Removal of metallic and organic contaminants from aqueous streams by novel filtration methods. 1997 annual progress report

'Graphite nanofibers, are a novel material that has been developed in the laboratory from the metal catalyzed decomposition of certain hydrocarbons (1). These structures possess a cross-sectional area that varies between 5 to 100 nm and have lengths ranging from 5 to 100 mm (2). High-resolution transmission electron microscopy studies have revealed that the nanofibers consist of extremely well-ordered graphite platelets (3), which are oriented in various directions with respect to the fiber axis. The arrangement of the graphene layers can be tailored to a desired geometry by choice of the correct catalyst system and reaction conditions, and it is therefore possible to generate structures where the layers are stacked in a ribbon, herring-bone, or stacked orientation. An example of the later structure is shown in the high resolution electron micrograph, Figure 1a, where the lines across correspond to individual planes of graphite that are separated at a minimum distance of 0.34 nm. The structural features of the nanofiber can be better appreciated in the schematic renditions, Figures 1b and 1c. The unique combination of small cross-sectional area, which is estimated to be on average 20 nm, and the abundance of exposed edges makes the material an ideal solid for adsorption. The suitability of the material for the selective adsorption of a variety of molecules is illustrated in Figure 1c, where it can be seen that adsorption could be achieved upon access of the molecule to the inner regions of the solid. One the most outstanding features of graphite nanofibers, is that the solid consists entirely of non-rigid wall nanopores that extend across the entire solid. The process for the synthesis of graphite nanofibers produced from the decomposition of hydrocarbons and carbon monoxide over selected metal surfaces at temperatures over the range 450 to 700 C has been optimized and it is possible to produce relatively large quantities of high purity material in short periods of time ca. 100 grams per hour. These structures have been found to exhibit unique behavior when exposed to hydrogen at elevated pressures and moderate temperatures.