Yanming Xue

Porous boron nitride with a high surface area: hydrogen storage and water treatment

We report on the synthesis of high-quality microporous/mesoporous BN material via a facile two-step approach. An extremely high surface area of 1687xa0m(2)xa0g(-1) and a large pore volume of 0.99xa0cm(3)xa0g(-1) have been observed in the synthesized BN porous whiskers. The formation of the porous structure was attributed to the group elimination of organic species in a BN precursor, melamine diborate molecular crystal. This elimination method maintained the ordered pore structure and numerous structural defects. The features including high surface area, pore volume and structural defects make the BN whiskers highly suitable for hydrogen storage and wastewater treatment applications. We demonstrate excellent hydrogen uptake capacity of the BN whiskers with high weight adsorption up to 5.6% at room temperature and at the relatively low pressure of 3xa0MPa. Furthermore, the BN whiskers also exhibit excellent adsorption capacity of methyl orange and copper ions, with the maximum removal capacity of 298.3 and 373xa0mgxa0g(-1) at 298xa0K, respectively.

Activated boron nitride as an effective adsorbent for metal ions and organic pollutants

Novel activated boron nitride (BN) as an effective adsorbent for pollutants in water and air has been reported in the present work. The activated BN was synthesized by a simple structure-directed method that enabled us to control the surface area, pore volume, crystal defects and surface groups. The obtained BN exhibits an super high surface area of 2078u2005m2/g, a large pore volume of 1.66u2005cm3/g and a special multimodal microporous/mesoporous structure located at ~ 1.3, ~ 2.7, and ~ 3.9u2005nm, respectively. More importantly, the novel activated BN exhibits an excellent adsorption performance for various metal ions (Cr3+, Co2+, Ni2+, Ce3+, Pb2+) and organic pollutants (tetracycline, methyl orange and congo red) in water, as well as volatile organic compounds (benzene) in air. The excellent reusability of the activated BN has also been confirmed. All the features render the activated BN a promising material suitable for environmental remediation.

Hybrid nanonet/nanoflake NiCo2O4 electrodes with an ultrahigh surface area for supercapacitors

AbstractAn integrated electrode consisting of hybrid nanonet/nanoflake NiCo2O4 grown on stainless steel mesh substrates exhibits a high specific capacitance while maintaining high-rate capability and good cycling stability. The specific capacitance reaches a maximum of 911xa0Fxa0g−1 at a current density of 10 A g−1, which can still retain 864xa0Fxa0g−1 (94.8xa0% retention) after 10,000xa0cycles. These much-improved electrochemical performances are attributed to the unique architecture of NiCo2O4 electrode. The interconnected nanonet NiCo2O4 with an ultrahigh surface area significantly facilitates the rapid ion/electron transport and guarantees good mechanical adhesion, while the ultrathin nanoflakes further extend the active sites for fast redox reactions for efficient energy storage.n FigureHybrid nanonet/nanoflake NiCo2O4 grown on stainless steel mesh exhibits superior capacitive performance and long-life stability as an integrated electrode for high-performance supercapacitors.

Organic Fluorescent Dyes Supported on Activated Boron Nitride: A Promising Blue Light Excited Phosphors for High-Performance White Light-Emitting Diodes

We report an effective and rare-earth free light conversion material synthesized via a facile fabrication route, in which organic fluorescent dyes, i.e. Rhodamine B (RhB) and fluorescein isothiocyanate (FITC) are embedded into activated boron nitride (αBN) to form a composite phosphor. The composite phosphor shows highly efficient Förster resonance energy transfer and greatly improved thermal stability, and can emit at broad visible wavelengths of 500–650u2005nm under the 466u2005nm blue-light excitation. By packaging of the composite phosphors and a blue light-emitting diode (LED) chip with transparent epoxy resin, white LED with excellent thermal conductivity, current stability and optical performance can be realized, i.e. a thermal conductivity of 0.36u2005W/mk, a Commission Internationale de 1Eclairage color coordinates of (0.32, 0.34), and a luminous efficiency of 21.6u2005lm·W−1. Our research opens the door toward to the practical long-life organic fluorescent dyes-based white LEDs.

Boron Nitride Quasi-Nanoscale Fibers: Controlled Synthesis and Improvement on Thermal Properties of PHA Polymer

High-purity h-BN quasi-nanoscale fibers were successfully synthesized by annealing oriented fiber-like precursor, an adduct of melamine with boric acid at a ratio of 1:2 (M · 2B), under ammonia flow. A series of experiments have been conducted to obtain an optimum condition for generating nanoscale precursor for the synthesis of h-BN quasi nanofibers with an average diameter of ∼500 nm and length of several hundred micrometers, respectively. The fiber is a polycrystal composed of numerous disordered h-BN layers, with some stacking voids and defaults. In addition, the effects of BN fibers on the thermal conductivity and stability of biodegradable polyhydroxyalkanoate (PHA) have been studied. It is worth noting that with the addition of 2 wt% BN fibers, the thermal properties (thermostability and thermal conductivity) of the as-prepared composites have been influenced substantially.

Electrospun CF-PHA Nanocomposites: Effect of Surface Modifications of Carbon Fibers

Biodegradable polyhydroxyalkanoate (PHA) based polymer nanocomposite filled with nanoscale carbon fibers (CFs) were prepared by electrospinning. To enhance the processability and thermal properties of the composites, the carbon fibers were treated with chemical reagents, namely n-octanol, silane coupling agent (KH-550), and nitric acid (HNO3). The SEM result shows that the composite fibers with nitric acid treated CFs have the finest diameters and many uniform thickness distributions. All surface treatments on carbon fibers have increased the glass transition temperatures and crystallinities of the composites, with nitric acid treatment being the best. The improvements further depended on the volume fraction of the carbon fibers.

Low-temperature collapsing boron nitride nanospheres into nanoflakes and their photoluminescence properties

Flake-like boron nitride (BN) nanocrystals with a uniform diameter of ~200 nm and thickness of ~20 nm were fabricated by directly transforming from BN nanospheres with the assistance of NaCl salt at 1300 °C. The transformation from nanospheres to nano-pies and further to nanoflakes was achieved in a simple procedure of Na or Cl ions intercalation/deintercalation procedure at such low temperature. The morphologies of the spherical precursor and resulting nanoflakes were almost identical. X-ray powder diffractions revealed that the BN nanoflakes (BNfs) were well crystallized in the hexagonal structure via graphitizing index calculation. Elemental content analysis, FTIR spectra and TEM images were also used to characterize the products. Strong ultraviolet (UV) emissions were detected by photoluminescence (PL) spectroscopic analysis, in which the emission regions could be facilely tuned by controlling the reaction temperature. Detailed studies indicated that the collapsing temperature of unstable BN nanospheres into nanoflakes was strongly dependent on the introduction of NaCl molten salts or not. We believe the use of the NaCl molten salt medium may enhance the kinetics of the crystallization and also purification. The green fabrication characteristics, such as using NaCl salt as the additive, energy saving (300 °C lower than the commercial process), non-toxicity of byproduct and easy scale-up, make the present novel synthetic route likely to be of interest to commercial-scale production of BN nanoflakes.

Processing and Characterizations of Nanofiller-Modulated poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Composites

ABSTRACT Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-based composites were prepared using nano-sized reinforcement fillers including carbon nanotubes, boron nitride particles, and aluminum borate whiskers. The nanofillers were first treated with polyaniline via in situ polymerization, then mixed with poly(3-hydroxybutyrate-co-3-hydroxyvalerate) solutions. Thermal analyses reveal that the additions of nanofillers in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) have increased the decomposition temperatures and thus improved the degradation resistance of the resins at elevated temperatures. Among the three types of fillers, the aluminum borate whiskers show the most significant increase, from 294.0 to 305.8°C. With a small amount of nanofillers, the mechanical performance of the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) polymer has been significantly improved. GRAPHICAL ABSTRACT

Controlled synthesis of boron nitride (BN) coating on Al4B2O9 nanowhiskers

BN-coated aluminum borate (Al4B2O9) nanowhiskers with a uniform diameter of ~20xa0nm have been successfully synthesized by sol–gel and post-thermal-treatment methods. Al4B2O9 precursor is prepared under a relatively low temperature then heat treated at higher temperatures. By controlling heat-treatment conditions, BN is favorably generated in the form of uniform coating on the surface of Al4B2O9 as illustrated by SEM and TEM observations. Owing to inertness, the BN layers improve the high-temperature stability of Al4B2O9, which is verified by XRD and SEM characterizations. The successful synthesis of the uniform fine BN-coated Al4B2O9 nanowhisker is of significance and has the potential to expand the commercial value of aluminum borate nanowhiskers.