Influence of calcination temperature on the structure, morphology and optical properties of electrospun pseudobrookite nanofibers

Novel crystalline iron-titanate fibers were synthesized for the first time to the best of our knowledge, through a simple, low cost electrospinning method followed by calcination treatment at different temperatures (500–750 °C for 3 h and at 500 °C for 6 h and at 550 °C for 4 h). The fibers were prepared from a precursor solution containing polyvinylpyrrolidone (PVP), iron(III) nonahydrate, titanium isopropoxide, N,N-Dimethylformamide and ethanol. As spun fibers were smooth, straight, beadless and uniform forming a nonwoven fibrous mat, with an average diameter of ca. 205 nm. Upon calcination in air the PVP matrice was removed and XRD and FTIR analysis showed that the duration of the calcination process, besides the temperature, had a direct influence on phase formation. Pure phase of pseudobrookite was obtained at 600 °C, 500 °C for 6 h and at 550 °C for 4 h. In addition, the morphology of obtained nanofibers was directly affected by the calcination temperature. The surface of fibers obtained after calcination was no longer smooth and the fiber diameter decreased due to complete degradation of PVP. At 700 oC and 750 °C, fibers were thicker which can be attributed to growth of Fe2TiO5 nanoparticles and simultaneous coalescence of small particles. All samples exhibited a type IV nitrogen adsorption isotherm with a type- H3 indicating slit-shaped mesoporous structure. The BET surface areas of 500 °C for 6 h, 550 °C for 4 h and 600 °C for 3 h were estimated to be 62, 38.7 and 33.2 m2/g, respectively