CHM 102: Fullerenes and Nanoscience - Key Concepts

Fullerenes are carbon allotropes with a closed mesh topology; empirical formula $C<em>n$ ; some $n$ values have multiple isomers. The famous member is buckminsterfullerene $C</em>{60}$ . Closed fullerenes are often called buckyballs; nested closed fullerenes are bucky onions; cylindrical fullerenes are carbon nanotubes (CNTs); bulk form is fullerite.
Discovered experimentally in 1985 after long prediction; discovery expanded carbon allotropes beyond graphite, diamond, and amorphous carbon; active area of chemistry, materials science, electronics, and nanotechnology.

Two major families: closed buckyballs (spherical) and open-ended cylindrical nanotubes; hybrids exist (e.g., buckybuds or carbon nanobuds).
Carbon nanotubes (CNTs): cylindrical fullerenes, diameters of a few nanometres, lengths from <1 µm to several millimetres; ends can be closed or open; sometimes diameter narrows toward the end.
Hybrid structures combine features of spheres and tubes; potential for novel properties.

Exceptional macroscopic properties: very high tensile strength, high electrical conductivity, high ductility, high thermal conductivity.
Proposed applications include:
- paper batteries (Rensselaer Polytechnic Institute, 2007)
- high-tensile cables for space elevators
CNTs are central to developments in nanotechnology, electronics, and advanced materials.

Fullerenes can act as conductors and as gas adsorbents.
Used as lubricants; some forms find cosmetic and biomedical applications.
CNTs and fullerenes are explored in organic photovoltaics (OPV), polymer additives, catalysts, water purification, biohazard protection, drug delivery, and advanced composites.
CNTs have potential in biomedical and pharmaceutical applications due to their unique properties.

Allotropy: elements existing in two or more crystalline forms in the same state.
Carbon’s main allotropes: Diamond and Graphite (and numerous other forms like graphene, Lonsdaleite, Diamane, Amorphous carbon).

Structure: sp³-hybridized, tetrahedral network; covalently bonds to four carbons; C–C bond length $d_{C-C}=154\ \text{pm}$ ; crystal structure is a diamond cubic lattice with eight atoms per unit cell.
Properties: extremely hard, high refractive index, excellent for polishing and cutting; insulator (all four valence electrons are used in covalent bonds).
Industrial uses: cutting, drilling, grinding, polishing; diamond anvils (high-pressure research);
Economic note: diamond is among the most expensive elements in its purified crystal form.

Structure: layered, planar sheets of carbon atoms (sp²) with delocalized pi electrons.
Electrical conduction: conducts electricity along the planes; not in the direction perpendicular to the planes.
Lubrication and heat resistance: graphite powder acts as a dry lubricant; high-temperature crucibles and nuclear applications.
Graphene: a single layer of graphite; exceptional electrical, thermal, and mechanical properties; potential to replace silicon in high-performance devices.
Other related allotropes: Lonsdaleite (hexagonal diamond), Diamane (2D diamond), and other carbon networks (Graphenylene, Carbophene, AA′-graphite, Amorphous carbon).

Definitions:
- Nanoscience: study of structures and processes at the scale of 1–100 nanometres (nm).
- Nanotechnology: manipulation of matter at the nanoscale for practical devices and systems.
Scale and effects: surface area to volume effects and quantum phenomena become significant at the nanoscale.
Size reference: $1\ \text{nm}=1\times 10^{-9}\ \text{m}$ ; typical bond lengths are ~ $0.12-0.15\ \text{nm}$ ; DNA diameter ~2 nm.
Approaches:
- Bottom-up: assemble from molecular components via molecular recognition and self-assembly.
- Top-down: sculpt from larger pieces with controlled patterns.
Fields involved: nanoelectronics, nanomechanics, nanophotonics, nanoionics, among others.
Applications: nanomedicine, nanoelectronics, biomaterials, energy, solar cells, displays, biosensors, etc.
Risks and regulation: toxicity, environmental impact, economics, and potential doomsday scenarios; ongoing regulatory discussions.

Key milestones:
- 1959: Richard Feynman's talk There's Plenty of Room at the Bottom, conceptual seed for nanoscale manipulation.
- 1974: Norio Taniguchi popularizes term "nanotechnology".
- 1986: K. Eric Drexler popularizes nanotechnology in Engines of Creation; co-founds The Foresight Institute.
- 1981: Scanning tunneling microscope (STM) enables visualization and manipulation of individual atoms; Nobel Prize awarded in 1986 to Binnig, Rohrer, Quate, and Gerber for related AFM developments.
Early commercialization: nanoscale products (e.g., silver nanoparticles in antimicrobials, nanoparticle sunscreens, carbon nanotube textiles).
Government investment: initiatives like the National Nanotechnology Initiative (USA) and European Framework Programmes to fund and coordinate nanotech research.
Mid-2000s: nanotechnology roadmaps emphasize atomically precise control, self-assembly, and molecular manufacturing concepts.

Nanometer scale: $1\ \text{nm} = 10^{-9}\ \text{m}$ ; carbon–carbon bonds are on the order of $0.12-0.15\ \text{nm}$ .
Nanotechnology spans multiple disciplines and application areas, from materials to medicine and electronics.
Distinct from microtechnology, nanotech exploits size-dependent quantum and surface phenomena to enable new capabilities at the molecular level.