SBIR Phase I: Removal of Toxic Microcystins in Water Using Graphite Nanofibers

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This Small Business Innovation Research (SBIR) Phase I project deals with the use of graphite nanofibers (GNF) as novel adsorption media for the removal of bio-toxins from water. Specifically, the research will focus on the removal of microcystin-LR, a potential biological weapon that could be used by terrorists to attack human beings. Various methods have been proposed for the removal of microcystins from aqueous media, including adsorption by activated carbon, chlorination, ozonation, permanganate, hydrogen peroxide, photolysis, and semiconductor photo-catalysis. Of these approaches, the activated carbon treatment appears to be one of the most effective procedures. Various microcystins can be adsorbed on the porous surface of activated carbon and the efficiency of removal depends upon the pore size and surface functionality. It is claimed that the dominant factor in the adsorption process is the volume of mesopores (2-50 nm diameter) rather than the volume of micropores (diameter 2 nm) or megapores (diameter 50nm). In addition, the removal efficiency gradually decreases over a period of time due to the accumulation of a bio-film on the activated carbon surface. The regeneration of the spent activated carbon is not a simple task and as consequently the contaminated material is frequently discarded. Improper disposal procedures of used activated carbons could give rise to serious problems because microcystins are known to persist for many years when stored in dry conditions at room temperature and to withstand many hours of boiling in water. Since GNF contain an abundance of edge sites, the surface functionality can easily be transformed to give either hydrophobic to hydrophilic properties. In addition, it has recently been discovered that following suitable thermal treatments it is possible to generate GNF structures that possess a large fraction of mesopores having average dimensions of 12 nm. This unusual blend of properties makes GNF ideal candidates for the adsorption of microcystins from water. Furthermore, the high degree of crystalline perfection exhibited by GNF enables one to heat the materials in the presence of oxidizing gases to temperatures in excess of 500 C, thereby allowing for the removal of trapped microcystins and the regeneration of the adsorbate.