Preparation, Transformation And Properties Of Carbon-Encapsulated Metal Nanoparticles

Carbon-encapsulated metal nanoparticles and onion-like hollow nanoparticles are both new nano-carbon materials. They have the similar spherical shell structure, in which graphite layers arrange around the center (filled with metal or hollow) . Because of their special structures and properties, they might have wide applications in areas such as high-density magnetic data storage, microwave absorption, catalyst and so on.Recently our research group proposed a novel method, co-pyrolysis, for the large-scale preparation of carbon-encapsulated metal nanoparticles using aromatic hydrocarbons as the carbon source and transition metal compounds as the metal source. It features many advantages such as simplicity, low temperature, good controllability and high yield.This research focused on the preparation of carbon-encapsulated metal nanoparticles by co-pyrolysis at 500℃, using an 100 vol% anisotropic mesophase pitch as carbon source and ferrocene, acetylacetone nickel as the metal sources, respectively. The further oxidation and carbonization of carbon-encapsulated iron nanoparticles indicated that a kind of hollow nanoparticles material was produced by the post-treatment. The onion-like hollow carbon nanoparticles were large-scale synthesized by co-pyrolysis of acetylene carbon black and ferric nitrate at 1000℃. In addition, anthracene and acetylacetone nickel, acetylacetone cobalt were also tried to synthesize carbon-encapsulated alloy nano-materials. The effect of the synthesis parameters on the formation and transformation of the products were investigated in detail. The morphology, structure and particular properties of the products were characterized via TEM, HREM, EDX, XRD, Raman and TG/DSC measurements, and the relationships between the morphology, structure and the synthesis parameters were investigated to realize the controllable preparation of the product. The formation mechanism and transformation behavior of products were also discussed briefly.The results showed that large amounts of carbon-encapsulated iron nanoparticles were obtained by co-pyrolysis of mesophase pitch and ferrocene. When the reaction was carried out at 500℃with the weight ratio of 20g : 30g of mesophase pitch to ferrocene, products with diameters ranging from 20 nm to 60 nm were obtained and the nuclear was proved to beα-Fe. Large amount of carbon-encapsulated nickel nanoparticles were also obtained from mesophase pitch and acetylacetone nickel. When the preparation was carried out at 500℃with the weight ratio of 20g : 35g, nanoparticles with diameter of 40nm were synthesized, while nickel was encapsulated in semi-graphitic carbon layers. Carbon-encapsulated Ni-Co alloy nanoparticles with the diameter of 40nm were prepared by co-pyrolysis at 450℃when the weight ratio of anthracene to Ni(acac)₂ and Co(acac)₃ was 10g: 10g: 10g. The carbon layer of the particles was semi-graphitic structure and the core was eutectic alloy with composition of 47.6 wt.%Co-52.4 wt.%Ni or 47.5 at.% Co-52.5 at.% Ni. By further oxidation and carbonization of carbon-encapsulated iron nanoparticles, it was found that onion-like hollow carbon nanoparticles were obtained through the diffusion and ejection of iron nanoparticles.Acetylene carbon blacks were heat treated at 1000℃in the presence of ferric nitrate. It was found that, with the increase of ferric nitrate loading from 4:1, 8:1, 12:1 to 16:1 (the weight ratio of ferric nitrate to acetylene carbon black), the yield of carbonized product decreased from 64.6%, 61.8%, 46.2% to 28.6%. Onion-like hollow carbon nanoparticles with diameter of 40 to 100 nm were generated, implying that the discontinuous short fragments of carbon black were reconstructed and transformed into turbostratic concentric graphitic layers by the iron-based catalytic graphitization.After carbonization at 1000℃, carbon-encapsulated iron nanoparticles present excellent properties of electromagnetism-dissipation. When the carbon-encapsulated nickel nanoparticles were used as the catalyst, they exhibit excellent properties of anti-agglomeration at 450℃and good catalysis for benzene hydrotreating at 200℃in hydrogen atmosphere. The effect of pressure, the ratio of hydrogen to benzene and airspeed on the catalytic properties of carbon-encapsulated Ni nanoparticles were also evaluated. Onion-like carbon nanoparticles were tested to work as a solid lubricant. The wear factor decreased by 40% to 0.17-0.18 using lubrication oil appended onion-like carbon nanoparticles, compared with that of lubrication oil without the nanoparticles addition.The above research afforded a novel and effective method for the preparation of various carbon nanomaterials. Moreover, it also provided a great advance for the industrialization and application of spherical core-shell carbon nanomaterials.