Fabrication of boron nitride nanotube-gold nanoparticle hybrids using pulsed plasma in liquid

Plasma, generated in liquid at atmospheric pressure by a nanosecond pulsed voltage, was used to fabricate hybrid structures from boron nitride nanotubes and gold nanoparticles in deionized water. The pH was greatly reduced, conductivity was significantly increased, and concentrations of reactive oxygen and nitrogen species in the water were increased by the plasma treatment. The treatment reduced the length of the nanotubes, giving more individual cuplike structures, and introduced functional groups onto the surface. Gold nanoparticles were successively assembled onto the functionalized surfaces. The reactive species from the liquid plasma along with the nanosecond pulsed electric field seem to play a role in the shortening and functionalization of the nanotubes and the assembly of gold nanoparticles. The potential for targeted drug delivery was tested in a preliminary investigation using doxorubicin-loaded plasma-treated nanotubes which were effective at killing ∼99% of prostate cancer cells.

Dielectric screening in atomically thin boron nitride nanosheets

Two-dimensional (2D) hexagonal boron nitride (BN) nanosheets are excellent dielectric substrate for graphene, molybdenum disulfide, and many other 2D nanomaterial-based electronic and photonic devices. To optimize the performance of these 2D devices, it is essential to understand the dielectric screening properties of BN nanosheets as a function of the thickness. Here, electric force microscopy along with theoretical calculations based on both state-of-the-art first-principles calculations with van der Waals interactions under consideration, and nonlinear Thomas-Fermi theory models are used to investigate the dielectric screening in high-quality BN nanosheets of different thicknesses. It is found that atomically thin BN nanosheets are less effective in electric field screening, but the screening capability of BN shows a relatively weak dependence on the layer thickness.

Oxygen-doped boron nitride nanosheets with excellent performance in hydrogen storage

Hydrogen is considered one of the best energy sources. However, the lack of effective, stable, and safe storage materials has severely prevented its practical application. Strong effort has been made to try new nanostructured materials as new storage materials. In this study, oxygen-doped boron nitride (BN) nanosheets with 2-6 atomic layers, synthesized by a facile sol-gel method, show a storage capacity of 5.7wt% under 5MPa at room temperature, which is the highest hydrogen storage ever reported for any BN materials. Importantly, 89% of the stored hydrogen can be released when the hydrogen pressure is reduced to ambient conditions. Furthermore, the BN nanosheets exhibit an excellent storage cycling stability due to the stable two-dimensional nanostructure. The first principles calculations reveal that the high hydrogen storage mainly origins from the oxygen-doping of the BN nanosheets with increased adsorption energies of H2 on BN by 20-80% over pure BN sheets at the different coverage. © 2014 Elsevier Ltd.

Temperature-dependent Raman spectra of bamboo-like boron nitride nanotubes

Phonon properties of boron nitride nanotubes (BNNTs) were investigated using Raman spectroscopy at different temperatures and new sp3- bonded BN vibrations were identified. The Raman peak of the E2g mode of BNNTs is found to be downshifted and broadened compared to that of hexagonal BN at the same temperature. By increasing the temperature, the energy of the E2g mode and the sp3-bonding mode are downshifted, with the temperature coefficients being -0.010 and -0.069cm-1/K, respectively. We attribute this downshifting to anharmonic effects as well as the elongation of the B-N bond in BNNT structures with increasing temperature. © 2014 The Japan Society of Applied Physics.

High-efficient production of boron nitride nanosheets via an optimized ball milling process for lubrication in oil

Although tailored wet ball milling can be an efficient method to produce a large quantity of two-dimensional nanomaterials, such as boron nitride (BN) nanosheets, milling parameters including milling speed, ball-to-powder ratio, milling ball size and milling agent, are important for optimization of exfoliation efficiency and production yield. In this report, we systematically investigate the effects of different milling parameters on the production of BN nanosheets with benzyl benzoate being used as the milling agent. It is found that small balls of 0.1-0.2 mm in diameter are much more effective in exfoliating BN particles to BN nanosheets. Under the optimum condition, the production yield can be as high as 13.8% and the BN nanosheets are 0.5-1.5 μm in diameter and a few nanometers thick and of relative high crystallinity and chemical purity. The lubrication properties of the BN nanosheets in base oil have also been studied. The tribological tests show that the BN nanosheets can greatly reduce the friction coefficient and wear scar diameter of the base oil.

Boron nitride nanosheets as improved and reusable substrates for gold nanoparticles enabled surface enhanced Raman spectroscopy.

Atomically thin boron nitride (BN) nanosheets have been found to be excellent substrates for noble metal particles enabled surface enhanced Raman spectroscopy (SERS), thanks to their good adsorption of aromatic molecules, high thermal stability and weak Raman scattering. Faceted gold (Au) nanoparticles have been synthesized on BN nanosheets using a simple but controllable and reproducible sputtering and annealing method. The size and density of the Au particles can be controlled by sputtering time, current and annealing temperature etc. Under the same sputtering and annealing conditions, the Au particles on BN of different thicknesses show various sizes because the surface diffusion coefficients of Au depend on the thickness of BN. Intriguingly, decorated with similar morphology and distribution of Au particles, BN nanosheets exhibit better Raman enhancements than silicon substrates as well as bulk BN crystals. Additionally, BN nanosheets show no noticeable SERS signal and hence cause no interference to the Raman signal of the analyte. The Au/BN substrates can be reused by heating in air to remove the adsorbed analyte without loss of SERS enhancement.

Highly crumpled boron nitride nanosheets as adsorbents: scalable solvent-less production

Boron nitride nanosheets (BNNSs), so-called “white graphene”, have recently received increasing attention, both theoretically and experimentally. Although many synthetic procedures have been proposed for the synthesis of BNNSs, finding a simple, solvent-less, catalyst-free, and large-scale production route is still a challenge. Here, a facile, solvent-less, low cost, and high yield process is developed, in which mechanical solid-state exfoliation allows scalable production of crumple BNNSs from commercial BN powders with a high surface area. Importantly, these BNNSs show unprecedentedly high adsorption of proteins described by various adsorption isotherms and kinetics models. In addition, the saturated BNNSs exhibit excellent recyclability, and maintain a high sorption capacity even after five cycles through simply regeneration process of heating in air. This easy recyclability route further demonstrates the great potential of BNNSs for water cleaning application.

Multifunctional polymer/porous boron nitride nanosheet membranes for superior trapping emulsified oils and organic molecules

Effective oil/water separation and removal of organic molecules from water are of worldwide importance for water source protection. Multifunctional sorbent materials with excellent sorption capacity, stability, and recyclability properties need to be developed. Here, flexible and multifunctional polymer/porous boron nitride nanosheets (BNNSs) membranes with high water permeability, exhibiting high effectiveness and stability in the purification of simulated wastewater tainted with either oil/water emulsion or organic molecules, are reported. Remarkably, the flexible nature of these porous membranes enables simplicity of operation for water remediation processing and ease of post-processing collection. The composite membrane also displays a remarkably high permeability of 8 × 10⁴ L μm m^-2 h^-1 bar^-1, roughly three orders of magnitude higher than pure polymer, and excellent filter efficiencies for the pharmaceuticals ciprofloxacin, chlortetracycline, and carbamazepine (up to 14.2 L g^-1 of BNNSs in the composite membrane for a concentration of 10 mg L^-1 ciprofloxacin) and the dye methylene blue (up to 9.3 L g^-1 of BNNSs in the composite membrane at a concentration of 30 mg L^-1). Exhausted membranes can be readily rejuvenated by simple washing with retention of their high-performance characteristics. The results demonstrate the potential efficacy and practicality of these membranes for water cleaning.

Boron nitride colloidal solutions, ultralight aerogels and freestanding membranes through one-step exfoliation and functionalization

Manufacturing of aerogels and membranes from hexagonal boron nitride (h-BN) is much more difficult than from graphene or graphene oxides because of the poor dispersibility of h-BN in water, which limits its exfoliation and preparation of colloidal solutions. Here, a simple, one-step mechano-chemical process to exfoliate and functionalize h-BN into highly water-dispersible, few-layer h-BN containing amino groups is presented. The colloidal solutions of few-layer h-BN can have unprecedentedly high concentrations, up to 30 mg ml(-1), and are stable for up to several months. They can be used to produce ultralight aerogels with a density of 1.4 mg cm(-3), which is ∼1,500 times less than bulk h-BN, and freestanding membranes simply by cryodrying and filtration, respectively. The material shows strong blue light emission under ultraviolet excitation, in both dispersed and dry state.

Field emission properties from boron nitride nanotube field emitters

Boron nitride nanotubes (BNNTs) have been studied as a field emission material due to their unique and excellent properties such as high oxidation resistance and negative electron affinity. However, field emission properties of BNNT field emitters were rarely reported until now because it is difficult to synthesize high purity BNNTs and fabricate stable BNNT field emitters. Here, we report high field emission properties from BNNT field emitters fabricated on a tungsten rod.

Raman microscopic analysis of internal stress in boron-doped diamond

Analysis of the induced stress on undoped and boron-doped diamond (BDD) thin films by confocal Raman microscopy is performed in this study to investigate its correlation with sample chemical composition and the substrate used during fabrication. Knowledge of this nature is very important to the issue of long-term stability of BDD coated neurosurgical electrodes that will be used in fast-scan cyclic voltammetry, as potential occurrence of film delaminations and dislocations during their surgical implantation can have unwanted consequences for the reliability of BDD-based biosensing electrodes. To achieve a more uniform deposition of the films on cylindrically-shaped tungsten rods, substrate rotation was employed in a custom-built chemical vapor deposition reactor. In addition to visibly preferential boron incorporation into the diamond lattice and columnar growth, the results also reveal a direct correlation between regions of pure diamond and enhanced stress. Definite stress release throughout entire film thicknesses was found in the OPEN ACCESS current Raman mapping images for higher amounts of boron addition. There is also a possible contribution to the high values of compressive stress from sp2 type carbon impurities, besides that of the expected lattice mismatch between film and substrate.

Atomically thin boron nitride: unique properties and applications

Atomically thin boron nitride (BN) is an important 2D nanomaterial, with many properties distinct from graphene. In this feature article, these unique properties and associated applications, often not feasible with graphene, are outlined. The article starts with characterization and identification of atomically thin BN. It is followed by demonstrating their strong oxidation resistance at high temperatures and applications in protecting metals from oxidation and corrosion. As flat insulators, BN nanosheets are ideal dielectric substrates for surface enhanced Raman spectroscopy (SERS) and electronic devices based on 2D heterostructures. The light emission of BN nanosheets in the deep ultraviolet (DUV) and ultraviolet (UV) regions is also included for its scientific and technological importance. The last part is dedicated to synthesis, characterization, and optical properties of BN nanoribbons, a special form of nanosheets.

Boron carbide reinforced aluminium matrix composite : physical, mechanical characterization and mathematical modelling

This paper investigates the manufacturing of aluminium-boron carbide composites using the stir casting method. Mechanical and physical properties tests to obtain hardness, ultimate tensile strength (UTS) and density are performed after solidification of specimens. The results show that hardness and tensile strength of aluminium based composite are higher than monolithic metal. Increasing the volume fraction of B4C, enhances the tensile strength and hardness of the composite; however over-loading of B4C caused particle agglomeration, rejection from molten metal and migration to slag. This phenomenon decreases the tensile strength and hardness of the aluminium based composite samples cast at 800 °C. For Al-15 vol% B4C samples, the ultimate tensile strength and Vickers hardness of the samples that were cast at 1000 °C, are the highest among all composites. To predict the mechanical properties of aluminium matrix composites, two key prediction modelling methods including Neural Network learned by Levenberg-Marquardt Algorithm (NN-LMA) and Thin Plate Spline (TPS) models are constructed based on experimental data. Although the results revealed that both mathematical models of mechanical properties of Al-B4C are reliable with a high level of accuracy, the TPS models predict the hardness and tensile strength values with less error compared to NN-LMA models.