Supporting Information Colorimetric Detection of Sulfite in Foods by a ...
Supporting Information Colorimetric Detection of Sulfite in Foods by a TMB−O2−Co3O4 Nanoparticles Detection System
Wenjie Qin1,2, Li Su3, Chen Yang1,2, Yanhua Ma1,2, Haijuan Zhang1,2, Xingguo Chen*1,2
1
State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou
730000, China 2
Department of Chemistry, Lanzhou University, Lanzhou 730000, China
3
School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang 453007, China.
* E-mail: [email protected] (X.-G. Chen). Tel: 86-931-8912763 Fax: 86-931-8912582
1
1
Characterization of Co3O4 NPs
2
The as-prepared Co3O4 NPs were identified as pure phases from the X-ray diffraction
3
(XRD) patterns (Figure S1) with a suitable crystalline cubic spinel structure (JCPDS
4
09–0418). Average size of the Co3O4 NPs was calculated to be approximate 5 nm by
5
Scherrer’s formula. Transmission electron microscopy (TEM) (Figure S2a) revealed that
6
Co3O4 NPs were cubic in shape and around 5 nm in size. Energy-dispersive X-ray (EDX)
7
analysis was used to determine the chemical composition of the as-prepared Co3O4 NPs.
8
The result from EDX spectra showed that the sample contains Co and O for Co3O4 NPs
9
(Figure S2b). X-ray Photoelectron Spectroscopy (XPS) was performed for investigation
10
of the chemical nature of Co3O4 NPs with partially filled valence bonds. The complete
11
survey XPS spectra of the Co3O4 NPs are displayed in Figure 2a. In survey spectra, the
12
main peaks can be clearly indexed to C 1s, O 1s, and Co 2p regions, indicating that no
13
other metallic or inorganic contaminants are present. High-resolution Co 2p spectrum
14
shows spin orbit splitting into 2p1/2 and 2p3/2 components, and both components
15
qualitatively contain the same chemical information. Therefore, in this study, only the
16
higher-intensity Co 2p3/2 bands were curve-fitted. Figure 2b and Figure 2c showed the
17
deconvoluted XPS spectra of Co 2p3/2 and O 1s of as-prepared Co3O4 NPs which were in
18
accord with the reported literature. 1 The results implied that Co3O4 NPs were successfully
19
synthesized by the hydrothermal method. As shown in Figure S3, the obtained zeta
20
potential value of Co3O4 NPs decreased with the increase of pH, and the isoelectric point
21
(IEP) was about 5.3. The value of zeta potential was 16 mV at pH 4.0, suggesting the
22
surface of Co3O4 NPs have a positive charge at pH 4.0. The BET surface area of Co3O4
2
23
NPs was 128.7 m2/g.
24
Terminal Time of TMB-O2-Co3O4 NPs System
25
Terminal time of TMB−O2−Co3O4 NPs system was determined by a series of
26
experiments. The mixed solutions of deionized water (80.0 μL)， TMB (150.0 μL, 5
27
mM), Co3O4 NPs (120.0 μL, 1.0 mg mL-1) and acetic acid-acetate buffer solution (2.65
28
mL, 0.2 M, pH 4.0) were maintained in a 40 °C water bath for 10 min to hold the
29
reaction, then kept them in an ice-water bath at different times respectively. The solutions
30
were then used to perform the adsorption spectroscopy measurement at 652 nm
31
wavelength. As shown in the Figure S4, the change of absorbance became very small
32
after 10 min. Therefore 10 min was chosen as a terminate time.
3
Table S1. The binding energy and peak area ratio of Co 2p3/2 and O 1s of Co3O4 NPs before and after the reaction peak assignment
Co3+ Co2+ Co2+ O 1s O−Co3+ O−Co2+ O−Co2+ OH O−Surf a No corresponding peak Co 2p3/2
Co3O4 NPs
Co3O4 NPs
(before the reaction)
(after the reaction)
BE (eV)
ratio (%)
BE (eV)
ratio (%)
779.2 780.4 781.7 529.5 530.6 531.5 -a 533.0
39.6 31.1 29.3 49.6 15.6 24.4 10.4
779.1 780.2 781.5 529.4 530.5 531.4 532.4 533.3
38.8 34.3 26.9 46.1 15.9 21.8 7.3 8.9
4
Figure S1. XRD patterns of Co3O4 NPs.
5
Figure S2. TEM images of Co3O4 NPs (a). EDX spectroscopy of Co3O4 NPs (b).
6
Figure S3. The values of zeta potential of Co3O4 NPs at different pH. The error bars represent the standard deviation of three measurements.
7
Figure S4. The absorbance of TMB oxidation system under different termination times at 652 nm.
8
Figure S5. Time-dependent absorbance evolution of TMB oxidation system at 652 nm in the presence of leaching solution (a) and Co3O4 NPs (b).
9
Figure S6. Amount of cobalt ions leaked from the Co3O4 NPs in the buffer solutions (pH 3.0−7.0).
10
Figure S7. DMPO spin−trapping EPR spectra in acetic acid−acetate buffer solution (0.2 M, pH 4.0) (a), acetic acid-acetate buffer solution (0.2 M, pH 4.0)+80 μg mL-1 Co3O4 NPs (b).
11
Figure S8. Time-dependent absorbance at 652 nm of TMB of different concentrations within 4 min (a). Time-dependent absorbance at 417 nm of ABTS of different concentrations within 4 min (b).
REFERENCES (1) Yang, J.; Liu, H.; Martens, W. N.; Frost, R. L., Synthesis and characterization of cobalt hydroxide, cobalt oxyhydroxide, and cobalt oxide nanodiscs. J. Phys. Chem. C 2009, 114, 111-119.
12
Wenjie Qin1,2, Li Su3, Chen Yang1,2, Yanhua Ma1,2, Haijuan Zhang1,2, Xingguo Chen*1,2
1
State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou
730000, China 2
Department of Chemistry, Lanzhou University, Lanzhou 730000, China
3
School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang 453007, China.
* E-mail: [email protected] (X.-G. Chen). Tel: 86-931-8912763 Fax: 86-931-8912582
1
1
Characterization of Co3O4 NPs
2
The as-prepared Co3O4 NPs were identified as pure phases from the X-ray diffraction
3
(XRD) patterns (Figure S1) with a suitable crystalline cubic spinel structure (JCPDS
4
09–0418). Average size of the Co3O4 NPs was calculated to be approximate 5 nm by
5
Scherrer’s formula. Transmission electron microscopy (TEM) (Figure S2a) revealed that
6
Co3O4 NPs were cubic in shape and around 5 nm in size. Energy-dispersive X-ray (EDX)
7
analysis was used to determine the chemical composition of the as-prepared Co3O4 NPs.
8
The result from EDX spectra showed that the sample contains Co and O for Co3O4 NPs
9
(Figure S2b). X-ray Photoelectron Spectroscopy (XPS) was performed for investigation
10
of the chemical nature of Co3O4 NPs with partially filled valence bonds. The complete
11
survey XPS spectra of the Co3O4 NPs are displayed in Figure 2a. In survey spectra, the
12
main peaks can be clearly indexed to C 1s, O 1s, and Co 2p regions, indicating that no
13
other metallic or inorganic contaminants are present. High-resolution Co 2p spectrum
14
shows spin orbit splitting into 2p1/2 and 2p3/2 components, and both components
15
qualitatively contain the same chemical information. Therefore, in this study, only the
16
higher-intensity Co 2p3/2 bands were curve-fitted. Figure 2b and Figure 2c showed the
17
deconvoluted XPS spectra of Co 2p3/2 and O 1s of as-prepared Co3O4 NPs which were in
18
accord with the reported literature. 1 The results implied that Co3O4 NPs were successfully
19
synthesized by the hydrothermal method. As shown in Figure S3, the obtained zeta
20
potential value of Co3O4 NPs decreased with the increase of pH, and the isoelectric point
21
(IEP) was about 5.3. The value of zeta potential was 16 mV at pH 4.0, suggesting the
22
surface of Co3O4 NPs have a positive charge at pH 4.0. The BET surface area of Co3O4
2
23
NPs was 128.7 m2/g.
24
Terminal Time of TMB-O2-Co3O4 NPs System
25
Terminal time of TMB−O2−Co3O4 NPs system was determined by a series of
26
experiments. The mixed solutions of deionized water (80.0 μL)， TMB (150.0 μL, 5
27
mM), Co3O4 NPs (120.0 μL, 1.0 mg mL-1) and acetic acid-acetate buffer solution (2.65
28
mL, 0.2 M, pH 4.0) were maintained in a 40 °C water bath for 10 min to hold the
29
reaction, then kept them in an ice-water bath at different times respectively. The solutions
30
were then used to perform the adsorption spectroscopy measurement at 652 nm
31
wavelength. As shown in the Figure S4, the change of absorbance became very small
32
after 10 min. Therefore 10 min was chosen as a terminate time.
3
Table S1. The binding energy and peak area ratio of Co 2p3/2 and O 1s of Co3O4 NPs before and after the reaction peak assignment
Co3+ Co2+ Co2+ O 1s O−Co3+ O−Co2+ O−Co2+ OH O−Surf a No corresponding peak Co 2p3/2
Co3O4 NPs
Co3O4 NPs
(before the reaction)
(after the reaction)
BE (eV)
ratio (%)
BE (eV)
ratio (%)
779.2 780.4 781.7 529.5 530.6 531.5 -a 533.0
39.6 31.1 29.3 49.6 15.6 24.4 10.4
779.1 780.2 781.5 529.4 530.5 531.4 532.4 533.3
38.8 34.3 26.9 46.1 15.9 21.8 7.3 8.9
4
Figure S1. XRD patterns of Co3O4 NPs.
5
Figure S2. TEM images of Co3O4 NPs (a). EDX spectroscopy of Co3O4 NPs (b).
6
Figure S3. The values of zeta potential of Co3O4 NPs at different pH. The error bars represent the standard deviation of three measurements.
7
Figure S4. The absorbance of TMB oxidation system under different termination times at 652 nm.
8
Figure S5. Time-dependent absorbance evolution of TMB oxidation system at 652 nm in the presence of leaching solution (a) and Co3O4 NPs (b).
9
Figure S6. Amount of cobalt ions leaked from the Co3O4 NPs in the buffer solutions (pH 3.0−7.0).
10
Figure S7. DMPO spin−trapping EPR spectra in acetic acid−acetate buffer solution (0.2 M, pH 4.0) (a), acetic acid-acetate buffer solution (0.2 M, pH 4.0)+80 μg mL-1 Co3O4 NPs (b).
11
Figure S8. Time-dependent absorbance at 652 nm of TMB of different concentrations within 4 min (a). Time-dependent absorbance at 417 nm of ABTS of different concentrations within 4 min (b).
REFERENCES (1) Yang, J.; Liu, H.; Martens, W. N.; Frost, R. L., Synthesis and characterization of cobalt hydroxide, cobalt oxyhydroxide, and cobalt oxide nanodiscs. J. Phys. Chem. C 2009, 114, 111-119.
12
