Nitrogen-Doped Silver-Nanoparticle-Decorated Transition-Metal Dichalcogenides as Surface-Enhanced Raman Scattering Substrates for Sensing Polycyclic Aromatic Hydrocarbons

Abstract

The modification of transition-metal dichalcogenides (TMDs), incorporating nitrogen (N) doping and silver nanoparticles (AgNPs) decoration on the skeleton of exfoliated MoS2 and WS2, was accomplished. The preparation of N-doped and AgNPs-decorated TMDs involved a one-pot treatment procedure in a vacuum-sputtering chamber under N plasma conditions and in the presence of a silver (Ag) cathode as the source. Two different deposition times, 5 and 10 s, respectively, were applied to obtain N-doped with AgNPs-decorated MoS2 and WS2 hybrids, abbreviated as N5-MoS2/AgNPs, N10-MoS2/AgNPs, N5-WS2/AgNPs, and N10-WS2/AgNPs, respectively, for each functionalization time. The successful incorporation of N as the dopant within the lattice of exfoliated MoS2 and WS2 as well as the deposition of AgNPs on their surface, yielding N-MoS2/AgNPs and N-WS2/AgNPs, was manifested through extensive X-ray photoelectron spectroscopy measurements. The observation of peaks at ∼398 eV derived from covalently bonded N and the evolution of a doublet of peaks at ∼370 eV guaranteed the presence of AgNPs in the modified TMDs. Also, the morphologies of N-MoS2/AgNPs and N-WS2/AgNPs were examined by transmission electron microscopy, which proved that Ag deposition resulted in nanoparticle growth rather than the creation of a continuous metal film on the TMD sheets. Next, the newly developed hybrid materials were proven to be efficient surface-enhanced Raman scattering (SERS) platforms by achieving the detection of Rhodamine B (RhB). Markedly, N10-MoS2/AgNPs showed the highest sensitivity for detecting RhB at concentrations as low as 10–9 M. Charge-transfer interactions between RhB and the modified TMDs, together with the polarized character of the system causing dipole–dipole coupling interactions, were determined as the main mechanisms to induce the Raman scattering enhancement. Finally, polycyclic aromatic hydrocarbons such as pyrene, anthracene, and 2,3-dihydroxynaphthalene, coordinated via π–S interactions with N-MoS2/AgNPs, were screened with high sensitivity and reproducibility. These findings highlight the excellent functionality of the newly developed N-MoS2/AgNPs and N-WS2/AgNPs hybrid materials as SERS substrates for sensing widespread organic and environmental pollutants as well as carcinogen and mutagen species.