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.