FROM FULLERENES TO GRAPHENE PASSING THROUGH CARBON NANOTUBES : SYNTHESIS, PROPERTIES AND APPLICATIONS OF quasi-NEW ALLOTROPES OF CARBON. Simone Musso spsp 22 and sp 33 hybridizations Carbon, having an electron configuration 1s2 2s2 2p2, forms a great variety of crystalline and disordered structures because it can exist in three different hybridizations, sp 3, sp 2, sp 1. sp 2 sp 3 Planar geometry Tetrahedral geometry Allotropic forms of C 3.4 Å Planar, sp 2 Cubic, sp 3 hybridization hybridization Graphite Diamond Planar geometry Tetrahedral geometry Allotropic forms of C 3.4 Å Planar, sp 2 Cubic, sp 3 hybridization hybridization Graphite Diamond Nanotube Physical and chemical properties areFullerene a direct consequence of the carbon-carbon bonds and lattice configuration Nanotube/Fullerene sp 2 + sp 3 character Allotropic forms of C 3.4 Å Planar, sp 2 Cubic, sp 3 hybridization hybridization Graphite Graphene Diamond Fullerene Carbon Nanotube Nanotube/Fullerene sp 2 + sp 3 character Allotropic forms of C 3.4 Å Planar, sp 2 Cubic, sp 3 hybridization hybridization Graphite Graphene Diamond Fullerene Carbon Nanotube Nanotube/Fullerene sp 2 + sp 3 character Discovery of fullerene or buckyball H. W. Kroto, J. R. Heath, S. C. O’Brien, R. F. Curl and R. E. Smalley, Nature 318 (1985) 162–63. Discovery of fullerene Before the C60 structure was considered beyond doubt, a sufficient amount of material had to be prepared for detailed spectroscopic analysis, but a lack of funds stopped the research.. Then, in 1990 Kratschmer and Huffman developed an arc discharge technique : DC Arc-discharge ddp ≈≈≈ 20 V I = 100-200 A T° →→→ 4000-6000°C He or Ar (600mbar) W. Krätschmer, L. D. Lamb, K. Fostiropoulos and D. R. Huffman, Nature 347 (1990) 354–58. Characterization of fullerene XRD MS FT-IR UV-Vis W. Krätschmer, L. D. Lamb, K. Fostiropoulos and D. R. Huffman, Nature 347 (1990) 354–58. Fullerenes 8.34 Å ; 7.66 Å C240 C540 C960 C70 (rugby-ballDifferent shaped ) fullerenes can be separated by means of chromatographic column. d= 7.1 Å C60 (bucky ball) Fullerene properties CHEMICAL REACTIVITY Fullerenes are non-toxic and are soluble in several organic solvents. Fullerenes are quite stable. However the spherical curvature produces angle strain that allows fullerenes to undergo characteristic reactions of addition to double bonds (hybridization turns from sp 2 to sp 3). C60 in organic solvents exhibits 5 stages of reversible oxidation/reduction, hence fullerene can work either as electrophiles or nucleophiles . C60 F18 Image created by Chris Ewels, www.ewels.info Fullerene properties DERIVATIVES: EXOHEDRAL , ENDOHEDRAL and ON-SITE DOPING Fullerenes, packed in fcc structure, can be intercalated with alkali and alkaline-earth metal atoms which provide electrons to the conduction band (from semi-conducting to metallic behavior). In 1991 potassium- doped fullerene (K 3C60 ) revealed superconducting behavior at 18K. L. Forrò and L. Mihaly, Rep. Prog. Phys. 64 (2001) 649-699. Fullerene properties DERIVATIVES: EXOHEDRAL , ENDOHEDRAL and ON-SITE DOPING In the endohedral doping a foreign atom is inserted in the inner cavity (M @ C ). This doping can be performed either by ion implantation or 60 CNTs !!! coevaporation of C and metal in arc discharge system. The on-site doping is achieved by replacing one carbon atom with a nitrogen atom ((C 59 N) 2 azafullerene). Image created by Chris Ewels, www.ewels.info L. Forrò and L. Mihaly, Rep. Prog. Phys. 64 (2001) 649-699. Fullerenes applications Hydrogen or oxygen storage : hydrogenation of fullerene produces hydrides. The reaction is reversible and can be catalyzed with metals (low pressure ). Catalyst : fullerene promotes the conversion of methane into higher hydrocarbons and inhibits coking reactions. Sensor : fullerene based capacitors can be used to detect ppm of H2S in N2, ppm of water in isopropanol. Diamond precursor : fullerene can be transformed to diamond at high pressure (RT) or can be used as a diamond nucleation center during CVD. Alloy strengthening/hardening (Ti), improvement of electrical conductivity of Cu alloys. Biomedical field : inhibition of human HIV replication and HIV-1 protease. Biological antioxidant (radical sponge). Allotropic forms of C 3.4 Å Planar, sp 2 Cubic, sp 3 hybridization hybridization Graphite Diamond Fullerene Carbon Nanotube Nanotube/Fullerene sp 2 + sp 3 character Discovery of CNTs Arc-discharge: from endohedral fullerene to CNTs Many scientific papers start citing ‘‘the discovery of carbon nanotubes by Iijima in 1991. .’’ S. Iijima, Nature 354 , (1991) 56 Discovery of CNTs First TEM evidences of nano --sized carbon tubes L.V. RadushKevich, V.M. LuKyanovich, Zurn. Fisic. Chim . 26 , (1952) 88 Discovery of CNTs What are CNTs? Rolled graphene sheet Diameter: 0,7 - 100 nm Length: from few tens of nm up to several mm Even ifif thethe curvature causes aahigherhigherstrain energy, aadefectdefect free CNT has anan overall lower energy state than graphite because dangling bonds areare removedremoved..ThisThisexplains high thermal stability and chemical inertnessinertness.. CNTs classification SWCNTs classification A CNT is characterized by its Chiral Vector ((CChh))== n ââ11 + m ââ22 and by the Chrial Angle ( θθθ) with respect to the zig zag axis Zig-zag n −−− m ≠≠≠ 3 ××× integer Semi-conductor behavior depending on the diameter. Chiral Armchair n −−− m = 3 ××× integer Metallic conductor behavior SWCNTs classification Armchair (5,5) θθθ = 30 °°° Zig Zag (9,0) θθθ = 0 °°° Chiral (10,5) 0°°°θθθ < 30° Characterization SEM HR-TEM TGA Air 20°C/min 1.6 100 1.4 80 1.2 1.0 60 0.8 40 0.6 Weight[%] 0.4 20 0.2 Weightderivative [%/°C] 0.0 0 -0.2 200 400 600 800 Temperature [°C] Raman spectroscopy XRD 1800 1591 cm -1 (100) 1600 G peak (002) 1400 1200 (*) -1 1344 cm 1000 D peak (*) 800 Intensity (a.u.) 600 (004) Intensity (arb.unit) 400 RBM 200 0 10 20 30 40 50 60 70 80 90 100 500 1000 1500 2000 2θ (°) Raman shift (cm -1 ) Properties of defect free CNTs Young’s modulus Tensile Strength Density (GPa) (GPa) (g/cm 3) MWCNT 1200 ∼150 2.6 SWCNT 1054 75 1.3 SWCNT bundle 563 ∼150 1.3 Graphite (in-plane) 350 2.5 2.2-2.6 Steel 208 0.4 7.8 Thermal conductivity Electrical conductivity (W/mK) RT (A/cm 2) MWCNT ∼3000 ≤10 9 SWCNT ∼6000 Depends on the chirality SWCNT bundle ∼3000 ≤10 9 Graphite (in-plane) ∼1700 ≤10 9 Diamond 2000 - 2500 Copper 401 10 6 Functionalization Chemical functionalization can be used to tune CNTs properties. Composite – improving compatibility matrix/filler Biomedical – improving biocompatibility, drug delivery, diagnosis Chemical (KMnO 4, HNO 3-H2SO 4) or plasma oxidation change surface properties while producing lattice defects (removable by annealing). Van der Waals interactions with porphyrin or pyrene derivatives are less effective. CNT properties/applications CNT synthesis High temperature methods Arc Discharge Laser ablation These techniques generate small amount of high quality CNTs by sublimation of graphite in presence of catalyst particles. Gas phase (vapor phase) methods Chemical Vapor Deposition (CVD) and plasma enhanced-CVD (PECVD) During CVD a conventional heat source is used to form CNTs by thermal cracking of hydrocarbons. A plasma source is used in PE-CVD to create a glow discharge which provokes a low temperature precursor dissociation Nanoparticles of Co, Ni or Fe are necessary to catalyze the growth CNT synthesis CVD Gas or low bp liquids can be used. The CVD technique is simple, low-cost, easily scalable for commercial production and allows to produce large amounts of CNTs with high purity. PECVD Plasma discharge sources: - direct current (DC), - alternating current (AC), - radio frequency (RF), V= -600V T° →→→ 400-800°C - hot-filament aided with DC, Ar or N 2 (0.1-30 Torr) - microwaves We do like gas phase techniques CVD allows to produce cm long CNTs. With direct spinning is also possible the synthesis of very long CNT ropes in situ. Ya-Li Li et al., Science 304 (2004) 276 S. Musso et al. Carbon 45 (2007) 1133-1136 CNT growth mechanism Two theories for the carbon-metal interaction: Dissolution and saturation of carbon atoms in metal nanoparticles and precipitation of carbon. The catalyst provokes dehydroaromatization (DHA) of cyclic molecules of hydrocarbon. Tip growth mechanism is due to a Base growth mechanism is due weaK adhesion of the catalyst to to a strong adhesion of the the substrate. catalyst to the substrate. Tip growth mechanism Stephan Hofmann et al., Nanoletters 7 (2007) 602 TOXICITY Factors influencing the safety of CNTs in vivo . Small CNT Big CNT Allotropic forms of C 3.4 Å Planar, sp 2 Cubic, sp 3 hybridization hybridization Graphite Graphene Diamond Fullerene Carbon Nanotube Nanotube/Fullerene sp 2 + sp 3 character Allotropic forms of C Graphene Graphite Graphene was largely studied from a theoretical point of view. The unsuccessful attempts to synthesize it seemed to confirm the theory that truly two- dimensional crystals (any kind of crystal) could not exist. InNanotube 2-D the thermal vibration of the atoms should leadFullerene to a displacement comparable to interatomic distance (thermodynamically unstable). The very large perimeter-to-surface ratio of 2-D crystals promotes a collapse. Discovery of Graphene?... Not yet Epitaxial Growth by CVD Graphene and few layers of graphene are grown on Ni Graphene is not free-standing and its properties are strongly affected by substrate: Significant charge transfer from the substrate to the epitaxial graphene Hybridization between the d orbitals of the substrate atoms and π orbitals of graphene, which significantly alters the electronic structure of the epitaxial graphene. Discovery of Graphene Free-standing graphene films (10 µµµm in size) were prepared by mechanical exfoliation (repeated peeling) of small mesas of highly oriented pyrolytic graphite (HOPG). K.S. Novoselov et al., Science 306 (2004) 666-669 MultiMulti--layerslayers graphene The electronic structure of graphene rapidly evolves with the number of layers, approaching the 3D limit of graphite at 10 layers.