Synthesis And Characterization Of WO₃Nanotubes/W₁₈O₄₉ Crystal Whisker Via A Coaxial Electrospinning Method

Tungsten trioxide is a kind of n-type semiconductor oxide material. It is widely usedin fuel cells, chemical sensors, photoelectric devices due to its propertiy of gas sensors,gasochromic, electrochromism and photocatalytic. Nano-tungsten oxide has moreexcellent physical and chemical propertiy because of its unique shape and size. Inrecent years, nano-tungsten oxide has been prepared successfully by researchers viahydrothermal synthesis method, sol-gel method, microemulsion method and templatemethod. But most of the above mentioned methods are very tedious. Compared withthem, coaxial electrospinning is a more effective, versatile method and the process issimplified to prepare the hollow nanofibers directly. As far as we know, synthesizing oftungsten oxide nanotubes and crystal whisker by coaxial electrospinning has not beenreported.In this paper, WO3nanotubes, nanofibers and W18O49crystal whisker were preparedby calcining the core-shell structured composite fibers in which10%pure PVA as thecore solution and PVA/AMT as the shell one via a coaxial electrospinning method withammonium tungstate as tungsten salt and PVA as polymer carrier. One dimensionalnanomaterials mentioned above were characterized by X-ray diffraction (XRD),fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM)and transmission electron microscopy (TEM).The spinning solution concentration and parameters to the fibers were studied duringthe preparation of core-shell structured composite fibers with pure PVA as core andPVA/AMT as shell. Finally, the PVA concentration of12%, applied voltage of12kv,collector distance of13cm, the feeding rate of syringe pump varies from3ul/min to10ul/min, the pure PVA (10%(w/v)) as inner solution were chosen as the optimalparameters to prepare the core-shell structured composite fibers. In thisexperiment, pure PVA was used as inner solution instead of general mineral oil forcoaxial electrospinning, which can achieve electrospinning both inner and outersolutions and avoid the gap between physical and chemical propertiy of two solutionsthat make it easier to implement coaxial electrospinning. The nanotubes of WO3withinner diameter of100nm, wall thickness of150nm were obtained after calciningcore-shell structured composite fibers at600oC for3h, and succeeded in preparingnanotubes by coaxial electrospinning method under the condition of similar inner and outer solutions.WO3nanofibers were prepared by electrospinning and calcinations, respectively.And we discussed four kinds of heat treatment process between WO3nanofibers andWO3powder. Finally, we find that when WO3nanofibers with little S powder wereplaced into a tubular furnace and heated to800oC for4h in an argon atmosphere canobtain nanorods of smooth surface and different lengths. The nanorods growindependently, the diameter distribute between170nm to250nm, the lengths between2-3μm, length to diameter ratio ranges from10to17, and the surface of some coarsernanorods has obvious convex chamfer edges or corners. The study shows that thenanorods have a unique crystal structure, namely it is W18O49crystal whisker.In the current work, WO3nanotubes and W18O49crystal whisker with large length todiameter ratio are first successfully prepared by coaxial electrospinning, which providea new way to fabricate WO3nanotubes and W18O49crystal whisker. At the same time,it provides a reference for other nanotube materials’ production.