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In Situ Photoreduction Synthesis of Fe(0)/Melamine CoreShell submicro-cubes for Efficient Photocatalytic H2 Evolution Fang He, Zhenyuan Song, Zhen Xing Wang, Shaoqin Peng, and Yuexiang Li ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.8b00134 • Publication Date (Web): 16 May 2018 Downloaded from http://pubs.acs.org on May 16, 2018

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ACS Applied Energy Materials

In Situ Photoreduction Synthesis of Fe(0)/Melamine Core-Shell Submicro-cubes for Efficient Photocatalytic H2 Evolution Fang He, Zhenyuan Song, Zhenxing Wang, Shaoqin Peng, Yuexiang Li* Department of Chemistry, Nanchang University, Nanchang, 330031, P.R. China

ABSTRACT: Exploring low-cost and noble-metal-free HER (hydrogen evolution reaction) cocatalysts such as Fe, Co or Ni for H2 evolution has drawn great attention in heterogeneous photocatalysis. Herein, for the first time, we reported a novel, facile approach to synthesize a Fe(0)/melamine composite HER cocatalyst through in situ photoreduction of Fe(II)-melamine complex at room temperature in the presence of Eosin Y (EY) and trimethylamine (TMA). The Fe(0)/melamine composite displays core-shell submicro-cubes, which shows superior photocatalytic H2 evolution performance and good stability. The melamine modified on Fe(0) surface not only keeps Fe from being oxidized, but also increases the electron transfer ability from EY to metal Fe(0) and decreases the HER overpotential, promoting efficient photocatalytic hydrogen evolution under visible light irradiation. This work provides a new strategy to obtain highly efficient stable photocatalyst via a facile in situ photoreduction approach by using lowcost earth-abundant elements (Fe, C, and N).

KEYWORDS: Fe(0)/melamine, core-shell, submicro-cube, photocatalytic, H2 evolution 1. INTRODUCTION Photocatalytic hydrogen evolution has received extensive attention due to its great potential

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on solving the energy crisis and environmental pollution problems.1-5 Great efforts have been made to develop efficient and low-cost photocatalyst for hydrogen evolution.6-9 It is well known that HER cocatalyst can efficiently enhance the photocatalytic H2 evolution performance, as it not only increases the charge carrier separation efficiency, but also serves as reaction active sites for H2 evolution. The noble metals such as Pt and Au usually act as excellent HER cocatalysts for enhancing photocatalytic activity.10-11 However, noble metals are rare and expensive, which greatly limits widespread applications. Therefore, it is quite necessary to explore low-cost and noble-metal-free alternatives such as Fe, Co or Ni for H2 evolution. Among which, Fe is a lowcost and earth-abundant metal. Fe(0) nano/submicro-particles can be obtained by various of different methods. Monodisperse Fe(0) nanoparticles were prepared via thermal decomposition of Fe(CO)5 under an argon atmosphere.12 Fe(0) nanoparticles can be also synthesized using Fe salt precursors in polyol.13-14 The first clearly successful synthesis of Fe nanocubes was reported by decomposition of a precursor (Fe[N(SiMe3)2]2) in mesitylene in a H2 atmosphere within a glovebox.15 Though Fe(0) nano/submicro-particles can be gained through above methods, the synthesis conditions are rigorous, which needs an inert atmosphere or non-aqueous solvents, greatly restricting the largescale synthesis and application. Furthermore, Fe(0) itself is unstable as it often suffers from being oxidized in air, which will affect its HER performance. Herein, we proposed a novel, facile approach to synthesize Fe(0)/melamine core-shell submicro-cubes through in situ photoreduction of Fe(II)-melamine complex at room temperature in the presence of Eosin Y (EY) and trimethylamine (TMA). The obtained Fe(0)/melamine coreshell submicro-cubes show superior photocatalytic H2 evolution activity than that of commercial nano Fe(0) in dye-sensitized reaction system under visible light irradiation. The effects of


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melamine coated on Fe(0) surface on electron transfer, HER overpotential, and photocatalytic H2 evolution activity have been investigated in detail. 2. EXPERIMENTAL 2.1. Materials. Melamine (MA, C3H6N6), Eosin Y (EY, bioreagent), Potassium hydroxide (KOH), commercial nano Fe(0), and trimethylamine aqueous solution (33 wt% TMA) were purchased from Sinopharm Chemical Reagent Co., Ltd. Ammonium iron(Ⅱ) sulfate hexahydrate was purchased from Xilong Scientific Co., Ltd. All chemicals were used as received without further treatment. 2.2. Preparation of HER cocatalyst by photoreducution. The HER cocatalyst was prepared by in situ photoreduction as follows: Firstly, 0.20 g melamine was dispersed in 40 mL distilled water by ultrasonication to form a clear solution. Subsequently, equal mass of (NH4)2Fe(SO4)2 aqueous solution was slowly added to the melamine aqueous solution under continuous magnetic stirring at room temperature for 2 h to get a complex precipitation. Afterwards, the precipitation was collected by centrifugation, and then washed three times with deionized water, and dried at 60 ºC in an oven for overnight, and the obtained powder was used as the precursor (Fe(II)/melamine) for the photoreduction. Lastly, 50 mg of the above precursor, with 20 mg of EY and 100 mL of TMA aqueous solution (1.1×10-1 mol L-1, pH =10 adjusted with 6.0 mol L-1 HCl solution) were added to a 200 mL Pyrex cell with a side flat window, and the resultant mixture was dispersed in an ultrasonic bath for 5 min. The top of the cell was sealed with a silicone rubber septum. The suspension was bubbled with N2 for 25 min to remove oxygen completely and then irradiated with a 400 W high-pressure mercury lamp equipped with a cut-off glass filter (λ≥ 420 nm). After 2 h of irradiation, the precipitation was


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collected and washed with deoxygenized water and absolute ethanol for several times, and then naturally dried in a glove box at room temperature. The sample was labelled as Fe(0)/melamine. 2.3. Characterization. X-ray diffraction (XRD) was carried out on a XD-2/3 polycrystalline X-ray diffractometer with nickel-fltered Cu Kα radiation as the X-ray source. The transmission electron microscopy (TEM) images and High-resolution TEM (HRTEM) images were obtained on a JEOL JEM2100(kabuskiki kaisha, Japan) equipped with an energy dispersive spectrometer (EDS). Fourier transform infrared (FTIR) spectra were measured utilizing FTIR Nicolet 5700 spectrometer. The fluorescence spectra were conducted on a Hitachi F-7000 fluorescence spectrophotometer using 516 nm as the excitation wavelength. 2.4. Electrochemical and Photoelectrochemical Measurements. The HER polarization curves of commercial nano Fe(0), photoreduced Fe(0)/melamine samples were performed on LK98B II electrochemical workstation (Tianjin Lanlike Co. Ltd., China) in a traditional three-electrode system. A glassy carbon electrode was used as the support of the working electrode, Pt wire as the counter electrode, and an Hg/HgO (1.0 mol L-1 NaOH) electrode as the reference electrode. The working electrode was prepared in an Ar atmosphere glove box as follows: First, 10 mg of the above samples and 10 µL of Nafion solution (Dupont, America) were dispersed in 1.0 mL ethanol by at least 1 h sonication to form a homogeneous ink. Then, 15 µL of the dispersion was dropped on the glassy carbon electrode. Finally, the electrode was obtained after naturally dried at room temperature in the glove box. For the linear sweep voltammetry (LSV) measurements, the scanning window was in the range from -0.80 V to -1.6 V, and the scan rate was 10 mV s-1. The measurement was conducted in a H type two-


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chamber electrolysis cell. The electrolyte is 1.0 mol L-1 KOH solution with the pH of 14. Before the measurement, the electrolyte system was bubbled with Ar for 25 min to remove oxygen. Ar was continuously flushed in the whole measurement process. The measured potentials without iR correction were converted to the reversible hydrogen electrode (RHE) scale according to the Nernst equation: E (RHE) = E(Hg/HgO) + 0.059 pH + 0.14 V Photoelectrochemical measurements were carried out in a standard three-electrode system on a LK98B II electrochemical workstation. Using Pt wire, Hg/HgO (1.0 mol L-1 NaOH), and prepared electrodes respectively act as counter electrode, reference electrode, and working electrodes. Using a 300 W Xe arc lamp with a UV-cut off filter (λ≥ 420 nm) as light source and 0.10 mol L-1 Na2SO4 aqueous solution containing 0.11 mol L-1 TMA with the pH of 10 (adjusted with 6.0 mol L-1 HCl solution) as the electrolyte. Working electrodes were prepared as follows: First, ITO glass was cleaned by sonication with distilled water, acetone and ethanol respectively for 30 min. Then, 10 mg of commercial nano Fe(0) or Fe(0)/melamine samples was ground with 1 mL ethanol to make slurry and the slurry was coated onto 1 cm × 1 cm ITO glass electrode by a spin coater. Last, the electrode was naturally dried at room temperature in argon atmosphere. 2.5. Photocatalytic reactions. Photocatalytic reaction was conducted in a 200 mL closed Pyrex cell with a flat side window for irradiation at room temperature. 10 mg of the prepared Fe(0)/melamine HER cocatalyst, 20 mg of EY and 100 mL of TMA aqueous solution (1.1×10-1 mol L-1, pH =10), and the resultant mixture was dispersed in an ultrasonic bath for 5 min. The suspension was bubbled with N2 for 25 min to remove oxygen completely, and then irradiated with a 400 W high-pressure mercury


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lamp equipped with a cut-off glass filter (λ≥ 420 nm). During the irradiation, the powder was remained in suspension by magnetic stirring. The top of the cell was sealed with a silicone rubber septum. Sampling was made intermittently through the septum. The produced H2 was analyzed on a GC1690 gas chromatograph (KeXiao Chemical Equipment Co. Ltd., thermal conductivity detector, 13X molecular sieve packed column, N2 gas carrier). In the stability test for Fe(0)/melamine, EY and TMA aqueous solution were renewed. Before next 4 h irradiation circle, the reaction system was flushed with N2 for 25 min. The apparent quantum efficiency (AQE) of EY-Fe(0)/melamine at different incident wavelengths monochromatic light could be estimated according to the following equation:

The reaction conditions including the reactor were the same as those for the photocatalytic reaction except using momochromatic LED lamps (UVEC-4, Shenzhen LAMPLIC Science Co Ltd, China) as the light resources. 3. RESULTS AND DISCUSSION The scheme for synthesis of Fe(0)/melamine core-shell submicro-cubes are engineered as follows: Firstly, melamine was dispersed in distilled water by ultrasonication to form a clear solution. Subsequently, equal mass of (NH4)2Fe(SO4)2 aqueous solution was slowly added to get complex precipitation (named as precursor Fe(II)/melamine). Lastly, Fe(II)/melamine was in situ photo-reduced in the presence of EY and TMA aqueous solution. Without irradiation and EY, the Fe(II)/melamine complex cannot be reduced to Fe(0), confirming the reduction of the precursor into metal Fe by photoexcited EY.


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When irradiated with visible light, the Fe(II)/melamine complex in EY and TMA aqueous solution system rapidly produced H2 and black nanoparticles were photogenerated in the meantime. The photogenerated black particles can be indexed to Fe(0) in the XRD pattern (Figure 1a). The peaks at 44.60, 65.00, and 82.30 respectively correspond to the (110), (200), and (211) plane of cubic α-Fe (JCPDS 06-0696),16 suggesting that the Fe(II)/melamine complex has been successfully photoreduced into Fe(0)/melamine composite in the presence of EY and TMA. Figure 1b shows the FT-IR spectra of melamine and Fe(0)/melamine. For melamine, the bands at 1351, 1458, and 1558 cm-1 can be assigned to the stretching mode of C-N heterocycles, while the broad band at 3420 cm-1 corresponds to the stretching vibration of N-H. Compared with pure melamine, Fe(0)/melamine shows similar absorption peaks with decreased intensities and significant shifts, which verifies the existence of melamine in the Fe(0)/melamine composite and the interaction between Fe(0) and melamine. The photoreduced Fe(0)/melamine composite exhibits core–shell submicro-cubes with the size of about 200 nm (Figure 2a, b). The selected rectangle in Figure 2b shows that (except for the element Cu from the support) Fe is detected in the EDS spectrum of the core part (Figure 2c). The magnified image of the core part displays that the lattice distance is about 0.20 nm, corresponding to (110) plane of metal Fe(0), and confirming the in situ formation of Fe(0) submicro-cubes derived from Fe(II)/melamine complex (Figure 2d). Figure 2e displays that no regular lattice fringes found in the magnified image of the selected oval shell layer in Figure 2b, owing to the poor crystallinity of melamine shell. Figure 2f shows that (except for Cu) Fe, C, N element are detected in the EDS spectrum of the shell part from the selected oval of Figure 2b, confirming the presence of melamine on the surface of Fe core.


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The photocatalytic performance was evaluated by photocatalytic H2 evolution reaction in EY and TMA aqueous solution under visible light irradiation (λ ≥ 420 nm). Figure 3a displays that the photocatalytic H2 evolution rate of Fe(0)/melamine composite is about 80 µmol h−1. After four runs for 16 h, no obvious deactivation in photocatalytic H2 evolution activity can be observed. Even when the irradiation time is extend to 32 h (eight runs), the activity of Fe(0)/melamine still keep unchanged (Figure 3b). These results suggest the good stability of the Fe(0)/melamine composite in EY and TMA system. To further investigate the stability of Fe(0)/melamine composite, the XRD, FT-IR, and TEM measurements of Fe(0)/melamine core-shell particles after photocatalytic H2 evolution for 16 h have been carried out. Compared with Fe(0)/melamine, no obvious position and intensity of the characteristic peaks change in the XRD patterns and FTIR spectra of Fe(0)/melamine after photocatalytic H2 evolution for 16 h (Figure 4), indicating the good stability of Fe(0)/melamine. Furthermore, both Fe(0)/melamine and Fe(0)/melamine after photocatalytic H2 evolution for 16 h display the cubic morphology (Figure 5a, b), which indicates that Fe(0)/melamine also maintains the core-shell submicro-cube structure after photocatalytic H2 evolution for 16 h. Moreover, the HAADF-STEM image (Figure 5c) and the corresponding elemental mapping images shows that Fe(0)/melamine also keeps the composition of C, N and Fe after photocatalytic H2 evolution for 16 h, further suggesting the good stability of Fe(0)/melamine. This indicates that melamine modified on the Fe(0) core surface can keep Fe(0) from being oxidized and thus improve the stability of the Fe(0). To study the role of melamine or EY in photocatalytic H2 evolution, respectively, a series of the control experiments have been carried out. As shown in Figure 6a, neither melamine (MA) nor EY-sensitized MA (EY-MA) displays photocatalytic H2 evolution activity, suggesting that


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melamine itself cannot act as HER active site. Fe(II)/MA complex without EY displays no photocatalytic H2 evolution activity, while EY-sensitized Fe(II) [EY-Fe(II)] itself shows photocatalytic H2 evolution rate of 19.5 µmol h−1, which suggests that both EY and Fe species plays an important role in photocatalytic H2 evolution and the photoreduced Fe(0) acts as the hydrogen evolution site. EY-sensitized Fe(II)/MA [EY-Fe(II)/MA] improves the photocatalytic H2 evolution activity by 2.1 times, and EY-Fe(0)/MA derived from in situ photo-reduction of EY-Fe(II)/MA complex further improves by 4.1 times, which is also much higher than that of EY-sensitized commercial nano Fe(0) [EY-nano-Fe(0)] and EY-sensitized the mixture of commercial nano Fe(0) and melamine [EY-nano-Fe(0)/MA]. These results demonstrates that both EY and Fe(0) modified with MA contribute to the optimum photocatalytic activity of EYFe(0)/MA. The apparent quantum efficiency (AQE) of EY-Fe(0)/melamine was measured using monochromatic light sources. The AQE values at 420, 470, 520, 545, 600 nm are 0.98, 16.6, 2.69, 0.65 and 0 %, respectively (Figure 6b). The light-induced electron transfer reactions of EY, EY-melamine, EY-commercial nano Fe(0), EY-Fe(0)/melamine composite were investigated by photoluminescence (PL) emission. EY exhibits a strong PL emission peak at about 545 nm, while no obvious intensity changes in EYmelamine compared with EY. EY-commercial nano Fe(0) displays lower PL intensity, and EYFe(0)/melamine composite shows the lowest PL intensity (Figure 7a). Based on the photoluminescence spectra of EY in the presence of melamine, Fe(0) and Fe(0)/melamine, we can conclude that the photoinduced electron can transfer from EY to metal Fe(0) and to Fe(0)/melamine but not to melamine. To further demonstrate the role of melamine in charge carrier transfer in EY-sensitized Fe(0)/melamine composite, the I-t measurements for EY-nano Fe(0) and EY-Fe(0)/melamine


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composite have been carried out. As shown in Figure 7b, EY-Fe(0)/melamine composite shows much higher photocurrent density than that of EY-nano Fe(0), which is consistent with the photocatalytic H2 evolution activity, which further verifies that melamine modified on photoreduced Fe(0) surface can effectively promote electron transfer compared with commercial nano Fe(0). To gain further understanding of the role of melamine, the LSV measurements for commercial nano Fe(0) and Fe(0)/melamine composite have been carried out. As shown in Figure 8, compared with commercial nano Fe(0), the Fe(0)/melamine composite shows an obvious enhanced HER activity and decreased HER overpotential, which indicates that the in situ photoreduced Fe(0) modified with melamine can effectively reduce HER overpotential and facilitate electron transfer. Overall, melamine modified on Fe(0) submicro-cube surfaces not only prevent it being oxidized, but also decrease HER overpotential, which promotes efficient hydrogen evolution reaction under visible light irradiation. Based on above analyses, a possible photocatalytic H2 evolution mechanism for EYFe(0)/melamine composite has been proposed (Figure 9). When EY is excited under visible light irradiation, its electron transits from HOMO (highest occupied molecular orbital) to LUMO (lowest unoccupied molecular orbital) to produce excited EY*. EY + hν → EY*

(1)

As the concentration of the electron donor trimethylamine (TMA, 1.1×10-1 mol L-1) is much higher than that of EY (2.9×10-4 mol L-1) in our reaction system, the EY* can react with TMA to form the reductive radical EY·-.17


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EY* + TMA → EY·- + TMAOX

(2)

The electron of the formed EY·− anion (-0.8 V vs NHE, or -3.7 V vs vacuum) 18 or EY* (-3.45 eV vs vacuum) 19 cannot transfer to the LUMO level of melamine (-0.27 eV vs vacuum) 20, which is consistent with the result from Figure 7a. However, it can transfer to metal Fe (the work functions at -4.5 eV vs vacuum). Due to the presence of interaction between melamine and metal Fe (Figure 1b), the electron transfer ability from EY* to metal Fe modified by melamine increases (Figure 7a), and the overpotential for hydrogen evolution decreases (Figure 8), leading to the effective reduction of water into H2 on Fe/melamine. EY·- /EY*+ Fe(0)/melamine → Fe-/melamine + EY/EY+

(3)

2H2O + 2e (Fe-/melamine) → H2 + 2OH-

(4)

The produced EY+ is recovered into EY by the electron donor TMA. EY+ + TMA → EY + TMAOX

(5)

4. CONCLUSIONS In summary, we construct an efficient cost-effective photocatalytic H2 evolution system through in situ photoreduction of Fe(II)-melamine complex to Fe(0)/melamine composite in the presence of EY and TMA. The Fe(0)/melamine composite displays core-shell submicro-cubes, which shows superior photocatalytic H2 evolution performance and good stability. Melamine modified on Fe(0) surface not only keeps Fe from being oxidized, but also increase the electron transfer ability from EY to metal Fe(0) for HER. This work represents a significant step for the construction of a highly efficient stable photocatalyst using low-cost earth-abundant elements (Fe, C, and N) rich in nature.


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AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (Y. Li) Notes The authors declare no competing financial interest. ACKNOWLEDGMENT We acknowledge the projects of Natural Science Foundation of China (21703095, 21563019, 21163012), the Nature Science Foundation of the Jiangxi Province (2017BAB206010, 20151BAB203013) and Foundation from State Key Laboratory of Chemical Resource Engineering (CRE-2016-C-102). REFERENCES 1. Zhang, W.; Li, Y.; Peng, S. Template-Free Synthesis of Hollow Ni/Reduced Graphene Oxide Composite for Efficient H2 Evolution. J. Mater. Chem. A 2017, 5, 13072-13078. 2. Li, Y.; Hou, Y.; Fu, Q.; Peng, S.; Hu, Y. H. Oriented Growth of ZnIn2S4/In(OH)3 Heterojunction by a Facile Hydrothermal Transformation for Efficient Photocatalytic H2 Production. Appl. Catal. B 2017, 206, 726-733. 3. He, F.; Chen, G.; Yu, Y.; Hao, S.; Zhou, Y. Zheng, Y. Facile Approach to Synthesize gPAN/g-C3N4 Composites with Enhanced Photocatalytic H2 Evolution Activity. ACS Appl. Mater. Interfaces 2014, 6, 7171-7179. 4. Xu, J.Y.; Li, Y.X.; Peng, S.Q.; Lu, G.X.; Li, S.B. EY-Sensitized Graphitic Carbon Nitride Fabricated by Heating Urea for Visible Light Photocatalytic Hydrogen Evolution: The Efect of the Pyrolysis Temperature of Urea. Phys. Chem. Chem. Phys. 2013, 15, 7657-7665. 5. Li, Y.X.; Wang, H.; Peng, S.Q. Tunable Photodeposition of MoS2 onto a Composite of Reduced Graphene Oxide and CdS for Synergic Photocatalytic Hydrogen Generation. J. Phys. Chem. C 2014, 118, 19842-19848. 6. Xu, J.Y.; Li, Y.X.; P, S.Q. Photocatalytic Hydrogen Evolution over Erythrosin B-Sensitized Graphitic Carbon Nitride with in Situ Grown Molybdenum Sulfide Cocatalyst. Int. J. Hydrogen Energy 2015, 40, 353-362. 7. Zhang, W.; Li, Y.; Peng, S. Facile Synthesis of Graphene Sponge from Graphene Oxide for Efficient Dye-Sensitized H2 Evolution. ACS Appl. Mater. Interfaces 2016, 8, 15187-15195. 8. He, F.; Chen, G.; Zhou, Y.; Yu, Y.; Li, L.; Hao, S.; Liu, B. ZIF-8 Derived Carbon (C-ZIF) as a Bifunctional Electron Acceptor and HER Cocatalyst for g-C3N4: Construction of a Metal-Free,


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All Carbon-Based Photocatalytic System for Efficient Hydrogen Evolution. J. Mater. Chem. A 2016, 4, 3822-3827. 9. Zhang, W.; Li, Y.; Zeng, X.; Peng, S. Synergetic Effect of Metal Nickel and Graphene as a Cocatalyst for Enhanced Photocatalytic Hydrogen Evolution via Dye Sensitization. Sci. Rep. 2015, 5, 10589. 10. Yang, J.; Yan, H.; Wang, X.; Wen, F.; Wang, Z.; Fan, D.; Shi, J.; Li, C. Roles of Cocatalysts in Pt–PdS/CdS with Exceptionally High Quantum Efficiency for Photocatalytic Hydrogen Production. J. Catal. 2012, 290, 151-157. 11. Tanaka, A.; Sakaguchi, S.; Hashimoto, K.; Kominami, H., Preparation of Au/TiO2 with Metal Cocatalysts Exhibiting Strong Surface Plasmon Resonance Effective for Photoinduced Hydrogen Formation under Irradiation of Visible Light. ACS Catal. 2012, 3, 79-85. 12. Farrell, D.; Majetich, S. A.; Wilcoxon, J. P. Preparation and Characterization of Monodisperse Fe Nanoparticles. J. Phys. Chem. B 2003, 107, 11022-11030. 13. Peng, S.; Wang, C.; Xie, J.; Sun, S. Synthesis and Stabilization of Monodisperse Fe Nanoparticles. J. Am. Chem. Soc. 2006, 128, 10676-7. 14. Wilcoxon, J. P.; Provencio, P. P. Use of Surfactant Micelles to Control the Structural Phase of Nanosize Iron Clusters. J. Phys. Chem. B 1999, 103, 9809-9812. 15. Dumestre, F.; Chaudret, B.; Amiens, C.; Renaud, P.; Fejes, P. Superlattices of Iron Nanocubes Synthesized from Fe[N(SiMe3)2]2. Science 2004, 303, 821-823. 16. Qiang, R.; Du, Y.; Zhao, H.; Wang, Y.; Tian, C.; Li, Z.; Han, X.; Xu, P. Metal Organic Framework-Derived Fe/C Nanocubes toward Efficient Microwave Absorption. J. Mater. Chem. A 2015, 3, 13426-13434. 17. Li, Y.X.; Li, H.; Li, Y.F.; Peng, S.Q.; Hu, Y. H. Fe-B Alloy Coupled with Fe Clusters as an Efficient Cocatalyst for Photocatalytic Hydrogen Evolution. Chem. Eng. J. 2018, 344, 506–513. 18. Liu, X.; Li, Y.X.; Peng, S.Q.; Lu, G.X.; Li, S.B. Modification of TiO2 with Sulfate and Phosphate for Enhanced EY-Sensitized Hydrogen Evolution under Visible Light Illumination. Photochem. Photobiol. Sci. 2013, 12, 1903-1910. 19. Min, S.X.; Lu, G.X. Promoted Photoinduced Charge Separation and Directional Electron Transfer over Dispersible Xanthene Dyes Sensitized Graphene Sheets for Efficient Solar H2 Evolution. Int. J. Hydrogen Energy 2013, 38, 2106-2116 20. Prabhaharan, M.; Prabakaran A.R.; Gunasekaran, S.; Srinivasan, S. Molecular Structure and Vibrational Spectroscopic Investigation of Melamine Using DFT Theory Calculations. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 2014, 123, 392–401.


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Figure 1. (a) XRD pattern of Fe(0)/melamine composite, (b) FT-IR spectra for melamine and Fe(0)/melamine composite.


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Figure 2. (a, b) TEM images, (c-f) HRTEM images and EDS spectra of the selected areas for Fe(0)/melamine composite.


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Figure 3. (a, b) Photocatalytic H2 evolution as a function of reaction time for EY-Fe(0)/melamine composite.


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Figure 4. (a) XRD patterns and (b) FT-IR spectra of Fe(0)/melamine, and Fe(0)/melamine after photocatalytic H2 evolution for 16 h.


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Figure 5. TEM images of (a) Fe(0)/melamine, and (b) Fe(0)/melamine after photocatalytic H2 evolution for 16 h; HAADF-STEM image (c) and the corresponding elemental mapping images of C, N and Fe for Fe(0)/melamine after photocatalytic H2 evolution for 16 h.


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Figure 6. (a) Photocatalytic H2 evolution rate of different samples with and without EY: melamine (MA, 10 mg), (NH4)2Fe(SO4)2 [Fe(II), 10 mg], Fe(II)/melamine complex [Fe(II)/MA, 50 mg], Fe(0)/melamine [Fe(0)/MA, 10 mg], commercial nano Fe(0) [nano Fe(0), 10 mg], the mixture (molar ratio 1:1, 10 mg) of the commercial nano Fe(0) and MA [nano-Fe(0)/MA)]. (b) Apparent quantum efficiency (AQE) of Fe(0)/melamine at different monochromatic wavelengths.


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Figure 7. (a) Photoluminescence (PL) spectra for EY, EY-melamine, EY-commercial nano Fe(0), and EYFe(0)/melamine composite. Conditions: 100 mL of 1.0×10-5 mol L-1 EY solution containing 5 mg of the added sample or none. (b) Photocurrent recorded in 0.1 M Na2SO4 at 0 V bias vs Hg/HgO for EY-nano Fe(0) and EY-Fe(0)/melamine composite.


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Figure 8. The HER polarization curves in 1.0 mol L-1 KOH solution (pH=14) at a sweep rate of 10 mV s-1 for commercial nano-Fe(0) and Fe(0)/melamine composite.


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Figure 9. Proposed mechanism for the photo-excited electron transfer in EY-sensitized Fe(0)/melamine.


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The table of contents graphic


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40x20mm (300 x 300 DPI)


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Melamine CoreâShell

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