Morphology and porosity enhancement of graphite nanofibers through chemical etching

The morphology, structure, and porosity of graphite nanofibers (GNFs) can be significantly modified through simple exposure of the GNFs to acids, followed by a high temperature treatment. This treatment leads to chemical etching, fiber rupture and/or partial exfoliation. The degree of these somewhat competing processes is dependent upon acid exposure conditions and thermal treatment temperature. As the temperature of thermal treatment is increased, both the surface area and pore volume of the modified GNFs are significantly increased. Low-temperature treatments (600-800 degrees C) tend to favor the formation of micropores, whereas higher temperatures (>800 degrees C) lead to the formation of mesopores. An extended heat treatment at 1000 degrees C after acid exposure produces a drastic increase of mesopores and a pronounced change in fiber morphology, evidenced by X-ray diffraction and electron microscopy. This ability to select the operative pore size of graphitic nanofibers may lead to applications of these materials for energy storage, size-selective catalysis, as well as separation techniques where a finely controlled graphitic pore structure is desired. (C) 2007 Elsevier Inc. All rights reserved.