Computational Investigations On Graphene-analogous Inorganic Materials

Graphene has been ranked as the hottest research star in the field of nanomaterials science in recent years because of its unique properties and promising applications. Inspired by the extensive investigations of graphene, researchers have also devoted much concern and interest to those graphene-analogous 2D inorganic materials with non-carbon compositions, and much progress has been made in this emerging new area. In this thesis, based on DFT computations, we have systematically studied various graphene-analogues in light of their fundamental properties(e.g., geometrical, electronic and magnetic properties) and functional applications(e.g., gas adsorption, energy storage and catalysis).We first investigated band gap engineering of BN via molecular doping and interfacial dihydrogen interactions. Specifically, the semiconducting BN sheets or ribbons are converted into p-type or n-type semiconductors when adsorping strong electron-accepting(TCNQ) or-donating(TTF) molecules via non-covalent interactions, and there exists interfacial charge transfer between them. Moreover, the hydrogenated BN bilayers are stacked together via interlayer B-H···H-N dihydrogen bonding, wherein the interactive(B)Hδ- and(N)Hδ+ are charged oppositely, and thus there exists electrostatic attraction between them. The hydrogenated BN bilayers with different configurations exhibit different electronic properties. Because of interfacial polarization and the resultant charge transfer, the meta-stable chair-type BN bilayer has extremely small band gap, while the more favorable boat- and stirrup-type BN bilayers preserve the insulating properties of the monolayer counterparts(no interfacial polarization and charge transfer). By exerting an external electric field, the most stable stirrup-type BN bilayer can be modified at a large scale from a wide-band-gap to a medium-band-gap semiconductor, and even into a metal.We additionally investigated electromagnetic properties of V2O5 monolayer and nanoribbons. V2O5 single-layer is a non-magnetic semiconductor, which is further converted into a magnetic metal by surface hydrogenation. For 1D V2O5 nanoribbons, armchair-type nanoribbons are non-magnetic semiconductors, while zigzag-type nanoribbons are ferromagnetic metals. Depending on the hydrogenation sites, both types of nanoribbons are modulated into non-magnetic semiconductors(when only the ribbon edges are hydrogenated) or magnetic half-metals(when both the surface and the edge atoms are hydrogenated).BN and V2O5 monolayers are derived from layered materials with weak interlayer interactions. Besides, graphene-like materials can also be obtained from layered materials with strong interlayers interactions(ionic or covalent bonding), such as MXene(exfoliated from layered MAX phase), and graphitic phase of Wurtzite materials.For MXene, we studied the electronic properties and Li storage capability of Ti3C2. Ti3C2 is a magnetic metal, while its functionalized derivatives [Ti3C2F2 and Ti3C2(OH)2] are non-magnetic semiconductors with small band gaps(Eg: 0.05eV), which favor the use of Ti3C2 as electrode materials. Li adsorption forms strong Coulomb interaction with Ti3C2-based hosts. Bare Ti3C2 exhibits a low barrier for Li diffusion and high Li storage capacity(320 mAh g-1). After surface functionalization, Li diffusion needs to overcome higher barriers and the theoretical Li capacities are decreased, thus surface decoration is detrimental in practical applications.For Wurtzite materials, we studied the electronic properties of ZnO and GaN. Bare ZnO nanosheets with polar(0001) surfaces would transform into graphitic structures when the thickness is less than 9 Zn-O bilayers. The graphitic ZnO nanosheets are semiconducting. When the polar surfaces are saturated by H, the initial Wurtzite configuration can be preserved, and the hydrogenated ZnO demonstrates versatile properties, denpending on hydrogenation site and thickness. Moreover, we studied surface, edge, and quantum effects on the electronic properties of GaN nanoribbons. For a realistic GaN nanoribbon with finite width and thickness, surface effect plays a more important role.Moreover, single-layer coordination polymers(CPs) are novel organic-inorganic hybrid materials with unique properties and functions, and we investigated two types of CPs([Cu2Br(IN)2]n and [NiC4S4]n). [Cu2Br(IN)2]n has a tendency to adsorb gas molecules. Particularly, NO and NO2 have strong interactions with [Cu2Br(IN)2]n and can effectively modify its electronic structure, suggesting its feasibility as molecular sensors. The nickel bis(dithiolene) sheet is perfectly planar with hexagonal symmetry, and exhibits cycloaddition reactivity towards ethylene. At the reduction condition, the adduct would dissociate into ethylene and nickel bis(dithiolene) anion. Thus, this sheet can bind and release ethylene in neutral and reduction conditions, respectively, indicating its potential as electrocatalyst in olefin purification.