In nanotechnology, a

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...

nanobud is a material that combines carbon nanotubes and spheroidal

fullerene A fullerene is an allotrope of carbon whose molecule consists of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with fused rings of five to seven atoms. The molecule may be a hollow sphere, ...

s, both allotropes of carbon, forming "

bud In botany, a bud is an undeveloped or embryonic shoot and normally occurs in the axil of a leaf or at the tip of a stem. Once formed, a bud may remain for some time in a dormant condition, or it may form a shoot immediately. Buds may be spec ...

s" attached to the tubes. Carbon nanobuds were discovered and synthesized in 2006. In this material, fullerenes are bonded with

covalent bonds A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...

to the outer sidewalls of the underlying nanotube. Consequently, nanobuds exhibit properties of carbon nanotubes and fullerenes. The mechanical properties and the electrical conductivity of the nanobuds are similar to those of carbon nanotubes. Canatu Oy, a Finnish company, claims the

intellectual property Intellectual property (IP) is a category of property that includes intangible creations of the human intellect. There are many types of intellectual property, and some countries recognize more than others. The best-known types are patents, cop ...

rights for nanobuds, its synthesis processes, and several applications.

Properties

Carbon nanobuds (CNBs) have some of the properties of

carbon nanotubes A scanning tunneling microscopy image of a single-walled carbon nanotube Rotating single-walled zigzag carbon nanotube A carbon nanotube (CNT) is a tube made of carbon with diameters typically measured in nanometers. ''Single-wall carbon na ...

, such as one-dimensional electrical conductivity, flexibility and manufacturing adaptability, as well as some of the chemical properties of

s. Examples of these properties include ability to engage in cycloaddition reactions and can easily form the chemical bonds capable of attaching to other molecules with complex structures. CNBs have a much higher chemical activity than single-walled carbon nanotubes (SWCNTs).Albert G. Nasibulin Ilya V. Anoshkin, Prasantha R. Mudimela, Janne Raula, Vladimir Ermolov, Esko I. Kauppinen, "Selective Chemical Functionalization of Carbon Nanobuds," ''Carbon'' 50, no. 11 (2012).

Electrical properties

CNBs have been shown to have electronic properties that differ from those of fullerenes and carbon nanotubes (CNTs). CNBs exhibit lower field thresholds, higher current densities, and electric field emissions than SWCNTs. The chemical bonds between the nanotube's wall and the fullerenes on the surface can lead to charge transfer between the surfaces. The presence of fullerenes in CNBs leads to smaller bundle formation and higher chemical reactivity. CNBs can engage in

cycloaddition In organic chemistry, a cycloaddition is a chemical reaction in which "two or more unsaturated molecules (or parts of the same molecule) combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity". T ...

reactions and form chemical bonds attaching molecules with complex structures, due to the greater availability of CNB surface to the reactants, the presence of π-conjugated structure and 5-atom rings with excess pirimidization energy. Formation energy indicated that the preparation of CNBs is

endothermic In thermochemistry, an endothermic process () is any thermodynamic process with an increase in the enthalpy (or internal energy ) of the system.Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015).''Principle of Modern Chemistry'', Brooks Cole. ...

, meaning that it is not favorable to create. All CNBs can conduct electricity, regardless of whether the single-walled CNT is a

metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...

lic or

semiconducting A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

base. The band gap of carbon nanobuds is not constant. It can change through the size of the fullerene group. The attachment of C₆₀ added to the armchair orientation of the SWCNT opens up the

band gap In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference ( ...

. On the other hand, adding it to a semiconducting SWCNT could introduce impurity states to the band gap, which would reduce the band gap. The band gap of CNBs can also be modified by changing the density of the carbons of the C₆₀ attached to the sidewall of the SWCNT.

Magnetic properties

Two structures of CNBs are ferromagnetic in their ground state, and two are nonmagnetic.Min Wang and Chang Ming Li, "Magnetic Properties of All-Carbon Graphene-Fullerene Nanobuds," ''Physical Chemistry Chemical Physics'' 13, no. 13 (2011). The attached C₆₀ molecule on the surface of the CNTs gives more space between the nanotubes-and adhesion between the single-walled CNTS can be weakened to prevent the formation of tight bundles of CNTs. Carbon nanobuds can be used as molecular support to prevent the matrix from slipping into composite materials and increasing their mechanical strength.

Structural properties

The stability of CNBs depends on the type of carbon bond that is dissociated in the cycloaddition. It has been shown that carbon atoms of the SWCNT near the fullerene C₆₀ molecule were pulled outward from the original wall surface due to the covalent bonding with cycloaddition between the fullerene and nanotube; in addition, their bonding was transformed from sp² to sp³ hybridization. An analysis using

Raman scattering Raman scattering or the Raman effect () is the inelastic scattering of photons by matter, meaning that there is both an exchange of energy and a change in the light's direction. Typically this effect involves vibrational energy being gained by a ...

spectroscopy shows that the CNB sample had stronger chemical modification compared to CNTs. It indicates that there is a carbon sp³ hybridization that occurs after the chemical addition creation of CNBs.

Synthesis

The single wall carbon nanotubes can react with

fullerenes A fullerene is an allotrope of carbon whose molecule consists of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with fused rings of five to seven atoms. The molecule may be a hollow sphere, ...

in the presence of water vapor or carbon dioxide. It produces a covalently linked material that looks similar to buds on a tree branch, hence the name "Nanobud".Anisimov, Anton. "Aerosol Synthesis of Carbon Nanotubes and Nanobuds.". (2010). The nanobuds form in abundance at 45 ppm of water vapour and higher. However, above 365ppm, the reaction will give a higher number of inactive catalyst particles in lieu of the nanobud.

References