Structural and optical characterization of electrospun TiO₂ nanofibers using titanium tetrabutoxide and titanium isopropoxide as precursors for photocatalytic applications

The structural and optical characterization of TiO₂ nanofibers (TiO₂-NF's) synthesised from two different chemical precursors, titanium tetrabutoxide (TNBT) and titanium isopropoxide (TTIP), obtained by electrospinning technique with controlled morphology and crystalline phase, is presented. Varying the distance between the needle tip and the collector called "air gap", it was possible to control the diameter and the formation of the fibers within the nanometric scale. The crystalline phase (CP) of the TiO₂-NFs was controlled through thermal treatment (TT) at 450 °C for 3 h, anatase phase. The chemical composition of the annealed electrospun TiO₂-NF was estimated by EDS, finding there is an excess of titanium that causes oxygen vacancies, which stimulate the CP transformation, from amorphous to anatase. By means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) was possible to corroborate the formation of TiO₂-NFs with a smooth morphology and well-defined shape. FTIR spectroscopy and Raman scattering results of electrospun TiO₂-NFs demonstrated changes in structural and optical properties caused by TT. By Raman scattering was found that the annealed TiO₂-NFs showed the anatase CP, which was corroborated by X-ray diffraction. At first sight, the surface morphology of the electrospun fibers was not affected by the choice of precursor; however, on closer review, the fibers prepared with the TTIP precursor showed a smaller crystal size of 8.51 nm and band gap energy of 3.38 eV, while the samples prepared with TNBT showed a smaller bandgap energy of 3.06 eV and a nanocrystal size of 10.98 nm. With both precursors at a working distance of 15 cm, homogeneous fibers are obtained, with a smaller diameter without the presence of morphological defects, called beds, and a better size distribution.