Nature of the Chemical Bond with applications to catalysis, materials science, nanotechnology,...

Nature of the Chemical Bond with applications to catalysis, materials

science, nanotechnology, surface science, bioinorganic chemistry, and energy

William A. Goddard, III, wag@wag.caltech.edu316 Beckman Institute, x3093

Charles and Mary Ferkel Professor of Chemistry, Materials Science, and Applied Physics,

California Institute of Technology

Lecture 12 February 3, 2014Formation bucky balls, bucky tubes

Course number: Ch120aHours: 2-3pm Monday, Wednesday, Friday

Teaching Assistants:Sijia Dong <sdong@caltech.edu>Samantha Johnson <sjohnson@wag.caltech.edu>

C60 fullerene

No broken bonds

Just ~11.3 kcal/mol strain at each atom

678 kcal/mol

Compare with 832 kcal/mol for flat sheet

Lower in energy than flat sheet by 154 kcal/mol!

Polyyne chain

precursors fullerenes, all even

All fullerens have 12 pentagonal rings

Mechanism for formation of fullerenes

Heath 1991: Fullerene road. Smaller fullerenes and C3 etc add on to pentagonal sites to grow C60Contradicted by He chromatography and high yield of endohedrals

Smalley 1992: Pentagonal road. Graphtic sheets grow and curl into fullerenes by incorporating pentagonal C3 etc add on to pentagonal sites to grow C60Contradicted by He chromatography

Ring growth road. Jarrold 1993. based on He chromatography

Arc environment: mechanism goes through atomic species (isotope scrambling)He chromatography Go through carbon rings and form fullerenes Has high temperature gradients

He chromatography (Jarrold)

Relative abundance of the isomers and fragments as a function of injection energy in ion drifting experiments

Conversion of bicyclic ring to fullerene when heated

Energies from QM

Force Field for sp1 and sp2 carbon clusters

4n vs 4n+2 for Cn Rings

Population of various ring and fullerene species with Temperature

Based on free energies from QM and FF

Bring two C30 rings together

Energetics (eV) for isomerizations converting bicyclic ring to monocyclic or Jarrold intermediates for n = 30, 40, 50

2 ringsTS to form tricyclic

E tricyclic

TS convert

TS to singlet

Bergman cyclization (leads to Jarrold

mechanism)

Energetics (eV) for initial steps of JarroldIf get here, then get

fullereneJarrold

pathway

Modified Jarrold

Number pi bonds

Downhill race from tricyclic to bucky ball

Number sp2 bonded centers

30 eV of energy gain as form Fullerene

Structures in Downhill race from tricyclic to bucky ball

Energy contributions to downhill race to fullerene

Number sp2 bonded centers

C60 dimer

Prefers packing of 6 fold face

De = 7.2 kcal/mol

Face-face=3.38A

Crystal structure C60

Expect closest packing: 6 neighbors in plane

3 neighbors above the plane and 3 below

But two ways

ABCABC face centered cubic

ABABAB hexagonal closet packed

Predicted crystal structure 3 months before experiment

Prediction of Fullerene Packing in C60 and C70 Crystals Y. Guo, N. Karasawa, and W. A. Goddard III

Nature 351, 464 (1991)

C60 is face centered cubic

C70 is hexagonal closest packed

Vapor phase grown Carbon fiber,

R. T. K. Baker and P. S. Harris, in Chemistry and Physics of Carbon, edited by P. L. Walker, Jr. and A. Thrower (Marcel

Dekker, New York, 1978), Vol. 14, pp. 83–165;

G. G. Tibbetts, Carbon 27, 745–747 (1989);

R. T. K.Baker, Carbon 27, 315–323 (1989).

M. Endo, Chemtech 18, 568–576 (1988).

Formed carbon fiber from 0.1 micron up

Xray showed that graphene planes are oriented along axis but perpendicular to

the cylindrical normal

Multiwall nanotubes

"Helical microtubules of graphitic carbon". S. Iijima, Nature (London) 354, 56–58 (1991).

Ebbesen, T. W.; Ajayan, P. M. (1992). "Large-scale synthesis of carbon nanotubes". Nature 358: 220–222.

Outer diameter of MW NT

inner diameter of MW NT

Single wall carbon nanotubes, grown catalytically

S. Iijima and T. Ichihashi, "Single-shell carbon nanotubes of 1-nm diameter".Nature (London) 363, 603–605 (1993) used NiD. S. Bethune, C.-H. Kiang, M. S. de Vries, G. Gorman, R. Savoy, J. Vazquez, and R. Beyers, "Cobalt-catalyzed growth of carbon nanotubes with single-atomic-layer walls".Nature (London) 363, 605–607 (1993). used Co

Ching-Hwa Kiang grad student with wag on leave at IBM san Jose

Single wall carbon nanotubes, grown catalytically

S. Iijima and T. Ichihashi, "Single-shell carbon nanotubes of 1-nm diameter".Nature (London) 363, 603–605 (1993) used NiD. S. Bethune, C.-H. Kiang, M. S. de Vries, G. Gorman, R. Savoy, J. Vazquez, and R. Beyers, "Cobalt-catalyzed growth of carbon nanotubes with single-atomic-layer walls".Nature (London) 363, 605–607 (1993). used Co

Catalytic Synthesis of Single-Layer Carbon Nanotubes with a Wide Range of Diameters C.- H. Kiang, W. A. Goddard III, R. Beyers, J. R. Salem, D. S. Bethune, J. Phys. Chem. 98, 6612–6618 (1994).Catalytic Effects on Heavy Metals on the Growth of Carbon Nanotubes and Nanoparticles C.-H. Kiang, W. A. Goddard III, R. Beyers, J. R. Salem, and D. S. Bethune, J. Phys. Chem. Solids 57, 35 (1995).Effects of Catalyst Promoters on the Growth of Single-Layer Carbon Nanotubes; C.-H. Kiang, W. A. Goddard III, R. Beyers, J. R. Salem, and D. S. Bethune, Mat. Res. Soc. Symp. Proc. 359, 69 (1995) Carbon Nanotubes With Single-Layer Walls," Ching-Hwa Kiang, William A. Goddard III, Robert Beyers and Donald S. Bethune, " Carbon 33, 903-914 (1995). "Novel structures from arc-vaporized carbon and metals: Single-layer carbon nanotubes and metallofullerenes," Kiang, C-H, van Loosdrecht, P.H.M., Beyers, R., Salem, J.R., and Bethune, D.S., Goddard, W.A. III, Dorn, H.C., Burbank, P., and Stevenson, S., Surf. Rev. Lett. 3, 765-769 (1996).

Ching-Hwa Kiang grad student with wag on leave at IBM san Jose

Kiang CNT form 1993

Distribution of diameters for carbon SWNT, Kiang 1993

Examples Single wall carbon nanotubes

Some bucky tubes

(8,8) armchair

(14,0) zig-zag

(6,10) chiral

Contsruction for (6,10) edge

(10,10) armchair carbon SWNT

13.46A diameter

40 atoms/repeat distance

(14,0) zig-zag Bucky tube

Crystal packing of (10,10) carbon

13.5ADensity

SWNT: 1.33 g/ccGraphite 2.27 g/cc

Ec Young’s modulusSWNT 640 GPa

Graphite 1093 GPa

Ea Young’s modulusSWNT 5.2 GPa

Graphite 4.1 GPaHeat formation

Graphite 0C60 11.4

(10,10) CNT 2.72

Vibrations in (10,10) armchair CNT

Carbon fibers and tubes

Mechanism for gas phase CNT formation

Polyyne Ring Nucleus Growth Model for Single-Layer Carbon

Nanotubes C-H. Kiang and W. A. Goddard III Phys. Rev. Lett. 76, 2515 (1996)

Mechanism for gas phase CNT formation

A two-stage mechanism of bimetallic catalyzed growth of single-walled carbon nanotubes Deng WQ, Xu X, Goddard WA

Nano Letters 4 (12): 2331-2335 (2004)

But mechanism of gas phase C SWNT, no longer important

The formation of Carbon SWNT by CVD growth on a metal nanodot on a support is now the preferred

mechanism for forming SWNT

Mechanisms Proposed for Nanotube Growth

Stepwise ProcessAdsorption

DehydrogenationSaturationDiffusion

NucleationGrowth

Vapor-Liquid-Solid (Carbon Filament) Mechanism

• Vapor carbon feed stock adsorbs unto liquid catalyst particle and dissolves. Dissolved carbon diffuses to a region of lower solubility resulting in super-saturation and precipitation of the solid product.

• Originally developed to explain the growth of carbon whiskers/filaments.

• Temperature, concentration or free energy gradient is implicated as the driving force responsible for diffusion.

Wagner, R. S.; Ellis, W. C. Appl. Phys. Lett. 1964, 4, 89. Bolton, et al. J. Nanosci. Nanotechnol. 2006, 6, 1211.

Yarmulke Mechanism

Dai, et al. Chem. Phys. Lett. 1996, 260, 471.Raty, et al. Phys. Rev. Lett. 2005 95, 096103.

• Carbon-carbon bonds form on the surface (either before or as a result of super-saturation).

• Diffusion of carbon to graphene coating can be an important rate limiting step.

• Coating of more than a complete hemisphere results in poisoning of catalyst.

• New layers can start beneath the original layer after/as it lifts off the surface resulting in MWNT.

Experimental Confirmation of a Yarmulke Mechanism

Hofmann, S. et al. Nano Lett. 2007, 7, 602.

Atomic-scale, video-rate environmental transmission microscopy has been used to monitor the nucleation and growth of single walled nanotubes.

Role of the Catalyst Particle in Nanotube Formation

• Size of catalyst particles is related to the diameter of the nanotubes formed.

• Catalyst nanoparticles are known to deform (elongate) during nanotube growth.

• Structural properties of select catalyst surfaces (Ni111, Co111, Fe1-10) exhibit appropriate symmetry and distances to overlap with graphene and allow thermally forbidden C2 addition reaction.

• Graphene is believed to stabilize the high energy nanoparticle surface. MWNT have been observed growing out of steps, which they stabilize. • Hong, S.; et al. Jpn J. Appl. Phys.

2002, 41, 6142.• Vinciguerra, V.; et al. Nanotechnol.

2003, 14, 655.• Hofmann, S. et al. Nano Lett.

2007, 7, 602

Tip vs. Base Growth Mechanisms

Huang, S.; et al. Nano Lett. 2004 4, 1025.Kong, J.; et al. Chem. Phys. Lett. 1998, 292, 567.

Same initial reaction step: absorbtion, diffusion and precipitation of carbon species.

Strength of interaction between catalyst particle and catalyst support determines whether particles remains on surface or is lifted with growing nanotube.

Images of nanotubes show catalyst particles trapped at the ends of nanotubes in the case of tip growth, or nanotubes bound to catalysts on support in the case of base growth. Alternatively capped nanotube tops show base growth.

A kite (tip) growth mechanism has been used to explain the growth of long (order of mm), well ordered SWNTs.

Limiting Steps for Growth Rates

Diffusion of reactive species either through the catalyst particle bulk or across its surface can play an important role in determining the rate of nanotube growth.

In the case of carbon species which dissociate less readily the rate of carbon supply to the particle can act as the rate limiting step.

The rate of growth must also take into account a force balance between the friction of the nanotube moving through the surrounding feedstock gas and the driving force for/from the reaction.

Vinciguerra, V.; et al. Nanotechnol. 2003, 14, 655.Hofmann, S. et al. Nano Lett. 2007, 7, 602.Hafner, J. H.; et al. Chem. Phys. Lett. 1998, 296, 195.

Nature of the Chemical Bond with applications to catalysis, materials science, nanotechnology,...

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