Interface engineering of flower-like ZIF-67 derived CoSe2/g-C3N4 heterojunction for efficient immobilization of elemental mercury

Elemental mercury (Hg 0 ) removal from coal combustion flue gas remains a significant challenge, primarily due to the limited uptake capacity and slow capture rate of commercial sorbents. Herein, the flower-like heterojunctions comprising ZIF-67-derived CoSe 2 uniformly dispersed in the layered g-C 3 N 4 (xCoSe 2 -CN), which were innovatively synthesized through an in-situ growth method followed by thermal selenization. The optimized 4CoSe 2 -CN exhibited exceptional Hg 0 capture performance, with an equilibrium capacity of 32.44 mg/g and an average rate of 10.47 μg/g/min, surpassing the most reported heterojunction materials. Furthermore, the satisfactory Hg 0 removal efficiency (>99 %) was maintained over a broad temperature window (25–140 °C) and under complex flue gas components. Notably, the sorbent demonstrated excellent recyclability, sustaining an average Hg 0 capture rate exceeding 90 % throughout five consecutive adsorption-regeneration cycles. The superior performance primarily originated from the heterojunction structure and the presence of under-coordinated selenide (Se 2 2− ). Interfacial electron redistribution modulated the electronic structure of CoSe 2 , inducing an upshift of d/p band centers and a reduced ∆ d-p band center gap, thereby significantly enhancing Hg 0 oxidation capability. Moreover, the Se 2 2− sites functioned as the dominant active centers for oxidizing Hg 0 to Hg 2+ and as binding sites for Hg 2+ to form HgSe. This work proposes an innovative strategy for designing MOF-derived heterojunction sorbents with modulated electronic structures to enable efficient Hg 0 capture.