New Boron Nitride B24N24 Nanotube

Structural, Electronic and Vibrational Properties of B24N24 Nanocapsules: Novel Anodes for Magnesium Batteries

We report on DFT-TDDFT studies of the structural, electronic and vibrational properties of B24N24 nanocapsules and the effect of encapsulation of homonuclear diatomic halogens (Cl2, Br2 and I2) and chalcogens (S2 and Se2) on the interaction of the B24N24 nanocapsules with the divalent magnesium cation. In particular, to foretell whether these BN nanostructures could be proper negative electrodes for magnesium-ion batteries, the structural, vibrational and electronic properties, as well as the interaction energy and the cell voltage, which is important for applications, have been computed for each system, highlighting their differences and similarities. The encapsulation of halogen and chalcogen diatomic molecules increases the cell voltage, with an effect enhanced down groups 16 and 17 of the periodic table, leading to better performing anodes and fulfilling a remarkable cell voltage of 3.61 V for the iodine-encapsulated system.

Boron nitride nanotube precursor formation during high-temperature synthesis: kinetic and thermodynamic modelling

We performed integrated modelling of the chemical pathways of formation for boron nitride nanotube (BNNT) precursors during high-temperature synthesis in a B/N₂mixture. Integrated modelling includes quantum chemistry, Quantum-classical molecular dynamics, thermodynamic modelling, and kinetic approaches. We demonstrate that BN compounds are formed via the interaction of molecular nitrogen with small boron clusters, rather than through interactions with less reactive liquid boron. (This process can also be described as N₂molecule fixation.) Liquid boron evaporates to produce these boron clusters (B_mwithm≤ 5), which are subsequently converted into B_mN_nchains. The production of such chains is crucial to the growth of BNNTs because these chains form the building blocks of bigger and longer BN chains and rings, which are in turn the building blocks of fullborenes and BNNTs. Additionally, kinetic modelling revealed that B₄N₄and B₅N₄species in particular play a major role in the N₂molecule fixation process. The formation of these species via reactions with B₄and B₅clusters is not adequately described under the assumption of thermodynamic equilibrium, as is demonstrated in our kinetic modelling. Thus, the accumulation of both B₄N₄and B₅N₄depends on the background gas pressure and the gas cooling rate. Long BN chains and rings, which are precursors of the fullborene and BNNT growth, form via self-assembly of components B₄N₄and B₅N₄. Our modelling results-particularly the increased densities of B₄N₄and B₅N₄species at higher gas pressures-explain the experimentally observed effect of gas pressure on the yield of high-quality BNNTs. The catalytic role of hydrogen was also studied; it is shown that HBNH molecules can be the main precursor of BNNT synthesis in the presence of hydrogen.

An all-purpose building block: B12N12 fullerene

We have theoretically shown that the boron nitride fullerene cage B(12)N(12) is an all-purpose building block for fabricating multifarious BN nanotubes. Firstly, we investigated the stability and structural of the boron nitride fullerene cage B(12)N(12) and the polymerized derivatives obtained from it. Interestingly we found out that two B(12)N(12) cages can spontaneously form one BN nanotube with two closed ends through the structural transformation when one cage meets another. These results indicated that the fullerene B(12)N(12) can be polymerized to build various remarkable polymers through the spontaneous structural transformation when they are together, which all have planer or tridimensional shapes with a hollow tubular structure, even at the juncture of the coalesced B(12)N(12). Simultaneously, after the structure optimization, the quadrangles at the juncture of the coalesced B(12)N(12) disappear to form a perfect surface only composed of hexagons. Then, we calculated the energy of all the considered nanostructures. The polymerization of the fullerene B(12)N(12) is exothermic and thus can form very stable derivative polymers. These theoretical conclusions stimulate us to use the fullerene B(12)N(12) as an all-purpose building block to construct various BN nanostructures for purpose of fundamental research and potential applications.

Magnetic endohedral transition-metal-doped semiconducting-nanoclusters

Endohedral first-row transition-metal-doped TM@Zn(i)S(i) nanoclusters, in which TM stands for the first-row transition-metals from Sc to Zn, and i=12, 16, have been characterized. In these structures the dopant metals are trapped inside spheroidal hollow semiconducting nanoclusters. It is observed that some of the transition metals are trapped in the center of mass of the cluster, whereas others are found to be displaced from that center, leading to structures in which the transition metals display a complex dynamical behavior upon encapsulation. This fact was confirmed by quantum molecular dynamics calculations, which further confirmed the thermal stability of endohedral compounds. In the endohedrally-doped nanoclusters in which the transition-metal atom sits on the center of mass, the host hollow cluster structure remains undistorted after dopant encapsulation. Conversely, if the encapsulated transition-metal atom is displaced from the center of mass, the host hollow cluster structure suffers a very tiny distortion. Additionally, it is found that there is negligible charge transfer between the dopant transition-metal atom and its hollow cluster host and, after encapsulation, the spin densities remain localized on the transition-metal atom. This allows for the atomic-like behavior of the trapped transition-metal atom, which gives rise to their atomic-like magnetic properties. The encapsulation free energies are negative, suggesting that these compounds are thermodynamically stable.