Electron-Deficient Au Nanoparticles Confined in Organic Molecular Cages for Catalytic Reduction of 4-Nitrophenol

Noble-metal nanoparticles are regarded as one of the most promising catalysts to reduce the organic pollutant 4-nitrophenol (4-NP). However, the inevitable agglomeration of noble-metal nanoparticles and their poor distributions in catalytic systems limit their performance. Here, we propose a strategy to encapsulate Au nanoparticles inside porous organic cages (POCs) of soluble RCC3 and stabilize the size of Au nanoparticles at ∼3.25 nm. Typically, the Au@RCC3 composite exhibits excellent 4-NP catalytic reduction performance, which is superior to the corresponding Au bulk catalyst and is also closely related to the size of Au nanoparticles. The normalized X-ray absorption near-edge structure (XANES) results indicate that the electron deficiency at the Au atoms in Au@RCC3 is due to the existence of the RCC3 cage, which is beneficial to accelerate the electron transfer from BH4– to 4-NP during the hydrogenation process. This is also shown by density functional theory (DFT), in which a low energy barrier of 1.03 eV exists for the Au12 cluster compared with 1.37 eV for the Au25 cluster. Therefore, the encapsulation of noble-metal nanoparticles with soluble POCs is an effective way to design and develop stable active catalysts rationally.