SiC-doped boron nitride nanotubes: computations of 11B and 14N quadrupole coupling constants

Abstract  

Density-functional theory calculations have been performed to investigate the properties of the electronic structures of silicon–carbon-doped boron nitride nanotubes (BNNTs). The geometries of zigzag and armchair BNNTs were initially optimized and the quadrupole coupling constants subsequently calculated. The results indicate that doping of B and N atoms by C and Si atoms has more influence on the electronic structure of the BNNTs than does doping of B and N atoms by Si and C atoms. The changes of the electronic sites of the N atoms are also more significant than those of the B atoms.     

Purification of boron nitride nanotubes through polymer wrapping

An effective method was proposed to remove obstinate boron nitride phase impurities in boron nitride nanotubes (BNNTs). The method is based on strong interactions between BNNTs and a conjugated polymer wrapping them and significant weight and size difference between BNNTs and impurities. The as-grown samples and purified samples were compared through detailed characterization, using scanning electron microscopy, transmission electron microscopy, and Raman and Fourier transformed infrared spectroscopy. The results reveal that impurities are effectively removed and resultant BNNTs possess perfect crystallization.     

Ab initio theoretical study of non-covalent adsorption of aromatic molecules on boron nitride nanotubes

We have studied non-covalent functionalization of boron nitride nanotubes (BNNTs) with benzene molecule and with seven other different heterocyclic aromatic rings (furan, thiophene, pyrrole, pyridine, pyrazine, pyrimidine, and pyridazine, respectively). A hybrid density functional theory (DFT) method with the inclusion of dispersion correction is employed. The structural and electronic properties of the functionalized BNNTs are obtained. The DFT calculation shows that upon adsorption to the BNNT, the center of aromatic rings tend to locate on top of the nitrogen site. The trend of adsorption energy for the aromatic rings on the BNNTs shows marked dependence on different intermolecular interactions, including the dispersion interaction (area of the delocalized π bond), the dipole-dipole interaction (polarization), and the electrostatic repulsion (lone pair electrons). The DFT calculation also shows that non-covalent functionalization of BNNTs with aromatic rings can give rise to new impurity states within the band gap of pristine BNNTs, suggesting possible carrier doping of BNNTs via selective adsorption of aromatic rings.     

A simple approach to covalent functionalization of boron nitride nanotubes

A novel and simple method for the preparation of chemically functionalized boron nitride nanotubes (BNNTs) is presented. Thanks to a strong oxidation followed by the silanization of the surface through 3-aminopropyl-triethoxysilane (APTES), BNNTs exposing amino groups on their surface were successfully obtained. The efficacy of the procedure was assessed with EDS and XPS analyses, which demonstrated a successful functionalization of ~15% boron sites. This approach opens interesting perspectives for further modification of BNNTs with several kinds of molecules. Since, in particular, biomedical applications are envisaged, we also demonstrated in vitro biocompatibility and cellular up-take of the functionalized BNNTs.     

DNA‐Mediated Assembly of Boron Nitride Nanotubes

The dispersion of nanomaterials in solutions is of primary importance for the improvement of their processability, but it also provides a way to investigate phase behavior and to assemble nanostructures in solvents. Several methods based on different interactions have been developed to disperse carbon nanotubes, whereas little development has been made for their boron nitride nanotube (BNNT) counterparts. A direct way to obtain long‐range ordering may be through spontaneous nematic ordering in solutions at sufficiently high concentrations of the nanomaterial fraction. Lyotropic nematics have been observed in various organic and inorganic systems. In this work, the strong interactions between DNA and BNNTs were exploited to fabricate high‐concentration BNNTs aqueous solutions by a simple method, and then, for the first time, nematic ordered ensembles of BNNTs were obtained by filtration. It is proposed that a localized liquid‐crystal phase appears during filtration, as the ordering trend for the BNNTs was found to depend on the concentration of the aqueous solutions of the BNNTs. Moreover, BNNTs were successfully localized on a predefined area by using a thiol‐modified DNA–BNNT hybrid.     

Nitrogen monoxide storage and sensing applications of transition metal–doped boron nitride nanotubes: a DFT investigation

The structural properties, electronic properties, and adsorption abilities for nitrogen monoxide (NO) molecule adsorption on pristine and transition metal (TM = V, Cr, Mn, Nb, Mo, Tc, Ta, W, and Re) doping on B or N site of armchair (5,5) single-walled boron nitride nanotube (BNNT) were investigated using the density functional theory method. The binding energies of TM-doped BNNTs reveal that the Mo atom doping exhibits the strongest binding ability with BNNT. In addition, the NO molecule weakly interacts with the pristine BNNT, whereas it has a strong adsorption ability on TM-doped BNNTs. The increase in the adsorption ability of NO molecule onto the TM-doped BNNTs is due to the geometrical deformation on TM doping site and the charge transfer between TM-doped BNNTs and NO molecule. Moreover, a significant decrease in energy gap of the BNNT after TM doping is expected to be an available strategy for improving its electrical conductivity. These observations suggest that NO adsorption and sensing ability of BNNT could be greatly improved by introducing appropriate TM dopant. Therefore, TM-doped BNNTs may be a useful guidance to be storage and sensing materials for the detection of NO molecule.

     

Dually-functionalized boron nitride nanotubes to target glioblastoma multiforme

Boron nitride nanotubes (BNNT) were functionalized under mild conditions, using a difunctional amine, such as glycine, with one of three targeting ligands, folic acid, a nerve growth factor, or an antibody against nerve growth factor. In addition, non-fouling BNNTs were obtained by a facile and versatile, non-destructive method via controlled surface-initiated grafting of polyzwitterions. The BNNTs were loaded with a fluorescent probe for convenient imaging of glioblastoma multiforme cells treated with BNNTs. BNNTs bearing targeting factors on their outer surface demonstrated an increased efficiency of internalization in glioblastoma multiforme cells, compared to non-modified BNNTs. The degree of internalization was affected both by the nature of the ligand/agonist linked to the BNNTs surface and by the presence of serum proteins. The polyzwitterion grafts prevented the spontaneous adsorption of serum proteins on the BNNTs.     

Glass fabrics self-cracking catalytic growth of boron nitride nanotubes

Glass fabrics were used to fabricate boron nitride nanotubes (BNNTs) with a broad diameter range through a combined chemical vapor deposition and self-propagation high-temperature synthesis (CVD-SHS) method at different holding times (0min, 30min, 90min, 180min and 360min). SEM characterization has been employed to investigate the macro and micro structure/morphology changes of the glass fabrics and BNNTs in detail. SEM image analysis has provided direct experimental evidences for the rationality of the optimized self-cracking catalyst VLS growth mechanism, including the transformation situations of the glass fabrics and the BNNTs growth processes respectively. This paper was the further research and compensation for the theory and experiment deficiencies in the new preparation method of BNNTs reported in our previous work. In addition, it is likely that the distinctive self-cracking catalyst VLS growth mechanism could provide a new idea to preparation of other inorganic functional nano-materials using similar one-dimensional raw materials as growth templates and catalysts.     

锂化硼氮纳米管的二阶非线性光学理论研究

基于硼氮纳米管(BNNTs), 研究了多重锂化硼氮纳米管Li_n-(n,0,l)BNNTs(n=6和8, l=2~4)的结构与非线性光学性质. 研究表明, 在Li_n-(n,0,l)BNNTs中, Li原子上的自然键轨道电荷接近+1(0.769～0.827 e), 表明Li原子上的电子转移到了硼氮纳米管上, 从而形成了多重锂盐. 同时发现, 增加管长和拓宽管径都可有效地增加体系的一阶超极化率. 更重要的是, Li_n-(n,0,l)BNNTs的紫外-可见吸收主要发生在270~290 nm附近, 且当管长增加时, Li_n-(n,0,l)BNNT的紫外-可见吸收光谱发生了蓝移, 改善了非线性与透光性之间的关系. 此外, Li_n-(n,0,l)BNNTs还具有良好的稳定性[垂直电离势(VIP)=5.85～6.0 eV].     

A co-precipitation and annealing route to the large-quantity synthesis of boron nitride nanotubes

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.     

Perfectly dissolved boron nitride nanotubes due to polymer wrapping

We report for the first time that boron nitride nanotubes (BNNTs) may be dissolved in organic solvents by wrapping them with a polymer. Transmission electron microscopy and cathodoluminescence studies indicate the strong pi-pi interactions between BNNTs and the polymer. A band gap ranging from 5.2 to 5.5 eV was documented for the BNNTs independent of their geometrical characteristics by using ultraviolet-visible absorption experiments on composite films and thin BNNT films prepared from solutions.     

A Particulate Biochromatographic Support for the Research of Arginase Inhibitors Doped with Nanomaterials: Differences Observed Between Carbon and Boron Nitride Nanotubes. Application to Three Plant Extracts

The arginase enzyme was bound to porous silica using a reactive polymer where two types of nanomaterials were entrapped, i.e., carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs). For the first time, it was shown that BNNTs were highly efficient for increasing the performance of a particulate bioactive support. Also, we demonstrated that BNNTs enhanced more strongly this effect in comparison with CNTs. In addition, with this novel bioactive support, the relative IC50 values of the well-known arginase inhibitors were found to be in agreement with those derived by the conventional spectrometric method. It was shown the ethylacetate extract of the roots of Spirotropis longifolia (SL) and of the ethanol extract of sunflower (Helianthus annuus) seed (SS) and Lonicera japonica Thunb, i.e., honeysuckle (H) on the arginase activity inhibited the enzyme activity.     

Electronic structures of organic molecule encapsulated BN nanotubes under transverse electric field

The electronic structures of boron nitride nanotubes (BNNTs) doped by different organic molecules under a transverse electric field were investigated via first-principles calculations. The external field reduces the energy gap of BNNT, thus makes the molecular bands closer to the BNNT band edges and enhances the charge transfers between BNNT and molecules. The effects of the electric field direction on the band structure are negligible. The electric field shielding effect of BNNT to the inside organic molecules is discussed. Organic molecule doping strongly modifies the optical property of BNNT, and the absorption edge is redshifted under static transverse electric field.     

Origins of thermodynamically stable superhydrophobicity of boron nitride nanotubes coatings

Superhydrophobic surfaces are attractive as self-cleaning protective coatings in harsh environments with extreme temperatures and pH levels. Hexagonal phase boron nitride (h-BN) films are promising protective coatings due to their extraordinary chemical and thermal stability. However, their high surface energy makes them hydrophilic and thus not applicable as water repelling coatings. Our recent discovery on the superhydrophobicity of boron nitride nanotubes (BNNTs) is thus contradicting with the fact that BN materials would not be hydrophobic. To resolve this contradiction, we have investigated BNNT coatings by time-dependent contact angle measurement, thermogravimetry, IR spectroscopy, and electron microscopy. We found that the wettability of BNNTs is determined by the packing density, orientation, length of nanotubes, and the environmental condition. The origins of superhydrophobicity of these BNNT coatings are identified as (1) surface morphology and (2) hydrocarbon adsorbates on BNNTs. Hydrocarbon molecules adsorb spontaneously on the curved surfaces of nanotubes more intensively than on flat surfaces of BN films. This means the surface energy of BNNTs was enhanced by their large curvatures and thus increased the affinity of BNNTs to adsorb airborne molecules, which in turn would reduce the surface energy of BNNTs and make them hydrophobic. Our study revealed that both high-temperature and UV-ozone treatments can remove these adsorbates and lead to restitution of hydrophilic BN surface. However, nanotubes have a unique capability in building a hydrophobic layer of adsorbates after a few hours of exposure to ambient air.     

Tremendous spin-splitting effects in open boron nitride nanotubes: application to nanoscale spintronic devices

Our calculations demonstrate that the intrinsic magnetism of boron nitride nanotubes (BNNTs) can be induced by their open ends, and the resulting magnetic moment is sensitive to the chirality of BNNTs. It is found that BNNTs, a pure sp-electron system, present a tremendous spin-splitting larger than 1 eV and that B-rich-ended and N-rich-ended BNNTs exhibit "conjugate", spin-polarized, deep-gap states. Tremendous spin-splitting effects combined with considerable local spin-polarizations at the open ends make BNNTs significant for applications of nanoscale spintronics such as spin-polarized electron emitters.     

Chemisorption of NH3 at the open ends of boron nitride nanotubes: a DFT study

Considering the thermodynamic aspects and reaction pathways of chemical adsorption of NH₃ molecule at the open ends of boron nitride nanotubes (BNNTs), theoretically, it was found that the open-ended BNNTs are able to cleave the N–H bond of NH₃ via a one- or two-stepwise mechanism. The N-enriched and B-enriched open-ended BNNTs show a nucleophilic and electrophilic behavior toward the NH₃, respectively. Besides, some effects of this chemical adsorption on the electronic properties of BNNTs were explored.     

DFT studies of functionalized zigzag and armchair boron nitride nanotubes as nanovectors for drug delivery of collagen amino acids

The interaction of collagen amino acids with (5, 5) armchair and (9, 0) zigzag single-walled boron nitride nanotubes (BNNTs) are studied using density functional theory. Our results show that the BNNTs can act as a suitable drug delivery vehicle of collagen amino acids within biological systems. DFT-LDA/DNP calculations revealed that the binding and solvation energies were negative for (5, 5)/(9, 0) BNNTs–collagen amino acid complexes implying the thermodynamic favorability and spontaneous interactions of collagen amino acids with BNNTs sidewall. These results were extremely relevant in order to identify the potential applications of functionalized BNNTs as drug delivery systems.     

Over 1.0 mm-long boron nitride nanotubes

Over 1.0 mm boron nitride nanotubes (BNNTs) were successfully synthesized by an optimized ball milling and annealing method. The annealing temperature of 1100 °C is crucial for the growth of the long BNNTs because at this temperature there is a fast nitrogen dissolution rate in Fe and the B/N ratio in Fe is 1. Such long BNNTs enable a reliable single tube configuration for electrical property characterization and consequently the average resistivity of the long BNNTs is determined to be 7.1 ± 0.9 × 10⁴ Ω cm. Therefore, these BNNTs are promising insulators for three dimensional microelectromechanical system.     

Atomic and electronic structures of fluorinated BN nanotubes: computational study

The atomic and electronic structures of fluorinated BN nanotubes (BNNTs) were investigated by generalized gradient approximation (GGA) density functional theory (DFT). The reaction energies of F2 with pristine single-walled BNNTs to form fluorinated BNNTs are exothermic up to 50% coverage. At lower F coverages (below 50%), fluorines prefer external attachments to boron atoms and stay as far away as possible. At 50% F coverage, fluorines favor attachment to all the boron atoms of the outer surface energetically. Such preferable fluorination patterns and highly exothermic reaction energies hold true for double-walled (and multiwalled) BNNTs when the outer tube surface is considered. Fluorination transforms BNNTs into p-type semiconductors at low F coverages, while high F coverages convert BNNTs into p-type conductors. Therefore, the electronic and transport properties of BNNTs can be engineered by fluorination, and this provides potential applications for fluorinated BNNTs in nanoelectronics.     

A convenient catalytic approach to synthesize straight boron nitride nanotubes using synergic nitrogen source

Straight boron nitride nanotubes (BNNTs) with pure hexagonal phase were conveniently prepared by heating the mixture of Mg(BO₂)₂ · H₂O, NH₄Cl, NaN₃ and Mg powder in an autoclave at 600 °C for 20–60 h. These BNNTs had diameters mainly ranging 30–300 nm and lengths up to 5 μm, and a majority of them had at least one closed end. Besides the traditional end tips, additional cone-like tips were frequently found to be attached on the BNNTs. The effects of temperature, reactants and the possible mechanism of the catalytic formation of the BNNTs are discussed.