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A highly selective optical probe for sensing of Fe3+ based on a water-soluble croconaine
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: DOI: Reference:
S1010-6030(17)30603-2 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 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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*
a
Jiangsu 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: [email protected]; [email protected] 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
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)
1.6
Absorbance
1.4 1.2 1.0 0.8 0.6 0.4
3+ Fe
0.2 0.0 300
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Absorbance
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3+
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SC
0
N 2 i + K+ Pb 2 + C u 2+ C 3 r + Ba 2 + Fe 3 + C d 2+ N + a C 2 a + M g 2+ C o 2+ Zn 2 + A 3 l + A + g
TI
Intensity (a.u.) 4000
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Figure 3
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7500 4000
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3000 2500 2000 1500 1000 500 0
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860
Wavelength (nm)
Figure 4
25
880
900
920
0.0
Figure 5
26
C 2 a + H g 2+ C 2 o + C u 2+
N + a
Pb 2 + C 3 r + Ba 2 + A + g C d 2+ A 3 l +
K+
Zn 2 + N 2 i +
Absorbance
TISC+Cations TISC+Fe3++Cations
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
Figure 6
27
a
2+
H g 2+ C 2 o + C u 2+
C
Pb 2 + C 3 r + Ba 2 + A + g C d 2+ A 3 l + N + a
N 2 i + K+
Zn 2 +
Intensity (a.u.) 4000
TISC+Cations TISC+Fe3++Cations
3500
3000
2500
2000
1500
1000
500
1.8
a
1.6
c
Absorbance
1.4
(a)
1.2 1.0 0.8 0.6 0.4 0.2
b 0.0 400
500
600
700
800
900
Wavelength (nm)
+EDTA 1.4
+EDTA Fe
3+
Absorbance
1.2
+EDTA
(b)
Fe3+
1.0
Fe3+
0.8 0.6 0.4 0.2 0.0
1
3
2
times
Figure7
28
1.6
TISC TISC+Fe3+
1.4
Absorbance
1.2 1.0
(a)
0.8 0.6 0.4 0.2
2
3
4
5
6
7
8
9
pH TISC TISC+Fe3+
3500 3000
Intensity
2500 2000
(b)
1500 1000 500 0 2
4
6
8
10
pH
Figure 8
29
10
1635 cm
100
-1
1178 cm
-1
b a
(a)
Transmittance %
90 80 70 60 1189 cm
-1
50 40 2000
1800
1600
1400
1200
1000
800
600
400
Wavenumber (cm-1)
100 98
Transmittance %
96
b
(b)
94
-1 3442 cm
a
92 90 88 86 84 82 80 4000
3800
3600
3400
3200
3000
2800
2600
Wavenumber (cm-1)
Figure 9
30
2400
2200
2000
Figure10
31
Figure11
32
Figure 12
33
S1010-6030(17)30603-2 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 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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*
a
Jiangsu 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: [email protected]; [email protected] 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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16
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
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)
1.6
Absorbance
1.4 1.2 1.0 0.8 0.6 0.4
3+ Fe
0.2 0.0 300
400
500
600
700
Wavelength (nm) Figure 1
22
800
900
0.6
1.6
(a)
Absorbance
1.2
△ Abs (727nm)
0.5
1.4
1.0
0.4
0 mM
0.3 0.2 0.1 0.0 0.0
0.8
0.2
0.4
0.6
0.8
Fe3+
1.0
Fe3+/[Fe3++SQ]
0.6
Fe
(b)
3+
0.4
0.0695 mM
0.2 0.0 300
400
500
600
700
Wavelength (nm) Figure 2
23
800
900
SC
0
N 2 i + K+ Pb 2 + C u 2+ C 3 r + Ba 2 + Fe 3 + C d 2+ N + a C 2 a + M g 2+ C o 2+ Zn 2 + A 3 l + A + g
TI
Intensity (a.u.) 4000
3500
3000
2500
2000
1500
1000
500
Cations
Figure 3
24
7500 4000
6500
3500
Intensity(a.u.)
7000 6000
Intensity(a.u.)
5500 5000 4500 4000
3000 2500 2000 1500 1000 500 0
3500
0.01
3000
0.02
0.03
0.04
0.05
0.06
0.07
Concentration of Fe3+ (mM)
2500
0 mM
2000
Fe3+
1500 1000
0.0695 mM
500 0 740
760
780
800
820
840
860
Wavelength (nm)
Figure 4
25
880
900
920
0.0
Figure 5
26
C 2 a + H g 2+ C 2 o + C u 2+
N + a
Pb 2 + C 3 r + Ba 2 + A + g C d 2+ A 3 l +
K+
Zn 2 + N 2 i +
Absorbance
TISC+Cations TISC+Fe3++Cations
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
Figure 6
27
a
2+
H g 2+ C 2 o + C u 2+
C
Pb 2 + C 3 r + Ba 2 + A + g C d 2+ A 3 l + N + a
N 2 i + K+
Zn 2 +
Intensity (a.u.) 4000
TISC+Cations TISC+Fe3++Cations
3500
3000
2500
2000
1500
1000
500
1.8
a
1.6
c
Absorbance
1.4
(a)
1.2 1.0 0.8 0.6 0.4 0.2
b 0.0 400
500
600
700
800
900
Wavelength (nm)
+EDTA 1.4
+EDTA Fe
3+
Absorbance
1.2
+EDTA
(b)
Fe3+
1.0
Fe3+
0.8 0.6 0.4 0.2 0.0
1
3
2
times
Figure7
28
1.6
TISC TISC+Fe3+
1.4
Absorbance
1.2 1.0
(a)
0.8 0.6 0.4 0.2
2
3
4
5
6
7
8
9
pH TISC TISC+Fe3+
3500 3000
Intensity
2500 2000
(b)
1500 1000 500 0 2
4
6
8
10
pH
Figure 8
29
10
1635 cm
100
-1
1178 cm
-1
b a
(a)
Transmittance %
90 80 70 60 1189 cm
-1
50 40 2000
1800
1600
1400
1200
1000
800
600
400
Wavenumber (cm-1)
100 98
Transmittance %
96
b
(b)
94
-1 3442 cm
a
92 90 88 86 84 82 80 4000
3800
3600
3400
3200
3000
2800
2600
Wavenumber (cm-1)
Figure 9
30
2400
2200
2000
Figure10
31
Figure11
32
Figure 12
33