Multi-stepwise charge transfer via MOF@MOF/TiO2 dual-heterojunction photocatalysts towards hydrogen evolution

Abstract

Rational manipulation of the photogenerated charge transfer inside the photocatalyst is key to enhancing the photocatalytic performance. Herein, inspired by the charge transport chain in natural photosynthesis, a novel multi-stepwise charge transfer strategy is proposed for the ingenious design of photocatalysts. To confirm the effectiveness of this strategy, a kind of MOF@MOF/TiO₂ dual-heterojunction was constructed by depositing TiO₂ nanoparticles on the surface of core–shell MOF@MOF hetero-frameworks. The energy band potentials of the three moieties in MOF@MOF/TiO₂ exhibit a multi-stepwise characteristic, wherein the slight gradient difference of energy bands helps in deconcentrating the charge in multiple energy bands and affords a smaller interface resistance, thus rendering a high charge transfer efficiency. Accordingly, compared with the single-heterojunction counterparts with one-step charge transfer including MOF@MOF and MOF/TiO₂, the MOF@MOF/TiO₂ dual-heterojunction achieves a much higher photocatalytic hydrogen evolution rate of 7.108 mmol g⁻¹ h⁻¹ under full-spectrum irradiation. This study may offer a deep insight into the charge transfer behavior in the photocatalytic process, along with the rational design of high-performance photocatalysts for sustainable energy conversion applications.