Boosting photocatalytic H₂O₂ production via triplet exciton-mediated singlet oxygen generation on a Bi@g-C₃N₄/ST-NS heterojunction

The escalating global energy crisis and environmental pollution has drawn increasing attention. As a green and sustainable alternative, photocatalytic H 2 O 2 synthesis has attracted widespread interest. In this study, we has designed a novel exciton-regulated photocatalyst (Bi@g-C 3 N 4 /ST-NS) by integrating bismuth-doped graphitic carbon nitride with porphyrin-based supramolecular nanostructures (ST-NS). The composite was synthesized through a sequential process involving solvothermal reaction, high-temperature calcination, and solution-phase self-assembly. We systematically investigated its crystal structure, photoelectronic properties, and the mechanistic basis of photocatalytic H 2 O 2 production. Characterization results confirmed the successful incorporation of Bi single atoms into the sixfold cavities of g-C 3 N 4 , forming a p-n heterojunction with ST-NS while preserving the crystallinity of the host matrix. The built-in interfacial electric field not only promoted efficient charge separation but also extended the visible-light absorption range and prolonged the carrier lifetime. Performance evaluations revealed that Bi@g-C 3 N 4 /ST-NS exhibited significantly enhanced H 2 O 2 generation activity compared to pristine Bi@g-C 3 N 4 , with optimal performance achieved at a 10:1 mass ratio. Under visible-light irradiation, the H 2 O 2 concentration reached 1134 μM in the reaction solution, representing a 2.5-fold improvement over Bi@g-C 3 N 4 . Mechanistic studies indicated that the heterojunction facilitated efficient intersystem crossing from singlet to triplet excitons. Rather than following the conventional superoxide radical (·O 2 - ) pathway, these triplet excitons activated ground-state oxygen to generate singlet oxygen ( 1 O 2 ) via resonance energy transfer. The subsequent highly selective two-electron reduction of 1 O 2 yielded H 2 O 2 , effectively circumventing the high-energy barrier steps associated with traditional pathways. This work thus presented a promising strategy for the rational design of high-efficiency photocatalytic systems through exciton regulation.