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Nanoscale materials have gained considerable interest because of their special properties and wide range of applications. Many types of boron nitride at the nanoscale have been realized, including nanotubes, nanocones, fullerenes, tori, and graphene sheets. The connection of these structures at the nanoscale leads to merged structures that have enhanced features and applications. Modeling the joining between nanostructures has been adopted by different methods. Namely, carbon nanostructures have been joined by minimizing the elastic energy in symmetric configurations. In other words, the only considerable curvature in the elastic energy is the axial curvature. Accordingly, because it has nanoscale structures similar to those in carbon, BN can also be joined and connected by using this method. On the other hand, different methods have been proposed to consider the rotational curvature because it has a similar size. Based on that argument, the Willmore energy, which depends on both curvatures, has been minimized to join carbon nanostructures. This energy is used to identify the joining region, especially for a three-dimensional structure. In this paper, we expand the use of Willmore energy to cover the joining of boron nitride nanostructures. Therefore, because catenoids are absolute minimizers of this energy, pieces of catenoids can be used to connect nanostructures. In particular, we joined boron nitride fullerene to three other BN nanostructures: nanotube, fullerene, and torus. For now, there are no experimental or simulation data for comparison with the theoretical connecting structures predicted by this study, which is some justification for the suggested simple model shown in this research. Ultimately, various nanoscale BN structures might be connected by considering the same method, which may be considered in future work. [ABSTRACT FROM AUTHOR]

A predictive model for determination partition coefficient (log P) of armchair polyhex BN nanotubes by using simple descriptors was built. The relationship between the octanol-water log P and quantum chemical descriptors, electric moments, and topological indices of some armchair polyhex BN nanotubes with various lengths and fixed circumference are represented. Based on density functional theory electric moments and physico-chemical properties of those nanotubes are calculated. [ABSTRACT FROM AUTHOR]

Density functional theory calculations were employed to investigate the electronic and structural behavior of a pristine boron nitride nanotube (BNNT) and a single-walled carbon nanotube (CNT) toward carbonyl sulfide (COS) gas adsorption. It was found that when a COS molecule is adsorbed on the CNT, an energy of about 6.0 kcal/mol is released and the HOMO-LUMO gap of CNT is decreased by about 38.7%. Thus, the electrical conductivity of the CNT is significantly increased, indicating that the CNT can produce an electronic noise at the presence of COS molecules. The recovery time for the COS desorption from the surface of CNT is calculated to be very short (~ 0.24 μs). Also, our finding and the literature review indicated that the CNT can selectively detect the COS gas among different ones including H 2 , H 2 CO, H 2 S, O 2 , etc. Compared to the CNT, the BNNT shows a higher reactivity toward the COS, but its electronic properties are insensitive to this gas. The adsorption energy of COS on the BNNT was calculated to be about 11.3 kcal/mol. [ABSTRACT FROM AUTHOR]

First principles calculations within the spin polarized density functional approximation have been addressed to investigate the energetic stability, electronic and optical properties of defective BN nanotubes. Our results show that the presence of carbon impurities interacting with vacancies gives rise to defective electronic levels inside the nanotube band gap. By calculating the absorbance index, we have obtained a strong inter-band optical absorption in the visible region (around 2.1 eV) showing that defective BN nanotubes could be an efficient catalytic semiconductor material to be used within solar energy for water splitting. In addition, we observe that the adsorption energy for one and two H 2 molecules on the defective surface is in the desired window for the system to be useful as a hydrogen storage medium. [ABSTRACT FROM AUTHOR]

We have applied density functional calculations to investigate carbon ad-dimer (CD) and boron-nitride ad-unit (BNU) defect formation in armchair ( n , n ), n =4, 5, and 6, as well as zigzag (7, 0) BN nanotubes. According to our results, tube diameter, orientations of defects on the sidewall of BN nanotubes and the pyramidalization angles affect the BN ad-unit defect formation, such that the defect formation in the (4, 4) armchair BNNTs with the highest curvature is the most favorable while the defect in the (7, 0) BNNT which have similar diameter with the (4, 4) armchair BNNT cost larger formation energy because of smaller pyramidalization angles. Replacing of BN units with carbon dimers in defect sites leads to the removing frustrated B–B and N–N bonds, and an energetically favorable configuration for defective BNNTs. Then, the defect formation energies of CD defective BNNTs are all negative values, and also the carbon doping of defective sites of BNU defective BNNTs are exothermic and almost independent of the tube diameter. BNU and CD defects reduce the HOMO–LUMO gaps of BNNTs while electronic structures of host materials does not obviously change and only local energy levels appears in the DOS plots. [ABSTRACT FROM AUTHOR]

Highlights: [•] The adsorption phenomena of H2S, HS, H2O2, and H2CO upon Ga-doped (8, 0) and (5, 5) BN nanotubes are studied using DFT calculations. [•] The significant charge transfers confirm the DOS changes near the Fermi level. [•] The interaction energies introduce Ga-doped (8, 0) BNNT as a promising sensor. [ABSTRACT FROM AUTHOR]

A novel co-precipitation and annealing route to the large-quantity synthesis of boron nitride nanotubes (BNNTs), using amorphous boron powder, iron nitrate nonahydrate (Fe(NO3)3·9H2O) and urea (CO(NH2)2) as the raw materials, was demonstrated. An intermediate Fe(OH)3·B was firstly prepared through a co-precipitation process and then annealed in flowing ammonia atmosphere at 1200 °C. It was found that the heat treatment at 800 °C during the annealing process could favor the growth of BNNTs. The BNNTs had an average diameter of 70 nm and possessed bamboo and quasi-cylindrical structures. The annealing temperature greatly affected the formation of BNNTs. Only BN particles could be obtained at lower temperature (e.g. 1100 °C), whereas thorn-like nanosheet-decorated BNNTs were fabricated at higher temperature (e.g. 1300 °C). A combination mechanism of solid–liquid–solid (SLS) and vapor–liquid–solid (VLS) model was suggested to be responsible for the growth of BNNTs. [ABSTRACT FROM AUTHOR]

Abstract: The adsorption of the biopolymer chitosan on the (5,0) and (5,5) boron nitride nanotubes (BNNTs) was theoretically analyzed by Molecular Simulations. The calculations were done using the well known density-functional theory within the local density approximation; the exchange-correlation term was modeled with the Perdew-Wang parameterization. The structural stability was based on the obtention of the minimum energy and non-complex vibrational frequencies. Different sites, charge (neutral, cation and anion) and orientations of chitosan, using the monomer unit, were considered. For the (5,5) nanotube, the minimum energy site corresponds to that when the monomer (for all charges assigned) is perpendicular to the nanotube; only structural stability was found in the anion assignment for the (5,0) nanotube. The chemisorption process is through the amine group modifying the semiconductor character of the nanotube to semimetallic one, with ionic properties, suggesting their solubilization on hydrophilic nanomaterials. [Copyright &y& Elsevier]

Abstract: In this paper, we have studied the boron adsorption induced magnetism in zigzag boron nitride nanotubes (BNNTs) and BN hexagonal sheets (h-BN sheet) as well as the magnetic interaction between the B-induced magnetic moment by using the first principle spin-polarized density functional calculations. It is found that the adsorption of a single B adatom on the external surface of BNNTs and h-BN sheet can induce spontaneous magnetization in the B-BNNTs system with a local magnetic moment of 1.0μB per B adatom regardless of the tube diameter and the bonding between the B atom and the BNNTs/BN sheets. An analysis of orbital hybridization indicates that two valence electrons participate in the bonding and the remaining one electron of the B adatom are confined at the adsorption site and contribute to the magnetism accordingly. The magnetic interactions between the B-induced magnetic moments on BNNTs have been explored. The magnetic B-BNNTs may be experimentally accessible when the coverage of Bad adatoms adsorbed on the external surface of BNNTs is low. [Copyright &y& Elsevier]

The vibrational contribution to static and dynamic (hyper)polarizabilities for the zigzag ( n,0) family of BN nanotubes, with n ranging from (6,0) to (36,0), has been obtained. Calculations were done by the finite field nuclear relaxation (FF-NR) method for periodic systems, newly implemented in the CRYSTAL code, using the Coupled Perturbed Kohn-Sham (CPKS) scheme at the B3LYP/6-31G* level for the required electronic properties. Both transverse and transverse-longitudinal tensor components are determined by applying finite, i.e. static, fields in the transverse direction. The magnitude of the vibrational term increases with the radius of the nanotube as determined by the increase in the field-induced geometric deformation. The resulting vibrational (hyper)polarizability varies from being dominant to negligible, when compared with the corresponding static electronic contribution. This depends upon the radius, as well as the property and the component, in a systematic manner. The extension to longitudinal components, not yet available, will be implemented next. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012 [ABSTRACT FROM AUTHOR]

Abstract: Boron nitride (BN) nanotubes with different yield and structure were synthesized on stainless-steel substrates, by heating mixture powders of amorphous boron and iron oxide (Fe2O3) at 1300°C in flowing ammonia atmosphere. It was found that Fe2O3 could affect the yield and structure of BN nanotubes dramatically through its adding amount in the starting materials. When the Fe2O3/B molar ratio was small, pure but low-yield BN nanotubes were obtained. Nearly no particle was observed in the product. Meanwhile, the nanotubes were generally hollow with very few B–O–Si–Mn species filled within the tube cavity or enwrapped in the walls. The yield of nanotubes obviously rose with the increase of Fe2O3/B ratio. However, the amounts of B–N–O–Si–Mn particles in the product (from which nanotubes grew in a radial pattern) and B–O–Si–Mn species within the cavity or the walls of the nanotubes also increased. The growth mechanism of the BN nanotubes was believed to be in the framework of vapor–liquid–solid (VLS) model. [Copyright &y& Elsevier]

Abstract: This article presents an overview of the up-to-date developments in boron nitride nanotubes (BNNTs), including theory, fabrication, structure, physical properties, chemical functionalization and applications. Soon after the discovery of carbon nanotubes, BNNTs were theoretically predicted, followed by their successful fabrication by arc-discharge in 1995. Subsequently, various methods were developed for the BNNT synthesis, although till now, the growth of highly pure single-walled BNNTs at large quantities remains a challenge. The physical property investigations reveal that BNNTs’ exhibit a stable wide band gap, superb mechanical strength, high thermal conductivity, ultra-violet light emission, etc. All these properties build up the solid basis for their future technological applications. Chemical modification is also a decent approach to adjust the BNNTs properties. In recent years the yield of multi-walled BNNTs has reached the grams level, that can allow their detailed chemical functionalization studies. So far, many kinds of functionalizations through different weak interactions and covalent bonding were developed. These treatments improved BNNT dispersions in solvents and extended their fields of applications. Moreover, some application-related studies on multi-walled BNNTs, such as composites fabrication, hydrogen storage, biocompatibility, and mechanical, and electrical breakdown tests have also been started in recent years. [ABSTRACT FROM AUTHOR]

Abstract: The unsatisfactory stability of CNT under high temperature or subject to strong oxidants has limited the potential use of p- and n-type field-effect transistors (FETs). Promisingly, boron nitride (BN) nanotubes are known to have the excellent resistance to oxidant and thermal stability at high temperature as well as the uniform electronic properties, which rends their possible application as alternative FET device. In this paper, through the theoretical computation of the noncovalent functionalization of BN nanotube by various aromatic molecules (including C10H8, C14H10, porphyrin, DDQ, and TCNQ molecules), we for the first time evaluate its possibility as a candidate of stable FET device. We find that: (i) these aromatic molecules can be stably adsorbed on the studied BN with the adsorption energy ranging from −0.22 (C10H8) to −0.42eV (porphyrin); (ii) the adsorption of electrophilic molecules on the outer sidewall of BN nanotube realizes a p-type semiconductor with a smaller band gap (~0.90eV); (iii) exoherdral adsorption of nucleophilic aromatic molecules leads to an n-type semiconductor. This novel BN nanotube-based material offers great promise for molecule electronics in terms of their good stability. [Copyright &y& Elsevier]

The preferable configuration and electronic structure of several types of free radical functionalized boron nitride nanotubes (BNNTs) were investigated by using density functional theory computations. All the free radicals have strong interaction with B atom in the tube, in spite of the electroaffinity of the radicals. However, though a large charge is transferred from tubes to NH2, OH or CN radicals, little change happens to the electronic structure of BNNTs, while COOH and COCl radicals introduce half-filled impurity levels around the Fermi level. Higher functionalization concentration leads to multiple impurity states around the Fermi level, and makes BNNTs p-type semiconductors. [ABSTRACT FROM AUTHOR]

Abstract: Using ab initio calculations we investigated the hydrogen storage in single-walled boron nitride nanotubes. We present the nature of hydrogen interaction in selected sites of a (5,5) and (9,9) BN nanotube. Our results show that BN nanotubes are preferable to carbon nanotubes for hydrogen storage applications due to their heteropolar binding nature of their atoms. In addition, by increasing the nanotube''s diameter – decreasing its curvature, more efficient binding energies of hydrogen can be achieved. [Copyright &y& Elsevier]

Abstract: Nitride nanotubes (BN-NTs) was synthesized by chemical vapor deposition (CVD) using BCl3 and NH3 at relatively low temperature within the channels of mesoporous silica SBA-15. TEM images confirmed the existence of BN-NTs. The BN-NTs were of uniform diameter about 7 nm, which was consistent with the channel diameter of the template SBA-15. Using this approach, it is easy to control the diameter of BN-NTs by adjusting the diameter of the channel of mesoporous silica host. [Copyright &y& Elsevier]

Boron nitride (BN) nanotubes were filled with nanowires made of Mg-containing compounds: a metallic Mg-based material; a MgO-based phase; and a thermally and chemically unstable oxygen-rich MgO2-based phase. Crystallography of the tubes and their fillings was studied using high-resolution transmission electron microscopy, electron energy loss spectroscopy and energy dispersive X-ray analysis. These compounds displayed markedly different behavior inside BN nanotube channels during in situ TEM electron-irradiation-induced and thermal heating. The interplay between phases, their morphology and phase transformations were observed under heating. Thus the applicability of chemically and thermally stable BN nanotubes as one-dimensional nanocrucibles for novel nanoscale metallurgy/chemistry in the practically important Mg–O system has been thoroughly documented. This opens up a pathway for BN nanotube-channel-confined reactions in other inorganic systems. [Copyright &y& Elsevier]

Continuous filling of BN nanotubes with Co has been obtained using high-temperature substitution synthesis from C nanotubes; this involves filling of C nanotubes with a Co melt accompanied with simultaneous C→BN conversion within tubular layers. Analytical transmission electron microscopy shows that 3d-transition metals, like Co, do not form compounds inside BN nanotubes; rather they form solid solutions with marginal C, N and/or B doping. Ordering of interstitial impurities in a Co crystal lattice has been frequently observed, which exclusively exhibits a certain threefold superlattice. Structural orientation relationship always exists between fillings and BN nanotubes, indicative of an epitaxial crystallization mode of an encapsulated Co filling on a BN innermost wall template. A prevailing crystallization phenomenon shows a certain {0 1¯ 1} plane of cubic Co coincides BN filament with an orientation relation of 〈0 1 1〉Co//〈1¯ 2 1¯ 0〉BN and 〈4 5 5〉Co//〈0 1 1¯ 0〉BN. This phenomenon possibly interprets the transition metals, Fe, Co and Ni, to be the most effective catalysts for the formation of C and BN nanotubes. [Copyright &y& Elsevier]

We present ab initio calculations of phonons in single-wall boron-nitride (BN) nanotubes. Raman and infrared (IR) active modes of isolated and infinitely long tubes are evaluated according to the nonsymmorphic rod groups of BN nanotubes. For tubes of finite length, the selection rules are less restrictive and give rise to additional modes, which may be observed in Raman and IR spectroscopy with an intensity depending on the tube length. Bundling of tubes is shown to have little effect on the phonon frequencies. However, arranging tubes in a large periodic array (larger than the wavelength of incoming light) gives rise to a strong frequency shift (longitudinal-optical-transverse-optical splitting) of certain modes due to the establishing of a macroscopic electric field. Modes of A1 symmetry experience a shift for laser light along the tube axis and E1 modes are split for light incidence in the perpendicular direction. [ABSTRACT FROM PUBLISHER]

BN nanotubes (BNNTs) are tubular structural materials similar to carbon nanotubes. Owing to their excellent mechanical strength, high thermal conductivity, good thermal and chemical stability, super hydrophobicity and excellent electrical insulation, they have broad application prospects in the fields of metallurgy, chemical industry, environment, catalysis and biomedicine, etc. The advantages, shortcomings and influencing factors of arc discharge method, chemical vapor deposition method and ball milling nitridation reaction method to prepare BNNTs were briefly summarized. In addition, the future research focus and direction of BNNTs were proposed. [ABSTRACT FROM AUTHOR]

Abstract: Using density functional theory calculations, we predict that single-walled hemispherical-caped boron nitride (BN) nanotubes with small diameters can be produced via the coalescence of stable nanoclusters. Specifically, the assembly of B n N n () clusters exhibiting particularly high stability and leading to armchair and BN nanotubes, respectively, are considered. The formed finite-length BN nanotubes have semiconducting properties with wide band gaps attractive to nano-device applications. [Copyright &y& Elsevier]

Boron nitride (BN) nanotubes were fabricated by arc-melting LaB6 and boron/FeOx powder compacts in nitrogen/argon gas atmosphere. The nanotubes were studied by high-resolution electron microscopy and energy dispersive X-ray spectroscopy. The diameters of the BN nanotubes are in the range of 10–100 nm. The present work indicates that La could be a good candidate as a catalyst to produce the BN fullerene-like materials by changing the ratio of LaB6/B. [Copyright &y& Elsevier]

Using the density functional theory, we report energetics and electronic structure of double-walled BN nanotubes, (n,0)@(15,0) and (m,0)@(20,0). We find that the most favorable double-walled nanotubes are (7,0)@(15,0) and (12,0)@(20,0) in which the inter-wall distance is about 3 A˚. We observe that the energy gap of double-walled BN nanotubes narrows due to the hybridization between σ and π states. We also find that the nearly free-electron state of the nanotubes induces peculiar charge transfer from the π states to the inter-wall region. [Copyright &y& Elsevier]

Conditions of H2 gas storage in B36N36 and C60 clusters, which were considered as a cap structure of boron nitride and carbon nanotubes, were predicted by first-principle single-point energy calculations. As a result of the calculations, H2 molecules would be introduced from hexagonal rings of the cage structure. BN fullerene materials store H2 molecules easier than carbon fullerene materials, and its stability for high temperature is expected to be good. [Copyright &y& Elsevier]

Structural dynamics and changes in electronic structures driven by photoexcited carriers are critical issues in both semiconducting and optoelectronic nanodevices. Herein, a phase diagram for the transient states and relevant dynamic processes in multiwalled boron nitride nanotubes (BNNTs) has been extensively studied for a full reversible cycle after a fs-laser excitation in ultrafast TEMs, and the significant structural features and evolution of electronic natures have been investigated using pulsed electron diffraction and femtosecond-resolved electron energy-loss spectroscopy (EELS). It is revealed that nonthermal anisotropic alterations of the lattice apparently precede the phonon-driven thermal transients along the radial and axial directions. Ab initio calculations support these findings and show that electrons excited from the π to π* orbitals in the BN nanotubes weaken the intralayer bonds while strengthening the interlayer bonds along the radial direction. Importantly, time-resolved EELS measurements show contraction of the energy bandgap after fs-laser excitation associated with nonthermal structural transients. This fact verifies that laser-induced bandgap renormalization in semiconductors can essentially be correlated with both the rapid processes of excited carriers and nonthermal lattice evolution.