A new green, ascorbic acid-assisted method for versatile synthesis of Au-graphene hybrids as efficient surface-enhanced Raman scattering platforms

A new green method for the synthesis of reduced graphene oxide-gold nanoparticle (rGO-AuNP) hybrids in aqueous solution that exploits the ability of ascorbic acid (AA) to operate as an effective dual agent for both graphene oxide (GO) and gold ion reduction is reported. Through careful investigation of the production of rGO-AuNP hybrids stabilized with polyvinylpyrrolidone (PVP), several versatile routes were devised with the aim of controlling the size, shape and distribution of AuNPs anchored onto the graphene sheets as well as the GO reduction. Particularly, when rGO is used as a platform for Au ion nucleation, a relative sparse distribution of AuNPs of size ranging from 20 nm to 50 nm is noticed. In contrast, when gold ions are added to the solution prior to any GO reduction, the density of large AuNPs is rather low relative to the uniformly packed small sized AuNPs (3-12 nm). The progress of GO reduction is explained by considering the contribution of the catalytic activity of AuNPs, besides the reducing activity of AA. Finally, a plausible mechanism for the nucleation and distribution of AuNPs onto the graphenic surface is assumed, highlighting the significance of oxygen moieties. The green method developed here is promising for the fabrication of gold-graphene nanocomposites with tunable surface decoration, suitable for surface-enhanced Raman spectroscopy (SERS).