The electrospun fibers of PMMA and vanadium oxide have a diameter between 200 and 500 nm as shown in Fig. 1 (top inset). After hydrothermal treatment, the fibrous morphology is main- tained, but they now have a belt-shape of 40–70 nm wide, 10– 20 nm thick and several micrometers long. From the powder X- ray diffraction, Fig. 1 (middle), which shows only 00l reflections, it is clear that this compound is layered with an interlayer spacing of 11.40 Å. This spacing and the missing 002 reflection is typical of the d-V4O10 phase and vanadium oxide xerogels [17–21]. However, the sharp and intense peaks observed in this XRD pattern indicate a high level of crystallinity. After the hydrothermal treatment the sample has become a dark green color, rather than the orange color V2O5