Yongzhe Wang

Temperature-controlled growth of α-Al2O3 nanobelts and nanosheets

α-Al2O3 Nanobelts and nanosheets with different morphologies and sizes have been successfully synthesized by a simple chemical route from H2O and Al in an argon atmosphere. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations show that the as-synthesized α-Al2O3 nanostructures consist of nanobelts and nanosheets. We find that the temperature distribution inside the alumina tube is the critical factor determining the morphologies and sizes of the α-Al2O3 nanostructures. Photoluminescence measurements showed a blue luminescence band in the wavelength range of 400–500 nm, which can be attributed to F+ centers in the α-Al2O3 nanostructures. The growth of these products is believed to be mainly determined by growth kinetics as well as thermodynamics.

Immobilization of sulfur by constructing three-dimensional nitrogen rich carbons for long life lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries have been considered as next-generation rechargeable energy storage systems due to their high theoretical energy densities and low cost; however, the capacity decay resulting from the shuttle of lithium polysulfides (LiPSs) hinders their practical application. Herein, we describe a strategy to synthesize highly pyridinic-N-doped three-dimensional (3D) carbons for the chemisorption of LiPSs, which consist of zeolitic imidazolate framework-8-derived carbon (ZIF-8(C)) coated on the surface of N-doped carbon nanotubes supported by carbon nanosheets (NCNTs–CS–ZIF-8(C)). Using the obtained carbons as sulfur hosts, the S/NCNTs–CS–ZIF-8(C) cathodes show a high sulfur utilization of 86% at 0.1 C, a low capacity decay rate of 0.052% per cycle over 700 cycles at 1 C and impressive cycling life that is 564 mA h g−1 after 700 cycles at 1 C. First principles calculations based on the Vienna Ab-Initio Simulation Package (VASP) reveal that increasing the amount of the pyridinic-N component can enhance the adsorption of LiPSs, which yields effective suppression of the LiPS shuttle.

Morella-rubra-like metal–organic-framework-derived multilayered Co3O4/NiO/C hybrids as high-performance anodes for lithium storage

Co3O4/NiO/C microspheres with a multilayered ball-in-ball hollow nanoarchitecture were synthesized via carbonization and oxidation treatments of Morella-rubra-like CoNi-based metal–organic frameworks (CoNi-MOFs). The shell walls of each ball were entirely composed of uniform nanorods. This unique multilayered hollow structure can strongly mitigate the change in the volume of the electrodes, which maintains the structural integrity of the Co3O4/NiO/C hybrids during the lithiation–delithiation process. In addition, the C scaffolds improve the conductivity of the electrode and function as a buffer material to mitigate the pulverization of Co3O4 and NiO nanoparticles. Therefore, in Li-ion cells, the multilayered Co3O4/NiO/C hybrids exhibit a high reversible capacity (864 mA h g−1 at 1 A g−1), an excellent rate capacity (421 mA h g−1 at 4 A g−1), and a long-lifetime cycling performance (776 mA h g−1, even after 1000 cycles at 1 A g−1) for Li storage.

Controllable synthesis of hollow copper oxide encapsulated into N-doped carbon nanosheets as high-stability anodes for lithium-ion batteries

Copper oxide is one of the promising anode materials for lithium-ion batteries (LIBs) due to its high energy density. However, it suffers from fast capacity fading and poor cycling stability, arising from the low electrical conductivity and the large volume expansion. Herein, we report a chemical vapor and solid deposition strategy for the synthesis of hollow copper nanoparticles supported by N-doped carbon nanosheets (Cu@NCSs) on Cu foil, adopting a polymer as the carbon source. After successive oxidation treatment, the construction of hollow copper oxide encapsulated into N-doped carbon nanosheets (CuO@NCSs) is achieved. The resulting products are used as anodes in LIBs, displaying a capacity of 688 mA h g−1 over 1000 cycles at 2 A g−1 and a capacity of 400 mA h g−1 at 4 A g−1. Such superior performance is attributed to the well-designed hollow CuO@NCS composites, which not only improve the electrical conductivity of electrode materials, but also allow easy penetration of electrolyte and mitigation of the volume expansion.

Visible-light-active silver- , vanadium-codoped TiO2 with improved photocatalytic activity

Abstract Optimized doped TiO2 is necessary for efficient visible light harvesting and widening the applications spectrum of TiO2-based materials. Titanium dioxide doped with silver and/or vanadium has been synthesized by one-pot hydrothermal method without post-calcination. Codoping induced visible light absorption while maintaining the photoactive anatase phase along with good crystallinity. Synthesized products are in nanometer range and possess high specific surface area. Having nearly spherical morphology, the particles are distributed and the particle size estimated from TEM observation is in accordance with the XRD results. Spectroscopic investigations reveal that the doped atoms successfully entered the TiO2 lattice modifying the band structure. The narrowed band gap allows visible light photons for absorption, and the codoped samples displayed enhanced visible light absorption among the synthesized samples. Photodegradation performance evaluated under visible light irradiations showed that silver- , vanadium-codoped TiO2 have the best visible light photocatalytic activity attributed to stable configuration, high visible light absorption, coupling between silver and vanadium and their optimal doping concentration.

Quantitative analysis of martensite and bainite microstructures using electron backscatter diffraction.

In the present work, ultra‐high‐strength steels with multiphase microstructures containing martensite and bainite were prepared by controlling the cooling rate. A new approach was proposed for quantitatively statistical phase analysis using electron backscatter diffraction (EBSD) based on the band contrast which correlates to the quality and intensity of the diffraction patterns. This approach takes advantage of the inherently greater lattice imperfections of martensite, such as dislocations and low‐angle grain boundaries, relative to that of bainite. These can reduce the intensity and quality of the EBSD patterns of martensite, which decrease the band contrast. Thus, combined with morphological observations, Gaussian two‐peak fitting was employed to analyze the band contrast profile and confirm the ranges of band contrast for the two phases. The volume fractions of bainite and martensite in different samples were determined successfully. In addition, the results show that increased cooling rates improve the proportion of martensite and the ratio of martensite to bainite. Microsc. Res. Tech. 79:814–819, 2016.

Determining E 1 and E 2 values for yttrium aluminum garnet ceramics using the Duane-Hunt limit

A major challenge when performing scanning electron microscopy and X‐ray analysis on many ceramic materials is their electrical insulation properties, which leads to buildup of the surface charge and reduced contrast in the secondary electron image. A new procedure was established to quantitatively determine the neutral state values, E1 and E2, of yttrium aluminum garnet (YAG) ceramics using the Duane‐Hunt limit (EDHL) of Bremsstrahlung, in order to eliminate this charge effect. Thirty‐eight EDHL values were linearly fitted with the last portion of X‐ray spectra acquired under the incident energy, E0, from 0.35 to 5.0 kV. According to the distribution of EDHL, two piecewise linear fitting was first employed with a breakpoint of 1.0 kV. Consequently, two intersection points of 0.54 and 2.48 kV, which correspond to E1 and E2 for YAG ceramics, were directly determined using a theoretical curve (EDHL = E0). As a result, the high‐resolution images of the YAG ceramic grain structure were successfully obtained using the calculated E1 and E2 values.