Search

Ammonium tetrafluoroborate, a cheap and commonly used chemical, was successfully utilized in this study to synthesize BN-coated MgF2nanowires and collapsed BN nanotubes, although previous investigations have indicated that the compound cannot be used as a chemical vapour deposition (CVD) reaction precursor of amorphous or crystalline BN. Our study reveals that when MgCl2is used as a promoter a crystalline BN phase can be obtained on a large scale. The MgCl2also controls the product morphology, resulting in collapsed BN-coated MgF2nanowires at the first stage of CVD. The detailed morphology of the composite nanowires also depends on the reaction temperature. Increase in temperature stimulates the nanowire formation. The MgF2inclusions can be fully removed via a simple high-temperature evaporation procedure, forming collapsed BN nanotubes of high purity and yield. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Closed-shell BO2− and BO− anions are proposed as high-efficiency luminescence centres in boron–nitrogen systems, which makes the anions localized and leads to a radiation transition. [ABSTRACT FROM AUTHOR]

Boron nitride nanohorns (BNNHs) are synthesized in large scale. Their morphology and structure were investigated by scanning electron microscopy and transmission electron microscopy. The hollow conical structure and particular aggregation behavior are revealed. Cathodoluminescence measurement is performed and ultraviolet light emission is observed, which indicates the potential applications of BNNHs in optical devices. [ABSTRACT FROM AUTHOR]

The fine regulation of catalysts by the atomic-level removal of inactive atoms can promote the active site exposure for performance enhancement, whereas suffering from the difficulty in controllably removing atoms using current micro/nano-scale material fabrication technologies. Here, we developed a surface atom knockout method to promote the active site exposure in an alloy catalyst. Taking Cu3Pd alloy as an example, it refers to assemble a battery using Cu3Pd and Zn as cathode and anode, the charge process of which proceeds at about 1.1 V, equal to the theoretical potential difference between Cu2+/Cu and Zn2+/Zn, suggesting the electricity-driven dissolution of Cu atoms. The precise knockout of Cu atoms is confirmed by the linear relationship between the amount of the removed Cu atoms and the battery cumulative specific capacity, which is attributed to the inherent atom-electron-capacity correspondence. We observed the surface atom knockout process at different stages and studied the evolution of the chemical environment. The alloy catalyst achieves a higher current density for oxygen reduction reaction compared to the original alloy and Pt/C. This work provides an atomic fabrication method for material synthesis and regulation toward the wide applications in catalysis, energy, and others. [ABSTRACT FROM AUTHOR]

Graphene as a coating material that shows high impermeability as an excellent barrier in oxidation and corrosion protection has been reported to be less stable at elevated temperature. Sometimes the formed galvanic cell between the graphene and protective surface will even increase the corrosion speed. In comparison, boron nitride (BN), which shows the same impermeability with graphene, is believed to be a better coating material with its superior thermal and chemical inertness. In this study, an in situ synthesis of BN coatings, grown by boron ink, on both carbon and Cu for anti-oxidation and anti-corrosion purposes has been demonstrated. Thermogravimetric analysis and electrochemical analysis reveal that the BN coatings can effectively prevent the carbon from being oxidized at high temperature in air and adequately slow down the corrosion rate of Cu in sodium chloride solution, respectively. These results indicate that boron ink assisted in situ BN coating has high potential in the applications of oxidation and corrosion protection. [ABSTRACT FROM AUTHOR]

Substantial effort has been devoted to endowing flexible and wearable supercapacitors with desirable functions and solving urgent concerns regarding their practical application, particularly materials selection, air permeability, self-healability, shape memory, integration, and modularization. This gives rise to challenges with regard to both suitable materials and device fabrication. This review highlights the current state-of-the-art of these supercapacitors pertinent to materials, fabrication strategies, and performance. Challenges and solutions are also discussed to further improve their practicality. The aim of this review is to make a timely summary of this emerging field and discuss future opportunities and challenges. [ABSTRACT FROM AUTHOR]

Polymer composites with enhanced mechanical, thermal or optical performance usually suffer from poor ductility induced by confined mobility of polymer chains. Herein, highly ductile UV-shielding polymer composites are successfully fabricated. Boron nitride (BN) materials, with a wide band gap of around ∼6.0 eV, are used as fillers to achieve the remarkably improved UV-shielding performance of a polymer matrix. In addition, it is found that spherical morphology BN as a filler can keep the excellent ductility of the composites. For a comparison, it is demonstrated that traditional fillers, including conventional BN powders can achieve the similar UV-shielding performance but dramatically decrease the composite ductility. The mechanism behind this phenomenon is believed to be lubricant effects of BN nanospheres for sliding of polymer chains, which is in consistent with the thermal analyses. This study provides a new design to fabricate UV-shielding composite films with well-preserved ductility. [ABSTRACT FROM AUTHOR]

Thermally conductive and electrically insulating polymer/boron nitride (BN) nanocomposites are highly attractive for various applications in many thermal management fields. However, so far most of the preparation methods for polymer/BN nanocomposites have usually caused difficulties in the material post processing. Here, an in situ grafting approach is designed to fabricate thermally conductive, electrically insulating and post-melt processable polystyrene (PS)/BN nanosphere (BNNS) nanocomposites by initiating styrene (St) on the surface functionalized BNNSs via reversible addition fragmentation chain transfer polymerization. The nanocomposites exhibit significantly enhanced thermal conductivity. For example, at a St/BN feeding ratio of 5:1, an enhancement ratio of 1375% is achieved in comparison with pure PS. Moreover, the dielectric properties of the nanocomposites show a desirable weak dependence on frequency, and the dielectric loss tangent of the nanocomposites remains at a very low level. More importantly, the nanocomposites can be subjected to multiple melt processing to form different shapes. Our method can become a universal approach to prepare thermally conductive, electrically insulating and melt-processable polymer nanocomposites with diverse monomers and nanofillers. [ABSTRACT FROM AUTHOR]

As a structural analogue of the carbon nanotube (CNT), the boron nitride nanotube (BNNT) has become one of the most intriguing non-carbon nanostructures. However, up to now the pre-existing restrictions/limitations of BNNT syntheses have made the progress in their research rather modest. This work presents a new route toward the synthesis of highly pure ultrafine BNNTs based on a modified boron oxide (BO) CVD method. A new effective precursor--a mixture of Li2O and B--has been proposed for the growth of thin, few-layer BNNTs in bulk amounts. The Li2O utilized as the precursor plays the crucial role for the present nanotube growth. The prepared BNNTs have average external diameters of sub-10 nm and lengths of up to tens of um. Electron energy loss spectrometry and Raman spectroscopy demonstrate the ultimate phase purity of the ultrafine BNNTs. Property studies indicate that the ultrafine nanotubes are perfect electrical insulators exhibiting superb resistance to oxidation and strong UV emission. Moreover, their reduced diameters lead to a dramatically decreased population of defects within the tube walls and result in the observation of near-band-edge (NBE) emission at room temperature. [ABSTRACT FROM AUTHOR]

Bending modulus of exfoliation-made single-crystalline hexagonal boron nitride nanosheets (BNNSs) with thicknesses of 25-300 nm and sizes of 1.2-3.0 um were measured using three-point bending tests in an atomic force microscope. BNNSs suspended on an SiO2 trench were clamped by a metal film via microfabrication based on electron beam lithography. Calculated by the plate theory of a doubly clamped plate under a concentrated load, the bending modulus of BNNSs was found to increase with the decrease of sheet thickness and approach the theoretical C33 value of a hexagonal BN single crystal in thinner sheets (thickness<50 nm). The thickness-dependent bending modulus was suggested to be due to the layer distribution of stacking faults which were also thought to be responsible for the layer-by-layer BNNS exfoliation. [ABSTRACT FROM AUTHOR]

Boron nitride (BN) microtubes were synthesized in a vertical induction furnace using Li2CO3 and B reactants. Their structures and morphologies were investigated using x-ray diffraction, scanning and transmission electron microscopy, and energy-dispersive x-ray spectroscopy. The microtubes have diameters of 1-3 um, lengths of up to hundreds of micrometers, and well-structured ultrathin walls only [?]50 nm thick. A mechanism combining the vapor-liquid-solid (VLS) and template self-sacrificing processes is proposed to explain the formation of these novel one-dimensional microstructures, in which the Li2O-B2O3 eutectic reaction plays an important role. Cathodoluminescence studies show that even at room temperature the thin-walled BN microtubes can possess an intense band-edge emission at [?]216.5 nm, which is distinct compared with other BN nanostructures. The study suggests that the thin-walled BN microtubes should be promising for constructing compact deep UV devices and find potential applications in microreactors and microfluidic and drug delivery systems. [ABSTRACT FROM AUTHOR]

Boron nitride nanotube (BNNT)/polystyrene (PS) composite films were fabricated for the first time using high-quality BNNTs synthesized via a chemical-vapor-deposition method. The composite films exhibited good transparency. Tensile tests indicated that the elastic modulus of the films was increased by ∼21% when a ∼1 wt% soluble BNNT fraction was in use. Dispersion of BNNTs in PS and interfacial interactions between them were investigated using transmission electron microscopy. The film thermal properties, such as stability to oxidation and glass transition temperatures were measured. The experimental results and simple theoretical estimates indicate that BNNTs is a promising additive material for polymeric composites. [ABSTRACT FROM AUTHOR]