A Direct Z-Scheme Quasi-2D/2D Heterojunction Constructed by Loading Photosensitive Metal-Organic Nanorings with Pd Single Atoms on Graphitic-C₃N₄ for Superior Visible Light-Driven H₂ Production

Rational design of Z-scheme composite photocatalysts with 2D/2D heterojunction is a promising method to convert solar energy into chemical fuels. Herein, a Pd2L2-type metal-organic nanoring (MAC-1), which can serve as a photochemical molecular device (PMD), is assembled by catalytic Pd2+ centers and photosensitive ligands (M-7). Then MAC-1 is combined with graphite-phase carbon nitride (g-C3N4) to construct a direct Z-scheme quasi-2D/2D composite material MAC-1/g-C3N4 with Pd single atoms. The optimized 3.5% MAC-1/g-C3N4 single-atom catalyst (SAC) shows better photocatalytic performance than g-C3N4, MAC-1, Pd/g-C3N4, M-7/Pd/g-C3N4, and 3.5% MAC-1/g-C3N4-mixed and also displays good durability for H-2 production. The H-2 yield rate of 22.3 mmol g(-1) h(-1) and the corresponding turnover number based on Pd or MAC-1 amount (TONPd/TONMAC-1) of 119 172/238 344 within 50 h are achieved for 3.5% MAC-1/g-C3N4, which is one of the highest records of all visible light-driven g-C3N4-based photocatalysts reported. Such remarkably enhanced activity can result from the enhanced charge carrier mobility, improved light absorption ability, enlarged heterojunction contact interface, and highly monodispersed Pd active sites. The Z-scheme SAC composed of metal-organic nanorings and g-C3N4 nanosheets therefore has great potential as an efficient and sustainable photocatalyst for solar-driven H-2 production.