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It is of increasing interest and an important challenge to develop highly efficient less-expensive cathode catalysts for anion-exchange membrane fuel cells (AEMFCs). In this work, we have directly prepared a carbon-supported CoS nanocatalyst in a solvothermal route and investigated the effect of heat-treatment on electrocatalytic activity and long-term stability using rotating ring-disk electrode (RRDE). The results show that the heat-treatment below 400 °C under nitrogen atmosphere significantly enhanced the electrocatalytic performance of CoS catalyst as a function of annealed temperature in terms of the cathodic current density, the half-wave potential, the HO2- product and the number of electrons transferred. The CoS catalyst that annealed at 400 °C (CoS-400) has exhibited a promising performance with the half-wave potential of 0.71 V vs. RHE (the highest one for non-precious metal chalcogenides), the minimum HO2- product of 4.3% at 0.60 V vs. RHE and close to the 4-electron pathway during the oxygen reduction reaction in 0.1 M KOH. Also, the CoS-400 catalyst has comparable durability to the Pt/C catalyst. [ABSTRACT FROM AUTHOR]

Three different morphologies of tungsten oxides, nanoparticles, nanosheets and hierarchical microspheres, have been successfully synthesized by a facile carboxyl-directed hydrothermal process. The chelation of carboxylic groups with W(OH)6 nuclei is recognized to be the origin of the morphological change. Gas-sensing measurements reveal that the sensing performance varies with WO3 morphology, and the hierarchical WO3 not only exhibits high sensitivity and fast response but also has low operating temperature to toxic NO2. The response of hierarchical WO3 is nearly 2 times and 10 times higher than those of the nanosheets and nanoparticles, respectively. The maximum response of hierarchical WO3 reaches 319 to 10 ppm NO2 at 200 °C. A relationship between morphology and crystal defect is established based on photoluminescence analysis. It is demonstrated that the change in defect feature in crystalline WO3 is responsible for its morphology-dependent gas-sensing properties. [ABSTRACT FROM AUTHOR]

Zero-dimensional Fe2O3 nanoparticles were successfully decorated on three-dimensional WO3 architectures to constitute a photocatalyst of Fe2O3@WO3 heterojunction. The obtained samples were characterized in detail by X-ray diffraction, scanning electron microscopy, elemental mapping, X-ray photoelectron spectroscopy and UV-Vis absorption spectra. The results indicate that rhombohedral α-Fe2O3 nanoparticles are homogeneously decorated on the surface of monoclinic WO3 architectures, and the constituted n+-n heterojunction results in "redshift" of the optical absorption. The photocatalyst of 1%Fe2O3@WO3 annealed at 400 °C exhibits the highest photocatalytic activity for degradation of Rhodamine B under visible light irradiation. The degradation obeys first-order reaction kinetics with an apparent rate constant of 0.057 min-1. It is suggested that the potential-energy difference between Fe2O3 and WO3 accelerates the separation of photogenerated electron-hole pairs, dominating the enhanced photocatalytic activity. The results presented herein provide new insight for development of a novel visible-light-driven photocatalyst and its potential application in harmful pollutant degradation. [ABSTRACT FROM AUTHOR]

Quantum-sized ZnO nanoparticles with crystallite size about 6 nm were successfully synthesized by low temperature sol-gel process using tetraethylorthosillicate (TEOS) as capping agent to prohibit the crystallite aggregating and Ostwald ripening as well as accelerate the ZnO crystalline formation. The crystallite size was the smallest under the synthesized condition of pH = 8. The appropriate calcination temperature for as-synthesized quantum-sized ZnO was 400 °C for 1 h. The ZnO sensor exhibited the highest response of 264 to 40 ppm NO2 and the highest selectivity of 8.8 and 13.7 respectively to CO and CH4 at the same gas concentration and operating temperature of 290 °C. The mechanism of TEOS action and gas sensing were also discussed. [ABSTRACT FROM PUBLISHER]

Quantum size ZnO crystals have been synthesized successfully by a room temperature sol-gel process using oleic acid (OA) as capping agent to control the particle size. The particle size and structure of ZnO nanocrystals have been charactirized by X-ray diffraction (XRD), transmission electron microscope (TEM) and Raman spectra analysis methods. The sensor based on ZnO powder calcined at 400 °C for 1 h exhibits the highest response of 280 to NO2 and the selectivity to CO and CH4 at the same concentration reaches 31 and 49 at operating temperature of 290 °C. The effect of calcination temperature on the performance of gas sensing has also been studied. [ABSTRACT FROM PUBLISHER]

This article discusses a study which investigated the precipitation of nanosized barium sulfate in a rotating liquid film reactor (RLFR). A rotor-stator system is a key component of the RLFR. Barium chloride and sodium sulfate solutions were mixed to create the thermodynamic driving force for precipitation. Particular focus is given to the powder X-ray diffraction patterns of barium sulfate precipitated in the RLFR. Results of the study showed that the nucleation and growth habit of barium sulfate were significantly affected by the RLFR.

Propane dehydrogenation (PDH) is an efficient technology for the direct production of propylene. Nevertheless, current PDH catalysts mainly rely on precious Pt or toxic Cr and especially undergo severe coke deposition. Herein, we report a Ru catalyst decorated by boron species (Ru-3B/Al2O3), which exhibits high catalytic performance for PDH. HAADF-STEM, EELS, and CO-FTIR characterization are used to identify the surface structure of the Ru active component, which shows that the high-energy unsaturated coordination sites, including corners, edges and step atoms for Ru-3B/Al2O3, are appropriately modified by BOx species. The encapsulation of high-energy active sites prone to C-C cracking and deep dehydrogenation leads to higher propylene selectivity (> 95%) and strong carbon resistance (kd 0.0007 min) over Ru-3B/Al2O3. The XPS and H2 -TPR results show that the migration of B species is driven by the reduction of B2 O3 to B2 O2 and that the coating degree of Ru particles is controlled by the chemical valance of Ru species. [ABSTRACT FROM AUTHOR]

In this work, we have developed an in situ growth method to synthesize spherical ZSM-5/α-Al2O3 composite on spherical α-Al2O3 and investigated the morphology, structure, and properties of this composite using scanning electron microscope (SEM), powder X-ray diffraction analysis (XRD), NH3-temperature program desorption (NH3-TPD) and low temperature N2 adsorption-desorption isotherm (BET). The results show that ca. 2.4 wt% ZSM-5 has been formed in the composite with a Si/Al ratio of 46.5 and an average particle size of 8.04 µm. Furthermore, the formed ZSM-5 markedly enhances the surface acidity and the BET surface area of spherical α-Al2O3 support. [ABSTRACT FROM AUTHOR]

Core–shell nanospheres, titania composite nanospheres containing [60]fullerene, were fabricated with sizes of about 100 nm by a layer-by-layer self-assembly procedure, and were characterized by TGA, FT-IR and XPS spectroscopy. [ABSTRACT FROM AUTHOR]

Three-dimensional PdAu nanoflowers have been designed and effectively synthesized through a procedure of dropping addition of the reductant, in which morphology evolution was recorded by capturing HRTEM images at continuous synthetic stages. HRTEM, positron annihilation spectroscopy, and in situ CO-IR results showed that synthesized flowerlike PdAu nanoalloys with a size of 30-55 nm were composed of several small PdAu building units and have abundant crystal defects as well as synergetic effects. The obtained colloidal PdAu nanoflowers were then immobilized onto MgAl mixed metal oxides as a novel catalyst for partial hydrogenation of acetylene. Due to its complex morphology, rich defective sites, and synergetic effect caused by the cooperation between building units, supported PdAu nanoflower-like catalyst exhibited not only much higher activity and selectivity but also preferable stability compared with the catalyst whose active component was shape- and size-similar to the building units of PdAu nanoflowers. [ABSTRACT FROM AUTHOR]

Abstract: Nanocrystalline ZnO–SnO2 composites as NO2 gas sensor materials have been successfully synthesized through a reverse microemulsion method for controlled grain size and morphology. This method was to create a water-in-oil (W/O) microemulsion that contained a minimal amount of surfactant and a maximum amount of water. Pseudo-ternary phase diagrams in the quaternary microemulsion system of cetyltrimethylammonium bromide (CTAB), n-pentanol, n-octane, and water (or aqueous solution of precursor salts) were presented and the effects of the alcohol chain length, the ratio of CTAB to alcohol or water, and the precursor salt concentration on the formation and stability of microemulsions were studied. The performance and structure of the nanocomposites synthesized with the optimal parameters in the phase diagrams of the microemulsions were characterized by Brunauer–Emmett–Teller (BET) specific surface measurement, transmission electron microscopy (TEM), and X-ray diffraction (XRD), and the gas sensing properties were examined. The experimental results showed that these nanocomposites were highly sensitive and selective for the detection of NO2 and CO, and the sensor response depended on the composition of the composites, calcination temperature, operating temperature and gas concentration in air. Their sensing performance was further enhanced through introduction of a small amount of metals or other oxides as dopants or surface coatings. The gas-sensing mechanism of the nanocomposites was discussed by temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopic (XPS) analysis and was attributed to chemical and electronic synergistic effects between the nanocomposites and the gases. [Copyright &y& Elsevier]