Structural and Reactivity Properties of Finite Length Cap-Ended Single-Wall Carbon Nanotubes

DFT Study of the Oxygen Reduction Reaction Activity on Fe-N₄-Patched Carbon Nanotubes: The Influence of the Diameter and Length

The influences of diameter and length of the Fe−N₄-patched carbon nanotubes (Fe−N₄/CNTs) on oxygen reduction reaction (ORR) activity were investigated by density functional theory method using the BLYP/DZP basis set. The results indicate that the stability of the Fe−N₄ catalytic site in Fe−N₄/CNTs will be enhanced with a larger tube diameter, but reduced with shorter tube length. A tube with too small a diameter makes a Fe−N₄ site unstable in acid medium since Fe−N and C−N bonds must be significantly bent at smaller diameters due to hoop strain. The adsorption energy of the ORR intermediates, especially of the OH group, becomes weaker with the increase of the tube diameter. The OH adsorption energy of Fe−N₄/CNT with the largest tube diameter is close to that on Pt(111) surface, indicating that its catalytic property is similar to Pt. Electronic structure analysis shows that the OH adsorption energy is mainly controlled by the energy levels of Fe 3d orbital. The calculation results uncover that Fe−N₄/CNTs with larger tube diameters and shorter lengths will exhibit better ORR activity and stability.

Exploring the effect of confinement on water clusters in carbon nanotubes

Using armchair-type single-walled carbon nanotubes (SWCNTs) of different sizes as model compounds for lignite, the effect of water molecule confinement on the water-holding capacity of lignite pores was investigated. Results indicated that the water-holding capacity of pores with diameters of <10 nm was eight times larger than that of pores with diameters of 100 nm. The configuration of the cluster of water molecules in each SWCNT and the binding energy between each SWCNT and the water molecules within it were calculated by means of density functional theory using a hybrid functional: M06-2X/6-311+G**, 6-31G*. The results prove that the configurations of the water molecules in the SWCNTs are very different to their configuration in the unconfined state. In vacuum, the cluster of three water molecules adopted a trimer configuration, while they presented a linear configuration in the 6.78 Å SWCNT. Similarly, in vacuum, the cluster of five water molecules formed a five-membered ring, while they favored a linear configuration in the 6.78 Å SWCNT, a zigzag configuration in the 8.14 Å SWCNT, and a trimer + 1 + 1 configuration (i.e., a trimer plus two isolated water molecules) in the 9.49 Å, 10.85 Å, and 13.75 Å SWCNTs. There was found to be a degree of competition between the coupling energy of the water molecules with the SWCNT and the hydrogen bonding among the water molecules. When the diameter of the SWCNT was >1 nm, the hydrogen bonding among the water molecules dominated, while the coupling energy of the water molecules with the SWCNT amounted to only 30-40% of the total interaction energy of the water molecules. Graphical Abstract Computed equilibrium structures of five water molecules confined in SWCNTs with diameters of 6.78 Å, 8.14 Å, 9.49 Å, 10.85 Å, and 13.75 Å, and in vacuum.

Regioselective multistep reconstructions of half-saturated zigzag carbon nanotubes

The open edge reconstruction of half-saturated (6,0) zigzag carbon nanotube (CNT) was introduced by density functional calculations. The multistep rearrangement was demonstrated as a regioselective process to generate a defective edge with alternating pentagons and heptagons. Not only the thermal stability was found to be enhanced significantly after reconstruction but also the total spin of CNT was proved to be reduced gradually from high-spin septet to close-shell singlet, revealing the critical role of deformed edge on the geometrical and magnetic properties of open-ended CNTs. Kinetically, the initial transformation was confirmed as the rate-determining step with relatively the largest reaction barrier and the following steps can take place spontaneously. © 2016 Wiley Periodicals, Inc.

Molecular dynamics study of the initial stages of catalyzed single-wall carbon nanotubes growth: force field development

Effective force fields for Ni-C interactions developed by Yamaguchi and Maruyama for the formation of metallofullerenes are modified to simulate the catalyzed growth of single-wall carbon nanotubes on Ni(n) clusters with n >20, and the reactive empirical bond order Brenner potential for C-C interactions is also revised to include the effect of the metal atoms on such interactions.