Theoretical Studies On The Catalytic Properties Of Low-dimension Carbon Material And Electronic Properties Of MoS₂

In this thesis, by using the first-principles method based on the density functional theory,we focused on studying three parts,the catalytic properties of carbon-nanotube(CNT) and graphene nanomaterials doped with nitrogen and boron, the indirect-direct bandgap transition and the gap width tuning in bilayer MoS2 superlattices.Firstly, we have made detailed studies on the catalytic properties of CNTs doped with B and N by the first-principles method. We have calculated the activation energy barriers and found that the CNTs doped with B and N exhibited efficient catalytic activities in CO oxidizing reaction. For the B and N co-doped CNTs, the catalytic properties were improved with the increase of the atomic distance between B and N. When B and N atoms banded together, the catalytic properties of CNTs were enhanced as the amount of N atoms increasing. It is because that in the bonded B and N co-doped CNT the lone-pair electrons from N dopant are largely neutralized by the vacant orbital of B dopant, and few electrons or vacant orbitals are left to conjugate with the carbon π system.In the second part, we have studied the catalytic properties of graphene doped with B and N by using the first-principles method. After detailed calculations of B-N, B-2N and B-3N doped graphene catalyzing CO oxidation reactions, we found that the energy barriers reduced as the doping density of N atoms increasing, that is to say the catalytic properties of graphene improved. For the case of the graphene doped with B-N dimer, the catalytic property of 3-BN doped structure is better than the B-N doped one.Finally, using the band-folding analysis and the first-principles method, we have carefully studied the electronic properties of the bilayer MoS2 superlattices. In the(N, M) bilayer MoS2 hexagonal superlattice, the bottom of the conduction band could be folded from K to Γ points resulting in the direct bandgap semiconductor if both N and M are integer multiple of 3. In the(P, Q) bilayer MoS2 orthogonal superlattice, the bottom of the conduction band could be folded to Γ points resulting in the direct bandgap semiconductor if Q is integer multiple of 3. Furthermore, the gap width could be tuned by the in-plane stretching and the perpendicular compressing. These studies could pave the path for designing the direct bandgap nanostructures and tuning their gap width toward the applications in the high-performance photo-electronic devices.