Triaxial electrospun mixed-phased TiO₂ nanofiber-in-nanotube structure with enhanced photocatalytic activity

Metal-oxide based nanostructures, with mixed crystalline phases and high specific surface area, are of great interest due to their excellent performance. Highly porous TiO₂ nanofiber-in-nanotube (NF@NT) structures are developed through triaxial electrospinning, followed by the annealing process. A mixed solution of polyvinyl pyrrolidone, tetrabutyl titanate, and di-isopropyl azodiformate are used in the outer and inner layers of the nanofibers, while paraffin oil is used in the middle layer for separation. Mesoporous TiO₂NF@NT structure is confirmed through the SEM images. FTIR spectrums reveal the transformation of as-spun polyvinyl pyrrolidone/tetrabutyl titanate/di-isopropyl azodiformate/paraffin oil triaxial nanofiber into TiO₂NF@NT after the annealing. XRD results show the maximum mixed phases (anatase and rutile) of TiO₂NF@NT at 450 °C. The transformation of anatase to rutile phase increases with increasing the temperature from 450 °C to 700 °C. BET analysis shows that TiO₂NF@NT has a higher specific surface area of ~149.67 m²/g compared to the normal TiO₂ nanofiber (~62.00 m²/g). TiO₂NF@NT performs better photo-degradation of the Sandalfix N.Blue (SNB) under UV-light irradiation than the normal TiO₂NFs. Moreover, TiO₂NF@NT, calcined at 450 °C temperature, had the highest SNB degradation (88.1%). These mixed-phase triaxial multifunctional structures could be employed in many applications.