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MnO Octahedral Nanocrystals and MnO@C CoreShell Composites: Synthesis,Characterization, and
Electrocatalytic Properties
Sangaraju Shanmugam and Aharon Gedanken*
Department of Chemistry and Kanbar Laboratory for Nanomaterials at the BarIlan 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
Outline
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Introduction
Experimental
Results and Discussion
Conclusion
Introduction
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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.
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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.
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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.
Experimental
KMnO4
0.1 M
CTAB
0.1 M
stirring
cetyltrimethylammo
nium permanganate
(CTAP)
A purple gel was formed and
was aged in air overnight
then filtered and washed
with water several times
A purple solild
(0.3 g)
was heated at 700°C
for 3 h
Furnace
XRD
HRTEM
Raman
spectrometer
Result and discussion
Figure 1. XRD pattern of the MnO product synthesized at 700 °C for
3 h.
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.
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.
D (Disorder) band
G (Graphitic) band
I(D)/I(G)=0.79
Figure 4. Raman spectrum of product obtained at 700 °C, showing
the presence of disorder graphitic carbon.
Figure 6. XRD patterns of
products obtained at (a) 600 °C, 6 h,
(b)700 °C, 12 h, and (c) 800 °C, 3 h.
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)
SCHEME 1: Schematic Representation of the
Formation of MnO Nanocrystals and MnO@C CoreShell Particles
Conclusion
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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.
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The product mainly consists of truncated cubes, cubes, hexagons, spheres, and
tetrahedra. The formation of octahedral MnO is accompanied by imprinted
carbon replicas.
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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.
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