Control of the size and morphology of metallic nanomaterials enables mastery of their properties to enhance their catalytic performances. In this work, uniform Co−B amorphous alloy nanoparticles were synthesized by a simple chemical reduction of [CoX 4 ] − with BH 4 − in the presence of Bu 4 P + . With the characterization of X-ray diffraction, selective area electronic diffraction, X-ray photoelectron spectroscopy, differential scanning calorimetry, and transmission electron microscopy, the resulting Co−B spherical nanoparticles were identified to be amorphous alloys in an average particle size around 55 nm. The synergistic effect of the halide anion and Bu 4 P + cation is essential for the formation of monodisperse and uniform spherical nanoparticles. During the Heck-type carbon−carbon coupling reactions and the hydrogenation of butyraldehyde to n-butanol, the as-synthesized Co−B catalyst was extremely active compared with the conventional Co−B obtained via the direct reduction of cobalt ions with BH 4 − in aqueous solution. In addition, the as-prepared Co−B amorphous alloy also exhibited recyclability during the hydrogenation of butyraldehyde due to better thermal stability, which was related to the higher surface B content and the uniform particle size. ■ INTRODUCTIONAmorphous alloys, a kind of metastable materials with longrange disordered but short-range ordered structure, have attracted growing attention from both academia and industry because of their superior corrosion resistance, high mechanical toughness, and excellent magnetic, electronic, and catalytic properties in comparison with their crystalline counterparts. 1−4 As heterogeneous catalysts, amorphous alloys have been widely studied because of their excellent catalytic performances. 1−7 To form and stabilize the amorphous structure, some metalloids (e.g., B or P) should be incorporated in amorphous alloys, thus significantly affecting their physical and chemical properties. 8,9 Chemical reduction of metallic ions with borohydride (BH 4 − ) in aqueous solution has been most often used to synthesize the kind of M−B amorphous alloy catalysts, 8,9 but vigorous and exothermic reactions between metallic ions and BH 4 − usually induce particle aggregation, thereby reducing catalytic activity. In addition, the nonuniform nanoparticles are also responsible for the ready crystallization of amorphous alloys. 10 Although size-control synthesis of M−B (M = Ni, Co) amorphous alloys could been achieved through microemulsions, 11,12 using large amounts of organic phase in these systems may cause several environmental problem in the preparation process. Recently, we successfully developed a facile method to prepare uniform M−B (M = Ni, Co) amorphous alloy nanoparticles using [M(NH 3 ) 6 ] 2+ as the metal source, 10,13 but the strong coordination of NH 3 to metallic ions and, thus, the very slow reduction process resulted in relatively large M−B particles (>100 nm) unfavorable for catalytic activity.The coordination of halide ligands to metallic ions is a welladdr...

Transition metal dichalcogenide nanostructures especially MoS2 have emerged as novel gas sensing materials. Particularly, MoS2-based optoelectronic devices activated by UV or visible light have been demonstrated as promising candidates for room temperature NO2 sensors. Here, we propose a novel room-temperature optoelectronic NO2 sensor based on sulfur-vacancy-enriched MoS2 (SV-MoS2). SV-MoS2 nanosheets were efficiently fabricated by a microwave-hydrothermal method, and their enhanced optical absorption and optoelectronic properties in the near-infrared (NIR) light region were experimentally and theoretically investigated. The optoelectronic gas sensors based on SV-MoS2 exhibited enhanced performance to ppb level of NO2 under NIR light illumination at room temperature. In addition, through functionalization with ZnO quantum dots, the SV-MoS2/ZnO nanocomposites exhibited a further enhancement in responses with fast response/recovery rates, full reversibility, and sub-ppb detection limit to NO2 at room temperature. The significant NO2 sensing improvement was due to the improved charge generation and transfer induced by sulfur vacancy under NIR light illumination. In addition, the sensor shows satisfied stability, reliable selectivity, and humidity resistance at room temperature. Therefore, this work provides an alternative approach to high-performance, low-power-consumption optoelectronic NO2 gas sensors working at room temperature, which can also be applied to other transition metal dichalcogenides for optoelectronic devices.

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Magnesium hydride has long been regarded as a promising candidate material for hydrogen and heat storage due to its high hydrogen capacity, reversibility, and low cost. Catalytic doping has been demonstrated as one of the most effective methods to improve hydrogen storage properties of MgH2. In this study, amorphous Ti45Cu41Ni9Zr5 and Ti40Cu47Zr10Sn3 alloys are used as additives for MgH2. Nanostructured MgH2 doped with amorphous or crystalline TiCu-based alloys are prepared by using a high-energy mechanochemical synthesis method. Results show that the amorphous TiCu additives provide enhanced catalytic effects compared to crystalline alloys of the same composition. Doping MgH2 using an amorphous Ti45Cu41Ni9Zr5 alloy yielded improved dehydrogenation kinetics compared to using crystalline Ti40Cu47Zr10Sn3 alloy. The analysis using transmission electron microscopy reveals that there are nanostructured catalytic particles uniformly distributed in the amorphous TiCu-catalyzed MgH2. The MgH2 system catalyzed by amorphous TiCu-based alloy shows little degradation during hydrogenation and dehydrogenation cycling at 300 °C. The amorphous TiCu-based catalysts are thermally stable at temperatures up to 360 °C. Heating the amorphous Ti45Cu41Ni9Zr5-catalyzed MgH2 to temperatures above 360 °C led to disproportionation of the catalyst alloy and the formation of MgCu2 and Ti2Cu. In addition, PCI analysis of the amorphous Ti45Cu41Ni9Zr5-catalyzed MgH2 shows a slight increase in hydrogen equilibrium pressure, resulting in a reaction enthalpy of −78.7 kJ/mol·H2 and an entropy of 145.0 J/K·mol·H2. The entropy calculated from this study is approximately 10 J/K·mol·H2 higher than values previously reported for undoped and catalyzed Mg–H systems.

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Two-dimensional boron synthesized by the chemical vapor deposition method is an atomically thin layer of boron with both light weight and metallicity.