1. MnO Octahedral Nanocrystals and MnO@C Core- Shell Composites: Synthesis,Characterization, and Electrocatalytic Properties Sangaraju Shanmugam and Aharon Gedanken* Department of Chemistry and Kanbar Laboratory for Nanomaterials at the Bar- Ilan UniVersity Center forAdVanced Materials and Nanotechnology, Bar-Ilan UniVersity, Ramat-Gan, 52900, Israel Advisor ：王聖璋 副教授 Advisee ：許祐元 J. Phys. Chem. B 2006, 110, 24486-24491

2. Outline Introduction Experimental Results and Discussion Conclusion

3. Introduction Nanocrystals with unique size-dependent electrical, optical, magnetic, and chemical properties are of interest to both fundamental science and technological applications. For future applications, tunable synthesis of nanocrystals with uniform shapes and sizes is of key importance. For manganese oxides, a wealth of chemical and physical methods have been developed for the synthesis of MnO nanostructures with well-controlled shapes, including spheres, quasi-cubes, octahedra,crosslike particles, wires, rods, dumbbells, and hexapods. We present a novel method for preparing octahedral MnO and MnO@C core-shell nanoparticles by the direct pyrolysis of a composite gel of potassium permanganate (KMnO4) and cetyltrimethylammomium bromide (C16H33N(CH3)3- Br, CTAB) in a specially made Let-lock union. The shapecontrolled synthesis was carried out by varying the reaction temperature and the duration.

4. Experimental

5. Result and discussion Figure 1. XRD pattern of the MnO product synthesized at 700 °C for 3 h.

6. Figure 2. (a) TEM image shows anisotropic MnO nanocrystals, arrows indicate the carbon shell sorrounding the MnO core, (b) selected area diffraction pattern of sample, indexed to cubic rock salt structure, and (c) an individual MnO octahedron and carbon replica alike are shown with arrows.

7. Figure 3. (a) TEM image of an individual octahedral MnO crystal, (b) tilted nanocrystal, edge outlines are depicted in the insets, (c) MnO@C core-shell nanoparticles, arrow shows the thickness of the carbon shell, and (d) HRTEM image of an edge of an MnO nanocrystal shows resolved lattice fringes of the (200) plane of MnO.

8. Figure 4. Raman spectrum of product obtained at 700 °C, showing the presence of disorder graphitic carbon. I(D)/I(G)=0.79 D (Disorder) bandG (Graphitic) band

9. Figure 5. TEM images of product synthesized at different temperatures (a) 600 °C for 6 h, (b) 700 °C for 12 h, and (c) 800 °C for 3 h. Arrows show the carbon shell on the MnO core in (a) and (b) Figure 6. XRD patterns of products obtained at (a) 600 °C, 6 h, (b)700 °C, 12 h, and (c) 800 °C, 3 h.

10. SCHEME 1: Schematic Representation of the Formation of MnO Nanocrystals and MnO@C Core- Shell Particles

11. Conclusion In summary, octahedral MnO nanocrystals and core-shell nanoparticles were synthesized by a simple and facile single step. The formation of octahedral MnO nanocrystals is assisted by the presence of cetyltrimethylammonium cation. The product mainly consists of truncated cubes, cubes, hexagons, spheres, and tetrahedra. The formation of octahedral MnO is accompanied by imprinted carbon replicas. When the MnO crystal size is small, a shell of carbon is present, giving rise to coreshell nanocrystals. As the crystal size of MnO increases, it separated from the surrounding shell, giving rise to the imprinting carbon hollow cubelike structures.

12. Thanks for your attention