Band restructuring of ordered/disordered blue TiO2 for visible light photocatalysis

Abstract

Black TiO₂ with/without noble metals has been proposed for visible light photocatalysis, but such structures still exhibit poor catalytic efficiency. Alternatively, phase-mixed TiO₂ such as the anatase and rutile phases has been commonly used for visible light catalysis with the inevitable inclusion of noble metals. Herein, we present a noble metal-free visible light photocatalyst, blue TiO₂, with type-II band-aligned ordered anatase/disordered rutile structures via phase-selective reduction with alkali metals. The changed band alignment in this heterostructure was identified by absorption and ultraviolet photoemission spectroscopy, which was further confirmed by transient charge separation. The band alignment of the type-I and type-II structures was clearly restructured by converting from the ordered to the disordered phase with a prolonged reduction period. We note that after this, light absorbance enhancement was also observed. After initiating the type-I structure in a pristine sample, the type-II structure was organized based on the disordered rutile phase during 3 days of Li-reduction. The type-II disordered rutile TiO₂ heterostructure exhibits a remarkable photocatalytic performance that is 55 times higher than that of conventional P25 TiO₂ in the solar-light driven hydrogen evolution reaction, owing to the efficient electron and hole separation of the type-II heterojunction. Furthermore, this restructured heterojunction type-II TiO₂ required 10 times less Pt as a co-catalyst for comparable photocatalytic performance, compared to Pt decorated type-I pristine anatase/rutile phase-mixed TiO₂.