Interfacial Charge‐Modulated Cs 2 AgBiI 6 /Cu@g‐C 3 N 4 Heterojunctions for Efficient Photocatalysis

ABSTRACT The construction of efficient heterojunction photocatalysts critically relies on the precise regulation of interfacial charge dynamics. However, conventional heterojunctions are often constrained by rigid band alignments and sluggish interfacial charge transfer due to severe charge‐carrier recombination. Herein, we report a novel strategy for directional interfacial charge modulation through the construction of Cs 2 AgBiI 6 /Cu@ultrathin g‐C 3 N 4 (CABI/Cu@UCN) heterojunction. Cu nanoclusters were anchored onto ultrathin g‐C 3 N 4 via a hydrothermal–photoreduction process, forming Schottky junctions that functioned as efficient electron extractors. Subsequently, the lead‐free double perovskite Cs 2 AgBiI 6 was coupled with Cu@UCN to construct a type‐II heterojunction. Owing to the synergistic driving force of interfacial built‐in electric fields, the distinctive “CABI→g‐C 3 N 4 →Cu” cascade charge‐transfer pathway enabled nearly dissipation‐free spatial separation efficiency of photogenerated electron–hole pairs. Under visible‐light irradiation, the optimized CABI/Cu@UCN composite exhibited outstanding photocatalytic activity and stability, achieving efficient degradation of various organic pollutants and antibiotics. The construction of the cascading heterogeneous structures facilitated the directional migration of electrons from CABI to UCN, and then to Cu, accompanied by significant interfacial charge redistribution. This work demonstrates that perovskite‐based heterostructures enable efficient photocatalytic degradation of dye and antibiotic pollutants through rational heterojunction design and interfacial charge regulation.