Calcinations nanofibers

Chromatography on polymer-based layers and their hyphenation to elution-based MS is only possible with nonsolvents of the polymer. Further ultrathin layer processing yielded calcined nanofibers produced by electrospinning of a solution of silica nanoparticles dispersed in polyvinylpyrrolidone followed by heating for calcination and selective removal of the polymer [21]. The application range was further expanded by producing PAN layers equipped with an incorporated photoluminescence indicator and used for the separation of preservatives. This was also the first application of this kind of UTLC layer hyphenated with ESI-MS [1]. 

Figure 2 presents some SEM pictures taken directly from suspensions of the fluffy precipitate of [Pt(NH3)4](HC03)2 in ethanol before addition of TEOS and representing the formation process of the templating Pt-salt nanofibers. Figure 2a shows the salt as it was received from the supplier. The micrograph 2b was taken after dissolution of the salt in water and re-precipitation with ethanol and, finally, micrograph 2c after the addition of TEOS and calcination. 

Figure 2. SEM representing the steps of the formation of nanofibers of [Pt(NH3)4](HC03)2, acting as templating units for the condensation of silicate monomers forming the Si02 nanotubes original salt (a), after re-precipitation in ethanol and after addition TEOS and calcination. The bars represent 4 pm.

The supported Ni catalysts (5 wt.%) for H2S oxidation were prepared by incipient wetness impregnation of the two supports, i.e. SiC grains and graphite felt coated with carbon nanofibers, with an aqueous solution of Ni(N03)2.6H20 (Merck). After drying overnight at 120°C, the catalysts were calcined at 350°C for 2h in order to decompose the nitrate salt and to form the nickel oxide. The corresponding sulfidic catalysts were obtained by sulfidation of NiO by reaction with a H2S/He flow at 300°C. 

Figure 7.17 SEM images of nanocomposites with hierarchial nanostructures prepared by electrospinning followed by calcination (a) V20s-Ta205 nanorods on Ti02 nanofibers, and (b) V2O5 nanorods on Si02 nanofibers. (Reprinted with permission from R. Ostermann et al. Nano Lett. 2006, 6, 1297. Copyright (2006) American Chemical Society.)...

If the oxidized carbon nanofibers are calcined at 573 K, the shoulder at 1740 cm and the band at 1720 cm becomes less pronounced (Fig. 4). The phenolic and asymmetric and S5nnmetric NO2 stretching vibration peaks have disappeared completely. Thus ketone, carboxylic, phenolic and nitro groups decompose if the carbon nanofibers are calcined at 573 K. The peak that remains at 1720 cm" is most likely due to lactones because these groups decompose between 600 and 950 K [31]. If the temperature is increased further to 873 K, the shoulder and peak at 1740 cm" and 1720 cm" have disappeared completely. It follows that the majority of the surface oxygen functional groups decompose at 573 K. 

Fig. 4. FTIR speetra of the oxidized and oxidized/calcined carbon nanofibers.

Fig. 5. XPS data in the Cu region for the calcined and uncalcined carbon nanofibers and high purity graphite. The spectra after removal of the asymmetric main contribution are shown on the secondary y-axes.

Fig. 8. TEM images of the oxidized carbon nanofibers supported cobalt catalysts, a. calcined at 573 K (xl30 000). b. Calcined at 873 K (x43 000).

Figure 2.11 SEM image of carbon nanospheres (left-above] and after (left-below] calcination of nanofibers prepared with carbon nanospheres, and XRD patterns of TiOj nanofibers (right] (a] and porous TiOj nanofibers (b]. Reprinted from Ref. 62, Copyright 2012 Shanhu Liu et al.

Loscertales et a/. prepared the silica nanotubes in a similar way by using tetraethyl orthosilicate (TEOS) as the sheath. Wang et al. recently reported the formation of nanochannels (60 nm or less) in silica nanofibers (Fig. 2.36). They used spin-on glass (SOG) and PVP mixture in the sheath and motor oil in the core. After electrospinning, the structure was calcinated to remove PVP and motor oil and to form Crosshnked SiOj wall. 

The first example is the work of Lu et al. [124] who fabricated polypyrrole (PPy)ATi02 coaxial nanocables, where the conductivity of PPy was integrated with the photocatalytic activity of Ti02 for applications in electrochromic devices, nonlinear optical systems, and photoelectrochemical devices. The synthetic approach consisted in (1) preparation of Ti02 fibers by sol-gel electrospinning and calcination of the polymer (PVP in the specific case), (2) physical adsorption of Fe " oxidant on the surface of Ti02 nanofibers, and (3) polymerization of pyrrole (from vapor) on the surface of Ti02 nanofibers. 

Fig. 2.11 Electrospinning and hot-pressing of metal oxide materials, (a) SEM image of the as-spun TiOj/PVAc composite fibers fabricated by electrospinning from a DMF solution, (b) SEM image of TiOj/PVAc composite fibers after hot-pressing at 120 °C for 10 min. (c) SEM image of unpressed TiO nanofibers after caicination at 450 °C. (d) SEM image of hot-pressed TiOj nanofibers after calcinations at 450 °C (Reprinted with permission from Kim et al. 2006, Copyright 2006 American Chemical Society)...

---