Direct z-scheme ZnCo2S4/MOF-199 constructed by bimetallic sulfide modified MOF for photocatalytic hydrogen evolution

This work reports a simple ultrasonic impregnation method, using MOF-199 as the carrier platform to construct direct Z-Scheme ZnCo2S4/MOF-199 (ZCS/M) for stable and efficient photocatalytic hydrogen (H2) evolution. Under simulated sunlight, ZCS/M shows high photocatalytic activity, with H2 evolution amount of 11.6 mmol·g−1·h−1, which is 48.4 and 83.3 times of MOF-199 and ZCS respectively, and the apparent quantum efficiency (AQY) reaches 4.92 % at 420 nm. The successful construction of direct Z-Scheme heterojunction greatly improves the separation of electron-hole pairs to promote photocatalytic H2 evolution. In addition, ZCS is evenly anchored on the surface of MOF-199, which effectively solves the problem that ZCS is easy to agglomerate, and exposes more active sites. In-situ XPS, VB, band gap, work function and Fermi level is used to analyze the Fermi level alignment, interfacial built-in electric field and band bending, and photocatalysis mechanism and path of electron migration is speculated. This work provides a new strategy for the design and construction of direct Z-Scheme heterojunction with transition metal sulfide on the platform of MOF to enhance photocatalytic H2 evolution during water splitting.