Metallic nanofibers

Metal and/or metal alloy nanowires/nanofibers have attracted considerable attention due to their potential applications in relation to transparent electrodes and metal catalysts with a ID structure. In this regard, metallic nanofibers such as Au, Cu, and Ni with high electrical conductivity have been prepared by electrospinning (Figure 13.3). Gries et al. suggested a new fabrication process for the synthesis of Au nanofibers. Au nanoparticles (NPs) were embedded within a matrix polymer of PVA (M = 195 000 g mol ) by electrospinning followed by the pyrolysis of PVA and a subsequent calcination step. The sintered Au NPs... 

Wu H, Hu LB, Rowell MW, Kong DS, Cha JJ, McDonough JR, Zhu J, Yang YA, McGehee MD, Cui Y (2010) Electrospun metal nanofiber webs as high-performance transparent electrode. Nano Lett 10(10) 4242-4248... 

Fig. 1(b) represents the selectivity to styrene as a ftmcfion of time fijr the above catal ts. It is observed that the selectivity to styrene is more than 95% over carbon nauofiber supported iron oxide catalyst compared with about 90% for the oxidized carbon nanofiber. It can be observed that there is an increase in selectivity to styrene and a decrease in selectivity to benzene with time on stream until 40 min. In particrdar, when the carbon nanofiber which has been treated in 4M HCl solution for three days is directly us as support to deposit the iron-precursor, the resulting catalyst shows a significantly lows selectivity to styrene, about 70%, in contrast to more than 95% on the similar catalyst using oxidized carbon nanofiber. The doping of the alkali or alkali metal on Fe/CNF did not improve the steady-state selectivity to styrene, but shortened the time to reach the steady-state selectivity. 

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. 

Therefore, carbon nanofibers (CNFs) as well as carbon nanotubes (CNTs) were synthesized,18,19 functionalized (with the catalytic active metal Co), and finally... 

Initially, for all three support materials a Co content of 20 wt.% was supposed to be deposited. Table 2.1 shows that functionalization of the herringbone nanofibers (HB-CNF) appeared to be most efficient since nearly all of the applied metal was adsorbed by the nanomaterial surface with impregnation (over 95%). 

However, the platelet nanofibers (PL-CNF) carry only about two-thirds of the loaded cobalt, and the nanotubes (MW-CNT) showed the most inefficient functionalization performance, exhibiting barely 50% of metal adsorption. 

Polymers consisting of but not limited to poly thiophene, polypyrrole and poly aniline have been extensively used to make polymer nanofibers. In general, any metal that can be electroplated has most likely appeared in a nanowire. Semiconductors, polymers, and insulators have also been used in the design of nanowires.Furthermore, different metals can be plated in succession to give striped nanowires. 

Application of transmission electron microscopy (TEM) techniques on heterogeneous catalysis covers a wide range of solid catalysts, including supported metal particles, transition metal oxides, zeolites and carbon nanotubes and nanofibers etc. 

---