Supporting Information: Synthesis of Nitrogen-Doped Graphene ...
Supporting Information:
Synthesis of Nitrogen-Doped Graphene Quantum Dots at Low Temperature for Electrochemical Sensing Trinitrotoluene
Zhewei Cai,a Fumin Li,b Ping Wu,*b Lijuan Ji,b Hui Zhang,b Chenxin Cai,b and Dominic F. Gervasio*a a
Department of Chemical & Environmental Engineering, University of Arizona, 1133 E. James E.
Rogers Way, Tucson, AZ 85721, USA b
Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of
Biomedical Functional Materials, National and Local Joint Engineering Research Center of Biomedical Functional Materials, College of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210097, P.R. China.
* Corresponding author, E-mail: [email protected] (P. Wu); [email protected] (D. F. Gervasio).
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Contents:
Figure S1. TEM, AFM image, and FTIR spectra of GO sheet. Figure S2. TEM and XPS spectra of the nanometer-sized GO pieces. Figure S3. SEM images of N-graphene, N-GQDs, and GQDs on GC electrode. Figure S4. Photograph of the N-graphene sheet under excitation of 365 nm. Figure S5. Diagram of electronic transition of triple carbenes. Figure S6. CV response of K3Fe(CN)6 at the N-GQDs/GC and GQDs/GC electrodes. Figure S7. EIS of K3Fe(CN)6/K4Fe(CN)6 at the bare GC, GQDs/GC, and N-GQDs/GC electrodes. Figure S8. I‒V curves for N-GQDs and GQDs. Figure S9. UV-Vis spectra of 100 ppb TNT before and after accumulated. Figure S10. Charge distributions of GQDs and N-GQDs. Figure S11. HOMO and LUMO spatial distributions for GQD and N-GQDs. Figure S12. LSV of TNT reduction at the N-GQDs/GC electrode after different accumulation time. Figure S13. LSV of TNT reduction at the N-GQDs/GC electrode at different pH. Figure S14. LSV of 2,4-DNT and 2-NT at the N-GQDs/GC electrode. Figure S15. HPLC responses of different water samples.
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Figure S1. Typical TEM (A) and AFM image (B) of the synthesized GO sheet. (C) FTIR spectra of the synthesized GO sheet (curve a) and N-GQDs (curve b).
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Figure S2. Typical TEM (A) and XPS spectra (B, C) of the nanometer-sized GO pieces.
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Figure S3. SEM images of N-graphene/GC (A), N-GQDs/GC (B), and GQDs/GC electrodes (C).
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Figure S4. Photograph of the N-graphene sheet under excitation of 365 nm.
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Figure S5. A diagram of electronic transition of triple carbenes at zigzag sites observed in the optical spectra of the N-GQDs.
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Current (µA)
50
0
N-GQDs GQDs
-50
0.0
0.2
0.4
0.6
Potential (V, vs. Ag/AgCl) Figure S6. Cyclic voltammograms for the N-GQDs/GC and GQDs/GC electrodes in 1 M KCl solution containing 1.0 mM K3Fe(CN)6. Scan rate: 100 mV/s.
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300
-Z'' (ohm)
200
100 GC GQDs N-GQDs 0 0
100
200
300
400
Z' (ohm) Figure S7. Nyquist plots of the bare GC, GQDs/GC, and N-GQDs/GC electrodes in 0.1 M KCl solution containing 5 mM K3Fe(CN)6/K4Fe(CN)6 (1:1) in the frequency range from 0.1 Hz to 100 kHz. Amplitude: 10 mV.
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Figure S8. I‒V curves for N-GQDs (a) and GQDs (b). Scan rate: 100 mV/s.
The electrical conductivity of the N-GQDs and GQDs was estimated from DC measurements. The samples (N-GQDs and GQDs) were pressed to the rods by a homemade two-electrode cell template (0.4 cm in diameter and 8.5 cm in length) under 20 MPa. Then, the rods of GQDs and N-GQDs were performed the current-voltage (I‒V) measurements on a CHI 760B electrochemical workstation. The voltage was scanned from ‒1.5 to 1.5 V with no applied gate voltage at 100 mV/s. The current response was recorded. The values of the electrical conductivity (σ) were calculated according the following equation (1): σ
where A is the surface area of the samples rod (in m2), l is the length of samples (in m), and the value I/V was taken as the slope of I‒V curves. The calculated σ of N-GQDs and GQDs is 1.22 × 103 S m‒1and 1.01 × 103 S m‒1, respectively.
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Absorbance (a.u.)
a
c
225
250
275
300
325
350
Wavelength (nm)
Figure S9. UV-Vis spectra of 100 ppb TNT before (curve a) and after accumulated by GQDs (curve b) and N-GQDs (curve c) for 150 s at 0 V.
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Figure S10. Charge distributions of GQDs (A), and pyridinic (B) and pyrrolic N-GQDs (C).
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HOMO
GQD
LUMO
α, β electrons
α electron
pyridinic N-GQDs
β electron
pyrrolic NGQDs
α, β electrons
Figure S11. HOMO and LUMO spatial distributions of α electron and β electron for GQD and pyridinic and pyrrolic N-GQDs.
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-2
Current Density (mA cm )
0.0
-0.1
0s
-0.2
-0.3
210 s -0.8
-0.6
-0.4
-0.2
Potenial (V, vs. AgCl/Ag)
Figure S12. LSV of TNT reduction at the N-GQDs/GC electrode in PBS (0.1 M, pH 7.0) after accumulated in TNT (100 ppb) solution at 0 V for (curve a to h): 0, 30, 60, 90, 120, 150, 180, and 210 s. Scan rate : 50 mV/s.
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-2
Current Density (mA cm )
0.05 0.00 -0.05 -0.10 -0.15 -0.20
pH=5 pH=6 pH=7 pH=8 pH=9
-0.25 -0.30 -0.8
-0.6
-0.4
-0.2
Potential (V, vs. Ag/AgCl)
Figure S13. LSV of TNT reduction at the N-GQDs/GC electrode in PBS (0.1 M) with different pH value (5, 6, 7, 8, 9). Before recording the LSV, the N-GQDs/GC electrodes were accumulated in TNT solution (100 ppb) for 150 s at 0 V. Scan rate : 50 mV/s.
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-2
Current Density (mA cm )
0.0
0.0
A
-0.1
-0.1
-0.2
-0.2
-0.3 -0.8
-0.6
-0.4
-0.2
Potantial (V. vs. Ag/AgCl)
-0.3
B
-0.8
-0.6
-0.4
-0.2
Potantial (V. vs. Ag/AgCl)
Figure S14. LSV of the N-GQDs/GC electrode in PBS (0.1 M, pH 7.0) after the it was accumulated in 100 ppb 2,4-DNT (A) and 2-NT solution (B) for 150 s at 0 V. Scan rate: 50 mV/s.
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40k
i h g f e d c b a
B 30k 4k
20k
Signal Area
50 a.u.
Signal Area
UV Absorbance (a.u.)
A
10k
3k 2k 1k 0
0 10 20 30 40 50
TNT concentration (ppb)
0 6
8
10
0
Rentation time (min)
100
200
300
400
500
TNT concentration (ppb)
Figure S15. (A) HPLC spectra of tap water (a-c), ground water (d-f), and lake water (g-i) contaminated with 2, 5, and 10 ppb TNT. (B) The standard curve of HPLC measurements of TNT with different concentration ranging from 2, 5, 10, 25, 50, 100, 250 to 500 ppb. Inset: The standard curve of HPLC measurements of TNT at low concentration. HPLC measurements were carried out according to U. S. EPA SW 846 method 8330. Column: C‒18 reversed-phase HPLC column; Mobile phase: 50/50 (v/v) methanol/organic-free reagent water; Flow rate: 1.5 mL/min; Injection volume: 100 µL; UV detector: 254 nm.
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Synthesis of Nitrogen-Doped Graphene Quantum Dots at Low Temperature for Electrochemical Sensing Trinitrotoluene
Zhewei Cai,a Fumin Li,b Ping Wu,*b Lijuan Ji,b Hui Zhang,b Chenxin Cai,b and Dominic F. Gervasio*a a
Department of Chemical & Environmental Engineering, University of Arizona, 1133 E. James E.
Rogers Way, Tucson, AZ 85721, USA b
Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of
Biomedical Functional Materials, National and Local Joint Engineering Research Center of Biomedical Functional Materials, College of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210097, P.R. China.
* Corresponding author, E-mail: [email protected] (P. Wu); [email protected] (D. F. Gervasio).
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Contents:
Figure S1. TEM, AFM image, and FTIR spectra of GO sheet. Figure S2. TEM and XPS spectra of the nanometer-sized GO pieces. Figure S3. SEM images of N-graphene, N-GQDs, and GQDs on GC electrode. Figure S4. Photograph of the N-graphene sheet under excitation of 365 nm. Figure S5. Diagram of electronic transition of triple carbenes. Figure S6. CV response of K3Fe(CN)6 at the N-GQDs/GC and GQDs/GC electrodes. Figure S7. EIS of K3Fe(CN)6/K4Fe(CN)6 at the bare GC, GQDs/GC, and N-GQDs/GC electrodes. Figure S8. I‒V curves for N-GQDs and GQDs. Figure S9. UV-Vis spectra of 100 ppb TNT before and after accumulated. Figure S10. Charge distributions of GQDs and N-GQDs. Figure S11. HOMO and LUMO spatial distributions for GQD and N-GQDs. Figure S12. LSV of TNT reduction at the N-GQDs/GC electrode after different accumulation time. Figure S13. LSV of TNT reduction at the N-GQDs/GC electrode at different pH. Figure S14. LSV of 2,4-DNT and 2-NT at the N-GQDs/GC electrode. Figure S15. HPLC responses of different water samples.
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Figure S1. Typical TEM (A) and AFM image (B) of the synthesized GO sheet. (C) FTIR spectra of the synthesized GO sheet (curve a) and N-GQDs (curve b).
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Figure S2. Typical TEM (A) and XPS spectra (B, C) of the nanometer-sized GO pieces.
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Figure S3. SEM images of N-graphene/GC (A), N-GQDs/GC (B), and GQDs/GC electrodes (C).
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Figure S4. Photograph of the N-graphene sheet under excitation of 365 nm.
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Figure S5. A diagram of electronic transition of triple carbenes at zigzag sites observed in the optical spectra of the N-GQDs.
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Current (µA)
50
0
N-GQDs GQDs
-50
0.0
0.2
0.4
0.6
Potential (V, vs. Ag/AgCl) Figure S6. Cyclic voltammograms for the N-GQDs/GC and GQDs/GC electrodes in 1 M KCl solution containing 1.0 mM K3Fe(CN)6. Scan rate: 100 mV/s.
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300
-Z'' (ohm)
200
100 GC GQDs N-GQDs 0 0
100
200
300
400
Z' (ohm) Figure S7. Nyquist plots of the bare GC, GQDs/GC, and N-GQDs/GC electrodes in 0.1 M KCl solution containing 5 mM K3Fe(CN)6/K4Fe(CN)6 (1:1) in the frequency range from 0.1 Hz to 100 kHz. Amplitude: 10 mV.
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Figure S8. I‒V curves for N-GQDs (a) and GQDs (b). Scan rate: 100 mV/s.
The electrical conductivity of the N-GQDs and GQDs was estimated from DC measurements. The samples (N-GQDs and GQDs) were pressed to the rods by a homemade two-electrode cell template (0.4 cm in diameter and 8.5 cm in length) under 20 MPa. Then, the rods of GQDs and N-GQDs were performed the current-voltage (I‒V) measurements on a CHI 760B electrochemical workstation. The voltage was scanned from ‒1.5 to 1.5 V with no applied gate voltage at 100 mV/s. The current response was recorded. The values of the electrical conductivity (σ) were calculated according the following equation (1): σ
where A is the surface area of the samples rod (in m2), l is the length of samples (in m), and the value I/V was taken as the slope of I‒V curves. The calculated σ of N-GQDs and GQDs is 1.22 × 103 S m‒1and 1.01 × 103 S m‒1, respectively.
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Absorbance (a.u.)
a
c
225
250
275
300
325
350
Wavelength (nm)
Figure S9. UV-Vis spectra of 100 ppb TNT before (curve a) and after accumulated by GQDs (curve b) and N-GQDs (curve c) for 150 s at 0 V.
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Figure S10. Charge distributions of GQDs (A), and pyridinic (B) and pyrrolic N-GQDs (C).
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HOMO
GQD
LUMO
α, β electrons
α electron
pyridinic N-GQDs
β electron
pyrrolic NGQDs
α, β electrons
Figure S11. HOMO and LUMO spatial distributions of α electron and β electron for GQD and pyridinic and pyrrolic N-GQDs.
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-2
Current Density (mA cm )
0.0
-0.1
0s
-0.2
-0.3
210 s -0.8
-0.6
-0.4
-0.2
Potenial (V, vs. AgCl/Ag)
Figure S12. LSV of TNT reduction at the N-GQDs/GC electrode in PBS (0.1 M, pH 7.0) after accumulated in TNT (100 ppb) solution at 0 V for (curve a to h): 0, 30, 60, 90, 120, 150, 180, and 210 s. Scan rate : 50 mV/s.
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-2
Current Density (mA cm )
0.05 0.00 -0.05 -0.10 -0.15 -0.20
pH=5 pH=6 pH=7 pH=8 pH=9
-0.25 -0.30 -0.8
-0.6
-0.4
-0.2
Potential (V, vs. Ag/AgCl)
Figure S13. LSV of TNT reduction at the N-GQDs/GC electrode in PBS (0.1 M) with different pH value (5, 6, 7, 8, 9). Before recording the LSV, the N-GQDs/GC electrodes were accumulated in TNT solution (100 ppb) for 150 s at 0 V. Scan rate : 50 mV/s.
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-2
Current Density (mA cm )
0.0
0.0
A
-0.1
-0.1
-0.2
-0.2
-0.3 -0.8
-0.6
-0.4
-0.2
Potantial (V. vs. Ag/AgCl)
-0.3
B
-0.8
-0.6
-0.4
-0.2
Potantial (V. vs. Ag/AgCl)
Figure S14. LSV of the N-GQDs/GC electrode in PBS (0.1 M, pH 7.0) after the it was accumulated in 100 ppb 2,4-DNT (A) and 2-NT solution (B) for 150 s at 0 V. Scan rate: 50 mV/s.
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40k
i h g f e d c b a
B 30k 4k
20k
Signal Area
50 a.u.
Signal Area
UV Absorbance (a.u.)
A
10k
3k 2k 1k 0
0 10 20 30 40 50
TNT concentration (ppb)
0 6
8
10
0
Rentation time (min)
100
200
300
400
500
TNT concentration (ppb)
Figure S15. (A) HPLC spectra of tap water (a-c), ground water (d-f), and lake water (g-i) contaminated with 2, 5, and 10 ppb TNT. (B) The standard curve of HPLC measurements of TNT with different concentration ranging from 2, 5, 10, 25, 50, 100, 250 to 500 ppb. Inset: The standard curve of HPLC measurements of TNT at low concentration. HPLC measurements were carried out according to U. S. EPA SW 846 method 8330. Column: C‒18 reversed-phase HPLC column; Mobile phase: 50/50 (v/v) methanol/organic-free reagent water; Flow rate: 1.5 mL/min; Injection volume: 100 µL; UV detector: 254 nm.
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