Unveiling the role of localized polaronic mid-gap states in enhanced carrier transfer in TiO2/BiVO4 heterojunctions under visible light irradiation

Abstract

Abstract TiO2/BiVO4 heterojunctions are considered to be one of the most promising materials for photocatalysts due to their extended carrier lifetime, high visible light response, and good stability. However, while Type-II TiO2/BiVO4 heterojunctions are well-studied, the fundamental mechanism behind the Type-I configurations remains unclear, particularly regarding their unexpected high photocatalytic activity despite theoretically unfavorable band alignment. Herein, we reveal that localized polaronic mid-gap states (SP states) can mediate efficient charge transfer and recombination in TiO2/BiVO4 using time-resolved photoluminescence (PL) spectroscopy and transient absorption spectroscopy (TAS), providing direct experimental evidence of this mechanism. The existence of SP states enables exceptional methyl orange degradation efficiency (nearly 100% in 1 h under visible light) despite the theoretically unfavorable Type-I alignment. This work redefines the potential of Type-I systems for visible-light photocatalysis by demonstrating how polaron engineering overcomes the limitations of traditional band structures, advancing their applications in solar utilization.