Browsing by Subject "carbon nanotube"

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Open Access
Adsorption and dissociation of hydrogen molecule on carbon nanotubes
(2004) Öztürk, Yavuz
Earlier, it has been suggested that carbon nanotubes can provide high storage capacity and other physical properties suitable for the fuel cell technologies. In this thesis we have investigated adsorption, desorption and dissociation of hydrogen molecule on the surface of the zigzag (8,0) single-wall carbon nanotube (SWNT) by carrying out extensive first-principles pseudopotential plane wave calculations within the Density Functional Theory (DFT). We found that while H2 molecule cannot be bound to the surface of bare SWNT, an elastic radial deformation leading to the elliptical deformation of the circular cross-section renders the physisorption of the molecule possible. Coadsorption of Li atom on the SWNT makes the similar effect, and hence enhances the physisorption. That an adsorbed H2 can be desorbed upon releasing the elastic radial strain is extremely convenient for the storage. In addition to that, we found that a Pt atom coadsorbed on the SWNT can form a strong chemisorption bond with a H2 molecule. If a single H2 molecule engages in interactions with more than one coadsorbed Pt atom at its close proximity it dissociates into single H atoms, which, in turn, make Pt-H bonds. The interaction between H2 and coadsorbed Pd atom is similar to Pt, but it is weaker. We believe that these findings clarify earlier controversial results related to the storage of H2 in carbon nanotubes, and makes important contributions to fuel cell technology.
Open Access
Probing interfacial processes on carbon nanotubes and graphene surfaces
(2012) Kakenov, Nurbek
The surface of low-dimensional carbon (carbon nanotubes and graphene) has unique electronic properties due to the delocalized p-orbitals. Very high carrier mobility with nanoscale dimension make carbon nanotubes and graphene promising candidates for high performance electronics. Besides electronic properties, the delocalized orbitals have a strong tendency to adsorb aromatic molecules via p-electronic interactions. The strong non-covalent interactions between the graphitic surface and organic molecules provide a unique template for supramolecular chemistry and sensing applications. A comprehensive understanding of these forces at atomic and molecular level still remains a challenge. In this thesis, we have used carbon nanotube networks and graphene as model systems to understand molecular interactions on carbon surface. We have developed processes to integrate these model materials with sensitive and surface specific sensors, such as surface plasmon sensor and quartz crystal microbalance. In the first part of the thesis, we integrated surface plasmon resonance (SPR) sensors with networks of single-walled carbon nanotubes to study interactions between SWNT and organic molecules. In the second part, we probe interfacial processes on graphene surface by mass detection. We anticipate that the developed methods could provide a sensitive means of detecting fundamental interaction on carbon surfaces.
Open Access
A study of adsorption of single atoms on carbon nanotubes
(2003) Durgun, Engin
The adsorption of individual atoms on the semiconducting and metallic singlewall carbon nanotubes (SWNT) have been investigated by using first-principles pseudopotential plane wave method within Density Functional Theory. The stable adsorption geometry and binding energy have been determined for a large number of foreign atoms ranging from alkali and simple metals to the transition metals and group IV elements. We have found that the character of the bonding and associated physical properties strongly depend on the type of adsorbed atoms, in particular on their valence electron structure. Our results indicate that the properties of SWNTs can be modified by the adsorbed foreign atoms. While the atoms of good conducting metals, such as Zn, Cu, Ag and Au, form very weak bonds, transition metal atoms, such as Ti, Sc, Nb and Ta, and group IV elements C and Si are adsorbed with relatively high binding energy. Owing to the curvature effect, these binding energies are larger than the binding energies of the same atoms on the graphite surface. We have showed that the adatom carbon can form strong and directional bonds between two SWNTs so that the tubes are connected. These connects can be used to produce nanotube networks or grids. Most of the adsorbed transition metal atoms excluding Ni, Pd and Pt have a magnetic ground state with a significant magnetic moment. Our results suggest that carbon nanotubes can be functionalized in different ways by their coverage with different atoms, showing interesting applications such as one-dimensional nanomagnets or nanoconductors and conducting connects etc.