The in-situ reduction of GO to RGO during synthesis of RGO-Ag3PO4 heterostructure was further validated from FTIR (Figure S2). The FTIR spectra of ...
Supporting Information
Scheme S1. Mechanism of formation of RGO-Ag3PO4 using ethanol as sacrificial agent.
Figure S1. Raman shift of pristine Ag3PO4 and xRGO-Ag3PO4.
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Figure S2. FTIR spectra of 4GO-Ag3PO4 and 4RGO-Ag3PO4.
The in-situ reduction of GO to RGO during synthesis of RGO-Ag3 PO4 heterostructure was further validated from FTIR (Figure S2). The FTIR spectra of 4RGO-Ag3PO4 prepared under visible light irradiation and 4GOAg3 PO4 prepared without irradiation were observed to be significantly different. The graph (Figure S1) shows stretching frequency of hydroxyl groups at 3375 cm-1, the aromatic C=O carbonyl stretching at 1650 cm-1, aromatic ring mode C=C skeletal vibration frequency at 1404 cm-1 and C-O epoxy group stretching at 1004 cm-1. The comparison of the above mentioned stretching and skeletal vibration frequencies of both the composites confirms the existence of a large quantity of oxygen functional groups in 4GO-Ag3 PO4. But, in case of 4RGO-Ag3PO4, hydroxyl, carbonyl and epoxy groups significantly decreased and the intensity of aromatic C=C stretching frequency at 1404 cm-1 is higher as compared to the 4GO-Ag3PO4 composite. Again, in case of 4GO-Ag3 PO4, the epoxy group is merged with P-O stretching vibrations at 1000 cm-1, which is prominently observed in 4RGOAg3 PO4. The results hereby confirm both the reduction of GO to RGO and also the formation of the heterostructure under visible light illumination.
Figure S3.
13
C MAS solid state NMR spectra of 4RGO-Ag3PO4 nanocomposite.
To further confirm the formation of heterostructure and the reduction of GO to RGO, 13C MAS solid state NMR spectroscopy was used to characterize 4RGO-Ag3 PO4 heterostructure (Figure S3). The magic angle spinning NMR experiment resulted in resonance at 60 ppm corresponds to tertiary alcohol; the 70 ppm resonance is a result of epoxy functional group. A lesser intense resonance peak centred at 136 ppm is supposed to have appeared at 130 ppm which relates to sp2 environment in case of graphene oxide. This shifting of resonance peak might be attributed to the presence of alkene bonded with silver phosphate environment in case of the heterostructure.
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Figure S4. (a) EIS spectra (b) I–V curves in the dark and under visible light illumination for pristine Ag3PO4 and 4RGO-Ag3PO4.
With reference to the report of Guo et al.,[S1] the conduction band and valance band offsets of RGO-Ag3 PO4 heterostructure photocatalyst was calculated as follows with reference to Type II staggered band alignment:[S2]
Valance band offset, ∆Ev = EvAg3PO4 – EvRGO Conduction band offset, ∆Ec = EgAg3PO4 -EgRGO - ∆Ev Barrier height, ∆EBH = EgRGO - ∆Ec Where EvAg3PO4 and EvRGO = valance band potential of Ag3 PO4 and RGO respectively, EcAg3PO4 and EcRGO = conduction band potential of Ag3PO4 and RGO, respectively, ∆EBH = the difference between the top of the valance band of RGO and bottom of conduction band of Ag3PO4. The values are of valance band offset, conduction band offset and barrier height are calculated to be 0.30, 1.07 and 2.13 eV, respectively.
Ag3d
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(b) Figure S5. (a) XPS survey (b) HRTEM image of used RGO-Ag3PO4.
n/2
Figure S6. Band gap energy calculation of 4RGO-Ag3PO4 using the formula h = A(h - Eg) (Where , , A, n and Eg are the absorption coefficient, light frequency, proportionality constant, integer (n = 1, 2, 4, 6) and band gap energy, respectively.).
In order to ascertain the process of the process of hydrogen evolution over RGO-Ag3PO4 under visible light illumination in a Z-scheme, an experiment was carried out for photodeposition of platinum using stoichiometric H2PtCl6.6H2O (1 wt.% with respect to 4RGO-Ag3 PO4) solution in the experimental condition of water splitting as was mentioned in the experimental section of main text, in a closed vessel for 3 h. Prior to the experiment the suspension was purged with N2. After 3 h, the sample was collected after proper washing with distilled water till the removal of chloride followed by drying at 70 oC. The Pt-RGO-Ag3PO4 thus formed by photodeposition route was characterised by XPS to examine the valance of Platinum. X-Ray photoelectron spectroscopy (XPS) measurements were performed on a VG Microtech Multilab ESCA 3000 spectrometer with a non-monochromatised Mg-Ka X-ray source. Energy resolution of the spectrometer was set at 0.8 eV withMg-Ka radiation at pass energy of 50 eV. The binding energy correction was performed using the C1s peak of carbon at 284.9 eV as a reference.
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Pt4f
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(b) Figure S7. (a) XPS survey (b) HRTEM image of Pt-RGO-Ag3PO4 prepared by photodeposition route during hydrogen generation via water splitting. References (S1) Y.M. Guo, L.P. Zhu, J. Jiang, L. Hu, C.L. Ye, Z.Z. Ye, Appl. Phys. Lett. 2012, 101, 052109. (S2) A. Franciosi, C.G. Van de Walle, Surf. Sci. Rep. 1996, 25, 1-140.
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