Ultrasonication-induced Co-based metal-organic framework nanoparticles for red-light photocatalytic aerobic oxidation

Herein, we successfully obtained a two-dimensional (2D) Co(II) metal-organic framework, [Co₂(PDPA)(H₂O)₈]_n (XAIU-4), by using Co(NO₃)₂·6H₂O and 5,5'-(phenazine-5,10-diyl)diisophthalic acid (H₄PDPA). Single-crystal X-ray diffraction revealed its staggered ABAB-layered arrangement, with interpenetration between layers forming a 2D + 2D → three-dimensional (3D) supramolecular architecture. XAIU-4 demonstrated remarkable photocatalytic activity for thioether oxidation and benzyl alcohol dehydrogenation under red-light irradiation. Ultrasonication of XAIU-4 crystals yielded nanoparticles (XAIU-4-NP) with enhanced photocatalytic activity, attributed to exposed Co(II) active sites and reduced charge-transfer resistance, which facilitated efficient electron-hole separation and substrate activation. This work not only presents a sustainable strategy for synthesizing sulfoxides and aromatic aldehydes under red light but also underscores the critical role of catalyst nanoparticles in optimizing photoredox performance.