Red-light-responsive Cd(II)-organic framework nanosheets for aerobic photocatalysis via dual reactive oxygen species

To develop noble-metal-free photocatalytic systems that integrate efficient light-harvesting ability with robust redox functionality within a well-defined porous architecture, we successfully synthesized a two-dimensional (2D) Cd(II) metal-organic framework (MOF), [Cd₂(PDPA)(H₂O)₂(DMF)₂]_n (XAIU-12), using Cd(NO₃)₂·4H₂O and 5,5'-(phenazine-5,10-diyl)diisophthalic acid (H₄PDPA). Compared with the previously developed anthracene-based XAIU-5, incorporation of the phenazine-containing PDPA^4- linker substantially broadens the optical response of XAIU-12, with a low-energy absorption extending to ca. 900 nm. Single-crystal X-ray diffraction reveals a highly ordered two-dimensional layered framework with a staggered interlayer arrangement. Subsequent ultrasonic exfoliation affords ultrathin XAIU-12 nanosheets with predominantly bilayer thickness (XAIU-12-NS), reduced charge-transfer resistance, and improved accessibility of framework sites. Notably, XAIU-12-NS retains pronounced photocatalytic activity under red-light irradiation at 660 nm, demonstrating that the broadened low-energy absorption is photochemically productive. These combined structural and electronic features enable efficient aerobic photocatalysis through both O₂˙^- and ¹O₂ pathways. Under light irradiation, XAIU-12-NS exhibits outstanding catalytic efficiency in aerobic oxidation processes, enabling transformations such as arylboronic acid hydroxylation and benzylic C(sp³)-H bond activation in reduced reaction times. This study presents a novel approach to noble-metal-free photocatalysis based on MOF-encapsulated dual functional sites and underscores the critical role of photocatalyst nanosheets in optimizing photoredox performance.