Elucidation of the function of oxygen moieties on graphene oxide and reduced graphene oxide in the nucleation and growth of silver nanoparticles

Abstract

The goal of the presented investigation was to study the differences in the decoration of graphene sheets, having various amounts of oxygen containing functional groups, with silver nanoparticles (AgNPs). The reduction of graphehe oxide (GO) was performed with the use of ascorbic acid (AA), leading to partially-reduced graphene oxide (PRGO) and reduced graphene oxide (RGO). The reduction process was monitored and confirmed by Raman Spectroscopy and Fourier Transform – Infrared Spectroscopy (FT-IR). The level of oxygen functional groups in the respective types of graphene was controlled by the duration of the reduction reactions. One-step synthesis of silver nanoparticles (AgNPs) was performed with no additional reducing agents in dark conditions in situ, i.e. directly on the graphene sheets deposited on a silicon wafer. It was proved that the presence of oxygen moieties on the graphene surface provides reactive sites for the spontaneous chemical reduction of Ag⁺ ions. It was also demonstrated that the amount of oxygen moieties on the surface of graphene plays an important role in the nucleation and growth of AgNPs. Moreover, it was found that the number of AgNPs investigated by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) increases with the amount of oxygen moieties, while their size decreases. Finally, it was found that the intensity of Raman bands characteristic of graphene are strongly increased for samples with AgNPs, due to surface enhancement Raman scattering (SERS).