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

Two types of core–shell heterostructure TiO 2 nanofibers (noted as core@shell TiO 2 NFs) were synthesized by sequential hydrothermal, calcination, and impregnation processes. Rutile TiO 2 nanofibers (R TiO 2 NFs) core with anatase TiO 2 nanoparticles (A TiO 2 NPs) shell is denoted as R@A TiO 2 NFs, and the reverse structure with anatase TiO 2 NFs core (A TiO 2 NFs) and rutile TiO 2 nanoparticles shell (R TiO 2 NPs) is denoted as A@R TiO 2 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 TiO 2 NFs have the highest activity under UV-B and UV-A irradiation, being nearly 3-fold higher as compared to AEROXIDE TiO 2 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 TiO 2 NFs heterostructures are decorated with Pt nanoparticles (Pt-A@R TiO 2 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.