Photocatalytic Evidence of the Rutile-to-Anatase Electron Transfer in Titania

Abstract

Layered anatase-rutile titania thin-films were synthesized via atmospheric-pressure chemical vapor deposition and characterized using X-ray diffraction, Raman spectroscopy and electron microscopy. The interposition of an amorphous TiO2-based interlayer allowed direct vapor deposition of anatase on a rutile substrate, which is otherwise hindered by templating. This resourceful approach and the subsequent crystallization of the amorphous layer after annealing of the films allowed investigation on the impact of an efficient interface of the two anatase-rutile phases in the photodegradation of a model organic pollutant. Clear evidence is presented on the synergy between the two polymorphs and more importantly, on the charge flow across the interface, which, against much conventional understanding, it involves electron transfer from rutile to anatase and is in agreement with a recent theoretical model and electron paramagnetic resonance data. Here, an increasing density of trapped electrons on the anatase surface of the A/R film is confirmed by photoreduction of silver. This observation is attributed to a defect-free efficient contact between the two phases and the presence of small rutile particles that promote rapid electron transfer at the A-R interface of the films.