Synthesis And Application Of Transition Oxide Fe₃O₄ And Zn₃(VO₄)₂

Transition metal oxides were widely used in different areas due to their multi-form of oxidation states as well as their special crystal structures. The main object of this paper is to develop simple methods for the synthesis of transition metal oxide magnetite (Fe3O4) and vanadium zinc oxide (Zn3(VO4)2) that will have potential applications in green and environmental-benign fields, to research the microwave absorption of Fe3O4 and its application in lithium ion batteries, and to investigate the application of Zn3(VO4)2 as electrode in lithium ion batteries. In this paper, we report simple methods to fabricate Fe3O4 and Zn3(VO4)2, and their structures and applications were investigated in detail.1. Well dispersed Fe3O4 single crystal nanoparticles were synthesized by a simple hydrothermal method. Box-like, plate-like morphology and micro-spheres were obtained via tuning the reaction conditions.2. Fe3O4 nanoparticles and paraffin composites are of good microwave absorption properties. When the matching thickness is 3 mm, the calculated reflection loss of the composite reaches a maximum value of-21.2 dB at 8.16 GHz with 30% volume fraction of Fe3O4. Wide region of microwave absorption is achieved for carbon coated Fe3O4. When the matching thickness is 4 mm, the calculated reflection loss of the composite with 70% volume fraction of carbon coated Fe3O4 exhibits broad microwave absorption ranges from 2.5 to 18 GHz.3. Electrochemical properties of Fe3O4 nanoparticles and microspheres as negative electrodes of lithium ion batteries were studied by conventional charge/discharge test, showing obvious charge/discharge platforms. For Fe3O4 nanoparticles electrode, the initial charge and discharge capacity at current density of 0.1 mA cm-2 arrived at 960 mAh g-1 and 1146 mAh g-1, respecitively. After 50th cycles, the charge and discharge capacity maintain at 101 mAh g-1 and 102 mAh g-1, respectively. The mean coulombic efficiency of Fe3O4 nanoparticles electrode during the charge/discharge test at current density of 0.1 mA cm-2 is 95.66%. For microsphere electrode, the initial charge and discharge capacity at current density of 0.1 mA cm-2 arrived at 856 mAh g-1 and 1141 mAh g-1, respectively, maintaining at 123 mAh g-1 and 126 mAh g-1 after 50 cycles. The mean coulombic efficiency of Fe3O4 microsphere electrode during the charge/discharge test at current density of 0.1 mA cm-2 is 95.95%. The differential charge/discharge capacity versus voltage curves of Fe3O4 nanoparticles and microspheres electrodes show obvious oxidation and reduction peaks that are in good accordance with charge/discharge platforms. It indicates a reaction between Fe3O4 and Li+during the charge and discharge process, which is likely to be 8Li++Fe3O4 (?) 3Fe+4Li2O.4. Zinc vanadium oxide hydroxide hydrate (Zn3(OH)2V2O7·nH2O) nanobelts were synthesized via a simple hydrothermal method. It is firstly found that the as-synthesized nanobelts are ferromagnetic at room temperature. By changing the reaction condictions, nanosheets and flower-like morphology were successfully synthesized. Zinc vanadium oxide particles were obtained via annealing Zn3(OH)2V2O7·nH2O nanosheets at air atmosphere. Photoluminescence measurement shows strong visible light emission ranges from 500 nm to 700 nm, and the green emission center was proved to come from Zn vacancies in Zn3(VO4)2. Electrochemical properties of Zn3(VO4)2 electrode were studied, which shows steady platforms near 0.15 V during the first discharge curves, endowing it with potential application in lithium ion battery.