Structural characterization of cup-stacked-type nanofibers with an entirely hollow core

Abstract

Straight long carbon nanofibers with a large hollow core obtained by a floating reactant method show a stacking morphology of truncated conical graphene layers, which in turn exhibit a large portion of open edges on the outer surface and also in the inner channels. Through a judicious choice of oxidation conditions, nanofibers with increased active edge sites are obtained without disrupting the fiber’s morphology. A graphitization process induces a morphological change from a tubular type to a reversing saw-toothed type and the formation of loops along the inner channel of the nanofibers, accompanied by a decrease in interlayer spacing.

Transitional behaviour in the transformation from active end planes to stable loops caused by annealing

“…The characteristics of these edge sites, especially for the form of tubular-type carbon (carbon nanotubes) [4]- [13], make it possible to utilize them in the fabrication of absorbent materials [14], catalyst-supports [15,16], field emitters, gas storage components [17] and polymer composites [18,19]. It is well known that highly reactive edge sites are transformed into stable multi-loops when heat treated at higher temperatures [5,12,20,21].…”

Comparative study of herringbone and stacked-cup carbon nanofibers

“…It is generally accepted that carbon nanotubes consist of single or multiple graphene sheets rolled into concentric cylinders: thus giving rise to single wall carbon nanotubes (SWNTs) or multi-walled carbon nanotubes (MWNTs) [4,5]. Recently, we described a new type of carbon nanofiber, "stacked-cup carbon nanofiber", which exhibited a unique morphology of stacked, truncated conical graphene layers (cups) along the fiber length [6][7][8].Previously, three different geometries of carbon nanofibers (e.g., platelet, 1 …”

“…Basic pre-conditions for synthesizing carbon nanotubes are metal catalyst, carbon precursor and thermal energy. Therefore, right combination of these three components makes it possible to selectively synthesize various types of carbon nanotubes, ranging from SWNTs and MWNTs to carbon nanofibers [6,17,18]. Most important factor for controlling the growth and therefore the properties of fibrous carbons are the nano-sized metal catalysts [9], which must catalytically decompose the carbon feedstock and provide relatively high carbon solubility.…”

“…The lower surface area and ASA (3-5 m 2 /g) for stacked-cup nanofiber is attributed to a smooth surface formed by the deposited carbon during nanofiber growth, which is an inevitable consequence of CVD process at higher reaction temperature. Therefore, by selecting the duration, temperature and time judiciously we can control the thickness of the deposited carbon [6] which manifests itself in TEM as small fringes roughly aligned along the fiber length. This layer acts as a protective layer, resulting in improved mechanical properties of single fibers.…”

“…Even though both fibers have two important common aspects: (1) Aggregate (50-100µm) 6) Relatively loosely packed morphology Closely packed macro-morphology 7) Deposited carbon…”