Investigation On The Synthesis And Properties Of Carbon Encapsulated Cobalt Nanoparticles

Carbon encapsulated cobalt nanoparticles(Co@C), which combine the excellent properties of the carbon shells and cobalt core, have exhibited the wide potential applications as magnetic functional materials, fuel cell materials, biomedical materials, adsorption materials and so on. However, the purity, morphology and magnetic properties of Co@C are still not satisfied currently, which limits their applications. Thus, there is great significance to further investigate the synthesis process and properties of Co@C.In this paper, Co@C were synthesized by chemical vapor deposition(CVD) method using Co as catalysts. The processes to synthesize Co@C on different types of catalyst carrier(Al2O3 and NaCl) were investigated. The influences of synthetic technological conditions on the structure and magnetic properties of Co@C were studied, and the synthetic mechanism of Co@C was analyzed. The preliminary discussion on the adsorption performance of Co@C was performed. The results may provide experimental basis for their applications in high density magnetic recording materials and water environmental restoration.Co@C were synthesized using Co/Al2O3 as catalysts and methane as carbon source by CVD method. The influences of synthesis temperature and catalyst content on the morphology and structure of Co@C were investigated. The magnetic properties of Co@C were measured. The results showed that, under the conditions of 700℃ and 5wt.% Co, the Co@C synthesized over Al2O3 carriers have a uniform grain size, good stability, high graphitization degree and yield. The study on the magnetic properties of Co@C synthesized at different temperatures showed that, under the conditions of 500℃ and 5wt.% Co, the grown Co@C have better magnetic properties, and the coercive force(Hc) reached 560.07 Oe. The content of carbon and the size of Co nanoparticles were the major factors influencing the magnetic properties of Co@C.In order to improve the purity and magnetic property, Co@C were synthesized by CVD using new Co/NaCl catalyst with acetylene as carbon source. The relationship of the synthesis temperature, catalyst content and synthesis time with the morphology, structure and magnetic property of Co@C were investigated. The magnetic and adsorption properties of Co@C were analyzed. The results showed that NaCl carrier can be completely removed through simple cleaning and centrifugal treatment to obtain Co@C with high purity. With the increase of synthesis temperature, the carbon layers transform from amorphous carbon or graphitic pieces to carbon sheets with high degree of graphitization. With the extension of synthesis time, the thickness of carbon layers increases gradually. Under the conditions of 400℃, 1wt.% Co and synthesis time of 30 min, uniform particle size, good thermal stability, high degree of graphitization and Hc can be obtained. And the Hc value relates to both the size of core Co and the thickness of carbon layers.The preliminary study about the adsorption performance of Co@C synthesized over NaCl carrier suggests that, Co@C have well adsorption and desorption abilities for methylene blue(MB). The adsorption percentages of MB decreased with the increase of initial MB concentrations. The isothermal adsorption pattern accords with the Freundlich equation. The adsorption process conforms to the pesudo-second-order kinetics equation.