A highly selective optical probe for sensing of Fe3+ based on a water-soluble croconaine

Article abstract of DOI:10.1016/j.jphotochem.2017.07.034

A highly selective water-soluble optical probe, 2,5-bis[2,3,3-trimethyl-3H-indole-5-sulfonic acid]-croconaine (TISC) was successfully synthesized. TISC can efficiently recognize Fe³⁺ with the existence of competing cations (Na⁺, Mg²⁺, Al³⁺, Cr³⁺, Zn²⁺, K⁺, Ca²⁺, Ba²⁺, Pb²⁺, Ni²⁺, Co²⁺, Ag⁺, Cu²⁺, Cd²⁺) in deionized water. The binding constant (K_a) of TISC-Fe³⁺ was calculated to be about 3.071?×?10⁴?M^?1. Correspondingly, the chelating mode of TISC-Fe³⁺ was confirmed by Job's plot, FT-IR and ¹H NMR. Moreover, Fe³⁺ and EDTA could be employed as inputs and the absorbance which was 745?nm as output so that a molecular logic gate could be realized, and the test strips of TISC showed a high selectivity to Fe³⁺.

Full text of DOI:10.1016/j.jphotochem.2017.07.034

Accepted Manuscript
Title: A highly selective optical probe for sensing of Fe3+
based on a water-soluble croconaine
Authors: Shouchen Ye, Chen Zhang, Jinfeng Mei, Zhongyu
Li, Song Xu, Xiazhang Li, Chao Yao
PII:
S1010-6030(17)30603-2
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jphotochem.2017.07.034
JPC 10760
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date:
Revised date:
Accepted date:
1-5-2017
7-7-2017
25-7-2017
Please cite this article as: Shouchen Ye, Chen Zhang, Jinfeng Mei, Zhongyu Li, Song
Xu, Xiazhang Li, Chao Yao, A highly selective optical probe for sensing of Fe3+
based on a water-soluble croconaine, Journal of Photochemistry and Photobiology A:
Chemistryhttp://dx.doi.org/10.1016/j.jphotochem.2017.07.034
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A highly selective optical probe for sensing of Fe3+
based on a water-soluble croconaine
Shouchen Yea,1, Chen Zhanga,1, Jinfeng Meib, Zhongyu Lia,b*, Song Xua,
Xiazhang Lia, Chao Yaoa*
aJiangsu Key Laboratory of Advanced Catalytic Materials and Technology,
School of Petrochemical Engineering, Changzhou University, Changzhou 213164, PR
China
b School of Environmental and Safety Engineering, Changzhou University,
Changzhou 213164, PR China
* Corresponding author. Tel.: +86-519-86330088; Fax: +86-519-86330088
E-mail address: zhongyuli@mail.tsinghua.edu.cn; yaochao420@163.com
1 These authors contributed equally.
1

Graphic Abstract
Highlights
1. A water-soluble croconium dye (TISC) based chemosensor for Fe3+ was
synthesized.
2. TISC chemosensor showed colorimetric and fluorescent dual-responses toward
Fe3+.
3. Chemosensor TISC exhibited highly selective recognition toward Fe3+.
4. Sensing mechanism of TISC for Fe3+ was also studied in detail.
Abstract
A highly selective water-soluble optical probe,
2,5-bis[2,3,3-trimethyl-3H-indole-5-sulfonic acid]-croconaine (TISC) was
successfully synthesized. TISC can efficiently recognize Fe3+ with the existence of
2

competing cations (Na+, Mg2+, Al3+, Cr3+, Zn2+, K+, Ca2+, Ba2+, Pb2+, Ni2+, Co2+, Ag+,
Cu2+, Cd2+) in deionized water. The binding constant (Ka) of TISC-Fe3+ was
calculated to be about 3.071×104 M-1. Correspondingly, the chelating mode of
TISC-Fe3+ was confirmed by Job’s plot, FT-IR and 1H NMR. Moreover, Fe3+ and
EDTA could be employed as inputs and the absorbance which was 745 nm as output
so that a molecular logic gate could be realized, and the test strips of TISC showed a
high selectivity to Fe3+.
Keywords: Water-soluble optical probe; Croconaine; Iron ion (III); Molecular logic
gate; Test strips
1. Introduction
Nowadays, people are exposed to transition and heavy metals via lots of pathways,
such as food, drinking water, atmospheric emission and industrial productions. Fe3+,
one of the indispensable trace element in organism, plays a vital role in numerous
physiological and pathological processes such as electron transfer, oxygen transport
and enzymatic catalysis [1-9]. However, the abnormal level of Fe3+ can induce various
disorders including Alzheimer’s disease, Parkinson’s disease, cancer and heart failure
[10-11]. Therefore, exact and real-time recognition of Fe3+ is vital to early diagnose
these disorders. Recently, a number of methods for qualitatively and quantitatively
detecting Fe3+ such as voltammetry [12], inductively coupled plasma mass
spectrometry [13], atomic absorption spectrometry [14]. But most of them require
3

costly and sophisticated instruments and tedious procedures of sample preparation,
which limits the practical usage in the recognition of Fe3+ [15]. Thus, there is a
pressing need for detecting Fe3+ with a high selectivity and reliable analytical strategy.
Near-infrared dyes (NIR) have been applied in various fields including biological,
spectroscopic and analytical studies [16]. Croconaine, one of the near-infrared dyes,
exhibits a strong absorption and high absorption coefficient in the region of 700-1400
nm. In addition, there is a potential binding site for metal ions due to the structure of
croconaine which contains N and O atoms. Recently, croconaines could be designed
and applied as colorimetric and fluorescent probes for detecting cations owing to its
superior optical properties of the strong photostability and large molar absorptivity.
However, few studies about croconaine-based probes were designed and synthesized
for detecting cations [17-18]. Hence, in this paper,
2,5-bis[2,3,3-trimethyl-3H-indole-5-sulfonic acid]-croconaine (TISC) as a
water-soluble “on-off” optical probe for sensing of Fe3+ was successfully designed
and synthesized.
2. Experimental section
2.1 Reagents and materials
Salts of the different cations were purchased from Shanghai Chemical Reagents
Company (China) and used without further purification. Stock solution of chlorinated
salts (Cr3+) and nitrate salts (Pb2+, Na+, Ni2+, Fe3+, Mg2+, K+, Zn2+, Ag+, Ca2+, Ba2+,
Cu2+, Co2+, Al3+ and Cd2) were prepared with 1.0 × 10-2 M in deionized water. Probe
4

TISC was dissolved in deionized water to obtain the stock solution (4.0 × 10-5 M).
2.2 Synthesis of 2,5-bis[2,3,3-trimethyl-3H-indole-5-sulfonic acid]-croconaine
The synthetic route of 2,5-bis[2,3,3-trimethyl-3H-indole-5-sulfonic
acid]-croconaine (TISC) was shown in Scheme 1. 4-Hydrazinobenzenesulfonic acid
(2 g, 10.627 mmol) and 3-methyl-2-butanone (0.915 g, 10.627 mmol) were dissolved
in acetic acid (30 mL). The solution was refluxed for 14 hours, then allowed to cool to
room temperature, and the precipitate was collected by filtration. The solid was
washed with diethyl ether and was dried under reduced pressure to afford compound 1
as a pink solid [19] (2.16 g, yield 85%). 1H NMR (300 MHz, DMSO-d6): δ 7.64(d, 1H,
J=1.5 Hz), 7.56 (dd, 1H, J=7.9, 1.6 Hz), 7.36 (d, 1H, J= 8.0 Hz), 2.23 (s, 3H), 1.25 (s,
6H). MS (ESI): m/z =240.00 [M+H]+, calcd m/z=239.06 for C11H13NO3S.
Compound 1 (0.337g, 1.408 mmol) and croconic acid (0.1g, 0.704 mmol) were
dissolved in the mixed solution of n-butanol (20 mL), toluene (20 mL) and pyridine (2
mL). The solution was refluxed for 10 h and the water was azeotropically removed.
After cooling to room temperature, the solvent was removed by distillation under
reduced pressure. The crude product was further purified by a silica gel column and
was dried under vacuum to achieve compound 2 as a blackish green solid (0.267,
65%). 1H NMR (300 MHz, DMSO-d6): δ 1.50 (s, 12H), 5.98 (s, 2H), 7.46 (s, 2H),
7.62 (d, 2H, J=8.3 Hz), 7.73 (s, 2H), 14.81 (s, 1H, N-H), 15.70 (s, 1H, N-H). 13C
NMR (126 MHz, DMSO-d6) δ 184.72, 176.86, 145.18, 140.82, 140.09, 126.25,
120.42, 112.55, 93.35, 49.92, 30.35, 25.04. FTIR (KBr): 3442.40 (-OH of SO3H
group), 2923.95 (-CH3 υas C-H), 2853.29 (-CH3 υs C-H), 1635.28 (C=O), 1559.86
5

(C=C), 1189.07 (C-O). MS (ESI): m/z =583.00 [M-H]-, calcd m/z =584.09 for
C27H24N2O9S2. HRMS (ESI, m/z): calculated for the (M-H)-.species (C27H24N2O9S2):
584.09, found: 585.531. Anal. calcd for C27H24N2O9S2: C,55.47; H,4.14; N,4.79;
O,24.63; S,10.97. found: C,54.60; H,4.13; N,4.68; O,26.28; S,10.31.mp > 300 oC.
2.3 Characterization
The infrared spectra were performed on a PROTÉGÉ 460 spectrometer, using KBr
discs. 1H NMR was obtained by a Bruker Avance III (300 MHz) and Bruker Avance
III (500MHz) using deuterated DMSO as the solvent and tetramethylsilane (TMS) as
an internal standard. Mass spectral study was carried out using Agilent Techologies
6540 UHD and LCMS-2020 mass spectrometer by-passing the LC step. UV-vis
spectra were collected on an UV-759 spectrophotometer in deionized water, using a
quartz cell with a path length of 1 cm. The pH levels of the stock solution were
measured using a PHS-3C Precision pH/mV Meter (Leici, Shanghai, China).
Fluorescence emission spectra were recorded on an F-280 spectrometer with a scan
rate 2400 nm/min at temperature. Fluorescence measurements were carried out with
excitation and emission slits widths of 10 nm and the excitation wavelength was 720
nm.
3. Results and discussion
3.1 UV-vis and fluorometric sensing properties of TISC
The studies of UV-vis and fluorometric sensing properties of TISC were carried out
with the existence of a variety of cations (Pb2+, Na+, Ni2+, Mg2+, K+, Cr3+, Fe3+, Zn2+,
Ag+, Ca2+, Ba2+, Co2+, Cu2+, Al3+ and Cd2+). Neither the color nor the UV-vis
6

absorption spectra of TISC solution change when upon adding other cations to TISC
solution except for Fe3+ (Fig. 1).
On the basis of above analyses, the titration experiments of TISC solution with
Fe3+ were investigated. Upon gradually adding Fe3+ to TISC solution, the absorption
band at 745 nm decreased bit by bit and one isosbestic point was observed at 428 nm
(Fig. 2). To further study the stoichiometry of TISC-Fe3+, using the Job's plot analysis
by constantly changing the mole fraction of Fe3+ under a range of 0-1 with a total
concentration of 4 × 10-5 M of [Fe3+ +TISC] solution. As depicted in Fig. 2a, it
showed that the value of [Fe3+]/[Fe3++TISC] demonstrated a maximum at 0.5 mole
fraction, which revealed the 1:1 binding mode of TISC-Fe3+. Meanwhile, TISC
solution exhibited a visual color change from green to brown (Fig. 2b). Moreover, the
binding constant (Ka) of TISC-Fe3+ was calculated by using Benesi-Hildebrand plot.
The magnitude of Ka was determined from the slope and intercept of the fitted straight
line, and the binding constant (Ka) was found to be about 3.071×104 M-1. The
Benesi-Hildebrand plot of [A0 /A0-A] versus [Fe3+]-1 exhibited a very good linearity
with R = 0.9907, which strongly supported the 1:1 (TISC-Fe3+) binding model (Fig.
S1) [20-22].
The sensing properties were also investigated by fluorescence spectroscopy. The
fluorescence intensity did not show any remarkable changes except for adding Fe3+ to
TISC solution (Fig. 3). The fluorescence intensity of TISC at 785 nm decreased bit
by bit as the concentration of Fe3+ increased (Fig. 4). The inset of Fig. 4 exhibited the
relationship between the concentration of Fe3+ and the fluorescence intensity of TISC
7

at 785 nm. Therefore, the above analyses clearly illustrated that TISC could be
utilized as a dual colorimetric and fluorescent probe for sensing of Fe3+ in deionized
water.
3.2 Competitive selectivity of TISC for detecting Fe3+with existence of other metal
ions
Achieving highly selective detection of the analyte with existence of numerous
potentially competing species is desired for any sensors [23]. Therefore, to prove the
usage of TISC as an ion-selective probe for sensing of Fe3+, the cross-contamination
experiments were carried out in the condition of Fe3+ coexisting with other metal ions.
Figs. 5 and 6 demonstrated that the chelating complex (TISC-Fe3+) still exhibited
similar UV-vis and fluorescence changes with existence of other cations. Thus, these
above results revealed that the selectivity of TISC for sensing of Fe3+ was not
influenced by other coexisting cations.
3.3 Response time and detection limit
Generally, achieving real-time recognition of the analyte is desired for any sensors
[24]. In our case, the response time of TISC to Fe3+ were found to be fast (Figs. S2
and S3). Upon adding Fe3+ to TISC solution, the absorbance or the fluorescence
intensity of TISC-Fe3+ achieved a balance in about 25s and 40s at room temperature,
respectively. Simultaneously, we also evaluated the linearity via plotting the
absorbance of TISC at 745 nm as a function of Fe3+ concentration under a range from
1.996 to 19.608 μM with a correlation of 0.99238 (Fig. S4). On the basis of 3 × δ/S,
the limit of UV-vis for detecting Fe3+ was about 3.833×10-7 M. Similarly, the
8

fluorescence limit of detection for Fe3+ was up to 4.676×10-7 M (Fig. S5). Therefore,
these above analyses illustrated that TISC could be utilized as a real-time and highly
selective probe for sensing of Fe3+ by using the UV-vis and fluorescence spectra.
3.4 Reversibility of TISC towards Fe3+
Reversible usage was a significant property for optical probes, which could reduce
the analysis cost [25]. Correspondingly, the experiments of reversibility were carried
out to investigated the reversible behavior of TISC-Fe3+ by adding EDTA to the
chelating complex of TISC-Fe3+. It was observed that TISC solution without Fe3+
exhibited a strong absorption peak at 745 nm (Fig. 7a, curve a), while the absorbance
of TISC decreased obviously upon adding 80 μM Fe3+ (Fig. 7a, curve b). Then, when
80 μM EDTA was added into the chelating complex (TISC-Fe3+), the absorbance of
TISC was almost completely restored (Fig. 7a, curve c). The results revealed that
EDTA could readily attack Fe3+ from the TISC-Fe3+ to form more stable Fe3+-EDTA,
and TISC were released. This process could be repeated 3 times (Fig. 7b), which
indicated that TISC-based probe could be reused.
3.5 TISC response to the pH
The effect of pH on the absorption and fluorescence response of TISC in the
absence and presence of Fe3+ (20 μM) were further evaluated. As depicted in Fig. 8,
the acid-base titration experiment was performed by altering the pH with HCl or
aqueous solution of NaOH. As shown in Fig. 8a, TISC in the absence and presence of
Fe3+ did not display any pronounced absorbance changes under the pH range of 2 to 6.
However, when the pH was changed between 6 and 9, the absorbance at 745 nm was
9

obviously decreased due to the deprotonation of the N cation in indole ring [26]. At
the same time, the separated hydrogen proton binded to the oxygen anion of croconyl
ring, which undergone a tautomer of the structure to cause a rupture of the
conjugation system (Scheme 2). Correspondingly, absorbance of TISC in the absence
and presence of Fe3+ trended to be stable until the pH value up to 9. The results of
fluorescence intensity changes were similar to that of absorbance (Fig. 8b). The
pH-controlled experiments showed that TISC could react to Fe3+ ions within the pH
of 2 to 6 with negligible changes in the absorption and fluorescence, which in turn
suggests that probe TISC possesses Fe3+ sensing activity with in a wide pH range.
3.6 Chelating mechanism of TISC towards Fe3+
To further study the chelating mechanism of TISC towards Fe3+, the experiment of
FT-IR and 1H NMR were carried out. It revealed that the carbonyl band of TISC at
1635 cm-1 did not shift, whereas the C-O band at 1189 cm-1 shift to 1178 cm-1 (Fig.
9a). The results clearly indicated that the C-O band of TISC chelates with Fe3+ upon
adding Fe3+ to TISC solution. In addition, although SO3H group was prone to
ionization in deionized water, as depicted in Fig. 9b, the stretching vibration
frequency of OH group of SO3H at 3442 cm-1 was not changed, which showed that
the OH group of SO3H was not involved in the metal ion binding.
Simultaneously, the binding mechanism of TISC-Fe3+ was deeply studied using 1H
NMR spectra (Fig. 10), which illustrated that the peaks at 14.81 and 15.70 ppm were
disappeared upon adding Fe3+ to TISC solution. Therefore, it can be seen that the N
moiety had a significant interaction with Fe3+. Moreover, the signal of aromatic
10

protons as multiplets in the region between 7 and 8 ppm were broadened and the
signal intensity at 5.98 ppm decreased which owing to the paramagnetic of iron [27].
Hence, in view of Job’s plot and obvious changes of FT-IR and 1H NMR, it clearly
demonstrated that the coordination of TISC with Fe3+ in 1:1 stoichiometry via N atom
and C-O moiety. The proposed chelating mechanism of TISC-Fe3+ was depicted in
Scheme 3.
3.7 Ppractical application of TISC
The study of molecular logic gate is a transdisciplinary field and has attracted
widespread attention [28]. In this case, the experiment of molecular logic function
was carried out by using TISC along with Fe3+ and EDTA as inputs in the absorption
mode. The absorbance minima at 745 nm appeared due to the chelation of TISC with
Fe3+. When EDTA was added to TISC solution, the absorbance at 745 nm increased.
The absorbance at 745 nm is 0 only when Fe3+ is present, whereas the values of other
function are 0. Hence, with Fe3+ and EDTA as inputs, TISC could be capable of
exhibiting the IMPLICATION function by using UV-vis absorption output. The
changes of UV-vis absorption at 745 nm with two inputs as Fe3+ and EDTA can be
taken as the IMPLICATION logic gate, which is a composition of a NOT gate and
one OR logic gate [29] (Fig. S6 and Fig. 11).
Motivated by the obvious change in the color of the chelating complex (TISC-Fe3+),
visually colorimetric test strips were prepared, which could be used to detect Fe3+
simply and directly. Hence, the test strips were prepared through immersing filters
papers in TISC (2.0×10-3 M) solution and dying in air. The test strips were used to
11

detect Fe3+ and other cations. As depicted in Fig. 12, upon adding Fe3+ and other
cations on the test kits respectively, an obvious color change was observed only
TISC-Fe3+ in visible light. Moreover, potentially competitive cations had no effect on
the recognition of Fe3+ by the test kits.
4. Conclusion
In conclusion, a water-soluble croconaine (TISC) was successfully synthesized to
highly detect Fe3+ when TISC solution with existence of other coexisting cations.
Meanwhile, TISC-Fe3+ induced an obvious color change, which provided a “naked
eye” detection. Moreover, the sensor TISC could be used as a recyclable materials in
the recognition of Fe3+. Correspondingly, the absorbance changes of TISC at 745 nm
upon adding Fe3+ and EDTA could be designed as an IMPLICATION logic gate.
Notably, the test strips were prepared and it exhibited a high selectivity to Fe3+.
Acknowledgments
This work was financially supported by Natural Science Foundation of Jiangsu
Province, China (BK20150259) and Natural Science Foundation of Changzhou City,
China (CJ20140053).
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Scheme and figure captions
Scheme 1. The synthetic route of TISC.
Scheme 2. Mechanism of TISC response to the pH.
Scheme 3. Chelating mechanism of TISC-Fe3+.
Fig. 1. The color change of TISC solution was observed upon adding cations after a
while in visible light (a) and UV-vis absorption spectra of TISC (4.0×10-5 M) solution
upon adding different cations (Pb2+, Al3+, Na+, Ni2+, Fe3+, Mg2+, K+, Cr3+, Zn2+, Cu2+,
Ag+, Ca2+, Ba2+, Co2+and Cd2+ ) (b).
Fig. 2. The changes of UV-vis absorption spectra of TISC upon adding Fe3+
(0-0.0695 mM). (Inset: (a) Job’s plot of TISC-Fe3+ (1.0×10-4 M) according to the
method for continuous variations, indicating the 1:1 stoichiometry of TISC-Fe3+, (b)
the color change of TISC solution before and after the addition of Fe3+).
Fig. 3. The changes of fluorescence spectra of TISC with existence of different
cations (Pb2+, Al3+, Na+, Ni2+, Fe3+, Mg2+, K+, Cr3+, Zn2+, Cu2+, Ag+, Ca2+, Ba2+,
Co2+and Cd2+ ).
Fig. 4. Fluorescence spectra of TISC (4.0×10-5 M) solution upon adding Fe3+
(0-0.0695 mM). (Inset: the relationship among the fluorescence intensity of TISC at
785 nm and the concentration of Fe3+).
Fig. 5. Absorbance of TISC solution with Fe3+ (1 equiv.) under condition of various
test cations (4 equiv.) (Note: λab = 745 nm).
Fig. 6. Fluorescence intensity of TISC solution (4.0×10-5 M) with Fe3+ (1 equiv.) in
the presence of various test cations (4 equiv.) (Note: λem = 785 nm).
17

Fig. 7. UV-vis absorption spectra of TISC (4.0×10-5 M) with existence of Fe3+ (80 μM)
with EDTA (80 μM) (a), Reversible investigation of TISC (4.0×10-5 M) for Fe3+ (80
μM) with addition of EDTA (80 μM) λab = 745 nm (b).
Fig. 8. UV-vis absorption spectra (a) and fluorescence spectra (b) of TISC in the
absence and presence of Fe3+ (20 μM) response to the pH.
Fig. 9. IR spectra of TISC (curve a) and TISC-Fe3+ (curve b).
Fig. 10. (a) 1H NMR spectra of TISC and TISC-Fe3+ in D2O (Note: for the chelating
complex, 1 equiv. of Fe3+ was added to TISC). (b) 1H NMR spectra of TISC and
TISC-Fe3+ in DMSO (Note: for the chelating complex, 1 equiv. of Fe3+ was added to
TISC)
Fig. 11. Truth table and the monomolecular circuit based on Fe3+ and EDTA as
chemical inputs and the absorbance of TISC at 745 nm as output.
Fig. 12. Photographs of TISC (2.0×10-3 M) and the response of cations on test papers
in visible light.
18

Scheme 1
19

Scheme 2
20

Scheme 3
21

(a)
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
2+ 2+
+
2+
3+
2+
+
TISC, Zn , Ni , K , Pb , Cr , Ba , Ag ,
2+ 3+ 2+ 2+ 2+ 2+
+
Cd , Al , Na , Ca , Mg , Co , Cu
(b)
3+
Fe
300
400
500
600
700
800
900
Wavelength (nm)
Figure 1
22

0.6
0.5
0.4
0.3
0.2
0.1
0.0
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
(a)
0 mM
Fe3+
0.0
0.2
0.4
3+
0.6
0.8
1.0
3+
Fe /[Fe +SQ]
3+
Fe
(b)
0.0695 mM
300
400
500
600
700
800
900
Wavelength (nm)
Figure 2
23

4000
3500
3000
2500
2000
1500
1000
500
0
+
2+
Pb
+
2+
Cu Cr
+
K
2+
Ba Fe
3+
2+
Ni
3+
2+
2+
2+
Cd
3+
2+
Ca
2+
SC
Ag
Na
Al
Zn
Co
TI
Mg
Cations
Figure 3
24

7500
7000
6500
6000
5500
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
4000
3500
3000
2500
2000
1500
1000
500
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
3+
Concentration of Fe (mM)
0 mM
Fe3+
0.0695 mM
0
740
760
780
800
820
840
860
880
900
920
Wavelength (nm)
Figure 4
25

TISC+Cations
TISC+Fe3++Cations
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
+
+
+
K
3+
Cr
2+
Ba
2+
2+
Ca
2+
Hg
2+
Co
2+
Zn
2+
Pb
3+
Al
2+
Ni
2+
Cu
Na
Ag
Cd
Figure 5
26

TISC+Cations
TISC+Fe3++Cations
4000
3500
3000
2500
2000
1500
1000
500
0
+
+
+
K
2+
2+
Pb
3+
Cr
2+
Cd
3+
Al
2+
Cu
2+
Ba
2+
Ni
2+
Hg
2+
Zn
2+
Co
Ag
Na
Ca
Figure 6
27

1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
a
c
(a)
b
400
500
600
700
800
900
Wavelength (nm)
+EDTA
1.4
+EDTA
Fe3+
1.2
1.0
0.8
0.6
0.4
0.2
0.0
+EDTA
Fe3+
(b)
Fe3+
3
1
2
times
Figure7
28

1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
TISC
TISC+Fe3+
(a)
2
3
4
5
6
7
8
9
10
pH
TISC
TISC+Fe3+
3500
3000
2500
2000
1500
1000
500
(b)
0
2
4
6
8
10
pH
Figure 8
29