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

Abstract

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.

Surface-Enhanced Raman Scattering Coupled with In Situ Raman Spectroscopy for the Detection of the OER Mechanism: A Mini-Review

“…The Raman resonance effect involves the transition of electrons from the HOMO (highest occupied molecular orbital) to the LUMO (lowest unoccupied molecular orbital) of the molecules (μ mol ) and the excitation transition from the valence band to the conduction band of the semiconductor surface (μ ex ). The PICT process occurs from the Fermi level of the metal surface to the HOMO/LUMO of the molecules . On the other hand, for the semiconductor substrates, the PICT process involves the transition from the HOMO of the molecule to the CB of the substrate and the VB of the substrate to the LUMO of the molecule.…”

MoS2 Nanosheets as Substrates for SERS-Based Sensing

“…CM is relatively complex but can generally be induced by charge transfer between molecules and substrates. Recently, increasing research results suggest that the CM effect cannot be ignored. − For instance, many carbon and semiconductor materials have only CM effect, without any EM effect, and can also exhibit very high SERS activity. − The enhancement factor (EF) of some semiconductor-based nanomaterials can even reach above 10 7 , which is equivalent to that of many metal nanostructures with EM effects. ,− More importantly, the CM effect is the key to achieve the specific enhancement. Therefore, investigating the CM effect of a semiconductor is of great significance for promoting the development of SERS.…”

Chemical Vapor Deposited 2D MoN Nanosheets as Stable and Uniform Surface Enhanced Raman Scattering Substrate with Thickness Dependent Sensitivity

“…The emerging 2 SERS substrates based on 2D materials provides a new opportunity for uniform SERS signals, due to their atomic flat surface which enables the uniform absorption of molecules. Graphene, boron nitride and transition metal dichalcogenides can be used as SERS substrate via chemical mechanism [24][25][26] . However, the sensitivity of the SERS substrates based on 2D materials is relatively low.…”