Hydrothermal Synthesis And Characterization Of Cofe 2 O 4 /mwnts Composites

Carbon nanotubes (CNTs) chemistry, as an interdisciplinary field of chemistry research and materials preparation, plays an irreplaceable role in the nano science and technology. CNTs have lots of unique properties, such as one dimensional nano-structure, high aspect ratio, good toughness, excellent electrical and thermal conductivity. Its hardness can be comparable with diamond. These properties entirely grant CNTs potential applications in field emission, high-frequency broadband electromagnetic wave absorption and thermal conductivity, hydrogen storage, and catalysis. It is significantly important to make a study on CNTs composites with high performance which can provide incomparable superiority when used in complex environment.This paper aimed to synthesize spinel ferrite/multi-walled carbon nanotubes (MWNTs) composites. In this study, MWNTs were coated by a layer of nano spinel ferrite particles to modify the magnetic properties and conductivity of MWNTs, hence improving the impedance match and finally enhancing the microwave-absorbing capability.Main work and results were summarized as follows:1) Hydrothermal synthesis of CoFe₂O₄ nano-particles was studied by optimizing lots of factors including reaction temperature, Co/Fe ratio in raw materials, precipitator and solvent. The influence of these factors on the phase, morphology, magnetic and electromagnetic parameters of the products was fully investigated. It was found that more orbicular CoFe₂O₄ nano-particles with larger size were obtained at a higher reaction temperature. CoFe₂O₄ nano-particles synthesized with NaAc and ethylene glycol (EG)/ water, as the precipitator and solvent respectively, were smaller and in narrower size distribution than in NaOH solution. By comparison, the average size of the CoFe₂O₄ nano-particles was reduced from 30nm¹00nm to 5¹0nm.2) To study the electromagnetic performance of spinel ferrite, Zn salts and Mg salts were added to the reaction system to synthesize multi-component ferrite nano-particles. Test results indicated permeability and complex dielectric parameters were optimized by dopping Zn2+ into cobalt ferrite nano-particles.3) MWNTs were first treated with mixed acid via hydrothermal way to increase active centers and functional groups to improve coating performance. FTIR was utilized to indentify content of oxygen element in the hydrothermal oxidized MWNTs. Results showed a large number of carboxyl (-COOH) and hydroxyl (-OH) were grafted.4) CoFe₂O₄/MWNTs composites were successfully synthesized by introducing hydrothermal oxidized MWNTs into the hydrothermal synthesis reaction of CoFe₂O₄. TEM images showed that MWNTs were uniformly coated with CoFe₂O₄ as water and NaOH were replaced with EG/H2O and NaAc. It was also found that the impedance match of MWNTs had been greatly improved by coating with CoFe₂O₄.5) Lastly, composites were mixed with PD-9B acrylic emulsion and coated on the aluminum plate. The results of wave reflection showed that Zn_0.5Co_0.5Fe₂O₄/MWNTs had better wave absorbing performance.