Preparation And Structure Of Carbon-Encapsulated Iron Nanoparticles

Carbon-encapsulated metal nanoparticles(CEMNs) are a new kind of carbon/metal nanocomposite,in which graphite layers arrange around metal nanoparticles located in the center to form core-shell structure.As the special structures and properties,CEMNs might have important applications in areas such as high-density magnetic data storage, ferrofluids,microwave absorption materials,oxidation-reduction catalyst, handling materials of radioactive waste and bio-medical materials.The research focused on the preparation of CEMNs by co-pyrolysis of aromatic heavy oil and ferrocene.The effect of the synthesis parameters on the formation and transformation of CEMNs were investigated in detail. The morphology,structure and particular properties of the product were characterized via TEM,XRD measurements,and the relationship between them and synthesis parameters were studied to realize the controllable preparation of the product.The formation mechanism and thermo-transformation behavior of CEMNs were elucidated.In addition, the further carbonization treatments on CEMNs were carried out and some interesting phenomenon and new results were obtained,which will provide a novel strategy for the research and development of various carbon nanomaterials.The results show that large amount of carbon-encapsulated iron nanoparticles(CEMNs) were obtained by co-pyrolysis of an aromatic heavy oil and ferrocene.Under the reaction temperature of 420℃,it showed that increasing the ferrocene content,reducing the pressure of the reaction system and prolonging the holding time are beneficial for the formation of the CEMNs with uniform size,obvious core-shell boundaries and the carbon-coated with high degree of graphite.The coated metal containing a small amount of Fe₃C is mainlyα-Fe.When the reaction was carried out at 420 with the weight ratio of 35wt%and the pressure of the reaction system at 1MPa Products with diameters ranging from 30nm to 60nm were obtained and the nuclear was proved to beα-Fe.By the analysis of raw feedstock and the investigation of the relationship among the morphology,structure of CEMNs and the synthetic parameters,it was concluded that the formation of CEMNs by co-pyrolysis method was based on the principle of condensation and polymerization in a vapor-liquid bi-phase by the aid of catalysis under pressure,and the catalysis of iron nanoparticles was based on the dissolution-precipitation mechanism.It is assumed that two essential factors must be met for the formation of the nanorods,including the sufficient amounts of iron clusters and moderate reaction activity in the system.By carbonization at 1000℃under N₂ atmosphere,the size of CEMNs became larger and the carbon shells were changed from the disordered into graphitic structure under the catalysis of nano-sized iron core.At the same time a large amount of hollow onion-like carbon nanoparticles emerged due to the ejection of iron nanoparticles.