Direct Z-Scheme Heterojunction Catalysts Constructed by Graphitic-CN and Photosensitive Metal-Organic Cages for Efficient Photocatalytic Hydrogen Evolution.

The demand for improving the activity, durability, and recyclability of metal-organic cages (MOCs) that work as photocatalytic molecular devices in a homogeneous system has promoted research to combine them with other solid materials. An ML type photosensitive metal-organic cage MOC-Q2 with light-harvesting ligands and catalytic Pd centers has been synthesized and further heterogenized with graphitic carbon nitride to prepare a robust direct Z-scheme heterojunction photocatalyst for visible-light-driven hydrogen generation. The optimized g-CN/MOC-Q2 (0.7 wt%) sample exhibits a high H evolution activity of 6423 μmol g h in 5 h, and a total turnover number of 39,695 after 10 h, significantly superior to the bare MOC-Q2 used in the homogeneous solution and the comparison sample Pd/g-CN/L-4. The enhanced performances of g-CN/MOC-Q2 can be ascribed to its direct Z-scheme heterostructure, which effectively improves the charge separation and transfer efficiency. This work presents a rational approach of designing a binary photocatalytic system through combing micromolecular MOCs with heterogeneous semiconductors for water splitting.