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RESEARCH PRODUCT

From Well-Defined Carbon-Rich Precursors to Monodisperse Carbon Particles with Hierarchic Structures

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The creation of nanoscale particles with well-defined structures has long been considered as a promising approach to generate materials with novel properties. Carbonaceous nanoparticles (CNPs) with defined architectures, such as carbon nanotubes (CNTs), C60, carbon onions, carbon spheres, and carbon rods are particularly attractive owing to their unique electronic properties and many potential applications. At the same time, when these CNPs are regularly organized, additional functions appear. Such materials are believed to have hierarchic structures, in which the organization of the CNPs forms the first-order structure (FOS) and the configuration of the single CNP forms the secondor higher-order structure (SOS or HOS). Because both the FOS and HOS are responsible for the properties of the bulk material, simple methods to prepare multidimensional carbon materials with hierarchic structures are needed. Template methods are commonly used to produce 3D order in which the silica opal or inverse opal crystals are the most frequently selected templates. Carbonaceous materials have been prepared in these templates by using sucrose or phenolic reactants as precursors, but only amorphous CNPs were obtained. Alternatively, chemical vapor deposition (CVD) over inverse opals was reported to produce crystalline carbons. Unfortunately, such CVD procedures resulted in inverse carbon opals, not CNPs, and the control over the carbon structures was limited. The preparation of well-defined CNPs with 3D organization is still a challenge owing to the difficulties of controlling molecular interactions at high temperatures. Recent studies on solid-state pyrolysis (SSP) have implied that the structures of CNPs could be controlled by choosing well-defined organometallic precursors. Thus, CNTs were obtained in high yield from SSP of diphenylethyne-metal complexes; while dicobalthexacarbonyl-functionalized poly(p-phenyleneethynylene) afforded carbon–cobalt spheres. Our previous SSP of dendritic polyphenylene–cobalt complexes resulted in uniformly shaped carbon–cobalt nanorods with rectangular cross sections, whereas disclike structures with extended p-systems furnished bamboolike CNTs and carbon shell/metal core cablelike structures. However, in all these experiments, the metal catalysts play a more important role for product formation than the chemical structure of the precursors; and these processes incorporate metals into the pyrolysis products. To prepare metal-free CNPs with defined structures, the design of the precursors requires more attention. Our recent attempts at precursordefined pyrolyses (PDP) produced graphitic nanotubes with brick-walled structures and CNTs with 3D porous-walled structures.