Core-Shell Heterostructures of Rutile and Anatase TiO₂ Nanofibers for Photocatalytic Solar Energy Conversion

Two types of core-shell heterostructure TiO₂ nanofibers (noted as core@shell TiO₂ NFs) were synthesized by sequential hydrothermal, calcination, and impregnation processes. Rutile TiO₂ nanofibers (R TiO₂ NFs) core with anatase TiO₂ nanoparticles (A TiO₂ NPs) shell is denoted as R@A TiO₂ NFs, and the reverse structure with anatase TiO₂ NFs core (A TiO₂ NFs) and rutile TiO₂ nanoparticles shell (R TiO₂ NPs) is denoted as A@R TiO₂ NFs. In our study, the photodegradation of organic dyes and Kelvin probe force microscopy (KPFM) analysis were applied to shed light on the mechanism of the excited electron-hole pair separation. The results of photodegradation showed that the A@R TiO₂ NFs have the highest activity under UV-B and UV-A irradiation, being nearly 3-fold higher as compared to AEROXIDE TiO₂ P25. The results in conjunction with KPFM measurements indicated that, in the heterostructure, electron-hole pairs are efficiently separated, the excited electrons stay in the anatase phase, and holes are injected to the rutile phase. When the A@R TiO₂ NFs heterostructures are decorated with Pt nanoparticles (Pt-A@R TiO₂ NFs), the nanocomposite is particularly active in photocatalytic hydrogen evolution from ethanol-water mixtures with a production rate of ∼8,500 μmol/h·g. Our study not only explains the role of anatase-rutile junctions in photocarrier separation, but also projects the development of other efficient photocatalytic heterostructures for green energy production and conversion.