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.