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.