Tubular Boron Research Articles

Transition Metal Behavior of Heavier Alkaline Earth Elements in Doped Monocyclic and Tubular Boron Clusters.

Quantum chemical calculations are carried out to design highly symmetric-doped boron clusters by employing the transition metal behavior of heavier alkaline earth (Ae = Ca, Sr, and Ba) metals. Following an electron counting rule, a set of monocyclic and tubular boron clusters capped by two heavier Ae metals were tested, which leads to the highly symmetric Ae2B8, Ae2B18, and Ae2B30 clusters as true minima on the potential energy surface having a monocyclic ring, two-ring tubular, and three-ring tubular boron motifs, respectively. Then, a thorough global minimum (GM) structural search reveals that a monocyclic B8 ring capped with two Ae atoms is indeed a GM for Ca2B8 and Ba2B8, while for Sr2B8 it is a low-lying isomer. Similarly, the present search also unambiguously shows the most stable isomers of Ae2B18 and Ae2B30 to be highly symmetric two- and three-ring tubular boron motifs, respectively, capped with two Ae atoms on each side of the tube. In these Ae-doped boron clusters, in addition to the electrostatic interactions, a substantial covalent interaction, specifically the bonding occurring between (n - 1)d orbitals of Ae and delocalized orbitals of boron motifs, provides the essential driving force behind their highly symmetrical structures and overall stability.

Designing a Four-Ring Tubular Boron Motif through Metal Doping.

Tubular boron clusters represent a class of extremely unusual geometries that can be regarded as a key indicator for the 2D-to-3D boron structural evolution as well as the embryos for boron nanotubes. While a good number of pure boron or metal-doped boron tubular clusters have been reported so far, most of them are two-ring tubular structures, and their higher-ring analogues are very scarce. We report herein the first example of a four-ring tubular boron motif in the cagelike global minimum of Be2B24+. Global-minimum searches of MB24q and M2B24q (M = alkali/alkaline-earth metals; q = 1+, 0, 1-) reveal that the most stable structure of Be2B24+ is a C2v-symmetric cage having a four-ring tubular boron moiety, whereas it is a high-lying isomer for those having a two/three-ring tubular boron motif for all other systems. The B24 framework in Be2B24+ can be viewed as consisting of two two-ring B12 tubular structures linked together at one side of the B6 rings along the high-symmetry axis and two offside B6 rings capped by two Be atoms. The Be2-B24 bonding is best described as Be22+ in an excited triplet state, forming two highly polarized covalent bonds with B24- in a quartet spin state. The unique ability of beryllium to make strong covalent and electrostatic interactions makes the Be2B24+ cluster stable in such an unusual geometry.

Construction of the Largest Metal-Centered Double-Ring Tubular Boron Clusters Based on Actinide Metal Doping

Metal doping has been considered to be an effective approach to stabilize various boron clusters. In this work, we constructed a series of largest metal-centered double-ring tubular boron clusters An@B24 (An = Th, Pa, Pu, and Am). Extensive global minimum structural searches combined with density functional theory predicted that the global minima of An@B24 (An = Th, Pu, and Am) are double-ring tubular structures. Formation energy analysis indicates that these boron clusters are highly stable, especially for Th@B24 and Pa@B24. Detailed bonding analysis shows that the significant stability of An@B24 is determined by the covalent character of the An-B bonding, which stems from the interactions of An 5f and 6d orbitals and B 2p orbitals. These results show that actinide metal doping is a feasible route to construct stable large metal-centered double-ring tubular boron clusters, offering the possibility to design boron nanomaterials with special physiochemical properties.

Structures, electronic and thermodynamic properties of NiB2n (n = 7–11) and their anions: A theoretical study

AbstractParticle Swarm Optimization (CALYPSO) searching method and density functional theory (DFT) were used to study structures, electronic, and thermodynamic properties of NiB2n0/− (n = 7–11) clusters at the TPSSh/6‐311 + G(d) level of theory. Results found that the lowest energy structures possess a Ni atom‐centered double ring tubular boron structures, NiB180/− except. Relative stabilities were analyzed via computing their vertical ionization potentials (VIP), vertical electronic affinity (VEA), adiabatic electronic affinity (AEA), HOMO‐LUMO gaps and hardness. The infrared spectra, Raman spectra and photoelectron spectra were computationally simulated to facilitate their experimental characterizations. At last, aromatic properties (nucleus independent chemical shift and anisotropy of the current induced density) and thermodynamic properties (enthalpy and entropy) with temperature were discussed in detail for studied systems.

Facile synthesis and luminescence properties of tubular BCNO phosphor with orange emission assisted by bamboo fiber

In this work, tubular boron carbon oxynitride (BCNO) phosphors with orange-emitting are synthesized by bamboo fiber assistance. The effects of different sintering temperatures on the structure, morphology, and photoluminescence (PL) performance of BCNO phosphors were investigated. The results revealed that with the increase of sintering temperature, compared with the BCNO synthesized without the template, the synthesized BCNO phosphor with bamboo fiber as template gradually becomes a hollow tubular structure. Meanwhile, when the sintering temperature is 700 ℃, the BCNO phosphor shows bright orange emission at 315 nm excitation wavelength, and the quantum yield (QY) is up to 75%. Moreover, the prepared BCNO phosphor has a sensitive and selective quenching effect on Fe3+ ion under 365 nm portable ultraviolet lamp irradiation. By using the obtained BCNO phosphor as a fluorescence labeling marker, the fingerprint recognition on the object surfaces also could be realized.

Novel B-N-Co surface bonding states constructed on hollow tubular boron doped g-C3N4/CoP for enhanced photocatalytic H2 evolution

Graphitic carbon nitride (g-C3N4) is a promising photocatalyst for water hydrogen evolution. Nonetheless, fast recombination of photogenerated electron-hole pairs and the slow kinetics of hydrogen production result in the unsatisfactory efficiency of solar hydrogen production. we address this issue by anchoring the cobalt phosphide (CoP) cocatalyst onto the one-dimensional boron doped g-C3N4 nanotube (B-CNNT) to construct B-N-Co surface bonding states in the B-CNNT/CoP photocatalyst. Spectroscopic measurement and density functional theory (DFT) calculations demonstrated that the B-N-Co bonds optimize the local electronic distribution of bonded Co and adjacent P atoms, strengthen the electrons’ delocalization capacity of Co atoms for high electrical conductivity and accelerate the photogenerated carrier transfer between B-CNNT and CoP, which lead to the enhanced photocatalytic activity of the B-CNNT/CoP photocatalyst for hydrogen evolution. B-CNNT/CoP-2.45% achieved a remarkable photocatalytic hydrogen production rate of 784 μmol g-1h−1 with an apparent quantum efficiency of 5.32% at 420 nm, which is significantly higher than demonstrated by CNNT/CoP-2.45% (153 μmol g-1h−1). Our findings provide insights into as well as establish theoretical and practical grounds for the development of low-cost, high-performance photocatalytic materials for hydrogen evolution.

First-principles study of ultrafast spin dynamics in Fe<i><sub>m</sub></i>B<sub>20</sub> (<i>m</i> = 1, 2) clusters

In this study, we use first-principles calculations to investigate the geometry, the electronic and the magnetic structure as well as to propose the laser-induced ultrafast spin dynamics on the tubular FeB<sub>20</sub> and Fe<sub>2</sub>B<sub>20</sub> clusters. Our results show that the FeB<sub>20</sub> is a stable configuration when its Fe atom gets preferably adsorbed inside the B<sub>20</sub> tube, while the Fe<sub>2</sub>B<sub>20</sub> is more stable configuration when one of its two Fe atoms is located inside and the other outside the boron tube. In the latter cluster, due to the higher number of d states introduced by the additional magnetic atom, the density-of-states in the low-energy region becomes higher, thus leading to richer spin dynamics. The different local geometries of the two Fe atoms lead to a multitude of many-body states with high degree of spin-density localization. Based on the calculated ground state and excited states and by using suitably tailored laser pulses we achieve ultrafast spin-flip and spin crossover scenarios for both structures. Besides, the spin-flips reach a high fidelity (above 89.7%) and are reversible, while the crossovers have lower fidelity (below 78%) and are irreversible. We also propose an ultrafast spin-transfer process from Fe2 to Fe1 for Fe<sub>2</sub>B<sub>20</sub>. The present investigation, in which we predict various ultrafast spin dynamic taken by magnetic atoms absorbed inside and outside of tubular boron clusters, is expected to provide significant theoretical guidance for the future experimental implementation and the potential applications of the relevant spin logic functional devices.

Effects of single and double nickel doping on boron clusters: stabilization of tubular structures in BnNim, n = 2-22, m = 1, 2.

A systematic investigation on structure, relative stabilities, dissociation behavior and bonding of the singly and doubly Ni doped boron clusters BnNim with n = 2-22 and m = 1-2, was carried out using density functional theory (TPSSh functional) calculations. Calculated results indicate that for n < 14, BnNim structures are generally formed by capping Ni atom(s) on the edge or the surface of the pure boron Bn frameworks. From n = 14, the Ni dopants exert stronger effects in such a way that the most stable isomers BnNim adopt the shape of the related double ring tubular boron structures. With n ≥ 20, the Bn double ring appears to possess a large enough volume to entirely enclose the Ni2 dimer. The B14Ni and B22Ni2 turn out to be remarkable species with enhanced thermodynamic stability with larger average binding energies along with surprising geometric structures. Their higher thermodynamic stability can be understood in terms of the MO energy levels predicted by a hollow cylinder model, and other electronic properties. The (2 0 2)-orbital derived from the model of particle in a hollow cylinder appears to play a key role in the stabilization of the boron double ring.

Lithium doped tubular structure in LiB20 and LiB20-: a viable global minimum.

We present a strategy by which the stability of tubular boron clusters can be significantly enhanced by doping the B20 cluster with a lithium atom. High-level quantum chemical calculations showed that the lowest energy structures of LiB20 and LiB20- are tubular structures with D10d symmetry, in which the lithium atom is located at the center of the tubular structure. Chemical bonding analysis revealed that the high-symmetry tubular boron clusters are characterized as charge transfer complexes (Li+B20- and Li+B202-), resulting in double aromaticity with delocalized π + σ bonding and strong electrostatic interactions between cationic Li+ and tubular boron motifs with twenty Li-B interactions. The unique bonding pattern of the LiB20 and LiB20- species provides a key driving force to stabilize tubular structures over quasi-planar structures, suggesting that electrostatic interactions resulting from alkali metals might unveil a new clue to the structural evolution of boron clusters.

A Practical Criterion for Screening Stable Boron Nanostructures

Due to the electron deficiency, boron clusters evolve strikingly with the increasing size as confirmed by experimentalists and theorists. However, it is still a challenge to propose a model potential to describe the stabilities of boron. On the basis of the 2c-2e and 3c-2e bond models, we have found the constraints for stable boron clusters, which can be used for determining the vacancy concentration and screening the candidates. Among numerous tubular structures and quasi-planar structures, we have verified that the stable clusters with lower formation energies bounded by the constraints, indicating the competition of tubular and planar structures. Notably, we have found a tubular cluster of B76 which is more stable than the B80 cage. We show that the vacancies, as well as the edge, are necessary for the 2c-2e bonds, which will stabilize the boron nanostructures. Therefore, the quasi-planar and tubular boron nanostructures could be as stable as the cages, which have no edge atoms. Our finding has shed light on understanding the complicated electron distributions of boron clusters and enhancing the efficiency of searching stable B nanostructures.

From Quasi-Planar B56 to Penta-Ring Tubular Ca©B56: Prediction of Metal-Stabilized Ca©B56 as the Embryo of Metal-Doped Boron α-Nanotubes.

Motifs of planar metalloborophenes, cage-like metalloborospherenes, and metal-centered double-ring tubular boron species have been reported. Based on extensive first-principles theory calculations, we present herein the possibility of doping the quasi-planar C2v B56 (A-1) with an alkaline-earth metal to produce the penta-ring tubular Ca©B56 (B-1) which is the most stable isomer of the system obtained and can be viewed as the embryo of metal-doped (4,0) boron α-nanotube Ca©BNT(4,0) (C-1). Ca©BNT(4,0) (C-1) can be constructed by rolling up the most stable boron α-sheet and is predicted to be metallic in nature. Detailed bonding analyses show that the highly stable planar C2v B56 (A-1) is the boron analog of circumbiphenyl (C38H16) in π-bonding, while the 3D aromatic C4v Ca©B56 (B-1) possesses a perfect delocalized π system over the σ-skeleton on the tube surface. The IR and Raman spectra of C4v Ca©B56 (B-1) and photoelectron spectrum of its monoanion C4v Ca©B56− are computationally simulated to facilitate their spectroscopic characterizations.

Manganese-centered tubular boron cluster - MnB16 (-): A new class of transition-metal molecules.

We report the observation of a manganese-centered tubular boron cluster (MnB16 (-)), which is characterized by photoelectron spectroscopy and ab initio calculations. The relatively simple pattern of the photoelectron spectrum indicates the cluster to be highly symmetric. Ab initio calculations show that MnB16 (-) has a Mn-centered tubular structure with C4v symmetry due to first-order Jahn-Teller effect, while neutral MnB16 reduces to C2v symmetry due to second-order Jahn-Teller effect. In MnB16 (-), two unpaired electrons are observed, one on the Mn 3dz(2) orbital and another on the B16 tube, making it an unusual biradical. Strong covalent bonding is found between the Mn 3d orbitals and the B16 tube, which helps to stabilize the tubular structure. The current result suggests that there may exist a whole class of metal-stabilized tubular boron clusters. These metal-doped boron clusters provide a new bonding modality for transition metals, as well as a new avenue to design boron-based nanomaterials.

Electronic Structure and Chemical Bonding in the Double Ring Tubular Boron Clusters

We analyzed the chemical bonding phenomena of the boron B2n tubes (n = 10–14). The B2n tubes represent stable hollow cylinders each having a double ring (DR) among pure boron clusters. The shapes of the molecular orbitals of a B2n DR can be predicted by the eigenstates of a simple model of a particle on a hollow cylinder, which shows both radial and tangential components. In a DR tube, strong diatropic responses to external magnetic field occur in both radial and tangential types of electrons, and thus confer it a characteristic tubular aromaticity. The presence of a consistent aromatic character contributes to the high thermodynamic stability of a DR. The number of electrons in a hollow cylinder should attain (4N + 2M) with M = 0 and 1 for both series of radial and tangential electrons, depending on the number of nondegenerate MOs occupied, to properly fill the electron shells. In the case of B20, M = 1 for both radial and tangential electrons, and the classical Huckel counting rule is thus recovered.

Improved hot-stamping analysis of tubular boron steel with direct measurement of heat convection coefficient

There are two types of hot-stamping processes, direct and indirect, depending on the sequence of the heating, forming, and quenching steps and the method used for each step. In this study, an indirect hot-stamping process consisting of forming at room temperature, heating, and water quenching was applied to develop a coupled torsion beam axle. The analysis results indicated that the application of the heat convection coefficient is critical in the simulations and must take into account the temperature and specific location in the model to ensure the accuracy of the heating and quenching analysis. The heat convection coefficients used in the analysis were directly measured at various positions of the tube (e.g., outside, inside, and bending region) using thermocouples, and the final values were determined through correlation between the actual tests and numerical analysis. The experimental and simulated final deformed shape and temperature distribution were in good agreement.

Quantum-chemical calculations of the piezoelectric characteristics of boron nitride and carbon nanotubes

The piezoelectric characteristics of boron-nitride and carbon nanotubes were calculated. The electronic structure of nanotubes was studied using the quantum-chemical semiempirical MNDO method within a molecular-cluster model. The piezoelectric constants e zzz, e xzz, and e xxx of boron nitride nanotubes of two structural modifications (n, n) (n = 5, 6, ..., 9) and (n, 0) (n = 6, 7, ..., 12) were calculated. The values of the piezoelectric constants e zzz of tubular boron nitride are found to be close in order of magnitude to the respective values obtained using nonempirical calculation methods. The piezoelectric constant e xzz of a (6, 6) carbon nanotube doped with substitutional point defects was calculated.

Electronic and mechanical properties of planar and tubular boron structures

We report the results of first-principles calculations showing that boron can form a wide variety of metastable planar and tubular forms with unusual electronic and mechanical properties. The preferred planar structure is a buckled triangular lattice that breaks the threefold ground state degeneracy of the flat triangular plane. When the plane is rolled into a tube, the ground state degeneracy leads to a strong chirality dependence of the binding energy and elastic response, an unusual property that is not found in carbon nanotubes. The achiral $(n,0)$ tubes derive their structure from the flat triangular plane. The achiral $(n,n)$ boron nanotubes arise from the buckled plane, and have large cohesive energies and different structures as a result. $(n,n)$ boron nanotubes have an internal relaxation mechanism that results in a very low Poisson ratio. The strong variation in elastic properties of boron nanotubes makes them the mechanical analogue of carbon nanotubes, and may make them ideal candidates for applications in composite materials and nanoelectromechanical systems.

Insulating tubular BN sheathing on semiconducting nanowires.

An effective method was developed for generation of insulating tubular boron nitride (BN)-sheathed nanostructures. ZnS nanowires and multilayered Si-SiO2 nanowires were successfully sheathed with insulating tubular BN-forming nanocables. Both the semiconductor nanowire cores and the BN sheaths are crystalline with well-uniform morphologies.

Characterization of tubular boron nitride filaments

Characterization of tubular boron nitride filaments