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

Abstract 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 (88.04%). These mixed-phase triaxial multifunctional structures could be employed in many applications.