Effects of precursor concentration on crystalline morphologies and particle sizes of electrospun WO3 nanofibers

Tungsten oxide (WO₃) nanofibers with different crystalline morphologies and various particle sizes were fabricated using an electrospinning technique. The nanofibers were prepared from mixtures of polyvinyl alcohol (PVA) and ammonium metatungstate hydrate (AMH) of various concentrations ranging from 4.2%w/v to 50.0%w/v. After calcination at 500 °C for 2 h, the nanofibers were observed to have a monoclinic crystal structure with diameters ranging from 30 to 250 nm. AMH concentration had a large influence on the resulting nanofiber morphology. Very low AMH concentration of 4.2%w/v led to the formation of WO₃ nanofibers having a very large area of monocrystalline structure. Higher AMH concentrations result in polycrystalline WO₃ nanofibers with joined nanoparticles along the fiber axis. The average particle size within the nanofibers increased from 29 to 66 nm as the AMH concentration increased from 8.3%w/v to 50%w/v. At these precursor concentration levels, primary particles were formed before PVA was completely burnt off, resulting in agglomeration of primary particles along the nanofiber axis.