▎ 摘　　要

Porous architectures of 3D-graphene assembled with noble metal (Au, Pd and Pt) nanoparticles were successfully fabricated through a one-step green route using a low-cost freeze-casting method. The as-synthesized noble metal/3D-graphene nanocomposites exhibit ultralow density and interconnected 3-D porous networks with a uniform distribution of noble metal nanoparticles. Time-correlated single photon counting (TCSPC) measurements reveal the energy and electron transfer at the interface of the graphene sheets and noble metals, which is maximum in the case of Pt/3D-graphene due to the small size of the Pt nanoparticles. The as-obtained noble metal/3D-graphene nanocomposites were applied to the reduction of 4-nitrophenol and methylene blue by NaBH4. The rates of reduction are in the order Pt/3D-graphene > Pd/3D-graphene > Au/3D-graphene for both the reduction reactions, signifying that the smallest noble metal nanoparticles possess the highest catalytic activity. The Pt/3D-graphene nanocomposite also exhibits excellent catalytic activity in comparison to the RGO/Pt nanocomposite, which is due to its unique 3D-porous structure. Moreover, the Pt/3D-graphene nanocomposite could be easily separated from the reaction solution by simple filtration and recycled for five cycles without the loss of its catalytic activity. Noble metal/3D-graphene nanocomposites can be utilized as attractive, low-cost, efficient fixed bed reactors and as easily separable catalysts in industrial applications for the reduction of 4-nitrophenol and methylene blue with high catalytic activity and exceptional absorption capability.