Optical spectroscopic probing of the interaction of graphene oxide-Au composite and Rhodamine 6G

Abstract

In this study, we report the results of a spectroscopic investigation of the interaction between cationic dye molecule, Rhodamine 6G (Rh6G), and graphene oxide (GO)-gold (Au) composite prepared in a two-step process. The graphene oxide is prepared via modified Hummer's method and followed by in-situ reduction of plasmonic particles is carried out to synthesize the composite materials. The formation of the composite is confirmed via Raman spectroscopy, UV–Vis absorption, and transmission electron microscopy studies. The GO-Au concentration-dependent UV–Vis absorption studies unambiguously illustrate the complex formation between GO-Au composite and Rhodamine 6 G dye with 4.44 × 10⁻⁴ ml/mg as the association constant. From the fluorescence emission analysis, an excellent concentration-dependent quenching efficiency of ∼94 % was observed for a concentration value of 96 µg/ml. However, analysis of the data reveals that the inner filter effect plays a critical role in experimentally observed quenching efficiency and the exclusion of the inner filter effect provides a realistic value of ∼86 % quenching efficiency when mixed with 96 µg/ml of GO-Au composite. Furthermore, the mechanism of quenching is found to be a result of both static as well as dynamic quenching occurring synergistically. The quencher concentration-dependent lifetime studies corroborate with the results obtained from the steady-state fluorescence studies. Such a 2D-plasmonic composite-dye mixture can find diverse applications in photonics, photocatalytic reactions, dye-removal, etc.