Fabrication and Enhanced Photoelectrochemical Performance of ...
Supporting Information for
Fabrication and Enhanced Photoelectrochemical Performance of MoS2/S-Doped g-C3N4 Heterojunction Film Lijuan Ye, † Dan Wang, ‡ Shijian Chen*, † †
School of Physics, Chongqing University, Shapingba, Chongqing 401331, People’s Republic of China.
‡
School of media and mathematics & Physics, Jilin Engineering Normal University, Changchun 130052, People’s Republic of China.
*
E-mail: [email protected].
S-1
Figure S1. The XRD patterns of precursors (Melamine and Thiourea).
Figure S2. The comparison between XRD patterns of mt-CN film sample and powder, as well as m-CN powder.
It can be seen that the main characteristic peaks of mt-CN film sample, mt-CN S-2
powder and m-CN powder all locate at 27.67o and are attributed to the (002) plane (d-spacing = 0.32 nm) of g-C3N4 polymer, which indicates the interlayer stacking and the distance between graphitic layers. The peaks around 13.00 o in m-CN and mt-CN powders are absence in mt-CN film, which is usually ascribed to the (100) plane (d-spacing = 0.68 nm) of g-C3N4 polymer and corresponds to the approximate dimension of the tri-s-triazine unit. The well matched XRD patterns between mt-CN film, mt-CN and m-CN powder suggest the prepared CN films in the closed system are tri-s-triazine based polymers, i.e. g-C3N4.
Figure S3. The Raman spectra of precursors (Melamine and Thiourea) excited by 532 nm laser.
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Figure S4. (a) The Raman spectra of mt-CN film, mt-CN powder, m-CN powder, and ITO substrate excited by 532 nm laser. (b) The local Raman vibrations of mt-CN film and powder, as well as m-CN powder excited by 633 nm He-Ne laser.
In Figure S4 (a), the short gray dashes show the Raman peaks (I─VIII) of mt-CN film sample, which are completely observed from the Raman spectra of mt-CN and m-CN powders. Besides, the small peak located at 707 cm-1 in the spectra of m-CN and mt-CN powders is a characteristic Raman peak of carbon nitride and arises from the out-of-plane vibration of C-C bond related with N content, as denoted as the “ L” band like in other literatures.1, 2 However, it disappears in that of mt-CN film sample. In Figure S4 (b), the He-Ne laser is used to excited such typical Raman mode. It can be seen that the 707 peak still appears in the spectra of mt-CN and m-CN powders but blue-shifts a little in mt-CN film sample, resulting in the appearance of 718 cm-1peak.
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Figure S5. (a) The survey XPS spectra of m-CN, mt-CN and mt-CN/MoS2 film samples. (b) The high-resolve spectra of C1s for m-CN and mt-CN films. (c) The high-resolve spectra of N1s for m-CN and mt-CN films. (d) The high-resolve spectra of S 2p for mt-CN film before and after eatching. The raw spectra, the fitted survey curves, the fitted components, and the baselines are represented by black, red, green and rose color lines.
The XPS survey spectra in Figure S5 (a) indicate that C and N elements are detected in all the film samples, and except In, Sn and O elements from ITO substrates, the S and Mo elements are detected in the mt-CN/MoS2 sample. Figure S5 (b) displays the C 1s spectrum of m-CN and mt-CN film samples. Except the adventitious carbon, the detected peaks at 287.89 eV for m-CN and 287.69 eV for mt-CN film sample are attributed to the tertiary carbon C-(N)3 in the g-C3N4 lattice, S-5
which shift towards lower binding energy compared with that of mt-CN/MoS2 film sample. The peak at ~ 400eV in the XPS spectrum of N 1s for m-CN and mt-CN film samples in Figure 5S (c) are usually ascribed to the tertiary nitrogen N–(C)3 groups, which shifts to higher binding energy compared with mt-CN/MoS2 film sample. The strong peak at ~398 eV and the weak peak around ~ 404 eV are usually attributed to the sp2 hybridized nitrogen C-N=C groups and the charging effects in the heterocycles, respectively.3, 4 Figure S5 (d) shows the high-resolve spectra of S 2p for mt-CN film before and after being etched. Before etching, the observed peak at 162.43 eV should be attributed to the C-S bond, which also appears in the mt-CN/MoS2 film sample, but shifting towards higher bind energy of 163.27 eV. The stronger peak at 168.48 eV probably arises from the S-O bonds due to surface adsorbed sulfur species like SO42-, which has been confirmed by the reported Sulfur K-edge X-ray absorption near edge structure (XANES) spectrum for the g-C3N4-xSx system.5 Also, this peak totally disappears after being etched by Ar+ sputtering for 20 s, leaving the peak presented C-S bond alone. This also demonstrates that the S impurities have been implanted homogeneously into CN materials by substituting the nitrogen sites after mixing thiourea into melamine.
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Figure S6. (a) The optical photographs of m-CN, mt-CN, and mt-CN/MoS2 film samples. (b) and (c) are the low-resolution surface SEM images of m-CN and mt-CN film samples.
Figure S7. The schematic diagram of the fabrication, structure and composition of film samples. S-7
Figure S8. The periodically illuminated photocurrent-potential (I−V) curve of m-CN film electrode under anodic scanning. The inset (a) is the periodically illuminated photocurrent-time (I−t) curves of m-CN film sample and bare ITO substrate under applied potential of +0.5 V vs. Ag/AgCl. The inset (b) is the I-V curves of m-CN film electrode before and after light irradiation.
From Figure S8, it is obvious that the photocurrent response of m-CN film sample becomes larger with the increasing positive polarization potential. Under the applied bias of +0.5 V vs Ag/AgCl, the instantaneous photocurrent response of m-CN film sample just remain steady at 2×10-7 A/cm2, as shown in the inset (a), which is much lower than that of mt-CN and mt-CN/MoS2 film samples.
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Figure S9. Electrochemical impedance spectra (EIS) Nyquist plots of mt-CN and mt-CN/MoS2 film electrodes under visible light irradiation in 0.1 mol/L Na2SO4 solution.
Table S1. The electrical Properties of ITO substrate, m-CN, mt-CN and mt-CN/MoS2 film samples. Carrier concentration
Resistivity
Mobility
Conduction
(cm-3)
(Ω.cm)
(cm2V-1s-1)
types
ITO
-1.116×1021
3.875×101
1.443×10-4
n
m-CN
-1.646×1018
1.033×103
3.672×10-3
n
mt-CN
-6.184 ×1014
2.046×102
4.932×10-1
n
mt-CN /MoS2
1.930×1018
3.747×101
8.633×10-4
p
Samples
S-9
Figure S10. The steady state photocurrent-potential (I−V) curves of mt-CN and mt-CN/MoS2 film samples before (dotted lines) and after light irradiation (solid lines) under anodic sweeping. The
V-axis (photocurrent=0) is indicated by the gray dotted line.
In contrast to the negligible current change of m-CN film sample under on-off light shown in the inset (b) of Figure S8, both mt-CN and mt-CN/MoS2 film samples show obvious steady state current difference due to the on-off light, as shown in Figure S10. For mt-CN film sample, the current almost remains zero in the dark with the polarization potential from -1.0 to 1.0 V vs. Ag/AgCl, while under light irradiation condition the anodic current starts from -0.76 V vs. Ag/AgCl and increases gradually, implying the photoanode role of the prepared mt-CN film sample. After forming heterojunction, a similar phenomenon is also observed in the mt-CN/MoS2 sample. Differently, the anodic photocurrent of mt-CN/MoS2 film sample occurs around -0.48 V vs. Ag/AgCl, as shown as the closer look in the inset, which suggests an anodic shift of photocurrent onset potential compared with the mt-CN film sample. More importantly, it has been reported that MoS2 is more naturally suited for using as a S-10
photocathode and could produce significant cathodic photocurrent response under negative polarization potential.5 Consequently, due to the growth of MoS2 layer on CN material, an apparent cathodic photocurrent is observed in mt-CN/MoS2 sample under polarization potential of -1.0 to -0.27 V vs. Ag/AgCl. However, the mt-CN/MoS2 sample still owns the potential of use as a photoanode. In addition, an apparent polarization current is observed for mt-CN/MoS2 sample in the dark and shows a gradual rise either because of charge-carrier shunting or Schottky barrier height lowering.6 Under the light irradiation, two oxidation peaks appear around 0.42 and 0.89 V vs. Ag/AgCl, which may be attributed to the discharge of photoactive species absorbed on the surface of mt-CN/MoS2 sample. These two photooxided peaks disappear during the subsequent chopped I-V measurement, which indicates the stability of mt-CN/MoS2 sample.
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References 1 Rodil, S. E.; Ferrari, A. C.; Robertson, J.; Milne, W. I. Raman and Infrared Modes of Hydrogenated Amorphous Carbon Nitride. J. Appl. Phys., 2001, 89, 5425-5430. 2 Chowdhury, A. K. M. S.; Cameron, D. C.; Hashmi, M. S. J. Vibrational Properties of Carbon Nitride Films by Raman Spectroscopy. Thin Solid Films, 1998, 332, 62-68. 3 Wang, X. J.; Yang, W. Y.; Li, F. T.; Xue, Y. B.; Liu, R. H.; Hao, Y. J. In Situ Microwave-Assisted Synthesis of Porous N-TiO2/g-C3N4 Heterojunctions with Enhanced Visible-Light Photocatalytic Properties. Ind. Eng. Chem. Res. 2013, 52, 17140-17150. 4 Dai, K.; Lu, L. H.; Liu, Q.; Zhu, G. P.; Wei, X. Q.; Bai, J.; Xuan, L. L.; Wang, H. Sonication Assisted Preparation of Graphene Oxide/Graphitic-C3N4 Nanosheet Hybrid with Reinforced Photocurrent for Photocatalyst Applications. Dalton Trans. 2014, 43, 6295-6299. 5 Liu, G.; Niu, P.; Sun, C. H.; Smith, S. C.; Chen, Z. G.; Lu, G. Q.; Cheng, H. M. Unique Electronic Structure Induced High Photoreactivity of Sulfur-Doped Graphitic C3N4. J. Am. Chem. Soc. 2010, 132, 11642-11648. 6 Chen, Z. B.; Forman, A. J.; Jaramillo, T. F. Bridging the Gap between Bulk and Nanostructured Photoelectrodes: The Impact of Surface States on the Electrocatalytic and Photoelectrochemical Properties of MoS2. J. Phys. Chem. C 2013, 117, 9713-9722.
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Fabrication and Enhanced Photoelectrochemical Performance of MoS2/S-Doped g-C3N4 Heterojunction Film Lijuan Ye, † Dan Wang, ‡ Shijian Chen*, † †
School of Physics, Chongqing University, Shapingba, Chongqing 401331, People’s Republic of China.
‡
School of media and mathematics & Physics, Jilin Engineering Normal University, Changchun 130052, People’s Republic of China.
*
E-mail: [email protected].
S-1
Figure S1. The XRD patterns of precursors (Melamine and Thiourea).
Figure S2. The comparison between XRD patterns of mt-CN film sample and powder, as well as m-CN powder.
It can be seen that the main characteristic peaks of mt-CN film sample, mt-CN S-2
powder and m-CN powder all locate at 27.67o and are attributed to the (002) plane (d-spacing = 0.32 nm) of g-C3N4 polymer, which indicates the interlayer stacking and the distance between graphitic layers. The peaks around 13.00 o in m-CN and mt-CN powders are absence in mt-CN film, which is usually ascribed to the (100) plane (d-spacing = 0.68 nm) of g-C3N4 polymer and corresponds to the approximate dimension of the tri-s-triazine unit. The well matched XRD patterns between mt-CN film, mt-CN and m-CN powder suggest the prepared CN films in the closed system are tri-s-triazine based polymers, i.e. g-C3N4.
Figure S3. The Raman spectra of precursors (Melamine and Thiourea) excited by 532 nm laser.
S-3
Figure S4. (a) The Raman spectra of mt-CN film, mt-CN powder, m-CN powder, and ITO substrate excited by 532 nm laser. (b) The local Raman vibrations of mt-CN film and powder, as well as m-CN powder excited by 633 nm He-Ne laser.
In Figure S4 (a), the short gray dashes show the Raman peaks (I─VIII) of mt-CN film sample, which are completely observed from the Raman spectra of mt-CN and m-CN powders. Besides, the small peak located at 707 cm-1 in the spectra of m-CN and mt-CN powders is a characteristic Raman peak of carbon nitride and arises from the out-of-plane vibration of C-C bond related with N content, as denoted as the “ L” band like in other literatures.1, 2 However, it disappears in that of mt-CN film sample. In Figure S4 (b), the He-Ne laser is used to excited such typical Raman mode. It can be seen that the 707 peak still appears in the spectra of mt-CN and m-CN powders but blue-shifts a little in mt-CN film sample, resulting in the appearance of 718 cm-1peak.
S-4
Figure S5. (a) The survey XPS spectra of m-CN, mt-CN and mt-CN/MoS2 film samples. (b) The high-resolve spectra of C1s for m-CN and mt-CN films. (c) The high-resolve spectra of N1s for m-CN and mt-CN films. (d) The high-resolve spectra of S 2p for mt-CN film before and after eatching. The raw spectra, the fitted survey curves, the fitted components, and the baselines are represented by black, red, green and rose color lines.
The XPS survey spectra in Figure S5 (a) indicate that C and N elements are detected in all the film samples, and except In, Sn and O elements from ITO substrates, the S and Mo elements are detected in the mt-CN/MoS2 sample. Figure S5 (b) displays the C 1s spectrum of m-CN and mt-CN film samples. Except the adventitious carbon, the detected peaks at 287.89 eV for m-CN and 287.69 eV for mt-CN film sample are attributed to the tertiary carbon C-(N)3 in the g-C3N4 lattice, S-5
which shift towards lower binding energy compared with that of mt-CN/MoS2 film sample. The peak at ~ 400eV in the XPS spectrum of N 1s for m-CN and mt-CN film samples in Figure 5S (c) are usually ascribed to the tertiary nitrogen N–(C)3 groups, which shifts to higher binding energy compared with mt-CN/MoS2 film sample. The strong peak at ~398 eV and the weak peak around ~ 404 eV are usually attributed to the sp2 hybridized nitrogen C-N=C groups and the charging effects in the heterocycles, respectively.3, 4 Figure S5 (d) shows the high-resolve spectra of S 2p for mt-CN film before and after being etched. Before etching, the observed peak at 162.43 eV should be attributed to the C-S bond, which also appears in the mt-CN/MoS2 film sample, but shifting towards higher bind energy of 163.27 eV. The stronger peak at 168.48 eV probably arises from the S-O bonds due to surface adsorbed sulfur species like SO42-, which has been confirmed by the reported Sulfur K-edge X-ray absorption near edge structure (XANES) spectrum for the g-C3N4-xSx system.5 Also, this peak totally disappears after being etched by Ar+ sputtering for 20 s, leaving the peak presented C-S bond alone. This also demonstrates that the S impurities have been implanted homogeneously into CN materials by substituting the nitrogen sites after mixing thiourea into melamine.
S-6
Figure S6. (a) The optical photographs of m-CN, mt-CN, and mt-CN/MoS2 film samples. (b) and (c) are the low-resolution surface SEM images of m-CN and mt-CN film samples.
Figure S7. The schematic diagram of the fabrication, structure and composition of film samples. S-7
Figure S8. The periodically illuminated photocurrent-potential (I−V) curve of m-CN film electrode under anodic scanning. The inset (a) is the periodically illuminated photocurrent-time (I−t) curves of m-CN film sample and bare ITO substrate under applied potential of +0.5 V vs. Ag/AgCl. The inset (b) is the I-V curves of m-CN film electrode before and after light irradiation.
From Figure S8, it is obvious that the photocurrent response of m-CN film sample becomes larger with the increasing positive polarization potential. Under the applied bias of +0.5 V vs Ag/AgCl, the instantaneous photocurrent response of m-CN film sample just remain steady at 2×10-7 A/cm2, as shown in the inset (a), which is much lower than that of mt-CN and mt-CN/MoS2 film samples.
S-8
Figure S9. Electrochemical impedance spectra (EIS) Nyquist plots of mt-CN and mt-CN/MoS2 film electrodes under visible light irradiation in 0.1 mol/L Na2SO4 solution.
Table S1. The electrical Properties of ITO substrate, m-CN, mt-CN and mt-CN/MoS2 film samples. Carrier concentration
Resistivity
Mobility
Conduction
(cm-3)
(Ω.cm)
(cm2V-1s-1)
types
ITO
-1.116×1021
3.875×101
1.443×10-4
n
m-CN
-1.646×1018
1.033×103
3.672×10-3
n
mt-CN
-6.184 ×1014
2.046×102
4.932×10-1
n
mt-CN /MoS2
1.930×1018
3.747×101
8.633×10-4
p
Samples
S-9
Figure S10. The steady state photocurrent-potential (I−V) curves of mt-CN and mt-CN/MoS2 film samples before (dotted lines) and after light irradiation (solid lines) under anodic sweeping. The
V-axis (photocurrent=0) is indicated by the gray dotted line.
In contrast to the negligible current change of m-CN film sample under on-off light shown in the inset (b) of Figure S8, both mt-CN and mt-CN/MoS2 film samples show obvious steady state current difference due to the on-off light, as shown in Figure S10. For mt-CN film sample, the current almost remains zero in the dark with the polarization potential from -1.0 to 1.0 V vs. Ag/AgCl, while under light irradiation condition the anodic current starts from -0.76 V vs. Ag/AgCl and increases gradually, implying the photoanode role of the prepared mt-CN film sample. After forming heterojunction, a similar phenomenon is also observed in the mt-CN/MoS2 sample. Differently, the anodic photocurrent of mt-CN/MoS2 film sample occurs around -0.48 V vs. Ag/AgCl, as shown as the closer look in the inset, which suggests an anodic shift of photocurrent onset potential compared with the mt-CN film sample. More importantly, it has been reported that MoS2 is more naturally suited for using as a S-10
photocathode and could produce significant cathodic photocurrent response under negative polarization potential.5 Consequently, due to the growth of MoS2 layer on CN material, an apparent cathodic photocurrent is observed in mt-CN/MoS2 sample under polarization potential of -1.0 to -0.27 V vs. Ag/AgCl. However, the mt-CN/MoS2 sample still owns the potential of use as a photoanode. In addition, an apparent polarization current is observed for mt-CN/MoS2 sample in the dark and shows a gradual rise either because of charge-carrier shunting or Schottky barrier height lowering.6 Under the light irradiation, two oxidation peaks appear around 0.42 and 0.89 V vs. Ag/AgCl, which may be attributed to the discharge of photoactive species absorbed on the surface of mt-CN/MoS2 sample. These two photooxided peaks disappear during the subsequent chopped I-V measurement, which indicates the stability of mt-CN/MoS2 sample.
S-11
References 1 Rodil, S. E.; Ferrari, A. C.; Robertson, J.; Milne, W. I. Raman and Infrared Modes of Hydrogenated Amorphous Carbon Nitride. J. Appl. Phys., 2001, 89, 5425-5430. 2 Chowdhury, A. K. M. S.; Cameron, D. C.; Hashmi, M. S. J. Vibrational Properties of Carbon Nitride Films by Raman Spectroscopy. Thin Solid Films, 1998, 332, 62-68. 3 Wang, X. J.; Yang, W. Y.; Li, F. T.; Xue, Y. B.; Liu, R. H.; Hao, Y. J. In Situ Microwave-Assisted Synthesis of Porous N-TiO2/g-C3N4 Heterojunctions with Enhanced Visible-Light Photocatalytic Properties. Ind. Eng. Chem. Res. 2013, 52, 17140-17150. 4 Dai, K.; Lu, L. H.; Liu, Q.; Zhu, G. P.; Wei, X. Q.; Bai, J.; Xuan, L. L.; Wang, H. Sonication Assisted Preparation of Graphene Oxide/Graphitic-C3N4 Nanosheet Hybrid with Reinforced Photocurrent for Photocatalyst Applications. Dalton Trans. 2014, 43, 6295-6299. 5 Liu, G.; Niu, P.; Sun, C. H.; Smith, S. C.; Chen, Z. G.; Lu, G. Q.; Cheng, H. M. Unique Electronic Structure Induced High Photoreactivity of Sulfur-Doped Graphitic C3N4. J. Am. Chem. Soc. 2010, 132, 11642-11648. 6 Chen, Z. B.; Forman, A. J.; Jaramillo, T. F. Bridging the Gap between Bulk and Nanostructured Photoelectrodes: The Impact of Surface States on the Electrocatalytic and Photoelectrochemical Properties of MoS2. J. Phys. Chem. C 2013, 117, 9713-9722.
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