Large‐scale, uniform, vertically standing graphene with atomically thin edges are controllably synthesized on copper foil using a microwave‐plasma chemical vapor deposition system. A growth mechanism ...for this system is proposed. This film shows excellent field‐emission properties, with low turn‐on field of 1.3 V μm−1, low threshold field of 3.0 V μm−1 and a large field‐enhancement factor more than 10 000.
Reduced graphene oxide (rGO)-encapsulated amine functionalized Fe3O4 magnetic nanospheres (AMs), were used to support Pt catalysts (Pt-rGO-AMs). The Pt-rGO-AMs were fabricated by modifying ...positively-charged aminopropyltrimethoxysilane on the surface of Fe3O4 nanoparticles (NPs) to form functionalized Fe3O4 NPs. Then negatively-charged graphene oxide (GO) was coated on the surface of the functionalized Fe3O4 nanospheres by electrostatic layer-by-layer self-assembly. Finally, Pt NPs were uniformly anchored on the surface of GO by a polyol reduction reaction and the GO was simultaneously reduced to rGO. The Pt-rGO-AMs exhibit excellent ferromagnetic property, which makes it possible to realize controllable on–off reactions and convenient recycling of catalyst materials. The electrochemical activity of the catalyst for methanol oxidation is significantly improved compared to Pt NPs absorbed on a rGO sheet and has better stability. The superior performance of this Pt-rGO-AMs catalyst is attributed both to the structure, which improve the accessibility of the Pt NPs by exposing them on the surface of the support, and to the greatly improved electronic conductivity of the support.
► Graphene nanosheets–MWCNTs (GNS–CNTs) composites as Pd electrocatalysts support were synthesized by in situ reduction method. ► The direct electrooxidation of HCOOH is improved on the GNS–CNTs ...based catalyst. ► Both activity and durability of GNS–CNTs based catalyst are improved greatly. ► Pd/GNS–CNTs catalysts exhibit excellent performance when the mass ratio of GO to CNTs is 5:1.
Graphene nanosheets–MWCNTs (GNS–CNTs) composites were synthesized by in situ reduction method, and then palladium nanoparticles (NPs) were supported on the GNS–CNTs by a microwave-assisted polyol process. Microstructure measurements showed that the graphene nanosheets and the CNTs formed a uniform nanocomposite with CNTs absorbed on the graphene nanosheets surface and/or filled between the graphene nanosheets. Compared to Pd/Vulcan XC-72R carbon, Pd/GNS, or Pd/CNTs catalysts, the Pd/GNS–CNTs catalysts exhibit excellent electrocatalytic activity and stability for formic acid electro-oxidation when the mass ratio of GO to CNTs is 5:1. The superior performance of Pd/GNS–CNTs catalysts may arise from large surface area utilization for NPs and enhanced electronic conductivity of the supports. Therefore, the GNS–CNTs composite should be a promising carbon material for application as electrocatalyst support in fuel cells.
The problems of high temperature and volume shrinkage are frequently encountered in the process of fabricating superhydrophobic graphene aerogels. We present ultralight graphene aerogels with ...superhydrophobicity and superoleophilicity by a vapor–liquid deposition process. The graphene aerogels are prepared by graphene oxide assembled into monolithic graphene hydrogel in dopamine-mediated aqueous solution at mild temperature and a sealed reaction, then by directional freezing and freeze-drying. Subsequent fluorinated alkyl silane is introduced to produce ultralight graphene aerogel by vapor–liquid deposition treatments; the surface of the aerogel has outstanding superhydrophobicity and superoleophilicity with water and oil contact angles of 160.2° and 0°, respectively. In addition, the resulting graphene aerogels showed super low density, large specific surface area, excellent adsorption capacities, and superior adsorption recyclability. Its adsorption capacity was higher than 109 g/g for the used common oils and organic solvents. Its properties suggest applications in the field of oil adsorption and oil–water separation. The new strategy may open up a new way to design high-performance superhydrophobic 3D graphene monoliths for water treatment.
Monodisperse iron oxide nanocrystals were synthesized by a simplified method using iron chloride as precursor. In the presence of Cl ions, the as-produced iron oxide nanocrystals preferred a cubic ...shape with {100} facets exposed. The function of halogens including Cl and Br ions on stabilizing {100} facets of spinel structured iron oxides, rather than the regulation of thermolysis kinetics and surfactants, was found influential on the shape control of nanocubes in this organic phase approach. The synthesis can be also extended for cobalt ferrite nanocubes and cobalt oxide polyhedrons.
Via electroless metal deposition, well-defined silver dendrites and thin porous silicon (por-Si) layers are simultaneously prepared in ammonia fluoride solution containing AgNO
3 at 50
°C. A ...self-assembled localized microscopic electrochemical cell model and a diffusion-limited aggregation mode are used to explain the growth of silver dendrites. The formation of silver dendritic nanostructures derives from the continuous aggregation growth of small particles on a layer of silver nanoparticles or nanoclusters (Volmer-Weber layer). Thin and homogeneous nanostructure por-Si layers display visible light-emission properties at room temperature. The investigation of the surface-enhanced Raman scattering (SERS) reveals that the film of silver dendrites on por-Si is an excellent substrate with significant enhancement effect.
Pentagonal-ring-structured PtP
2
bulk crystals and the two-dimensional (2D) PtP
2
with rich theoretical physical and chemical properties have attracted considerable attention for the applications in ...high-performance electronic and optoelectronic devices. Here, high-quality PtP
2
single crystals have been successfully prepared by using a tin flux method with the optimal molar ratios of Pt and P. 3D weak localization effect and negative magnetoresistance (NMR) are observed in the high-quality PtP
2
single crystals for the first time. Crystalline structure, magnetization, and optical spectral characterizations have demonstrated that the defects in PtP
2
crystals can suppress the NMR effect and magnetic ordered states. These findings open up a way to synthesize the bulk and low-dimensional noble-metal-based phosphides of high quality and provide new platforms for studying the different correlated electronic states.
Ultrathin SnSe nanosheets (9–20 nm) are synthesized on molten polydimethylsiloxane by chemical vapor deposition. Thickness‐dependent Raman features persist even with thickness over 10 nm. Meanwhile, ...anisotropy of field‐effect mobility along b and c axes is observed above 240 K. Finally, thermopower can be easily modified by gate bias and temperature.
In a microwave tube the energy of electrons in an electron beam, which are usually generated by a thermionic cathode, is modulated such that it is transformed into electromagnetic wave energy. In ...this paper, we modulated the field emission using AC signals.A field emission current with AC components was attained by adding a small AC voltage to a high extracting DC voltage. We observed two phenomena related to the AC components of the field emission current. First, when the DC component of the extracting voltage was low, the current measured in the circuit was dominated by the displacement current. Second, besides the fundamental frequency component, higher order harmonics were also observed in the field emission current.
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