Sono-synthesis approach in uniform loading of ultrafine Ag nanoparticles on reduced graphene oxide nanosheets: An efficient catalyst for the reduction of 4-Nitrophenol.

In this research, a facile, one step and eco-friendly sonochemical rout was utilized to the synthesis of a new nanocomposite by Ag nanoparticle anchored on reduced graphene oxide (rGO-Ag-U). Sonication was carried out by using low frequency ultrasound (20 kHz) under ambient condition. In this way, graphene oxide and Ag+ ions simultaneously reduced by polyol without using any additional reactants or capping agents. The polyol serves as both solvent and low toxic reducing agent. To achieve the best synthesis condition of rGO-Ag-U nanocomposite, the effects of irradiation time, ultrasonic amplitude and reaction temperature were investigated. In comparison, the synthesis of rGO-Ag was also carried out via reflux as a classical method (rGO-Ag-C). It was found that ultrasonic irradiation for 10 min at 70% amplitude was sufficient for the synthesis of rGO-Ag-U. Several analytical techniques were used to characterize the resulting nanocomposites such as UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The UV-Vis spectra show a shift of GO band to a higher wavelength which is due to the reduction of sp3 sites. The results of TEM also confirm the smaller Ag nanoparticle (about 18 nm) which uniformly decorated on rGO nanosheets by sonochemical method than classical method. The experimental data suggest that among the synthesized nanocomposites, rGO-Ag-U exhibited better catalytic activity (kapp = 1.18 min-1) towards the reduction of 4-Nitrophenol to 4-Aminophenol in the presence of sodium borohydride (NaBH4).