Silver Nanoparticle Decorated Reduced Graphene Oxide (rGO) Nanosheet: A Platform for SERS Based Low-Level Detection of Uranyl Ion

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Abstract
Herein, a simple wet-chemical pathway has been demonstrated for the synthesis of silver nanoparticle conjugated reduced graphene oxide nanosheets where dimethylformamide (DMF) is judiciously employed as an efficient reducing agent. Altogether, DMF reduces both silver nitrate (AgNO3) and graphene oxide (GO) in the reaction mixture. Additionally, the presence of polyvinylpyrolidone (PVP) assists the nanophasic growth and homogeneous distribution of the plasmonic nanoparticle Ag(0). Reduction of graphene oxide and the presence of aggregated Ag NPs on reduced graphene oxide (rGO) nanosheets are confirmed from various spectroscopic techniques. Finally, the composite material has been exploited as an intriguing platform for surface enhanced Raman scattering (SERS) based selective detection of uranyl (UO22+) ion. The limit of detection has been achieved to be as low as 10 nM. Here the normal Raman spectral (NRS) band of uranyl acetate (UAc) at 838 cm–1 shifts to 714 and 730 cm–1 as SERS bands for pH 5.0 and 12.0, respectively. This distinguished Raman shift of the symmetric stretching mode for UO22+ ion is indicative of pronounced charge transfer (CT) effect. This CT effect even supports the higher sensitivity of the protocol toward UO22+ over other tested oxo-ions. It is anticipated that rGO nanosheets furnish a convenient compartment to favor the interaction between Ag NPs and UO22+ ion through proximity induced adsorption even at low concentration.

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