SERS effect of selectively adsorbed dyes by hydrothermally-produced MoS nanosheets

The electro-magnetic mechanism and chemical transfer mechanism coexist in the surface-enhanced Raman scattering (SERS) procedure. However, the latter is regretfully neglected due to the poor chemical transfer efficiency without the aid of a direct chemical bond. Herein, to further explore the CM Raman enhancement and understand the mechanism of SERS, Raman testing and the adsorption experiment have been carried out with respect to the exploration and application of metal-free SERS substrate. Thus, functional organic group-modified MoS nanosheets have been prepared via the hydrothermal method, and this as-prepared MoS shows an apparent Raman signal enhancement effect when serving/as the Raman substrate. Compared with those without organic groups (purchased MoS) and those with one organic group removed (annealed MoS), it is found that the minimum detection concentration of Rhodamine B (RhB) with the as-prepared functional MoS nanosheets could be 0.1 ppm, while the detection limit of annealed as-prepared MoS nanosheets and commercially purchased MoS powders were only 1 ppm and 10 ppm, respectively. Fourier transition infrared spectroscopy has revealed that the surface of the as-prepared MoS nanosheets was passivated by-NH and C═C and C═O groups. The lone pair electrons in-NH and the p-bond electrons in C═C and C═O groups would coordinate the nitrogen ethyl of RhB, forming a direct chemical bond, which could significantly contribute to the charge transfer. This led to efficient adsorption of the RhB molecule, which is key to achieving the SERS effect with the prepared MoS nanosheets substrate.