Direct Z-scheme Bi-HOF/g-C3N4 heterojunction: construction and interfacial charge regulation

Bi-HOF/g-C 3 N 4 direct Z-scheme heterojunction was constructed. • Bi N/Bi O bonds enhanced interfacial charge transfer. • BHG-3 achieved 97.26% MB removal under visible light. • ·O 2 − and h + were identified as dominant active species. • BHG-3 showed good stability and broad pollutant applicability. To integrate the visible-light-harvesting capability of g-C 3 N 4 with the interfacial electron-transfer function of hydrogen-bonded organic frameworks (HOFs), a Bi-HOF/g-C 3 N 4 (BHG) direct Z -scheme heterojunction was constructed via a facile hydrothermal assembly strategy. Structural and surface chemical characterizations confirmed the successful formation of the heterojunction, where strong interfacial coupling was established through Bi–N/Bi–O coordination bonds and hydrogen-bonding interactions. Photoelectrochemical and spectroscopic analyses revealed that the BHG heterojunction markedly promoted charge separation and migration, as evidenced by an enhanced photocurrent response, reduced interfacial charge-transfer resistance, and suppressed recombination of photogenerated carriers. The optimized BHG-3 composite exhibited excellent visible-light photocatalytic activity, achieving 97.26% removal of methylene blue (MB) within 40 min, with an apparent reaction rate constant 3.39 times higher than that of pristine g-C 3 N 4 . Moreover, BHG-3 showed good cycling stability, favorable tolerance to selected coexisting inorganic anions and degradation capability toward several model organic contaminants. Radical trapping experiments and mechanistic analyses confirmed a direct Z -scheme charge-transfer pathway, in which electrons enriched on g-C 3 N 4 and holes retained on Bi-HOF synergistically participated in pollutant degradation. The possible photodegradation pathway of MB over BHG-3 was further proposed based on LC-MS analysis. This work provides insight into interfacial charge regulation in HOF-based photocatalysts and offers a feasible strategy for developing efficient visible-light-driven systems for organic pollutant degradation.