One-step synthesis of three-dimensional graphene/multiwalled carbon nanotubes/Pd composite hydrogels: an efficient recyclable catalyst for Suzuki coupling reactions

In this paper, a simple one-pot hydrothermal procedure to create three-dimensional (3D) graphene/multiwalled carbon nanotubes/Pd (G/MWCNTs/Pd) composite hydrogels with a unique porous nanostructure was reported. During the formation of the G/MWCNTs/Pd composites, 2D graphene sheets and 1D MWCNTs were self-assembled to form interconnected porous microstructures and ultrafine Pd NPs were in situ grown on the 3D carbon-based skeleton simultaneously. In the as-obtained nanocomposites, MWCNTs not only prevented the close restacking of graphene sheets to increase the specific surface area but also provided an additional transport path to the catalyst surfaces which facilitated reactant transport. The G/MWCNTs/Pd composites proved to be an efficient, recyclable, and robust catalyst for the Suzuki cross-coupling reactions under mild aerobic conditions, which was attributed to the 3D macroporous framework with high specific surface area, numerous activation sites, and efficient transport pathways for improving the catalytic performance. Moreover, catalyst separation could be easily achieved by simple filtration, and the catalyst could be reused for at least six runs without significant loss in catalytic activity. Additionally, nearly no Pd species was released from the G/MWCNTs/Pd composites during the catalytic reactions, showing the heterogeneity in the present catalysis system.