Photocontrollable Organic Cage Encapsulated Palladium Nanoparticles: Catalytic Reduction of Nitrobenzene Derivatives

Porous organic cages possess an internal cavity and stable aromatic backbones with multiple palladium binding sites, which are suitable for controlled synthesis and stabilization of palladium nanoparticles. In recent years, various types of porous organic cages have been employed to construct nanoparticles for catalytic reactions. However, few organic cages constructed by photoresponsive units have been used to control catalytic reactions by photo irradiation. Herein, stable photo-controllable organic cages of POC-1 are constructed from dithienylethene with aldehyde and cyclohexanediamine through dynamic imine chemistry, showing a typical 3+6 molecular configuration. The metal nanoparticles of palladium are encapsulated by the organic cages as nanocatalysts, which are characterized by high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) and Cryo-Transmission Electron Microscopy (cryo-TEM). Through the TEM analysis, it can be concluded that 2.5 nm Pd nanoparticles could be stabilized in open form organic cages, while 2.0 nm Pd nanoparticles could be encapsulated in closed-form cages. As compared with the catalytic reduction of nitroaromatics by ultraviolet-visible spectroscopy (UV-Vis), the catalytic rate of Pd@ o-POC-1 is about four times higher than that of Pd@ c-POC-1. In-situ illumination experiments demonstrates that catalytic reaction activity is significantly associated with the varying loading amounts of palladium in the open/closed cages, which might be related to the size of the cavity of open and closed forms. Compared to the closed form, the open form exhibits higher catalytic reduction performance due to its higher palladium loading. This study provides a novel idea for utilizing photo-controlled organic cages encapsulating nanoparticles in catalytic reactions, offering broad application prospects.