Determination of concentration of adsorbed molecules by Raman spectroscopy and optical imaging

In this paper, solution soaking is used to deposit Rhodamine 6G (R6G+) dye molecules on two-dimensional materials, i.e., graphene and molybdenum disulfide (MoS2), which concentrate the solution-phase R6G+ molecules into a solid thin film. The concentration of adsorbed molecules on graphene/MoS2 can be calculated using graphene 2D/MoS2 A1g peak as an internal standard. It is found that optical imaging also provides a quantitative way to determine the concentration of adsorbed molecules whose results are further confirmed by atomic force microscopy. The obtained results will facilitate the fabrication of surface-enhanced Raman scattering substrates using two-dimensional materials. Adsorptive removal of various dyes to lighten effluent pollution from industries is a basic and applied research area. Carbon-based materials are well-known adsorbents for dyes. Using optical imaging, the dynamic processes of solution-dependent R6G+ sorption and desorption onto graphene are monitored. Our results also shed light on potentially using graphene materials as adsorbents for toxic and carcinogenic molecules.