Was sind Kohlenstoff-Nanomaterialien?
Kohlenstoff-Nanomaterialien sind Allotrope von Kohlenstoff, bei denen Atome in Nanostrukturen mit außergewöhnlichen Eigenschaften angeordnet sind. Alle Kohlenstoff-Nanomaterialien basieren auf sp²-Hybridisierung, bei der jedes Kohlenstoffatom drei σ-Bindungen mit Nachbarn in einem ebenen hexagonalen Gitter bildet, wobei das verbleibende p-Orbital delokalisierte π-Bindungen bildet, die einzigartige elektronische Eigenschaften提供. Die drei Haupttypen sind Graphen (2D-Blätter), Kohlenstoff-Nanoröhren (gerollte Graphenröhren) und Fullerene (geschlossene Käfige).
Graphene
Structure: Single layer of carbon atoms arranged in a 2D honeycomb lattice. It's the basic building block for
other carbon allotropes. Each carbon atom is sp² hybridized with bond length of 1.42 Å.
Electronic Properties: Zero-gap semiconductor with linear energy dispersion (Dirac cones) at K points.
Charge carriers behave as massless Dirac fermions with extremely high mobility (~200,000 cm²/V·s).
The density of states vanishes at the Dirac point, creating unique quantum transport phenomena.
Mechanical Properties: Strongest material ever measured with tensile strength of 130 GPa and
Young's modulus of 1 TPa. Can withstand strains up to 25%.
Thermal Properties: Exceptional thermal conductivity of ~5000 W/m·K at room temperature,
exceeding diamond. Phonon transport dominates heat conduction.
Carbon Nanotubes (CNTs)
Structure: Cylindrical tubes formed by rolling graphene sheets. Characterized by chirality (n,m) which
determines their electronic properties. The chiral vector Cₕ = na₁ + ma₂ defines how the graphene sheet rolls.
Classification by Chirality:
• Armchair (n=n): Always metallic (e.g., (5,5), (10,10))
• Zigzag (m=0): Metallic if n is multiple of 3, otherwise semiconducting
• Chiral (n≠m≠0): Metallic if (n-m) is multiple of 3, otherwise semiconducting
Properties: Electronic properties depend on chirality and diameter. Metallic CNTs can carry current
densities up to 10⁹ A/cm² (1000x copper). Thermal conductivity ~3000 W/m·K. Mechanical properties similar to graphene
with tensile strength up to 100 GPa.
Fullerenes (C₆₀)
Structure: Closed cage molecules resembling a soccer ball (truncated icosahedron). C₆₀ consists of
12 pentagons and 20 hexagons, with each carbon atom bonded to three others. The pentagons introduce curvature
allowing the sheet to close.
Properties: Band gap of ~1.9 eV (semiconductor). Can accept up to 6 electrons in electrochemical
reduction. Forms molecular solids with FCC structure. Used in organic photovoltaics and as electron acceptors.
Endohedral Fullerenes: Atoms or small molecules can be trapped inside the cage (e.g., La@C₈₂),
creating unique properties for quantum computing and medical applications.
Carbon Nanofibers
Structure: Stacked cone or platelet structures with diameters of 50-200 nm, larger than CNTs.
Can consist of multiple nested nanotubes or graphitic layers at various angles.
Properties: Good electrical conductivity, mechanical strength, and surface area.
Used as catalyst supports, in energy storage electrodes, and for composite reinforcement.
More cost-effective than single-walled CNTs for many applications.