Synthesis and Characterization of Metal (Pt, Pd and Fe)-graphene Composites

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1 Journal of the Korean Ceramic Society Vol. 8, No., pp. 17~11, 011. DI:10.191/KCERS Review Synthesis and Characterization of Metal (Pt, Pd and Fe)-graphene Composites Ming-Liang Chen, Chong-Yeon Park, Jong-Geun Choi, and Won-Chun h Department of Advanced Materials Science & Engineering, anseo University, Seosan 6-706, Korea (Received February 0, 011; Accepted March 9, 011) ABSTRACT In this study, we prepared graphene by using the modified ummers-ffeman method and then introduced the metals (Pt, Pd and Fe) for dispersion on the surface of the graphene for synthesis of metal-graphene composites. The characterization of the prepared graphene and metal-graphene composites was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis and transmission electron microscopy (TEM). According to the results, it can be observed that the prepared graphene consists of thin stacked flakes of shapes having a well-defined multilayered structure at the edge. And the metal particles are dispersed uniformly on the surface of the graphene with an average particle size of 0 nm. Key words : Graphene, Metal, XRD, TEM G 1. Introduction raphene, since its first discovery in 00, is a single layer of carbon atoms arranged in a D honeycombed lattice, has unusual electronic properties that arise from the hybridization of unbound fourth electrons in orbitals extending vertically above and below the plane spreading across the whole of the graphene sheet. 1-) This inexpensive material possesses good thermal and electrical conductivity, good mechanical strength, and more surface area than expensive carbon nanotubes (CNTs). Graphene sheets have a unique ability to promote fast electron transfer kinetics for a wide range of electro active species. In addition, functionalized graphene has made the realization of composite electrodes possible. It has been also demonstrated that grapheme, with zero band gap and high carrier mobilities and concentrations, shows nearly ballistic transport at room temperature. 6) Exfoliated graphene sheets are predicted to have a large surface area close to 600 m g 1, 7) making graphene nanosheets a highly desirable and ideal candidate for use in two-dimensional (D) catalyst support. The properties of graphene can be extended by integrating it with other nanomaterials to form unique hybrid materials. ne approach is to decorate the surface of graphene sheets with nanocrystals. The fabrication of graphene materials decorated by metal nanoparticles is expected to lead to graphene nanocrystal hybrids with enhanced properties such as high catalytic activity and excellent electrochemical properties. With Corresponding author : Won-Chun h wc_oh@hanseo.ac.kr Tel : Fax : this purpose, some metal nanoparticles such as Au, Ag, Pt, Pd and Co have been successfully attached onto graphene. 8-1) In this paper, we report on the synthesis of graphene and metal treated graphene (metal-graphene) by using the modified ummers-ffeman method. The prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X- ray (EDX) analysis and transmission electron microscopy (TEM).. Experimental.1. Synthesis of graphene For the synthesis of graphene, graphene oxide (G) was prepared first, and then graphene was obtained after reduction of the graphene oxide using a reduction agent. Graphite (KS-6) was selected as the starting material. Graphene oxide was prepared from graphite according to a modification of the ummers-ffeman method. 1) In brief, graphite powder (10 g) was dispersed in cold concentrated sulphuric acid (0 ml, 98 wt.%, and dry ice bath) and potassium permanganate (KMn, 0 g) gradually added with continuous vigorous stirring and cooling to prevent the temperature from exceeding 9 K. The dry ice bath was removed and replaced by a water bath and the mixture was heated to 08 K for 0. h with gas release under continuous stirring, followed by slow addition of deionized water (60 ml), which produced a rapid increase in solution temperature up to a maximum of 71 K. The reaction was maintained for 0 min in order to increase the oxidation degree of the graphite oxide product and then the resultant bright-yellow suspension was terminated by addition of more distilled water (10 ml) followed by hydrogen peroxide solution (, 0 %, 0 ml). The solid product was sep- 17

2 18 Journal of the Korean Ceramic Society - Ming-Liang Chen et al. Vol. 8, No. electron microscope (Jeol, JSM-00, Japan). EDX spectroscopy was used to perform the elemental analysis of the composites. The state of the dispersed graphene was observed using transmission electron microscopy (TEM, Jeol, JEM- 010, Japan). TEM at an acceleration voltage of 00 kv was used to investigate the number and the stacking state of the graphene layers on various samples. TEM specimens were prepared by placing a few drops of sample solution on a carbon grid.. Results and Discussion Fig. 1. Preparation procedure of graphene oxide and graphene. arated by centrifugation at 000 rpm and washed initially with % Cl until sulphate ions were no longer detectable with barium chloride. Solid product was then washed three times with acetone and air dried overnight at 8 K. After sonication for 0 min, the graphite oxide was transformed to graphene oxide. The reduction of graphene oxide was performed as follows: Twenty-five milligrams of the graphene oxide powder was placed in a cup and 00 ml de-ionized water was then added. Ten minutes of magnetic stirring at 00 rpm yielded an inhomogeneous brown suspension. The resulting suspensions were further treated with a reduction agent, hydrazine solution (1:, volume ratio of hydrazine to de-ionized water), under ultrasonication (0. h, J) and after drying at 7 K, the sample was reduced from graphene oxide to just graphene. The preparation procedure is shown in Fig Synthesis of metal-graphene composites PtCl, PdCl and Fe(C ) were used as the metal source. An identical amount of graphene oxide was immersed in the above metal ion solutions and refluxed at 7 K for h with stirring by a magnetic bar. After the temperature of the mixture was brought down to room temperature, the mixture was filtered through a What-man filter paper. The solid obtained was collected and washed with distilled water five times. After being dried in a vacuum at K for 8 h, the metal-graphene composites were prepared; these were termed Pt-graphene, Pd-graphene and Fe-graphene according to the use of PtCl, PdCl and Fe(C ) as metal source, respectively... Characterization XRD measurements were performed for graphene and metal-graphene samples at room temperature. XRD patterns were obtained with a diffractometer (Shimata XD-D1, Japan) using CuKa radiation. SEM was used to observe the surface state and structure of the samples using a scanning XRD peak patterns of graphene and metal-graphene composites are shown in Fig.. Typical (00) and (100) peaks of graphene (Fig. (a)) were observed at θ of ~6 o and ~ o, respectively, which could be indexed to the characteristic peaks (00) and (100) plane reflections of graphite from the graphene (JCPDS No ). 1,1) These peaks were found to decrease when the metal particles dispersed on the surface of graphene for all of metal-graphene composites, which can be seen in Fig. (b), (c) and (d). Moreover, some peaks could also be observed from the XRD patterns of the metalgraphene composites. For the Pt-graphene sample, there are peaks at around 9.7 o, 6. o and 67. o, which could be indexed to the characteristic peaks (111), (00) and (0) of Pt (JCPDS No ). 1,16) For the Pd-graphene sample, there are peaks at around 0.1 o, 6.6 o and 68.1 o, which could be indexed to the characteristic peaks (111), (00) and (0) of Pd (JCPDS No ). 17,18) For the Fe-graphene sample, there are peaks at around 18. o, 0.1 o,. o, 7. o and 6.8 o, which could be indexed to the characteristic peaks (111), (0), (11), (11) and (0) of magnetite Fe (JCPDS No. 0-07). 19-1) No peaks for impurities were detected from XRD patterns. These results indicate the high purity of the prepared samples. It is important to note that the average size of Pt, Pd and Fe dispersed on the graphene, calculated by the Debye-Scherrer equation, is about 0 nm, 1.6 nm and.8 nm, respectively. Fig.. XRD patterns of graphene (a), Pt-graphene (b), Pd-graphene (c), and Fe-graphene (d).

3 March 011 Synthesis and Characterization of Metal (Pt, Pd and Fe)-graphene Composites 19 Fig.. SEM microphotograph of graphene (a), Pt-graphene (c), Pd-graphene (e) and Fe-graphene (g), and EDX spectra of the corresponding samples (b, d, f and h). Fig. shows the SEM microphotographs of graphene and metal-graphene with EDX spectra of the corresponding samples. All of the samples show plate like forms without any amorphous or other kind of crystallized phase particles, as can be seen in the SEM microphotographs in Fig.. The morphology of graphene is observed as a flaky texture reflecting its layered microstructure, as shown in Fig. (a). The larger interspaces of the layer and the thinner layer edges of graphene can be clearly seen in Fig. (a). After treatment by metal sources, the metal particles are dispersed on the surface of graphene or imbedded into the graphene sheets. The EDX spectra demonstrate that the graphene mainly contains elemental C, as can be seen in Fig. (b). Apart from the elemental C, Fig. shows the EDX

4 10 Journal of the Korean Ceramic Society - Ming-Liang Chen et al. Vol. 8, No. REFERENCES Fig.. TEM images of graphene (a), Pt-graphene (b), Pd-graphene (c), and Fe-graphene (d). spectra of Pt-graphene (d), Pd-graphene (f) and Fe-graphene (h), which confirm the presence of Pt, Pd and Fe nanoparticles in the corresponding samples. Some impurity elements, which would come from the experimental procedure, can also be observed in the EDX spectra. TEM images of graphene with a scale of 0. µm and Ptgraphene, Pd-graphene, Fe-graphene with a scale of 0. µm are shown in Fig.. The TEM image of graphene (Fig. (a)) shows the D structure of graphene sheets and indicates that the surface is very smooth. The morphology of G is one of thin stacked flakes of shapes with well defined multilayered structures at the edge. The TEM images of the metal-graphene samples show the graphene sheets and metal nanoparticles. A uniform dispersion of metal particles on the graphene sheet can be observed in Fig. (b, c and The size of nanoparticles is about 0 nm for all of the d). metal-graphene samples. -). Conclusion We have successfully prepared graphene by using the modified ummers-ffeman method and dispersed the metals Pt, Pd and Fe on the surface of the graphene. XRD results show the typical (00) and (100) peaks of graphene in all of the samples; Pt, Pd and Fe peaks can also be observed in the Pt-graphene, Pd-graphene and Fe-graphene composites. TEM images of graphene show the D structure of graphene sheets and a surface that is very smooth. A uniform dispersion of metal particles on the graphene sheet, with an average particle size of 0 nm, can be observed from the TEM images of the metal-graphene samples. Thus, it can be considered that prepared metals (Pt, Pd and Fe)graphene could be used as photocatalysts, optical sensors and electracatalysts for a range of applications. 1. K. S. Novoselov, A. K. Geim, S. V. Morozov, and D. Jiang, Electric Field Effect in Atomically Thin Carbon Films, Science, (00).. A. K. Geim and K. S. Novoselov, The Rise of Graphene, Nat. Mater., (007).. Y. Zhang, Y. W. Tan,. L. Stormer, and P. Kim, Experimental bservation of the Quantum all Effect and Berry's Phase in Graphene, Nature, (00).. J. C. Meyer, A. K. Geim, and M. I. Katsnelson, The Structure of Suspended Graphene Sheets, Nature, (007).. Y. Zhu, S. Murali, W. Cai, X. Li, J. W. Suk, J. R. Potts, and R. S. Ruoff, Graphene and Graphene xide: Synthesis, Properties, and Applications, Adv. Mater., 906- (010). 6. K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, M. I. Katsnelson, I. V. Grigorieva, S. V. Dubonos, and A. A. Firsov, Two-dimensional Gas of Massless Dirac Fermions in Graphene, Nature, (00). 7. S. Stankovich, D. A. Dikin, G.. B. Dommett, and K. M. Kohlhass, Graphene-based Composite Materials, Nature, 8-86 (006). 8. F.. Li,. F. Yang, C. S. Shan, Q. X. Zhang, D. X. an, A. Ivaska, and L. Niu, The Synthesis of Perylene-coated Graphene Sheets Decorated with Au Nanoparticles and its Electrocatalysis Toward xygen Reduction, J. Mater. Chem., (009). 9. R. Pasricha, S. Gupta, and A. K. Srivastava, A Facile and Novel Synthesis of Ag-graphene-based Nanocomposites, Small, -9 (009) M. A. assan, V. Abdelsayed, A. E. R. S. Khder, and K. M. AbouZeid, Microwave Synthesis of Graphene Sheets Supporting Metal Nanocrystals in Aqueous and rganic Media, J. Mater. Chem., (009). 11. C. Xu, X. Wang, and J. W. Zhu, Graphene-metal Particle Nanocomposites, J. Phys. Chem. C, (008). 1. J.. Warner, M. A. Bachmatiuk, and M. Wilson, Examining Co-based Nanocrystals on Graphene Using Low-voltage Aberration-corrected Transmission Electron Microscopy, ACS Nano, (010). 1. W. C. h and F. J. Zhang, Preparation and Characterization of Graphene xide Reduced from a Mild Chemical Method, Asian J. Chem., (011). 1. K. Gotoh, T. Kinumoto, E. Fujii, A. Yamamoto,. ashimoto, T. hkubo, A. Itadani, Y. Kuroda, and. Ishida, Exfoliated Graphene Sheets Decorated with Metal-metal xide Nanoparticles: Simple Preparation from Cation Exchanged Graphite xide, Carbon, (011). 1. W. C. h, F. J. Zhang, and M. L. Chen, Characterization and Photodegradation Characteristics of rganic Dye for Pt-titania Combined Multi-walled Carbon Nanotube Composite Catalysts, J. Ind. Eng. Chem., (010). 16. M. L. Chen, F. J. Zhang, and W. C. h, Preparation and Catalytic Properties of Pt/CNT/Ti Composite, J. Kor. Cera. Soc., (010). 17. Y. F. an, D. Kumar, and D. W. Goodman, Particle Size Effects in Vinyl Acetate Synthesis ver Pd/Si, J. Catal.,

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