Carbon Nanofibers for Environmental Applications

Catalytically grown carbon nanofibers (CNF) are a newly developed type of material produced from the decomposition of selected carbon-containing gases over metal particles. These materials consist of nano-sized graphite platelets separated a distance of at least 0.335 nm and stacked in various orientations with respect to the fiber axis. Such an arrangement results in a unique structure that is composed of an infinite number of extremely short and narrow pores, suitable for the sequestering of small molecules. We have attempted to capitalize on this blend of properties by using such structures for the selective removal of organic contaminants from aqueous streams. The approach is predicated on the principle that a strong interaction of the organic impurity with the non-polar basal plane regions of the graphite platelets will be established without concomitant saturation of the solid with excess water molecules. Experimental results indicate that nanofibers possessing a structure in which the graphite platelets are aligned perpendicular to the fiber axis and possessing high degree of structural perfection exhibit superior selective adsorption properties with respect to removal of alcohols from aqueous media over that displayed by active carbon. Adsorption was enhanced when the carbon nanofibers were initially subjected to a treatment in 1M hydrochloric acid. In contrast, when this step was carried out in the presence of 1M nitric acid the beneficial properties of the nanofibers were effectively suppressed. On the other hand, a similar treatment in 1M sulfuric acid produced a pattern of behavior that was, for the most part, intermediate between these cases. An analogous series of experiments carried out with nanofibers possessing a structure in which the graphite platelets were oriented at an angle with respect to the fiber axis did not result in the same degree of selective capture of the alcohols. A rationale is presented to account for this diverse pattern of behavior.