Carbon nanohorns consist of single-wall, horn-like tubes approx. 3–25 mm in diameter and 20–150 nm in length, which are closed at one end with a cone. The cone can exhibit various aperture angles. Typically, the angle is approx. 20°.
The single-wall carbon nanotubes (CNHs) generally occur as an aggregate with a particle size ranging from 100 nm to several µm. Three different types of aggregates with approximately conical structure are differentiated and characterised as dahlia-like, bud-like and seed-like; these are essentially dependent on the synthesis parameters. Like graphenes and carbon nanotubes, carbon nanohorns also possess good electrical and thermal conductivity, as well as high mechanical stability and high specific surface area. Conversely, they also have high microporosity and can be dispersed homogeneously in pure water without the addition of dispersing agents, as well as in non-polar solvents.
Carbon nanohorns can be produced using arc discharge and fast quenching of the reaction gases in water or through laser evaporation of carbon. Both processes deliver very pure fractions of nanohorns, since they make do without catalysts. Subsequent purification can largely be dispensed with.
Their high porosity lends nanohorns to potential applications such as gas storage, especially the storage of methane, or use as a catalyst or catalyst carrier, especially for electrode materials for fuel cells. Their use in electronic components, and as a biosensor in pharmaceutical industry, is also of interest.