Chitosan assisted synthesis of 3D graphene@Au nanosheet composites: catalytic reduction of 4-nitrophenol

Abstract

We report the eco-friendly chitosan assisted synthesis of 3D graphene@chitosan@Au nanosheet (3DG@CS@AuNSs) composites without using any toxic reductants or capping agents. The 3D graphene network consists of few-layer graphene sheets. One the one hand, the interfacial energy between graphene and Au nanostructures is significantly weakened due to the existence of chitosan polymers, serving as “glue” for anchoring Au nanosheets on the surface of 3D graphene. On the other hand, chitosan contains abundant hydroxyl and amine groups acting as reducing and stabilizing agents for the formation and even distribution of Au nanosheets. Mild redox reaction between hydrochloroauric ions and hydroxyl and amine groups occurred under thermal conditions due to the matching electrochemical potentials of the oxidants and reductants. The as-prepared 3DG@AuNSs exhibited much higher activities than that of 3DG@Au nanoaggregates towards the reduction of 4-nitrophenol, as well as more convenient recyclability than other supported Au NPs in terms of a robust free-standing foam structure. Furthermore, high performance liquid chromatography was also applied to monitor the emergence of 4-aminophenol during reaction. The present studies not only build a new route for the design of a robust and free-standing foam catalyst based on the integration of graphene and Au nanostructures by the assistance of a natural polymer, but also shed deep insight on the understanding of the synergistic catalytic activity towards nitrophenols.