Study On Preparation And Properties Of The Spongy Porous Magnetic Materials

Spongy porous magnetic materials are a new type of functional materials because of their low density, high specific surface area, strong magnetic response, and thus have potential applications in various fields, including adsorption separation, catalysis, electromagnetic wave absorption, water treatment, magnetic device, biological medicine, antibacterial etc. Using glucose as a green chemical template and transition metal nitrates as raw materials. A series of the spongy porous materials are fabricated by a co-precipitation/sintering technology. Meanwhile, the formation mechanism for spongy materials is elucidated. By modulating their morphology, composition, and textural properties, spongy porous materials will exhibite promising applications in antibacterial, catalysis, electromagnetic wave-absorbing materials.The research contents are as follows:A green versatile glucose-engineered precipitation/sintering process was developed for the selective and mass preparation of spongy porous ferrite micro-polyhedra with tunable morphology, texture, and composition. Some kinetic factors, such as the molar ratio of glucose to metal nitrates, reaction temperature, sintering temperature and time, can be expediently employed to modulate their aspect ratio, shape, size, composition, and textural properties. In this protocol, glucose functions as reductive, protecting agents, structure-directing agents, and sacrificial templates to guide the assembly of sheet-like nuclei into polyhedral precursors and the formation of spongy porous structures. The Fe3O4 sponges can be obtained via sintering the precursors under N2. Fe3O4 spongy powders obtained at γ= 1:3 exhibit excellent absorption properties. The absorption bandwidth (RL≤-20 dB) is 7.7 GHz, relative to coating thicknesses of 1.8 mm to 5.5 mm. In particular, a minimum RL of-60.09 dB can be observed at 5.76 GHz, with a matching thickness of 4.0 mm. Owing to larger EM parameters, multiresonant behavior, and dissipative current, spongy porous Fe3O4 polyhedra exhibited the enhanced microwave-absorbing properties.Sponge-like ZnO/ZnFe2O4 hybrid micro-hexahedra with diverse textures andcompositions were futher fabricated by the thermal decomposition of hexahedral zinc/iron oxalate precursors, starting from a glucose-engineered co-precipitation process. Moreover, modulation in crystal size, composition, and textural properties of spongy ZnO/ZnFe2O4 micro-hexahedra was easily achieved by varying the Zn2+/Fe3+ feeding ratio and the annealing temperature. The antibacterial property of the products was analyzed by testing ATP (Adenosine Triphosphate). Results showed that oxidative stress was the governing mechanism for the antibacterial activity of ZnO/ZnFe2O4 hybrid materials. Moreover, we found that the higher reactive oxygen species yields and the resulting antibacterial activity were exhibited by the ZnO/ZnFe2O4 micro-hexahedra formed at lower sintering temperatures rather than the pure ZnO and Fe2O3. The enhanced antibacterial properties were likely caused by the spongy ZnO/ZnFe2O4 heterostructures, improving the probability of photoinduced charge separation and broadening the visible-light absorption.A green versatile glucose-engineered precipitation/sintering process was futher developed for the selective, large-scale growth of ZnO/Ni/ZnxNiyFe3-x-yO4 hybrid micro-polyhedra. Modulation over composition, grain size, and specific surface area can be expediently achieved by changing the Fe3+/Ni2+/Zn2+ molar ratio (γ) andsintering temperature (Ts). Relationships between structure and properties were systematically investigated. Relatively high Ts and the proper addition of Zn2+ improved static magnetic properties of the hybrid materials. The ZnO/Ni/ZnxNiyFe3-x-yO4 hybrid micro-hexahedra formed at 700 ℃ and γ = 2:0.5:0.5 showed a minimum reflection loss (RL) of -36.52 dB at 10.0 GHz with absorbing frequency (RL≤-20 dB) from 4.59 GHz to 18.0 GHz, corresponding to 1.7 mm to 5.5 mm coating thickness.The enhanced absorption performances were attributed to the additional multiphase interface, multiresonance, and good matching and absorbing properties of the hybrid materials.