Unfolding the Impact of H2-Reduction Treatment in Enhancing the Photocatalytic Activity of Rutile TiO2 Based on Photocarriers Dynamics

Abstract

In the pursuit of efficient titania photocatalysts for water splitting, several strategies have been employed. One of these is reduction of titania (TiO2) via treatment under hydrogen atmosphere, a promising technique to improve the photocatalytic performance. It has been proposed that electron injection induced by reduction on TiO2 demonstrated an improved photocatalytic activity. However, the dynamical processes involving the photogenerated charge carriers in reduced TiO2 have not been fully explored and understood yet. In this work, we employ time-resolved absorption spectroscopy (TAS) and photoluminescence (PL) measurements to unravel the impact of H2 reduction treatment on the photocarriers in rutile TiO2 (R-TiO2). TAS results revealed that the photoexcited electrons are preferentially filling the shallower trap states of reduced R-TiO2, with the lowest energy limit of ∼0.25 eV below the conduction band minimum, much shallower than that of nonreduced R-TiO2 (∼0.62 eV). Furthermore, these favorable effects of H2-reduction resulted in notable increase of long-lived shallow-trapped electrons, substantially extending the lifetimes of electrons and holes. PL measurements strongly support the positive impact of H2 reduction treatment: the NIR emission (∼850 nm) is largely quenched, indicating that the radiative recombination of deep trapped electrons and holes is significantly reduced. The combined PL and TAS results shed light on the impact of H2 reduction on R-TiO2, and this strategy can be potentially useful for further development of other photocatalytic materials.