Fig. 1A shows a surface SEM image of as-electrospun composite
nanofibers prepared from the mixture solution of W(OC2H5)6, PVP
and P123. This image exhibits randomly oriented nanofibers each
with a smooth surface. The average diameter of the composite
nanofibers was 233±46 nm as displayed in the inset. A corresponding
SEM image after the 500 °C heat treatment of the composite
sample is shown in Fig. 1B, clearly indicating distinct changes in
diameter and surface morphology. The average diameter decreased to
85±37 nm, and the nanofiber surface became extremely rough. In
more magnified SEM images, the nanofibers were observed to have
formed by agglomerating small-sized particles less than 50 nm along
the axial direction. This diameter reduction could be due to the
calcination of organic polymer ingredients from the as-prepared
composite nanofibers. Furthermore, the formation of a rough surface
suggests that WO3 nanoparticles were effectively produced from the
tungsten oxide precursors and located along the 1-D direction during
the calcination process.