Efficient Synthesis of Ultrafine Gold Nanoparticles with Tunable Sizes in a Hyper-Cross-Linked Polymer for Nitrophenol Reduction

The development of metal nanoparticles supported in porous materials is important for the development of highly efficient heterogeneous catalysis. Because of the quantum-size effect, the size of the metal nanoparticles is key to achieving high catalytic activity. Therefore, the tuning of nanoparticle size is a critical step for efficient heterogeneous catalytic systems. Hyper-cross-linked polymers (HCPs) with tunable surface area, high stability, narrow pore size, and low cost have found intriguing applications in heterogeneous catalysis as catalyst supports. Herein, we report that gold nanoparticles can be controlled within the size range of 1.7-5.1 nm in HCPs simply by modulating the loading mass ratio of HAuCl₄·4H₂O/HCP-TPMT. The resulting heterogeneous catalysts showed high catalytic activity and recyclability toward catalytic reduction of 4-nitrophenol. In addition, we found that the smallest Au nanoparticle sizes exhibited the highest normalized reaction constant (K_nor). These results demonstrate an effective strategy for preparing size-controllable metal nanoparticles by using hyper-cross-linked polymers as catalyst supports for heterogeneous catalysis.