Kai Huang

Controllable synthesis of hexagonal WO3 nanostructures and their application in lithium batteries

Novel hexagonal WO3 (h-WO3) nanorods have been successfully prepared on a large scale by a simple hydrothermal method by adding Na2SO4. Uniform nanorods with diameters of 100–200 nm and lengths of up to several micrometres are obtained. The morphology evolvement and the growth mechanism were studied carefully with different quantities of Na2SO4. Different experimental parameters can lead to different structures and morphologies of the final products in our experiment. The current understanding of the growth mechanism of these nanostructures potentially provides important information about the structure design and morphology-controlled synthesis of WO3 and other oxides. The electrochemical performances of the as-prepared h-WO3 nanowires as anode materials of Li-ion batteries have also been investigated. These batteries have a discharge capacity of 215 mA h g−1 at the initial cycles and show an extreme capacity retention. The results imply that these h-WO3 nanorods are promising anode materials for Li-ion batteries.

Hydrothermal synthesis and microwave absorption properties of Fe3O4 nanocrystals

Well-dispersed Fe3O4 nanocrystals were synthesized by a simple hydrothermal method. The as-synthesized products were characterized by field emission scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, x-ray diffraction, vibrating sample magnetometer and vector network analysis. The complex permittivity and permeability of paraffin wax and Fe3O4 with different Fe3O4 volume fractions were measured to increase linearly with the increase in the volume fraction of Fe3O4. The magnetic loss was caused mainly by natural resonance, which is in good agreement with the Kittel equation results. When the matching thickness is 3 mm, the calculated reflection loss reaches a maximum value of −21.2 dB at 8.16 GHz with 30% volume fraction of Fe3O4.

Synthesis of α-Fe2O3 dendrites by a hydrothermal approach and their application in lithium-ion batteries

Hematite α-Fe2O3 dendrites with lengths of 1–4.5 µm along the trunk were synthesized by a low-temperature hydrothermal method. The morphology and the crystal structure of the final products were characterized. The magnetic evaluations showed that the as-prepared α-Fe2O3 dendrites have a high coercivity. The electrochemical performance as anode material for lithium-ion batteries was further evaluated by charge–discharge measurement. It was demonstrated that the material could provide an initial capacity of 1560 mA h g−1, 1095 mA h g−1 and 670 mA h g−1 at a current density of 0.1 mA cm−2, 0.2 mA cm−2 and 1 mA cm−2, respectively.

W18O49 Nanowires as Ultraviolet Photodetector.

Photodetectors in a configuration of field effect transistor were fabricated based on individual W18O49 nanowires. Evaluation of electrical transport behavior indicates that the W18O49 nanowires are n-type semiconductors. The photodetectors show high sensitivity, stability and reversibility to ultraviolet (UV) light. A high photoconductive gain of 104 was obtained, and the photoconductivity is up to 60 nS upon exposure to 312 nm UV light with an intensity of 1.6 mW/cm2. Absorption of oxygen on the surface of W18O49 nanowires has a significant influence on the dark conductivity, and the ambient gas can remarkably change the conductivity of W18O49 nanowire. The results imply that W18O49 nanowires will be promising candidates for fabricating UV photodetectors.

Photoluminescence and magnetism in Co-doped ZnO powder

Spindle-like ZnO doped with 2–5 at% cobalt powders were prepared by a low temperature aqueous solution method. The structural and magnetic properties of the products were investigated. The obtained products were identified to be of hexagonal wurtzite structure without any impurity phase. Also, the Co was incorporated in the ZnO lattice as Co2+ and substituted for the Zn site with no evidence of metallic Co. Ferromagnetic behaviour was clearly observed at room temperature for the Co-doped samples. Photoluminescence intensity due to the vacancies varies with the Co concentration, and the ferromagnetism moment increases with the increment of oxygen vacancies.