Synthesis of structured hollow microspheres with sandwich-like hybrid shell of RGO/Pd/m-SiO2 for highly efficient catalysis

The development of easy-to-operate strategies for fabricating stable and efficient nanostructured catalysts based on noble metal nanoparticles is of great significance. Here we report a facile method to prepare the hollow microsphere with sandwich-like hybrid shell composed of an interlayer of palladium nanoparticles (Pd NPs) in between the inner shell of reduced graphene oxide (RGO) and outer shell of mesoporous silica (m-SiO2), denoted as RGO/Pd/m-SiO2 hollow microsphere. Our approach involves the use of polystyrene microsphere as template to firstly deposit the RGO and then Pd NPs and finally to coat the hybrid SiO2 containing porogens, followed by the calcination to simultaneously obtain interior cavity and mesoporous outer shell. Our method is facile because it avoids pretreatment of template surface and functionalization/modification of any of shell components. More importantly, the as-prepared RGO/Pd/mSiO(2) hollow microspheres exhibit several distinguished advantages for catalytic applications, including the sandwich-like hybrid shell effectively preventing Pd NPs from aggregation and leaching, and the stabilizer-free surface of Pd NPs as well as the synergistic interaction of the Pd NPs and RGO. Consequently, these hollow microspheres show superior catalytic activity and stability in the reduction of p-nitrophenol by sodium borohydride. Moreover, it is also found that, the thickness and porosity of m-SiO2 outer shell can influence the catalytic activity of the RGO/Pd/m-SiO2 hollow microspheres. Overall, our results have provided important implications for rational design of hybrid shell of hollow microspheres with appropriate composition and configuration to boost the catalytic performance of noble metal NPs.