fullerenes: properties - university of guelph · fullerenes: properties fullerenes are important in...
TRANSCRIPT
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19-1
Fullerenes: Properties
Fullerenes are important in nanoscience because they can be usedto form nanostructures. Either pure Carbon or modified.
C60: stable at room Temp and pressure
Shape is called a truncated octahedron
90 edges, 32 faces and 60 vertices (one for each carbon)
of the 32 faces: 12 are pentagons and 20 are hexagons
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19-2
Euler's Theorem f + v = e +2
single bonds
double bonds
diameter = 7.10D
1.40D
1.46D
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All carbons are equivalent
13C NMR (see CHEM 2070)
19-3Nuclear Magnetic Resonance
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C70: see that the Carbons are of 5 types
19-4)H f0
C60 42.5kJ/mol C70 40.4 kJ/mol
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19-5
Fullerene Synthesis
In Nature: high energy processes
We looked at these in lectures 13 and 14 (also see book chapter 4)
14-8
Arc Discharge
Developed in early 1980’s
Forms SWCNT as longAs catalyst is present
Rather dirtyMany unwanted products
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19-6
Best method is by combustion of a hydrocarbon fuel at low pressure
-cleaner products
- requires less energy
Purification
A practical laboratory-scale method for purification of soot enriched in C60 and C70 starts with extraction in toluene followed by filtration. The solvent is evaporated and the residue (the toluene-soluble soot fraction) redissolved in toluene and subjected to column chromatography. C60 elutes first with a purple color and C70 is next displaying a reddish-brown color
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19-7
Physical and Chemical Reactions of Fullerenes
Fullerenes are soft electrophiles
-accept electrons from a donor molecule -
e.g., hydrogen, methyl groups and amines
Three ways to modify Fullerenes
1. endohedral: --- encapsulate something inside it2. exohedral :-- react with surface3. assembly into bigger structures
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19-8
as we saw in lectures 7 and 8C60 is fcc and has a nn dist of 10 D
balls rotate freely in solid state at RT
cohesive energy is about 1.5 eV(about 150 kJ/mol)
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19-9
Exohedral Fullerenes
Fullerenes can be modified by chemical methods
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19-10
Putting C60 on surfaces
note S linkage to gold -- very common method
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C60 dimers
Further polymerization can occur
Double bonds on adjacent C60's are broken by laser or UV-light
undergo [2+2] cycloaddition reaction (see CHEM 2060 last lecture)
Rhombohedral, linear, tetragonal forms can be made
19-11
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19-12
4. Carbon Nanotubes
We met these briefly before (lecture 12)
"bottom-up" synthesis
Two types: single walled carbon nanotubes SWCNT
multiwalled (MWCNT): Focus here is on SWCNT
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19-13
STRUCTURE
Three main types: 1. Armchair 2. Zig-Zag and 3. Chiral
These are best introduced if we unroll a tube and lay it flat
roll this way : Armchair tube
zig-zagchiral
(called a graphene sheet)
apex of hexagon is parallel to longitudinal axis
apex of hexagon is parallel to circumference
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19-14
Vector NotationMost nanotubes have the chiral form and are conveniently described using a vector notation.
The origin of the vector intersects two equivalent points (centre of a hexagon) on the graphene sheet.
In the figure the axes are shown for armchair and zigzag tubes: chiralaxis is sum of others
more next lecture
1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0 11,0 12,0
1,1 1,1 3,1 4,1 5,1 6,1 7,1 8,1 9,1 10,1 11,1 12,1
2,2 3,2 4,2 5,2 6,2 7,2 8,2 9,2 10,2 11,2
3,3 4,3 5,3 6,3 7,3 8,3 9,3 10,3 11,3
4,4 5,4 6,4 7,4 8,4 9,4 10,4
5,5 6,5 7,5 8,5 9,5 10,5
0,0
6,6 7,6 8,6 9,6 10,6
7,7 8,7 9,7
Armchair
ZigzagChiralangle
13,1
12,2
12,3
11,4
11,5
7,7
10,6
13,0
8,7 9,7 10,7
8,8 9,8