1. Synthesis Results Future Work Conclusions
Synthesis of high temperature titania nanofibers
P. Katta, L . Khatri, R.D. Ramsier and G.G. Chase
Synthesis
Rutile titania nanofibers are synthesized using electrospinning and sol-gel coating techniques. A large sheet of nylon-6 nanofibers are synthesized using electrospinning. Rotating cylinder (Fig.1) is used to obtain large sheet of electrospun nylon-6 nanofibers. The electrospun nanofibers are then coated using a modification of a published sol-gel recipe in order to obtain uniformly coated nanofibers (Fig. 2). The resultant nanofibers are heated to 275oC to pyrolize the nylon-6, during which shrinkage indicative of mass loss is observed (Fig. 3). Titania nanofibers thus obtained have nm diameters. Titania usually undergoes an anatase-rutile phase transformation when the temperature is raised above 450oC. During synthesis, however, the rutile phase can be obtained in acidic media. Scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) analysis are used to characterize the synthesized nanofibers. Since our focus is on synthesizing nanofibers which can be used at high temperatures, rutile titania nanofibers are synthesized instead of anatase. FTIR results show a small amount of nylon-6 polymer retained in the nanofibers after heating the nanofibers to 275oC (fig. 4). Pure titania nanofibers are obtained when the nanofibers are heated to 700oC (Fig. 5).
Abstract
The objective of our work is to synthesize high temperature nanofibers which can be used above 1500oC. Electrospinning is used as the part of the synthesis method. Electrospun polymer nanofibers are subsequently modified to obtain high temperature titania nanofibers. Titanium dioxide, or titania, has a very high melting temperature in the range °C. Titania is chemically stable, non-toxic and easy to handle. Titania is inert and does not react with many acids or bases, and is an excellent support for catalytic surface reactions. Therefore, we have selected titania as the synthesis material for high temperature nanofibers that will then be packed to form filters.
Filters made with titania nanofibers have potential for a wide range of applications in catalytic cracking and high temperature filtration. High temperature nanofiber-based filters are expected to be economical as they can be used to filter impurities from hot exhaust gases with minimal retrofitting. The titania nanofibers synthesized in this work are analyzed by scanning electron microscopy (SEM) and fourier transform infrared (FTIR) spectroscopy.
Fig.1 Rotating cylinder for obtaining large sheet of nanofibers.
Fig. 4 FTIR spectrum of titania nanofibers after heating at 275oC for 2 hours. Nylon-6 polymer is still retained in the nanofibers.
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Fig. 2. SEM image at magnification and 20 kV of titania coated nylon-6 nanofibers obtained through the sol gel coating technique. The average diameter of the fibers is about nm.
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Fig. 3. SEM image at magnification and 20 kV of thermally treated titania nanofibers obtained through the sol gel coating technique. These fibers are heated in an oven at 275oC for 2 hours. The average diameter of the fibers is about 150 nm.
Results
Sol-gel coated nylon-6 nanofibers are obtained by uniform growth of titania nanoparticles onto the surface of polymer nanofibers. These nanofibers are heated slowly to 275oC in an oven in order to obtain titania nanofibers. Shrinkage in the diameter of the nanofibers is observed when the nanofibers are heated to 275oC. The shrinkage is due to the thermal degradation of the polymer in the nanofibers. When the coated nanofibers are heated to 700oC pure titania nanofibers are obtained (Fig. 5). The fibrous structure is still retained even after heating the nanofibers to 700oC.
Fig. 5 FTIR spectrum of pure titania nanofibers after heating at 700oC for 1 hour.
Future Work
Fiber properties such as melting temperature, fiber size, etc. will be measured.
Mechanical and chemical stability of these nanofibers will be tested.
High temperature nanofibrous filter media will be prepared using the synthesized titania nanofibers.
Filter properties such as permeability, porosity, durability, tensile strength etc. will be measured.
Overall efficiency of filters containing nanofibers will be compared with the overall efficiency of filters without nanofibers.
Filter tests will be conducted to study the filter properties such as flow rate, pressure drop, capture efficiency, etc.
Finally, an analytical model correlating various parameters will be developed.
Conclusions
Micron sized titania fibers and hollow tubes have been reported in the literature previously, but the titania nanofibers synthesized through this technique have diameters approximately 150 nm and the nanofibers are long enough to form nonwoven mats. The synthesis process used is easy and cost effective when compared to other synthesis methods.