Synthetic routes to nanostructured carbon: Platelets, scrolls, tubes and GEMs.

摘要

The future of nanotechnology depends on the synthesis of high quality nanomaterials. Metathesis and intercalation/exfoliation chemistry promise scalable and inexpensive synthetic routes to nanostructured forms of carbon. The solid-state metathesis reaction between calcium carbide (CaC2) and hexachloroethane (C2Cl6) produces crystalline graphite powder. The addition of 6 mole percent iron sulfide (FeS) catalyzes the growth of single- and multi-walled carbon nanotubes in a yield of 25%, calculated using transmission electron microscopy. By changing the catalyst and its concentration, graphite encapsulated metal (GEM) nanoparticles can be synthesized. The synthesis of graphite encapsulated iron particles has been optimized to produce high yield, high quality nanoparticles for use in magnetic composites.;Intercalation and exfoliation chemistry provide another approach to nanostructured carbon. The first-stage intercalation compound KC8 is readily formed by heating graphite powder with potassium metal at 200°C. Exfoliation using ethanol produces thin graphite nanoplatelets (GNP) in solution. Sonication of the dispersion causes the sheets to roll-up, thus forming carbon nanoscrolls, a structure analogous to multi-walled carbon nanotubes, in over 80% yield. A large volume expansion (greater than 15 fold) is observed for the dried carbon nanoscroll powder. Thermal gravimetric analysis of the carbon nanoscrolls shows a decrease in thermal stability with oxidation occurring at 450°C, 200°C less than pristine graphite.;Nanofiber composites of 1--4 weight percent graphite nanoplatlets in polyacrylonitrile (PAN) formed via electrostatic spinning demonstrate an improved Young's modulus with increasing weight percent GNP. With an aspect ratio of over 1000, the graphite nanoplatelets provide an effective means for stress transfer and serve as an excellent reinforcement for nanofiber composites.