S-scheme heterojunction/Schottky junction tandem synergistic effect promotes visible-light-driven catalytic activity

Designing photocatalysts with high light utilization and efficient photogenerated carrier separation for pollutant degradation is one of the important topics for sustainable development. In this study, hierarchical core-shell material α-Fe2O3@ZnIn2S4 with a step-scheme (S-scheme) heterojunction is synthesized by in situ growth technique, and MXene Ti3C2 quantum dots (QDs) are introduced to construct a double-heterojunction tandem mechanism. The photodegradation efficiency of α-Fe2O3@ZnIn2S4/Ti3C2 QDs to bisphenol A is 96.1% and its reaction rate constant attained 0.02595 min−1, which is 12.3 times that of pure α-Fe2O3. Meanwhile, a series of characterizations analyze the reasons for the enhanced photocatalytic activity, and the charge transport path of the S-scheme heterojunction/Schottky junction tandem is investigated. The construction of the S-scheme heterojunction enables the photo-generated electrons of α-Fe2O3 and the holes of ZnIn2S4 to transfer and combine under the action of the reverse built-in electric field. Due to the metallic conductivity of Ti3C2 QDs, the photogenerated electrons of ZnIn2S4 are further transferred to Ti3C2 QDs to form a Schottky junction, which in turn forms a double-heterojunction tandem mechanism, showing a remarkable charge separation efficiency. This work provides a new opinion for the construction of tandem double heterojunctions to degrade harmful pollutants.