Theoretical study of addition reactions of heavy carbenes to carbon and boron nitride nanotubes

In an effort to gain insight into the activation energies and reaction enthalpies of the chemical functionalization of carbon and boron nitride nanotubes, calculations using density functional theory have been carried out for the cycloaddition of a heavy carbene to a single-walled carbon (SWCNT; C(130)H(20)) and a boron nitride (SWBNNT; B(65)N(65)H(20)) nanotube. The (CH(3))(2)X + SWCNT and (CH(3))(2)X + SWBNNT (X = C, Si, Ge, Sn, and Pb) reactions are the subject of the present study. All the stationary points were determined at the B3LYP/LANL2DZ level of theory. The major conclusions that can be drawn from this work are as follows: (i) Considering both the activation barrier and reaction enthalpy based on the model calculations presented here, it is found that the order of (CH(3))(2)X reactivity is X = C > Si > Ge > Sn > Pb, irrespective of whether cycloaddition is to a SWCNT or a SWBNNT sidewall. That is to say, (CH(3))(2)C and (CH(3))(2)Si can readily add to the sidewalls of SWCNT and SWBNNT, whereas (CH(3))(2)Ge, (CH(3))(2)Sn, and (CH(3))(2)Pb are unreactive. (ii) Since the chemical reactivities of SWCNT and SWBNNT sidewalls closely resemble those of the small C(16)H(10) and B(8)N(8)H(10) molecules, at least in a qualitative sense, the use of the above small molecules as models is sufficient to provide qualitatively correct results. (iii) Our theoretical observations indicate that all the (5,5) SWCNT and SWBNNT cycloadducts favor opened rather than closed three-membered ring structures. (iv) The theoretical investigations demonstrate that the singlet-triplet splitting of the carbene species (R(2)X) as well as that of the small model molecules can be used as a diagnostic tool to predict the addition reactivities of carbene analogues and sidewalls of various nanotubes, respectively. Moreover, the results obtained in this work allow a number of predictions to be made.     

Disiline-doped boron nitride nanotubes: A computational study

The properties of the electronic structure of the Disiline-doped boron nitride nanotubes (Disiline-BNNTs) are investigated by a density functional theory (DFT) calculation. The structural forms are firstly optimized and the CS tensors calculated. Subsequently, the chemical-shielding isotropic (CS^I) and chemical shielding anisotropic (CS^A) parameters are found. The shielding values of boron (B) and nitrogen (N) atoms were calculated by Gauge-Including Atomic Orbital (GIAO), Continuous Set of Gauge Transformations (CSGT) and Individual Gauges for Atoms in Molecules (IGAIM) methods, using B3LYP/6-311+G*. The B3LYP level of theory with IGAIM was the best method to evaluate the theoretical chemical shifts for studied models. The results reveal a significant effect of Disiline doping on the chemical shielding tensors at the sites of those ¹¹B and ¹⁵N nuclei located in the nearest neighborhood of the Disiline-doped ring. Furthermore, the values of dipole moments and HOMO-LUMO gaps change in the Disiline-doped models in comparison with the original pristine model.     

Solubilization of boron nitride nanotubes

A successful attempt in the functionalization and solubilization of boron nitride nanotubes is reported, and a functionalization mechanism based on interactions of amino functional groups with nanotube surface borons is proposed.     

A novel precursor for synthesis of pure boron nitride nanotubes

A novel precursor, a mixture of B2O2 and Mg which is generated in situ by reacting B and MgO at 1300 degrees C, can be used to effectively synthesize bulk amounts of pure BN nanotubes with Mg evaporated from the final product; transmission electron microscope observation for the synthesized BN nanotubes indicates that defects present strongly depend on the tube diameter.     

Selective synthesis of boron nitride nanotubes by self-propagation high-temperature synthesis and annealing process

Four types of BN nanotubes are selectively synthesized by annealing porous precursor in flowing NH₃ and NH₃/H₂ atmosphere at temperature ranging from 1000 to 1200 °C in a vertical furnace. The as-synthesized BN nanotubes, including cylinder, wave-like, bamboo-like and bubble-chain, are characterized by XRD, FTIR, Raman, SEM, TEM and HRTEM. Three phenomenological growth models are proposed to interpret growth scenario and structure features of the four types of BN nanotubes. Selectivity of nanotubes formation is estimated as approximately 80-95%. The precursor containing B, Mg, Fe and O prepared by self-propagation high-temperature synthesis (SHS) method plays a key role in selective synthesis of the as-synthesized BN nanotubes. Chemical reactions are also discussed.     

SnO2 nanoparticle-functionalized boron nitride nanotubes

Boron nitride nanotubes (BNNTs) were synthesized by a carbon-free chemical vapor deposition method using boron and metal oxide as reactants. Then SnO(2) nanoparticles were functionalized on them via a simple wet chemistry method. Detailed transmission electron microscopy (TEM) observations reveal that SnO(2) nanoparticles may cover the tube surface or be encapsulated in tube channels. The lattice distances of both BNNT and SnO(2) have been changed due to the strong interactions between them. The band gap energy of SnO(2) particles is found enlarged due to the size effect and interaction with BNNTs.     

Electronic structure of octagonal boron nitride nanotubes

The effect of an octagonal lattice configuration on a boron nitride nanotube is explored using first principle calculations. Calculations show that the formational energy of an octagonal boron nitride nanotube (o‐BNNT) is an exothermic reaction. Boron and nitrogen atoms within an o‐BNNT have an average of 2.88 electrons and 9.09 electrons, respectively, indicating ionic‐like bonding. In addition, the electronic structure of the octagonal boron nitride nanotube shows semiconductive properties, while h‐BNNT is reported to be an insulator. Additional o‐BNNTs with varying diameters are calculated where the results suggest that the diameter has an effect on the binding energy and bandgap of the o‐BNNT. The defect sites of the o‐BNNT are reactive against hydrogen where a boron defect is particularly reactive. Thus, this work suggests that physical and chemical properties of a boron nitride nanotube can be tailored and tuned by controlling the lattice configuration of the nanotube.     

Immobilization of proteins on boron nitride nanotubes

We report for the first time that proteins are immobilized on boron nitride nanotubes. It is found that there is a natural affinity of a protein to BNNT; this means that it can be immobilized on BNNT directly, without usage of an additional coupling reagent. For the most effective immobilization, noncovalently functionalized BNNTs should be used. The effect of immobilization was studied using high-resolution transmission electron microscopy and energy dispersion spectroscopy.     

Infrared response of multiwalled boron nitride nanotubes

We report the infrared (IR) response of bulk samples of multiwalled boron nitride nanotubes, produced by a substitution reaction from single walled carbon nanotubes, which is dominated by two characteristic BN-vibrations at 800 and 1372 cm-1.     

Thin boron nitride nanotubes with unusual large inner diameters

BN nanotubes, displaying the characteristics of few concentric layers (2–6 layers) but unusual large inner diameters (ranging from 8 to more than 10 nm), are synthesized by a chemical vapor deposition (CVD) method on -Al₂O₃ micrometer-range particles. The inner diameters are at least 5 nm larger than the previously reported BN nanotubes of similar layers. Some BN nanotubes are observed to be filled with B–N–O-based amorphous materials. Crystalline core fillings (in the form of boron carbide nanorods) were also discovered. The discussions suggested that the CVD growth behavior of BN nanotubes may be closely dependent on the underlying substrates, which may be helpful to the possible rational synthesis of BN nanotubes.     

Theoretical study on interaction of hydrogen with single-walled boron nitride nanotubes. II. Collision, storage, and adsorption

Collision and adsorption of hydrogen with high incident kinetic energies on a single-walled boron nitride (BN) nanotube have been investigated. Molecular-dynamics (MD) simulations indicate that at incident energies below 14 eV hydrogen bounces off the BN nanotube wall. On the other hand, at incident energies between 14 and 22 eV each hydrogen molecule is dissociated at the exterior wall to form two hydrogen atoms, but only one of them goes through the wall. However, at the incident energies between 23 and 26 eV all of the hydrogen atoms dissociated at the exterior wall are found to be capable of going inside the nanotube and then to recombine to form hydrogen molecules inside the nanotube. Consequently, it is determined that hydrogen should have the incident energy >22 eV to go inside the nanotube. On the other hand, we find that the collisions using the incident energies >26 eV could result in damaging the nanotube structures. In addition our MD simulations find that hydrogen atoms dissociated at the wall cannot bind to either boron or nitrogen atoms in the interior wall of the nanotube.     

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.     

A first principles study on organic molecule encapsulated boron nitride nanotubes

The electronic structures of boron nitride nanotubes (BNNTs) doped with organic molecules are investigated using density functional theory. An electrophilic molecule introduces acceptor states in the wide gap of BNNT close to the valence band edge, which makes the doped system a p-type semiconductor. However, with typical nucleophilic organic molecules encapsulation, only deep occupied molecular states but no shallow donor states are observed. There is a significant electron transfer from a BNNT to an electrophilic molecule, while the charge transfer between a nucleophilic molecule and a BNNT is negligible. When both electrophilic and nucleophilic molecules are encapsulated in the same BNNT, a large charge transfer between the two kinds of molecules occurs. The resulting small energy gap can strongly modify the transport and optical properties of the system.     

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.     

Hydrogen uptake in boron nitride nanotubes at room temperature

Hydrogen uptake capacities of 1.8 and 2.6 wt % were obtained on BN multiwalled nanotubes and bamboo-like nanotubes, respectively, under approximately 10 MPa at room temperature. The preliminary results show that chemical interactions mainly take place between hydrogen and BN. Taking into consideration the uniform semiconducting electronic property and ultimate stable chemical and thermal stability, BN nanotubes may exhibit some interesting possibilities in storing hydrogen. This will also provide some viewpoints on designing the carbon-based hydrogen storage system.     

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.     

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.     

In situ real-time study buckling behavior of boron nitride nanotubes with axial compression by TEM

The real time analysis structure evolution of BNNT with compression showed that the formation of V-shape in the post-buckling before BNNT fracture was reversible.     

DFT study on the structural and electronic properties of Pt-doped boron nitride nanotubes

First-principles calculations based on density functional theory were carried out to investigate the structural and electronic properties of Pt substitution-doped boron nitride (BN) nanotubes. The electronic and structural properties were studied for substituted Pt in the boron and the nitrogen sites of the (BN) nanotube. The band gap significantly diminishes to 2.095 eV for Pt doping at the B site while the band gap diminishes to 2.231 eV for Pt doping at the N site. The band density increases in both the valence band and the conduction band after doping. The effects of the hardness and softness group 17 (halogen elements) were calculated by density functional theory (DFT).     

Structural and electronic properties of fluorinated boron nitride nanotubes

The effects of F doping on the structural and electronic properties of the (5, 5) single-walled boron nitride nanotube (BNNT) are investigated by using the density functional theory method. The chemiadsorption of F maintains the hexagonal BN network, increases the lattice constant, and introduces acceptor impurity states. On the other hand, substitutional doping of F destroys the hexagonal BN network, decreases the lattice constant, but does not alter the insulating feature of the BNNT. The observed insulator-to-semiconducting transition, a lattice contraction, and a highly disordered atom arrangement in the sidewall of BNNTs upon F doping appear to be most reasonably attributed to a codoping of dominating substitutional F over chemiabsorbed F, which can induce deep donor impurity states, a lattice contraction, and a destruction of the hexagonal BN network simultaneously.