Highly Exothermic and Superhydrophobic Mg/Fluorocarbon Core/Shell Nanoenergetic Arrays

Mg/fluorocarbon core/shell nanoenergetic arrays are prepared onto silicon substrate, with Mg nanorods as the core and fluorocarbon as the shell. Mg nanorods are deposited by the glancing angle deposition technique, and the fluorocarbon layer is then prepared as a shell to encase the Mg nanorods by the magnetron sputtering deposition process. Scanning electron microscopy and transmission electron microscopy show the core/shell structure of the Mg/fluorocarbon arrays. X-ray energy-dispersive spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy are used to characterize the structural composition of the Mg/fluorocarbon. It is found that the as-prepared fluorocarbon layer consists of shorter molecular chains compared to that of bulk polytetrafluoroethylene, which is proven beneficial to the low onset reaction temperature of Mg/fluorocarbon. Water contact angle test demonstrates the superhydrophobicity of the Mg/fluorocarbon arrays, and a static contact angle as high as 162° is achieved. Thermal analysis shows that the Mg/fluorocarbon material exhibits a very low onset reaction temperature of about 270 °C as well as an ultrahigh heat of reaction approaching 9 kJ/g. A preliminary combustion test reveals rapid combustion wave propagation, and a convective mechanism is adopted to explain the combustion behaviors

Needle-like Co₃O₄ Anchored on the Graphene with Enhanced Electrochemical Performance for Aqueous Supercapacitors

We synthesized the needle-like cobalt oxide/graphene composites with different mass ratios, which are composed of cobalt oxide (Co₃O₄ or CoO) needle homogeneously anchored on graphene nanosheets as the template, by a facile hydrothermal method. Without the graphene as the template, the cobalt precursor tends to group into urchin-like spheres formed by many fine needles. When used as electrode materials of aqueous supercapacitor, the composites of the needle-like Co₃O₄/graphene (the mass ratio of graphene oxide­(GO) and Co­(NO₃)₂·6H₂O is 1:5) exhibit a high specific capacitance of 157.7 F g^–1 at a current density of 0.1 A g^–1 in 2 mol L^–1 KOH aqueous solution as well as good rate capability. Meanwhile, the capacitance retention keeps about 70% of the initial value after 4000 cycles at a current density of 0.2 A g^–1. The enhancement of excellent electrochemical performances may be attributed to the synergistic effect of graphene and cobalt oxide components in the unique multiscale structure of the composites

Enhanced Thermal Decomposition Properties of CL-20 through Space-Confining in Three-Dimensional Hierarchically Ordered Porous Carbon

High energy and low signature properties are the future trend of solid propellant development. As a new and promising oxidizer, hexanitrohexaazaisowurtzitane (CL-20) is expected to replace the conventional oxidizer ammonium perchlorate to reach above goals. However, the high pressure exponent of CL-20 hinders its application in solid propellants so that the development of effective catalysts to improve the thermal decomposition properties of CL-20 still remains challenging. Here, 3D hierarchically ordered porous carbon (3D HOPC) is presented as a catalyst for the thermal decomposition of CL-20 via synthesizing a series of nanostructured CL-20/HOPC composites. In these nanocomposites, CL-20 is homogeneously space-confined into the 3D HOPC scaffold as nanocrystals 9.2–26.5 nm in diameter. The effect of the pore textural parameters and surface modification of 3D HOPC as well as CL-20 loading amount on the thermal decomposition of CL-20 is discussed. A significant improvement of the thermal decomposition properties of CL-20 is achieved with remarkable decrease in decomposition peak temperature (from 247.0 to 174.8 °C) and activation energy (from 165.5 to 115.3 kJ/mol). The exceptional performance of 3D HOPC could be attributed to its well-connected 3D hierarchically ordered porous structure, high surface area, and the confined CL-20 nanocrystals. This work clearly demonstrates that 3D HOPC is a superior catalyst for CL-20 thermal decomposition and opens new potential for further applications of CL-20 in solid propellants

Gram-Scale Synthesis of Graphene Quantum Dots from Single Carbon Atoms Growth via Energetic Material Deflagration

Graphene quantum dots (GQDs) with quantum confinement and size effect are proposed to be applicable in photovoltaic, nanodevices, and so on, due to extraordinary electronic and optical properties. Here we report a facile approach to synthesize gram-scale GQDs from active carbon atoms, which are obtained via the deflagration reaction of polytetrafluoroethylene (PTFE) and Si, growing from high- to low-temperature zones when traveling through the deflagration flame in a short time with releasing gas as the carrier medium. The prepared GQDs were aggregated into carbon nanospheres; thus, Hummer’s method was utilized to exfoliate the GQD aggregations into individual GQDs. We show that the length of GQDs is ∼10 nm and the exfoliated GQDs solution presents an obvious fluorescence effect with a strong emission peak at 570 at 460 nm excitation. And these GQDs are demonstrated to be excellent probes for cellular imaging. Furthermore, we propose a growth mechanism based on computer simulation, which is well verified by experimental reproduction. Our study opens up a promising route for high-yield and high-quality GQDs, as well as other various quantum dots