One-pot environmentally friendly amino acid mediated synthesis of N-doped graphene–silver nanocomposites with an enhanced multifunctional behavior

Abstract

The present paper reports the one-pot synthesis of N-doped graphene–Ag nanocomposites (N-GrAg) involving the in situ generation of Ag nanoparticles (NPs). The simultaneous reduction of GO and Ag⁺ to produce N-GrAg has been achieved under mild reaction conditions using an environmentally benign reducing agent, glycine, in aqueous medium without adding any external stabilizer. XRD and SAED analyses revealed the presence of Ag in the fcc structure. HRTEM analysis shows a ‘d’ spacing of 0.236 nm corresponding to the highest intensity (111) reflection of Ag which matches the fcc structure. The N-doping of graphene and its uniform decoration by Ag NPs (with an av. dia. of 17.5 nm) having a relatively low surface atomic % of Ag (0.309) are evidenced by TEM and XPS analyses. Raman spectroscopy has also revealed that the decoration of N-Gr with Ag NPs resulted in the enhancement of the D and G bands by about 365%. The presence of Ag in N-GrAg prevents the folding of the graphene sheet as was revealed by TEM analysis. The supramolecular interactions of Ag with different moieties of N in N-GrAg were evidenced by IR, ¹³C NMR and XPS analyses, which resulted in the enhancement of its surface area and electrical conductivity as compared to that of N-Gr. The presence of Ag NPs on N-Gr increased the current response in cyclic voltammetry by more than seven fold as compared to that of N-Gr. These nanocomposites exhibited a fairly high SERS activity for 4-aminothiophenol, employed as the probe molecule, and allowed its detection at a 50 nM concentration even for the fairly small sized Ag NPs used in the present work.