Chemically Engineered Sulfur Vacancies on Few-Layered Molybdenum Disulfide Nanosheets for Remarkable Surface-Enhanced Raman Scattering Activity

In recent years, molybdenum disulfide nanosheets (MoS2 NSs) with sulfur surface defects have been used for surface-enhanced Raman scattering (SERS). However, methods to generate sulfur defects on the MoS2 NS surface are sophisticated and expensive. In this study, we present a relatively straightforward approach to quickly creating sulfur defects on MoS2 NSs by chemical treatment with NaBH4. Few-layered MoS2 NSs (FL-MoS2 NSs) were formed by exfoliating bulk-MoS2 in isopropanol. By oxidation–reduction reactions of FL-MoS2 NSs mixed with a suitable concentration of NaBH4, the resulting MoS2 NSs with abundant sulfur defects (SV-FL-MoS2 NSs) can be obtained. Spectroscopic and electron microscopic methods are used to demonstrate sulfur defects in SV-FL-MoS2 NSs. Rhodamine (R6G) and rhodamine-B (RhB) were used as Raman analytes to evaluate the SERS efficiency of SV-FL-MoS2 NSs. The developed SERS substrate provided detection limits of 1 × 10–8 M for both R6G and RhB, with enhancement factors of 2.21 × 106 and 4.02 × 106, respectively. Our measurements of SV-FL-MoS2 NSs' energy band gap and R6G/RhB confirmed that charge transfer (CT) and tight molecular contacts are responsible for their excellent SERS sensitivity. With the development of new, low-cost semiconductor-based SERS materials, this discovery could impact materials science and biosensing platforms.