Gold nanoparticles deposited on MnO2 nanorods modified graphene oxide composite: A potential ternary nanocatalyst for efficient synthesis of betti bases and bisamides

Abstract

The decoration of novel nanostructures such as nano particle and nanorod on the surface of graphene oxide (GO) generate potential heterogeneous nanocatalyst. Highlighting this, in the present work, we have designed a ternary GO-MnO2-Au nanocomposite by decorating MnO2nanorods on the surface of graphene oxide via hydrothermal method, followed by deposition of Au nanoparticles on GO-MnO2 surface. The prepared nanocomposite was thoroughly characterised by different instrumental techniques such as X-Ray diffraction (XRD),Fourier transform infrared spectroscopy (FTIR),Raman spectroscopy, Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), High resolution Transmission electron microscopy (HRTEM), X-Ray photo electron spectroscopy (XPS), N2 adsorption desorption Brunauer–Emmett–Teller (BET) isotherm and Inductively coupled plasma - optical emission spectrometry (ICP-OES). FESEM and TEM images demonstrated that the MnO2 forms rod like structure having diameter of 60–100 nm and are uniformly distributed over the GO surface. HRTEM image clearly signifies gold (Au) nanoparticles having diameter of 7 ± 1.9 nm homogeneously distributed throughout the GO-MnO2 surface. Elementary state of Au and tetravalent nature of Mn as well as reduction of functional group after the decoration was confirmed from XPS studies. The catalyst GO-MnO2-Au was found to be the superior catalyst for synthesis of biologically active molecules such as Betti bases and Bisamides. The high catalytic activity of the materials can be attributed to the small and homogeneous distribution of gold nanoparticles, high redox potential of rod shaped MnO2 and the synergistic effect between GO, MnO2 and Au. All the reaction conditions were optimised by varying catalyst dosage, effect of solvent and temperature. The GO-MnO2-Au was easily recycled with minimal leaching and the product yield was found to be 85–90% after 4th cycle demonstrating the stability and durability of our nanocomposite.