Tunable hierarchical TiO2 nanostructures by controlled annealing of electrospun fibers: formation mechanism, morphology, crystallographic phase and photoelectrochemical performance analysis

Abstract

Highly crystalline hierarchical TiO 2 nanostructures of morphology ranging from one-dimensional regular fibers, hollow tubes, porous rods and spindles were achieved from electrospun TiO 2 /composite fibers by annealing at temperatures ranging from 400 C, 500 C, 600 C, 700 C, and 800 C, with a ramp rate of 5 C min À1 , and at a pressure of 1 mbar. Crystallographic structure, crystallite size, surface morphology and surface area of annealed TiO 2 nanostructures were analysed by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and Brunauer-Emmett-Teller (BET) method. The analysis of post-annealing process on electrospun TiO 2 nanofibers showed an orderly change in the crystallographic phase transformation with corresponding change in their surface morphologies. XRD and HRTEM analysis confirmed the phase transformation of highly crystalline anatase phase to rutile with crystallite size varied from 11 nm to 36 nm upon tuning the annealing temperature. Interestingly, TiO 2 nanostructures annealed at 700 C showed the formation of biphasic TiO 2 hollow tubes with stoichiometry phase compositions of 45.74% anatase and 54.25% rutile. A possible formation mechanism was proposed based on series of temperature-dependent experiments. To evaluate the potential use of these TiO 2 nanostructures, dye sensitized solar cell (DSSC) was fabricated using the post-annealed TiO 2 nanostructures as photoanode. A higher conversion efficiency (h) of 4.56% with a short circuit current (J sc ) of 8.61 mA cm À2 was observed for highly ordered porous anatase TiO 2 nanorods obtained upon annealing at 500 C under simulated AM1.5 G (100 mW cm À2 ), confirming that surface area of TiO 2 resulted out of porous structure played dominant role.

TiO2 surface nanostructuring for improved dye loading and light scattering in double-layered screen-printed dye-sensitized solar cells

“…The cracked surfaces of the nanorods help to maintain a high surface area for dye absorption, while the one-dimensional rod structure helps scatter the incoming sunlight, thereby increasing the optical path. Double-layered DSSCs made with these cracked nanorods have a relatively high cell efficiency of 7.29 % which is comparable with many state of the art DSSCs fabricated from decorated nanorods [7,[17][18][19]. This shows that the surface-modified nanorod structures in this study are worthy of further study in the design of more efficient double-layered DSSC anodes.…”

Oxygen vacancies and interfaces enhancing photocatalytic hydrogen production in mesoporous CNT/TiO2 hybrids

“…1b). The choice of polymer is crucial; fibres that are electrospun using polyvinyl acetate (PVAc), for example, form only short "spindles" when are annealed at similar temperatures [29], presumably due to decomposition of PVAc occurring at lower temperature compared to PVP. The final materials produced after polymer removal (400 • C in air) and crystallisation (500 • C in Ar) preserve the fibrillar structure but with a high porosity, as shown in Fig.…”

Characterization and acetone gas sensing properties of electrospun TiO2 nanorods

“…At present, SnO 2 , ZnO, WO 3 and TiO 2 are the main gas sensitive materials [1][2][3][4]. Semiconductor TiO 2 has a direct bandgap of 3.0 eV for the rutile and 3.2 eV for the anatase phase [5].…”