Metal Atom-Doped Co3O4 Hierarchical Nanoplates for Electrocatalytic Oxygen Evolution

Electrocatalysts based on hierarchically structured and heteroatom-doped non-noble metal oxide materials are of great importance for efficient and low-cost electrochemical water splitting systems. Herein, the synthesis of a series of hierarchical hollow nanoplates (NPs) composed of ultrathin Co₃O₄ nanosheets doped with 13 different metal atoms is reported. The synthesis involves a cooperative etching−coordination−reorganization approach starting from zeolitic imidazolate framework-67 (ZIF-67) NPs. First, metal atom decorated ZIF-67 NPs with unique cross-channels are formed through a Lewis acid etching and metal species coordination process. Afterward, the composite NPs are converted to hollow Co₃O₄ hierarchical NPs composed of ultrathin nanosheets through a solvothermal reaction, during which the guest metal species is doped into the octahedral sites of Co₃O₄. Density functional theory calculations suggest that doping of small amount of Fe atoms near the surface of Co₃O₄ can greatly enhance the electrocatalytic activity toward the oxygen evolution reaction (OER). Benefiting from the structural and compositional advantages, the obtained Fe-doped Co₃O₄ hierarchical NPs manifest superior electrocatalytic performance for OER with an overpotential of 262 mV at 10 mA cm⁻², a Tafel slope of 43 mV dec⁻¹, and excellent stability even at a high current density of 100 mA cm⁻² for 50 h.     

Novel rose-type magnetic (Fe3O4, γ-Fe2O3 and α-Fe2O3) nanoplates synthesized by simple hydrothermal decomposition

Rose-type magnetic nanoplates (RTMNPs) were synthesized by a simple hydrothermal decomposition method where FeCl₂·4H₂O was solely used as a precursor. The synthesized nanoplates were characterized using XRD, FE-SEM, UV-vis absorption (reflectance) spectra and magnetic hysteresis loops. The resulting nanoplates were in the ranges of size 350-500 nm and width 60-70 nm with high crystallinity, purity (shown by XRD) and reproducibility. These iron oxide nanoplates have a great potential in magnetic nanodevices and biomagnetic applications.     

Direct Conversion of Single‐Layer SnO Nanoplates to Multi‐Layer SnO2 Nanoplates with Enhanced Ethanol Sensing Properties

Direct conversion of single‐layer SnO nanoplates to multi‐layer SnO₂ nanoplates is achieved by annealing in an O₂ ambient at 700 °C. For 50 ppm ethanol, the sensitivities of the multi‐layer SnO₂ nanoplates are more than double that of single‐layer SnO₂ nanoplates, which are also formed from the single‐layer SnO. The higher sensitivity of the multi‐layer nanoplates is attributed to their larger surface/volume ratio. The facile fabrication of interconnected multi‐layer SnO₂ nanoplates at low temperature directly on a Si substrate and sensing chip without the aid of catalysts offers vast advantages over competing methods for the fabrication of high‐sensitivity SnO₂ sensors.     

Tuning the thermal,mechanical, and combustion properties of NC-TEGDN-RDX propellants via incorporation of graphene nanoplates

ABSTRACT

Graphene nanoplates (GNPs) were incorporated into a solid composite propellant (NC-TEGDN-RDX) to tune the thermal, mechanical, and combustion properties of the material. Physical, thermal, and combustion properties of NC-TEGDN-RDX with <2 wt% addition of GNPs were characterized using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), tensile/compressive/impact strength testing, and constant volume combustion experiments. Microstructure of the composite propellants examined using SEM demonstrated uniform dispersion of the GNPs at low-weight percent additives (<1 wt%), but began to show large agglomerations of the additives at higher additive content. Decomposition enthalpy of the propellant with 1 wt% GNPs increased by ~130 J/g compared to neat propellants. Moreover, the maximum burning rate was observed for samples containing 1 wt% GNPs, with values of 19 cm/s at 20°C and 17 cm/s at ?40°C. Dynamic vivacity of the propellant achieved a maximum upon addition of 1 wt% GNPs. The pressure exponent of the propellant decreased with the addition of GNPs, as well. The mechanical properties including tensile, compressive, and impact strength were improved at 20°C and ?40°C. These results demonstrate that the addition of GNPs may offer new methods by which to tune and improve thermal decomposition, thermal conductivity, combustion performance, and mechanical properties of the NC-TEGDN-RDX propellants.     

Synthesis of microsized gold nanoplates by a self-seeding method in ethanol solution

Single-crystalline gold nanoplates with microsized edges have been synthesized by a simple self-seeding method with the assistance of aniline in an ethanol solution. The as-synthesized gold nanoplates showed strong absorption in near infrared region (NIR). Investigation suggests the amount of aniline added to the reaction solution plays a key role in the generation of nanoplates. A possible formation mechanism for these gold nanoplates is also proposed.     

Thermal decomposition synthesis of single-crystalline porous ZnO nanoplates self-assembled by tiny nanocrystals and their pore-dependent magnetic properties

High quality porous ZnO nanoplates with a pure crystal phase of hexagonal wurtzite structure were fabricated by thermal decomposition route for the first time. Electron microscopy investigations show that each porous ZnO nanoplates has a single-crystalline nature, which is self-assembled by tiny nanocrystals. The size and pore density of the ZnO nanoplates can be tuned by only changing the amount of zinc source. Magnetic investigations show that the magnetic phase can be converted from paramagnetism to ferromagnetism at room temperature, by increasing the pore density of ZnO nanoplates. The ZnO nanoplates with highest pore density show a d° room-temperature ferromagnetic characteristic, and the saturation magnetization reaches 26 memu/g. Several experimental evidences, including XPS, PL and ESR spectra, demonstrate that the defects of singly charged oxygen vacancies related to the pore density contribute to the long-range ferromagnetic ordering in the dopant-free porous ZnO nanoplates. This finding suggests that the pore-dependent ferromagnetism can be manipulated by tuning the surface-volume ratio, which is significant for the understanding and exploration of diluted magnetic semiconductors.