(513g) Silica Nanofiber Mats Containing Transition Metal Oxide Crystals Via Electrospinning and Sol-Gel Synthesis

One dimensional, inorganic, nanosized fiber mats are of interest for their high thermal stability and large surface to mass ratios. Recently, silica nanofiber mats have been produced using a novel sol-gel synthesis/electrospinning technique without using any polymer binder. Utilizing silica as a matrix allows metal oxide precursors to be included by directly adding them to the sol-gel precursor. With this technique the growth of crystalline metal oxides on silica fibers can be achieved while fiber morphology is preserved during calcination. In the current study, we develop sub-micron scale vanadia/silica fiber mats by electrospinning silica sol-gel precursor containing vanadium oxytriisopropoxide (VOTIP), followed by calcinations at high temperatures. The resulting silica nanofibers containing V₂O₅ crystal particles can be used to detect trace amounts of toxic or flammable gases, including ammonia and hydrocarbons. We anticipate that this simple and versatile electrospinning/sol-gel directed approach to conducting layers that combine a large surface area as well as electrical interactions will lead to more sensitive detection, e.g., in sensing gases. Dispersing V₂O₅ nanoparticles onto the surface of silica nanofibers allows outstanding specificity and selectivity in gas sensing to be gained because nanofiber mats provide a highly porous template where the gas can flow through it and thereby effectively utilize the entire active sites of metal oxide crystals on the fibers. SEM images show the electrospun inorganic fibers are sub-micron in diameter and their morphology is maintained after calcination. Physisorption experiments reveal the silica nanofiber mats have a high surface area of 170 m²/g and calcination temperature greatly affects surface area. FT-IR spectra exhibit Si-O vibrations and indicate the presence of V₂O₅ in the fibers. XPS studies reveal the ratio of Si to O is close to 0.5 on the surface of fibers and the amount of vanadium on the surface of the fibers increases with calcination. XRD diffraction patterns show the silica nanofibers are amorphous and that orthorhombic V₂O₅ crystals have formed after calcination. TEM images also demonstrate the growth of vanadia crystals on the surface of the fibers after calcination. Finally, a coaxial electrospinning scheme has successfully been employed to selectively place V₂O₅ in the skin layer and thus on the surface of the fibers. Coaxial electrospinning is also utilized to include other metal oxides on the fiber surface such as TiO₂, Fe₂O₃, and SnO₂, and the effect of coexisting metal oxides on the catalytic and sensing performance will be presented.