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

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 x 10(-4) ml/mg as the association constant. From the fluorescence emission analysis, an excellent concentration-dependent quenching efficiency of similar to 94 % was observed for a concentration value of 96 mu g/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 similar to 86 % quenching efficiency when mixed with 96 mu g/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.