.86
ꢁ16.18
6.1
ꢁ8.60
ꢁ4.41
1.09
7.59
8.95
ꢁ14.98
ꢁ12.34
11.6
ꢁ1.15
ꢁ4.20
ꢁ1.11
ꢁ10.82
9
.20 (1H, s), 8.03 (2H, d, J = 8.40 Hz), 8.00 (1 H, s), 7.59 (2H,
ꢁ
1
d, J = 8.40 Hz), 7.43 (1H, s), 7.26 (1H, s). IR (KBr, cm ):
3110, 2846, 2819, 2750, 1690, 1610, 1520, 1310, 1060, 835.
4.02
3.32
4-(N,N-Di-n-butylamino)benzaldehyde 2. This compound
1
was prepared according to the literature.
3
ꢁ8.58
5.79
6.68
4
-Dibutylaminobenzyl alcohol 3. Compound 2 (11.7 g, 50
mmol) was dissolved in methanol (350 mL) in an ice-bath.
NaBH (3.80 g, 100 mmol) was added before the temperature
was allowed to rise to room temperature. After refluxing for
h, the solvent was removed under vacuum. Water was added
to the residue, and the product was extracted with CH Cl
6.85
9.15
Ag(I)
4
a
1
3+
2
Error stands for the metrical error of Fe . Error symbolizes the
2
metrical error of total iron.
2
2
.
The organic phase was washed with water and saturated NaCl
solution two times, respectively. Then it was dried with
anhydrous magnesium sulfate. The solvent was removed to
give a yellow product, which did not need to be isolated.
physiological studies. Although the sensor has a few deficien-
2
+
cies, it can determine the respective amounts of Fe
and
3
Fe in the solution.
+
2
+
3+
Fe and Fe ions can be detected at least down to 1.97 ꢀ
ꢁ
7
ꢁ7
M, respectively, when TBIB is
(4-Dibutylaminobenzyl)triphenylphosphonium iodide 4. The
1
0
M and 1.67 ꢀ 10
ꢁ
5
mixtures of CHCl (100 mL), H O (3.50 mL), PPh (10.7 g,
3
employed at 1 ꢀ 10 M in water. The range makes this
2
3
4
0.0 mmol), HAc (7.30 g, 0.120 mol), KI (6.70 g, 40.0 mmol),
system quite sensitive, so the detection of small quantities of
2
+
3+
Fe ion and Fe ion is feasible.
and compound 3 (9.40 g, 40.0 mmol) were stirred and refluxed
for 10 h. After the solvent was removed, the toluene was added
to the residue. Stirring and refluxing were continued for an
hour. It was subsequently cooled in a refrigerator overnight to
give a white solid. After filtration, the solid was washed with
Conclusions
We have made full use of the characteristics of the terpyridine
3+
1
THF and dried to give compound 4 (18.7 g, yield 76.5%). H
2
+
to synthesize a novel sensor for Fe
and Fe
ions in
NMR (CDCl , 300 MHz) d: 0.93 (6H, t, J = 7.20 Hz), 1.30
3
aqueous solution. Our sensor system displayed a unique new
(
4H, m), 1.47 (4H, m), 3.18 (4H, t, J = 7.65 Hz), 4.95 (4H, d,
peak at around 567 nm in the absorption spectra upon the
2
addition of Fe
J = 12.91 Hz), 6.37 (2H, d, J = 8.70 Hz), 6.82 (2H, d, J =
+
3+
or Fe , and the color of the solution
8
.70 Hz), 7.68 (12H, m), 7.80 (3H, m).
changed. In particular, the sensor can measure the respective
2
amounts of Fe and Fe in aqueous solution. To sum up, it
+
3+
4-(4-(1H-Imidazol-1-yl)styryl)-N,N-dibutylbenzenamine 5.
2
+
3+
showed high selectivity and sensitivity for Fe and Fe in
aqueous solution in the presence of other metal ions. It is a
Compound 4 (7.30 g, 12.0 mmol), compound 1 (1.70 g, 10.0
mmol) and solid NaOH (4.00 g, 100 mmol) were crushed in a
mortar for 15 min. The powder was dissolved in CH Cl . The
2
+
3+
potential Fe and Fe chemosensor through UV/Vis spec-
trometry.
2
2
organic phase was washed thoroughly with water and
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saturated NaCl solution, and then was dried with anhydrous
magnesium sulfate. After filtration, the CH Cl was removed.
CaCl
2
, Cu(NO
3
)
2
ꢃ 3H
2 3 2 3
O, Pb(NO ) , NaCl, KCl, AgNO ,
2
2
respectively, dissolved in deionized water.
The crude product was purified by silica-gel column chroma-
tography with ethyl acetate as the eluent to give the yellow
1
Acknowledgements
product (1.90 g, yield 51.0%). H NMR (CDCl , 400 MHz) d:
3
The work was supported by grants from the National Natural
Science Foundation of China (50532030, 50325311,
0
.95 (6H, m), 1.34 (4H, m), 1.50 (4H, m), 3.29 (4 H, m), 6.63
2H, d, J = 8.84 Hz), 6.87 (1H, d, J = 16.24 Hz), 7.04 (1H, d,
J = 16.24 Hz), 7.21 (1H, s), 7.28 (1H, s), 7.32 (2H, d), 7.38
2H, d, J = 8.84 Hz), 7.54 (2H, d, J = 6.70 Hz), 7.85 (1H, s).
(
5
0335050), the Doctoral Program Foundation of the Ministry
of Education of China, the Education Committee of Anhui
Province (2006KJ032A, 2006KJ135B), the National Natural
Science Foundation of Anhui Province (070414188), The
Team for Scientific Innovation Foundation of Anhui Province
(2006KJ007TD), the Key Laboratory of Opto-Electronic In-
formation Acquisition and Manipulation (Anhui University),
the Ministry of Education, the Person with Ability Founda-
tion of Anhui University.
(
0
00 0 0 00
-(4 -Bromomethylphenyl)-2,2 :6 ,2 -terpyridine 6. This
4
8
compound was prepared according to the literature.
0
0
00
3
-{4-[2-(4-Dibutylaminophenyl)vinyl]phenyl}-1-(4-[2,2 :6 ,2 ]
0
terpyridin-4 -yl-benzyl)-3H-imidazol-1-ium bromide 7. A mix-
ture of compound 6 (3.40 g, 8.50 mmol) and compound 5 (3.15
g, 8.50 mmol) in 1,4-dioxane (30.0 mL) was stirred at 100 1C
for three days, under refluxing. A brown viscous liquid was
obtained which was washed with ethyl ether. The crude
compound was purified by silica-gel column chromatography
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(
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=
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6
1
1
1
1
6
6
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Dujols, F. Ford and A. W. Czarnik, J. Am. Chem. Soc., 1997, 119,
7386; (d) K. G. Thomas, K. J. Thomas, S. Das and M. V. George,
Chem. Commun., 1997, 597.
4
7
47
6
.11; N, 10.83. Found: C, 72.66; H, 6.14; N, 10.71%. IR (KBr,
ꢁ
1
cm ): 2952, 2926, 2874, 2357, 1590, 1522, 1380, 1180, 792.
8
9
J. X. Yang, H. W. Gao, Z. J. Hu and M. H. Jiang, J. AOAC Int.,
2005, 88, 866.
General instrumentation and reagents for titration experiments
(a) T. Ghosh, B. G. Maiya and A. Samanta, Dalton Trans., 2006,
795; (b) S. P. Gromov, E. N. Ushakov, O. A. Fedorova, I. I.
Baskin, A. V. Buevich, E. N. Andryukhina, M. V. Alfimov, D.
Johnels, U. G. Edlund, J. K. Whitesell and M. A. Fox, J. Org.
Chem., 2003, 68, 6115; (c) E. Quinlan, S. E. Matthews and T.
Gunnlaugsson, Tetrahedron Lett., 2006, 47, 9333.
Absorption spectra were recorded with a Model S-4100 spec-
trophotometer (Scinco Instruments, Korea). A Model BS110S
electronic balance (Sartorius Instruments, Beijing) was used to
accurately weigh the standard substances. A Model RO DI
Water Ultra Purification System (Hi-tech Instruments, Shang-
hai, China) was used to produce the deionized water. The
solution pH was measured with a Model pHS-25 acidity meter
10 (a) D. A. Jose, D. K. Kumar, B. Ganguly and A. Das, Org. Lett.,
004, 6, 3445; (b) S. Y. Moon, N. R. Cha, Y. H. Kim and S. K.
Chang, J. Org. Chem., 2004, 69, 181.
2
1
1 (a) B. G. G. Lohmeijer and U. S. Schubert, Macromol. Chem.
Phys., 2003, 204, 1072; (b) R. Dobrawa, M. Lysetska, P. Ballester,
¨ ¨
M. Grune and F. Wurthner, Macromolecules, 2005, 38, 1315.
(
Shanghai Precise Sci. Instrum., China). Standard stock solu-
2
+
tion of Fe
was prepared every time by dissolving ammo-
1
2 (a) H. W. Gao, J. F. Zhao, Q. Z. Yang, X. H. Liu, L. Chen and L.
T. Pan, Proteomics, 2006, 6, 5140; (b) H. W. Gao, S. Q. Xia, H. Y.
Wang and J. F. Zhao, Water Res., 2004, 38, 1642; (c) H. W. Gao,
H. Y. Wang, S. Y. Zhang and J. F. Zhao, New J. Chem., 2003, 27,
nium iron(II) ((NH ) Fe(SO ) ꢃ 6H O, A. R., Shanghai
4
2
4 2
2
Chemical Reagents, China) in deionized water. Standard stock
3
+
solution of Fe
was prepared by dissolving FeCl
3
2
ꢃ 6H O
1
1
649; (d) H. W. Gao, X. Q. Lu and J. R. Ren, Anal. Sci., 2005, 21,
043.
which was purchased from the Institute for Reference Materi-
als of SEPA, Beijing, China. The solutions of other metal ions
1
3 Y. Ren, X. Q. Yu, D. J. Zhang, D. Wang, M. L. Zhang, G. B. Xu,
X. Zhao, Y. P. Tian, Z. S. Shao and M. H. Jiang, J. Mater. Chem.,
2002, 12, 3431.
were prepared from Cd(NO
3
)
2
ꢃ 4H
2
O, Cr(NO
3
)
3
ꢃ 9H
2
O,
Zn(NO Co(NO ꢃ 6H O, Ni(NO
3
)
2
,
3
)
2
2
3
)
2
ꢃ 6H O, MgSO
2
4
,
9
10 | New J. Chem., 2007, 31, 906–910
This journal is ꢂc the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2007