1 / 28

Carbon Fullerenes

Carbon Fullerenes. Formation. Basic model Clustering Chains, rings, tangled poly-cyclic structures or graphite sheets Annealing (no collisions) Random cage, open cage, closed cage structures Elimination of dangling bonds Fullerenes Stone-Wales transformation Migration of pentagons

romney
Download Presentation

Carbon Fullerenes

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Carbon Fullerenes

  2. Formation • Basic model • Clustering • Chains, rings, tangled poly-cyclic structures or graphite sheets • Annealing (no collisions) • Random cage, open cage, closed cage structures • Elimination of dangling bonds • Fullerenes • Stone-Wales transformation • Migration of pentagons • Rearrangement to lower energy • Critical parameters • Annealing time • Annealing temperature • 10-1 ms; 1000-1500 K for the laser method • 100 s; 1000 K for the arc discharge method

  3. Formation • Picture models • Pentagon road (1) • Addition of dimers and trimers leaving pentagons as a deffect • Reduction of dangling bonds, adjacent pentagons too much stress • Ring pentagon road (2) • Stacking of proper size of C rings • Pentagon annealing • Fullerene road (3) • Linear chains up to C10 • Rings C10 to C20, fullerene from C30, • Addition of C2 at two neighboring p-s • Ring annealing (4) • Big rings, bi/tri-cyclic structures (C60+) anneal under high T conditions • Chain annealing (5) • Long chain with spiral structure • Graphite road (6) • C10 clusters, graphite sheet, curling • Nanotube road (7) • Chips of carbon nanotubes 1

  4. Formation • Molecular dynamics (MD) simulations • Many-body potential function • Kinetic energy of clusters • Classical mechanics • translation, vibration and rotation • Clustering • Collisions of atoms or clusters: grow and fragmentation of cluster • Cooling: collisions with buffer gas and radiation • Annealing between collisions T = 3000 K

  5. Formation • Temperature dependence of cluster structures • Collision-free annealing of C60 • Stone-Wales transformation

  6. Formation • Fullerene-like cage structures 2500<T<3500 • Extrapolation roughly agrees with experimental conditions

  7. Formation C24 flat cluster, 0 s • Model of charges at bonds • Molecules: classical dynamics • Electrons: quantum mechanics • Ground and excited states • Interaction potentials • Covalent bonds, rotation, torsional vibration • Interaction between atoms and electrons • bonding electron pairs at the centers of the covalent bonds • unshared electrons at approximately the same distance from the carbon atoms • Classical equations of motion for both • Folding of flat carbon clusters • Unshared e– rearrange and form symmetrical sphere layer outside the fullerene Semispheroid, 50 ps Fullerene, 150 ps

  8. Formation • Another QM and MD simulation • Density functional theory • Ring fusion spiral zipper mechanism • C atoms combine to C2 and C3 • n<10: linear chain Cn • sp hybrid prefer linear geometry • 10<n<30: ring • Energy gain in killing dangling bonds overcompensates for strain energy caused by folding • n>30: ring structure can grow in fullerene

  9. Synthesis • Graphite vaporization or ablation • Laser • Resistive heating • AC or DC arc • Pyrolysis of hydrocarbons • Flame combustion • Laser • Torch or tube furnace • Ion implantation • Temperature of condensation and annealing • 1000÷1500 K • C60 $30/gram The first published mass spectrum of carbon clusters in a supersonic beam produced by laser vaporization of a carbon target in a pulsed supersonic nozzle operating with a helium carrier gas.

  10. Fullerenes are made wherever carbon condenses. It just took us a little while to find out. Smalley Synthesis • Laser vaporization of graphite • laser-vaporization supersonic cluster beam technique (Rice Univ., Texas) • 1985: H. W. Kroto (Sussex Univ., Brighton) & R. E. Smalley (Rice) • Experiment • Nd:YAG • 300 mJ, 535 nm, 5ns • Rotating graphite disk • Plasma of vaporized carbon atoms • 10 000 K • High-density helium pulse • Condensation and transport • “Integration cup” • Adjusts the time of clustering • Supersonic expansion • Frizzing out the reactions • Ionization by excimer laser • Mass spectrometer

  11. Synthesis • Laser evaporation of doped carbon

  12. Synthesis • Resistive heating of graphite • Carbon rod in 100 torr helium • Kratschmer-Huffman 1990 • First macroscopic quantities of C60 • Carbon arc • AC or DC arc in 100 torr helium • 60 Hz, 100÷200 A, 10÷20 V rms • Continuous graphite rod feedeing The generator design based on the Kratschmer-Huffman apparatus.

  13. Synthesis • Pyrolysis of hydrocarbons • Benzene, acetylene, toluene • Polycyclic aromatic hydrocarbons PAH • Naphtalene • Mechanism • Removal of hydrogen • Curling of joined rings • Optimum conditions • Very low pressure and high temperature • Examples • Combustion of benzene • Premixed flame of benzene and oxygen with argon • 20 torr, C/O 0.995, 10% Ar, 1800 K • Acetylene/oxygen/argon flame • Adding Cl2 increases fullerene yield • Torch heating of naphtalene • Heating torch • Pyrolysing torch: propane/oxygen 1000 ºC • Laser pyrolysis • Photosensitizer SF6 + C2H4 • CO2 laser 100÷180 W, 300 torr Pyrolysis apparatus Mechanism of formation of a partial C60 cage from naphthalene

  14. Synthesis • Low-pressure benzene/oxygen diffusion flame • p = 12 ÷ 40 torr, Tmax = 1500 ÷1700 K • Precursor PAH • Elimination of CO from oxidized PAH thought to be a source of C pentagons • Highest yield of fullerenes • High soot formation • High dilution with argon

  15. Synthesis • Atmospheric pressure combustion Syringe injector Benzene, Dicyclopentadiene, Pyridine (C5H5N), Thiophene (C4H4S) Oxy-acetylene torch (Ferrocene (C10H10Fe) – Fe@C60) Stainless steel plate on water-cooled brass block (< 800 K)

  16. Synthesis • DC arc torch dissociation of C2Cl4 (tetrachlorethylene) Operating conditions: Torch power: 56 kW He flow rate: 225 slm C2Cl4 feed rate: 0.29 mol/min

  17. Synthesis • Ion implantation • Carbon ions 120 keV • Copper substrates 700÷1000 ºC • Thin film (diamond, fullerenes, onions) • Endohedral fullerenes • Evaporation of fullerene (C60) onto a substrate • Ions of dopant N@C60

  18. Solid State C60 - Fullerite • Face-centered cubic (fcc) • The most densely packed structure • Lattice constant a = 14.17 Ǻ • Weak Van der Waals bonds • Soft • Molecules spin nearly freely around centers • Simple cubic (sc) • T<261 K • Fixed rotational axis • 4 C60 molecules arranged at vertices of tetraeder, spinning around different but fixed axis • Weak coulombic interaction • Fixed orientation of molecules • T<90 K: molecules entirely frozen • Polymeric • Covalent bonds • Photo-excitation, molecular collisions, high-pressure/temperature, ionization • Insolvable in toluene

  19. Purification • Extraction from carbon soot • Cn<100 solvable in aromatic solvents • Toluene, benzene, hexane, chloroform • C60 magenta • C70 dark red • Cn>100 high boiling-solvents • trichlorbenzene • Separation by chromatograph

  20. Derivatives • Intercalation (fullerides) • Octahedral or tetrahedral inter. sites • Alkali or alkaline-earth metal atoms • Na, K, Rb, Cs, Ca, Sr and Ba) • Charge transfer to the cage • Superconductors • Polymers Polymerized Rb1C60 C60-Fullerene tetrakis(dimethylamino)ethylene - ferromagnet

  21. Derivatives • Heterofullerenes • Substitution of an impurity atom with a different valence for C on the cage • B, N, BN Nb • C59X (X=B,N): nonlinear optical properties • Deformation of the electronic structure, strong enhancement of chemical activity • Radicals which can be stabilized by dimerization Azafullerenes: (a) C59N, (b) C59HN, and (c) (C59N)2 C48N12

  22. Derivatives • Exohedral • Covalent addition of atom or molecule • Hydrogenation • C60H18, C60H36 • Fluorination • C60F36, C70F34, C60F60 (teflon balls) • Oxidation • Organic groups and complexes (eta2-C70-Fullerene)-carbonyl-chloro-bis(triphenylphosphine)-iridium C60Cl6

  23. Derivatives • Endohedral • Synthesis • Evaporation of doped carbon • Arc, laser • Ion implantation • M@C60 • Noble gases • without overlap of Van der Waals radii • Metallofullerenes • B, Al, Ga, Y, In, La • Stabilize cages not fulfilling isolated pentagon’s rule (n<60) • With permanent dipole moment form di/trimers and large aggregates on metal surfaces and C60 films • Alkali metals • Lanthanide metals • N, P (Group V) Synthesis of microcapsules for medical applications N@C60 He@C60

  24. Properties • C60 electron affinity EA = 2.65 eV (Cl 3.62, ) • more electronegative than hydrocarbons • Dissolves in common solvents like benzene, toluene, hexane • Readily sublimes in vacuum around 400°C • Low thermal conductivity • Pure C60 is an electrical insulator • C60 doped with alkali metals shows a range of electrical conductivity: • Insulator (K6 C60) to superconductor (K3 C60) < 30 K • Interesting magnetic and optical properties • Ferromagnetism • At high pressure C60 transfoms to diamond • C60 soft and compressible brown/black odorless powder/solid • Flexible chemical reactivity breathing vibrational mode Pentagonal pinch mode

  25. Properties • Simulation of C60-C240 collision • Simulation of C60 melting Kinetic energy = 10 eV Kinetic energy = 100 eV Kinetic energy = 300 eV David Tomanek Theoretical Condensed Matter Physics Michigan State University

  26. Potential applications • Lubrication • Molecular-sized ball bearing • Not economical • Superconductors • Intercalation metal fullerides • (Semi)Conductors • Excellent conductors when compressed • Photoconductors • add conducting properties to other polymers as a function of light intensity • Optical Limiters • C60 and C70 solutions absorb high intensity light: protection for light-sensitive optical sensors • Atom Encapsulation • Radioactive waste encapsulation • Ho@C82 Rh-C60 polymer with vacancies Excess spin density Dipole moment of magnitude 2.264 Debye per C60 unit

  27. Potential applications • Diamond films • Smoother than vaporizing graphite • Novel polymers • Optoelectronic nanomaterials and buliding blocks for nanotechnology • Endohedral fullerenes • Nanobots • Medical applications • Magnetic Resonance Imaging markers • Metal organic complex (toxic Ga) • contrast agents, tracers • anti-viral (even anticancer) agents • neuroprotective agents • fullerene-based liposome drug delivery systems • deployment of fullerene therapeutics to targeting vehicles MRI fullerene contrasting agent • Water soluble tail (red & gray) • Encapsulates 2 gadolinium metal atoms (purple) and 1 scandium (green) attached to central nitrogen atom • H2O molecules (red & yellow)

  28. Potential applications • Potential AIDS inhibitor • HIV reproduces by growing long protein chains • Protein is cut in the active site of enzyme HIV-protease • Derivative of C60 has been synthesized that is soluable in water Model of C60 docked in the binding site of HIV-1 protease

More Related