Abstract
A mixed-valent oxide-catalytic carbonization process for synthesizing monodispersed carbon spheres at very low cost is reported for the first time. The carbon spheres are formed by catalytic carbonization of natural gas (primarily methane) with the assistance of mixed-valent metal oxides. The catalyst is reusable and the entire synthesis process produces no environmental waste. The product can be controlled by temperature to produce macroscopic quantities and a high percentage (>95%) of nano sized carbon spheres; thus, measurements of their physical properties can be performed easily. The carbon spheres are solid and comprise layered graphitic flakes. The sphere is nucleated from a pentagonal carbon ring, followed by a spiral shell growth. When the sphere grows larger, graphitic flakes of atomic thickness are nucleated on the surface owing to the nucleation of the paired pentagonal-heptagonal (P-H) carbon rings. The combination of the P-H carbon rings with the hexagonal networks produces eight basic graphitic configurations for forming spheres. The unique microstructures of the carbon spheres make them chemically active, mechanically hard and electronically interesting. The carbon spheres can be accreted by a treatment in acetone. The mechanism for the accretion is attributed to the interaction of the hydrogen and oxygen atoms of the acetone molecules with the adsorbed hydrogen and/or oxygen foreign atoms at the edges of the open graphitic flakes on the surface. The high chemical activity of the carbon spheres can have important applications in catalysis. The accretion of the carbon spheres may improve significantly the strength of composite materials made using the spheres. The use of mixed-valence metal oxides as catalysts has opened a new field in catalyst research and applications.