Room-Temperature Growth of Carbon Nanofibers
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Room-Temperature Growth of Carbon Nanofibers Jason K. Vohs,1 Jeffery E. Raymond, Jonathan J. Brege, Steven Rozeveld,3 Geoffrey L. Williams,2 and Bradley D. Fahlman1* Departments of Chemistry1 and Biology,2 Central Michigan University, Mount Pleasant, MI 48859 3 Dow Chemical Company, Midland, MI 48667 ABSTRACT We describe the growth of amorphous carbon nanofibers (CNFs) from iron-encapsulated dendrimer catalysts at ambient temperature and pressure conditions. Both fourth-generation poly(propyleneimine) (PPI) and poly(amidoamine) (PAMAM) dendrimers were suitable macromolecular hosts for the catalytic species. Average nanofiber diameters range from 10 - 15 nm, with lengths in excess of 20 microns. INTRODUCTION Ordered carbonaceous growth typically requires high-energy methods such as arc discharge[1] or decomposition of hydrocarbon-based precursors using laser,[2] plasma,[3] or thermolytic techniques.[4] For the latter technique, temperature regimes on the order of 600– 1000 °C are most common, with a few recent reports citing lower temperatures using halogenated precursors,[5,6,7] or through alkali-metal catalyzed transformation of bulk carbon allotropes.[8,9] Sailor et al. have reported the first growth of non-amorphous carbon deposits at room temperature.[10] However, their electrochemical synthesis did not produce nanostructural carbon; due to the absence of nanosized catalytic seeds, the diameters of their fibers were > 5µm, and contained copious amounts of Cl, H, N, and O impurities. The applications for nanostructural carbon allotropes are currently limited by their insolubility in common solvents. While existing CNT-polymer composites feature simple polymer folding around CNTs,[11] we are focused on the design of composites that feature more intimate connections between the polymeric host and carbon allotrope. Our approach features the controlled formation of nanostructural carbon directly from the architecture of dendritic polymers. To this end, we recently reported the first low-temperature (175 °C) method to synthesize carbon nanotubes directly from metal-encapsulated dendrimers under high-pressure conditions.[7] Here we show milder conditions for metal@dendrimer catalyzed nanostructural carbon growth - at ambient temperature and pressure from metal reduction of tetrachloroethylene in organic solvents. For the first time, the complexity associated with carbon nanofiber (CNF) growth has been reduced to solvent-mediated stirring on a benchtop. EXPERIMENTAL DETAILS I. Preparation of the dendritic catalyst G4-PPI dendrimer (0.4156 g, 0.12 mmol) was dissolved in 20-mL of water. FeCl3•6H2O (0.5123 g, 1.89 mmol) was dissolved in 20-mL of water. These two solutions were combined and
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mixed for 1 hr. NaBH4 (0.3303 g, 8.73 mmol) was dissolved in 15-mL of water. The NaBH4 solution was then added dropwise to the Fe/PPI solution. Upon addition, there was noticeable gas formation and precipitation of a dark solid. The solution was allowed to stir for 1 hr, centrifuged to isolate the dark solid, and air-dr
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