[en] Two interesting carbon nanostructures, the double helices and the nanobraids, have been synthesized by pyrolysis of acetone at 715 deg. C, using iron nanoparticles as catalysts. The double helix was formed by two nanofibers, strictly coiled together with a strikingly constant pitch. Such a rope-like structure usually extended hundreds of microns in length, and provided excellent strength, stability and flexibility. The nanobraids appeared to be partially rolled up from carbon layers. Electron microscopy was applied to characterize these carbon forms

[en] Vanadium oxide (V₂O₅) microspheres have attracted considerable attention in the energy field due to their unique properties such as high stability and electrochemical activity. Here, massive V₂O₅ microspheres with smooth surface, hollow cavity and uniform particle sizes (0.4–1.5 μm), were synthesized by a facile spray pyrolysis process. Post-treatment at predefined temperatures effectively turned the microsphere shell into stacked nanorods with widths of 100 nm and lengths of 500 nm when processed at 500 °C for 3 h under nitrogen atmosphere, with enhanced crystallinity. When applied as cathode materials for supercapacitors, the post-treated V₂O₅ microspheres at 500 °C exhibited improved specific capacitance and longer discharge time. This is an effective method to manufacture massive V₂O₅ microspheres with tailored structure and potential applications in high-performance energy storage materials. (paper)

[en] The thermoelectric properties of Bi₂Sr₂Co₂O_y + x wt% nano SiC (x = 0.00, 0.025, 0.05, 0.1, 0.2, and 0.3) prepared by the solid-state reaction method were investigated from 300 K to 923 K. The resistivity can be reduced effectively by adding a small amount of SiC nano particles, which is attributed to the increase of the carrier concentration. At the same time, the Seebeck coefficients can be improved effectively due to the energy filtering effect that low energy carriers are strongly dispersed at the interface between the SiC nano particles and the matrix. The decrease of thermal conductivity is due to the increase of the scattering ability of the phonons by the SiC nanoparticles distributed at the boundary of the matrix. As a result, the Bi₂Sr₂Co₂O_y + x wt% SiC composites exhibit better thermoelectric properties. The maximum ZT value 0.24 is obtained when x = 0.05 at 923 K. Compared with the sample without SiC nano particles, the ZT value is increased by about 59.7%. (paper)

[en] Ce-doped Ce_xBi_2-xTe_2.7Se_0.3 (x = 0-0.3) nanopowders were synthesized by the hydrothermal method and the obtained nanopowders were hot-pressed into bulk at 673 K under a pressure of 60 MPa in vacuum. The results show that Ce doping has significant effects on the morphologies of the nanopowders. With increasing Ce doping amount the morphology of the nanopowder changes from nanosheets to nanorods. The thermoelectric (TE) properties measurements show that Ce doping can increase the electrical conductivity greatly, but has little effect on improving Seebeck coefficient and thermal conductivity. There is an optimum value of Ce doping amount. The Ce_0.2Bi_1.8Se_0.3Te_2.7 sample shows a highest figure of merit of 0.85 at 413 K as compared to other samples prepared in same conditions. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] With excellent mass transport properties, graphene oxide (GO)-based lamellar membranes are believed to have great potential in water desalination. In order to quantify whether GO-based membranes are indeed suitable for reverse osmosis (RO) desalination, three sub-micrometer thick GO-based lamellar membranes: GO-only, reduced GO (RGO)/titania (TO) nanosheets and RGO/TO/chitosan (CTS) are prepared, and their RO desalination performances are evaluated in a home-made RO test apparatus. The photoreduction of GO by TO improves the salt rejection, which increases slowly with the membrane thickness. The RGO/TO/CTS hybrid membranes exhibit higher rejection rates of only about 30% (greater than threefold improvement compared with a GO-only membrane) which is still inferior compared to other commercial RO membranes. The low rejection rates mainly arise from the pressure-induced weakening of the ion–GO interlayer interactions. Despite the advantages of simple, low-cost preparation, high permeability and selectivity of GO-based lamellar membranes, as the current desalination performances are not high enough to afford practical application, there still remains a great challenge to realize high performance separation membranes for water desalination applications. (paper)

[en] Introducing the nanosecond phase into thermoelectric materials is an effective strategy to improve their thermoelectric properties. In this study, the influence of nano Y${}_2$O${}_3$ dispersion on the resistivity, Seebeck coefficient and thermal conductivity of Cu${}_2$Se + x mol% Y${}_2$O${}_3$ (x = 0, 0.5, 1.0, 2.0, 3.0) was investigated. Their resistivity and Seebeck coefficient have no obvious change under the combined effects of the microstructure and the energy filtering. Especially, Y${}_2$O${}_3$ dispersion can inhibit the recrystallization of Cu${}_2$Se and make the lamellar grains thinner, thus scattering phonon and reducing the thermal conductivity effectively. When x = 1.0, the thermal conductivity reaches a minimum of 0.65 W/K·m at 923 K. The dimensionless thermoelectric figure of merit (ZT) value of the Cu${}_2$Se + 1.0 mol% Y${}_2$O${}_3$ sample reaches 1.81 at 923 K. The study indicates that nano rare earth oxides are relatively effective second-phase that can reduce thermal conductivity, which may be further promoted for other thermoelectric materials.

[en] Optically pumped ultraviolet lasing at room temperature based on GaN microwire arrays with Fabry–Perot cavities is demonstrated. GaN microwires have been grown perpendicularly on c -GaN/sapphire substrates through simple catalyst-free chemical vapor deposition. The GaN microwires are [0001] oriented single-crystal structures with hexagonal cross sections, each with a diameter of ∼1 μ m and a length of ∼15 μ m. A possible growth mechanism of the vertical GaN microwire arrays is proposed. Furthermore, we report room-temperature lasing in optically pumped GaN microwire arrays based on the Fabry–Perot cavity. Photoluminescence spectra exhibit lasing typically at 372 nm with an excitation threshold of 410 kW cm⁻². The result indicates that these aligned GaN microwire arrays may offer promising prospects for ultraviolet-emitting micro/nanodevices. (paper)

[en] Theoretically, nanosecond phase dispersion is an effective method to optimize the performance of thermoelectric materials due to the energy filtering effect and strong phonon scattering. Because of the chemical stability of La${}_2$O${}_3$, it may be used as a second phase material in Bi${}_2$Te${}_{2.7}$Se${}_{0.3}$ matrixes. After the introduction of La${}_2$O${}_3$, its electric transport performance decreases slightly, but its thermal transport performance increases further. Finally, its thermoelectric performance is optimized. At 455 K, the maximum dimensionless thermoelectric figure of merit (ZT) value of Bi${}_2$Te${}_{2.7}$Se${}_{0.3}$ + 0.5 wt% La${}_2$O${}_3$ reaches 0.97. The experimental results demonstrate that La${}_2$O${}_3$ dispersion can improve the thermoelectric properties of Bi${}_2$Te${}_{2.7}$Se${}_{0.3}$ effectively.

[en] A cation-controlled selective anion transportation through graphene oxide (GO) membranes is demonstrated in this work. The results reveal that the trans-membrane transport of different anions can be modulated by the corresponding cations. The diverse interactions among anions, cations, and the negatively charged GO membranes are responsible for selective anion permeation through GO membranes. During the ion penetration, electrical potential differences can be generated across drain and source as well as across GO membranes; based on this, the ion distributions around GO membranes can be determined. The results indicate that local ion ordering can be achieved by GO membranes. Interestingly, for the cases of KNO_3, Ca(NO_3)_2, and Ba(NO_3)_2, alternate aggregations of metallic cations and NO_3"− anions can be formed around GO membranes, demonstrating the fantastic ability of these membranes for ordering the ions locally in solutions. In addition, based on the electrical potential differences generated by different salts, chlorides are demonstrated to be ideal sources for efficient practical electricity production compared to sulfates and nitrates, while the different voltage signals generated can be used to identify different source solutions for liquid sensing applications. These results indicate that GO membranes can find potential applications in membrane separation, energy generation, ion recognition, and local ion organizing. (paper)

[en] In this report, we have prepared a magnetic catalyst with well-dispersed Ni nanoparticles embedded in SiO₂@C core-shell materials. A resorcinol-formaldehyde (RF) resin layer containing Ni source was in situ grown on the SiO₂ spheres through polymerization process. The Ni species and RF layer in the precursor simultaneously were transformed into Ni nanoparticles and carbon layer through the heat treatment. The loading mass and size of Ni nanoparticles can be adjusted by changing the additional amount of Ni source, which can provide efficient active sites and control the catalytic reduction of 4-NP. As-prepared SCN-3 with the higher density dispersion revealed better catalytic activity than other catalysts in terms of shorter induction time (70 s) and higher mass-normalized rate constant (261.44 s⁻¹ mg⁻¹). Moreover, SiO₂@C/Ni nanocomposite provided an excellent catalytic efficiency with no obvious deactivation (~ 100%) over the 5 cycles.

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