Homo‐Hetero Double Junction Coupling Weakens Exciton Effects to Enhance Selective Photocatalytic O2 Activation on Carbon Nitride

Abstract Exciton effects caused by the inherent dielectric confinement in the 2D material carbon nitride (CN) severely limit the transfer of photogenerated carriers and the selective generation of free radicals. Herein, a homo‐hetero double junction coupling strategy is reported to address these challenges. Ternary homojunction carbon nitride (HCCN) functionalized with cyano and cyanamide groups is constructed with a built‐in electric field that efficiently separates the electron–hole into different structural units, thereby reducing reverse charge recombination and weakening exciton effects. The introduction of α‐Fe 2 O 3 (FO) subsequently constructs the homo‐hetero double junction catalyst FO/HCCN with a built‐in electric field 127 times stronger than HCCN, which promotes the directional migration of carriers after exciton dissociation and achieves ≈100% selective generation of ·O 2 − from O 2 . These results suggest that FO/HCCN achieves 99.6% removal of tetracycline within 20 min, with a degradation rate 12 and 46 times higher than FO/CN and HCCN, respectively. In addition, the system shows excellent stability and cyclability in real‐life light experiments and trace organic contaminant removal. This homo‐hetero double junction coupling strategy opens up new avenues in weakening exciton effects and precisely controlling the generation of free radicals.