Nanofibers types

Hu, B., Chen, C., Frueh, S.J., Jin, L., Joesten, R. and Suib, S.L. (2010) Removal of aqueous phenol by adsorption and oxidation with doped hydrophobic cryptomelane-type manganese oxide (K-OMS-2) nanofibers. Journal of Physical Chemistry C, 114, 9835-9844. 

The potential of carbon nanomaterials for the Fischer-Tropsch synthesis was investigated by employing three different nanomaterials as catalyst supports. Herringbone (HB) and platelet (PL) type nanofibers as well as multiwalled (MW) nanotubes were examined in terms of stability, activity, and selectivity for Fischer-Tropsch synthesis (FTS). 

Concerning the Fischer-Tropsch synthesis, carbon nanomaterials have already been successfully employed as catalyst support media on a laboratory scale. The main attention in literature has been paid so far to subjects such as the comparison of functionalization techniques,9-11 the influence of promoters on the catalytic performance,1 12 and the investigations of metal particle size effects7,8 as well as of metal-support interactions.14,15 However, research was focused on one nanomaterial type only in each of these studies. Yu et al.16 compared the performance of two different kinds of nanofibers (herringbones and platelets) in the Fischer-Tropsch synthesis. A direct comparison between nanotubes and nanofibers as catalyst support media has not yet been an issue of discussion in Fischer-Tropsch investigations. In addition, a comparison with commercially used FT catalysts has up to now not been published. 

The multiwalled nanotubes as well as the herringbone type carbon nanofibers were synthesized in-house in a quartz glass fluidized bed reactor via chemical vapor deposition (CVD). The method is described in detail elsewhere.19 The platelet nanofibers, in contrast, were purchased from the company FutureCarbon GmbH (Bayreuth, Germany). 

As can be seen from Figure 2.1, cobalt was deposited on the carbon nanomaterials quite homogeneously. Hence, the cobalt particle sizes of the three catalyst types vary only little. The Co/nanofiber materials exhibit cobalt particle diameters of roughly 10 nm. In case of the nanotubes, particle sizes ranging from 5 to 7 nm were observed. 

FIGURE 2.1 Cobalt functionalized (a) platelet type carbon nanofibers, (b) herringbone type carbon nanofibers, and (c) carbon multiwalled nanotubes. 

The experimental results obtained with carbon nanofibers and nanotubes fit into the tendencies obtained with the other type of carbon materials, indicating that hydrogen adsorption on these materials is also taking place by a physisorption process. 

The second chapter by Dieter Klemm, Dieter Schumann, Hans-Peter Schmauder, and coworkers focuses on the recent knowledge of cellulosics characterized by a property-determining supramolecular nanofiber structure. Topics in this interdisciplinary contribution are the types of nanocelluloses and their use in technical membranes and composites as well as in the development of medical devices, in veterinary medicine, and in cosmetics. 

Furthermore, meshes have been composed of multilayers consisting of different polymers. Matsuda and coworkers produced bilayer meshes of a thick polyurethane microfiber mesh and a thin nanofiber mesh composed of type I collagen. The material decouples mechanical properties from the biochemical functionality of collagen to form a prototype scaffold for artificial grafts [194],... 

Hydrogen-storage characteristics of samples of four types were studied as synthesized MgH2(l), MgH2 after mechanical activation, m/a (2) MgH2-graphite (3) and MgH2-carbon nanofibers (CNF) both after mechanical activation. 

In recent years, we have seen an explosive interest in nanomaterials, in particular in nanofibers, nanofilaments, and nanotubes of the very different chemical composition. The interest arises from the specific mechanical and physicochemical properties of these nano objects, which allow them to be used, for example, as specific adsorbents, catalyst supports, reinforcing components of composite materials, and so on. The most cited generic types of nanomaterials are carbon nanofilaments and nanotubes. Numerous methods for preparing these carbon materials are known. However, the simplest method seems to be thermal pyrolysis of various carbon contain ing precursors (e.g., carbon monoxide, saturated and unsaturated hydro carbons, etc.) in the presence of special catalysts that are typically nanosized particles of nickel, cobalt, iron metals, or their alloys with different metals. 

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