Preparation And Properties Of Metal Nanoparticle Catalysts Embeded Between Two Supports Of Reduced Graphene Oxide Nanosheets And A Polypyrrole Layer

As a catalyst, Metal nanoparticles provide a powerful driving force for the development of new energy and environmental remediation. Metal nanoparticles have a big progress in catalytic, however, four problems appear with practical application of metal nanoparticles: first, the surface energy inevitably increases,which leads to the tendency of aggregation; second, the nanoparticles are difficult to be separated from reaction solution; third, the nanoparticles easily fall off from support surface, as they directly expose to the reaction media and no strong interaction exists between the supports and nanoparticles; fourth, the as-prepared metal nanoparticles usually only exhibit spherical morphology. It is well known that the catalytic reactions take place on the nanostructure surface, slight changes in the sizes, structures, compositions or morphologies can influence catalytic activity.Therefore, the development of metal nanostructures with non-spherical morphologies, especially the controllable morphologies, is of great importance.Herein, we provide an idea to solve this problem. Through a simple way, the catalysts with metal nanoparticles embedded between reduced graphene oxide(r GO)nanosheets and conducting polymers(PPy) were prepared. This synthetic method is simple, and the resulting metal nanostructures not only exhibited high activity, but also had good stability with high service life. The catalysts could be quickly separated from the reaction solution by magnet and reused without obvious catalytic loss. Particularly, their morphologies could be easily turned to be spherical,coral-like and porous cluster-like via simply changing experimental parameters, and can further improve the catalytic activity realizing the purpose of efficient use of catalysts.The catalysts with Pd and γ-Fe2O3 nanoparticles embedded between reduced graphene oxide nanosheets(r GS) and N-doped carbon nanosheets(NCS) were prepared through a two-step method. Firstly, graphene oxide nanosheets(GS)/prussian blue(PB)-Pd/polypyrrole(PPy) composites were synthesized by using pyrrole monomer as reductant, K3Fe(CN)6 and Pd Cl2 as oxidants in the presence of GS via a redox reaction. Subsequently, the as-obtained GS/PB-Pd/PPy composites were calcinated in N2 atmosphere. During the heat-treatment,carbonization of PPy to NCS, conversion of nonmagnetic PB to magnetic γ-Fe2O3 nanoparticles, and reduction of GS to r GS were finished, simultaneously.r GS/Fe2O3-Pd/NCS composites exhibited good catalytic activity toward reduction of 4-nitrophenol. The rate constant k and turnover frequency were calculated andcompared with recent reports. Owing to γ-Fe2O3 nanoparticles, the r GS/Fe2O3-Pd/NCS composites could be quickly separated by magnet and reused without obvious decrease in activity.We have introduced a one-step method to prepare Pdx Auy bimetallic nanostructures supported on reduced graphene oxide(r GO) nanosheets and wrapped in a polypyrrole(PPy) layer. By using a pyrrole monomer as a special reducing agent for metal salts, the morphologies of Pdx Auy bimetallic nanostructures could be easily turned to be spherical, coral-like and porous cluster-like via simply changing dosage or molar ratio of Pd Cl2 and HAu Cl4?4H2O. The roles of the pyrrole monomer and r GO support in formation of r GO/Pdx Auy/PPy composites were investigated in detail. Transmission electron microscopy, elemental mapping analysis, X-ray diffraction, X-ray photoelectron spectroscopy and Fourier-transform infrared spectra were used to characterize their morphologies, structures and compositions. Compared with corresponding r GO/Pd/PPy and r GO/Au/PPy composites, the as-prepared r GO/Pdx Auy/PPy composites displayed enhanced catalytic activity towards the reduction of 4-nitrophenol.