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A proof-of-concept of the enhancement in thermoelectric properties using C/BCN core/shell nanotube heterojunctions has been reported. We demonstrated a scalable two-step reaction route to produce C/BCN core/shell nanotubes with bulk quantities. Systematic X-ray photoelectron spectroscopy (XPS) and atomic-scale high-resolution transmission electron microscope electron energy loss spectroscopy (HRTEM-EELS) characterizations indicate that the synthetic heterostructures with CNT core and BCN shell can be prepared by the developed method. Thermoelectric property measurements revealed that moderate BCN shell effectively improves the Seebeck coefficient, leading to a 6.4-fold increase in thermoelectric power factor of 0.64 μW/mK 2 . Our study provides a fundamental understanding for the rational design of nanostructured heterojunctions for improved thermoelectric properties of carbon-based materials. [ABSTRACT FROM AUTHOR]

We report the efficient productions of single- and few-layered graphene and molybdenum disulphide (MoS 2 ) nanosheets using a surfactant-free, water-assisted liquid-phase exfoliation (LPE) of graphite and MoS 2 bulk powders in N-methylpyrrolidinone (NMP). Extensive absorption spectroscopic study and materials characterizations indicate that the addition of water to NMP was not only effective on the exfoliation yields but also the stability of the colloidal dispersions of exfoliated nanosheets in the water-NMP mixed solvent upto 18 months. Detailed micro Raman spectroscopic analysis suggests the defects of the exfoliated graphene nanosheets were reduced using the developed water-assisted LPE in NMP. [ABSTRACT FROM AUTHOR]

Electrochemical supercapacitors (SCs) have received much attention since their high power density, short charge/discharge duration and long cycle life. Heteroatom–doped carbonaceous materials have been investigated due to their exceptional electrochemical properties. In this study, boron–doped multi–walled carbon nanotubes (B–MWCNT) were synthesized by a novel ammonia–assisted substitution reaction. Argon atmosphere with ammonia was utilized as etching gas to create defects on MWCNT surface and boron trioxide was applied as boron source. The specific capacitance is much larger for the SC with B–MWCNT (40.00 F/g) than that with MWCNT (8.35 F/g), owing to the better conductivity for the former case. [ABSTRACT FROM AUTHOR]

Abstract: Sintering of the AlN powder synthesized by a combustion synthesis method, which was developed recently by the present authors, was studied by using a microwave sintering technique. A single mode microwave cavity was used and an insulation package with a simple configuration was developed. A high sintering temperature (1900°C or higher) and a stable and uniform heating were readily achieved. A temperature measurement technique using a thermocouple with extrapolation was established to obtain the sintering temperature. A percent theoretical density of 99.5% and a thermal conductivity of 186W/mK were obtained for a specimen which was sintered at 1900°C with a soaking time of 30min and 3wt.% of Y2O3 added. The effects of sintering aid (i.e., Y2O3) and sintering temperature on densification, microstructure and thermal conductivity of the sintered specimens were investigated. [Copyright &y& Elsevier]

Graphene quantum dots (GQDs) were formed by liquid-phase exfoliation in an ultrasonic bath using platelet graphite nanofibers (PGNFs) as the raw material and dimethyl sulfoxide (DMSO) as the exfoliation agent. PGNFs, carbon fibers with graphene nanosheets stacked perpendicular along the fiber axis, were sectioned layer by DMSO for 3 h with ultrasonic assistance to create GQDs. The diameters of the derived GQDs were in the range of 10–30 nm and fewer than five graphene layers were formed. X-ray photoelectron spectroscopy analysis revealed that no functional groups were grafted onto the GQDs during the process, indicating that the synthetic route produced high-quality GQDs. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H 2 O 2 ) is an essential mediator for most of the oxidative biological reactions in enzyme-based biosensor systems, such as glucose oxidase, cholesterol oxidase, and alcohol oxidase. Synthesis of new catalysts to detect the concentration of H 2 O 2 more precisely is indispensable for enzyme-based electrochemical biosensors. In this study, boron-doped graphene nanosheets (BGNs) with 2.2 atomic percentage (at%) boron doping level and a hierarchical microstructure were synthesized by an atmospheric-pressure carbothermal reaction as a noble-metal free catalyst for sensing H 2 O 2 . The isolated boron atoms on the BGNs surface act as the electrocatalytic sites by transferring charges to neighbor carbon atoms, and the hierarchical microstructure provides multidimensional electron transport pathways for charge transfer and therefore enhances the electrocatalytic ability. BGNs possess a higher reduction current in the cyclic voltammetry (CV) measurement than that of pristine graphene nanosheets (GNs) over the detection range of 0.0 to 10.0 mM at −0.4 V ( vs. Ag/AgCl). The BGNs modified electrochemical sensor shows a linear range from 1.0 to 20.0 mM of H 2 O 2 with a sensitivity of 266.7 ± 3.8 μA mM −1 cm −2 and limit of detection (LOD) of 3.8 μM at a signal-to-noise (S/N) ratio of 3. The beneficial hierarchical microstructure and the synergetic effects arising from doping boron in GNs accomplish the better performance of the BGNs modified electrochemical sensor. [ABSTRACT FROM AUTHOR]

Helium bubble formation was examined by scanning/transmission electron microscopy (S/TEM) in Fe-9/10Cr binary alloys and two dispersion strengthened nanostructured alloys (CNA3 and 14YWT containing 5–10 nm diameter carbide and oxide particles, respectively) after ex-situ and in-situ He implantation to ~10,000 appm at 500 to 900 °C. The combination of high-resolution STEM images and electron energy loss spectroscopy (EELS) revealed that the Y-Ti-O nanoparticles in 14YWT were uniformly distributed and exhibited a one-to-one relationship for bubble attachment to the nanoclusters. In the in-situ experiment at 900 °C, grain boundary cracking was severe in the Fe-10Cr model alloy, but not in the nanostructured alloys. From 500 to 900 °C, the bubble size generally increased with increasing irradiation temperature, while the bubble density decreased with increasing temperature. At the same temperatures, the bubble size in the implanted materials was in the order of Fe-9/10Cr > CNA3 > 14YWT, while the bubble density showed the opposite order. The observed bubble number densities for the nanostructured alloys are comparable to the nanoparticle density, suggesting that the nanoparticles in both alloys were effective in trapping He. Our results indicate that very high He concentrations can be managed in nanostructured alloys by sequestering the helium into smaller bubbles (which leads to a lower volume swelling value) and to shield He from the grain boundaries. This can be attributed to the much higher sink strength associated with the nanoclusters or the He trapping ability between different types of nanoclusters. [Display omitted] [ABSTRACT FROM AUTHOR]