Morphology variation of nanofibers from controlling matter diffusion in calcination processes

One dimensional metal oxide materials with verious morphologies were successfully fabricated via a single nozzle electrospinning method and subsequent calcination process. The matter diffusion in calcination process plays an important role for the morphology. With low heating rate of 1 or 5 °C/min, SnO2 samples tended to form solid nanofibers consisted of small nanoparticles with uniform size. Using same conditions, CeO2 samples preferred to form belt morphology while Co3O4 tended to form a chain. This is ascribed to the difference of diffusion of these metal oxides during calcination. To fabricate hollow fibers, a two-step calcination route was used. A heating rate of 1 °C/min was used at less than 300 °C to create dense solid fiber. Low heating rate at low temperature could be beneficial to enhancing Kirkendall effect remarkably. A heating rate of 15 °C/min was used during temperature rising from 300 to 550 °C, in which the quick decomposition of poly(vinylpyrrolidone) occurred. Such quick decomposition resulted in the fast diffusion of metal oxides to the surface layer of fibers. SnO2, CeO2, and SnO2/CeO2 hollow fibers were successfully fabricated through the two-step calcination. In addition, SnO2 and Co3O4 tended to form on SnO2/CeO2 and Co3O4/CeO2 composite structure during calcination process.