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

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 AgNp, on their surface, yielding N-MoS2/AgNps and NWS2/AgNp was manifested through extensive X-ray photoelectron spectroscopy measurements. The observation of peaks at similar to 398 eV derived from covalently bonded N and the evolution of a doublet of peaks at similar to 370 eV guaranteed the presence of AgNp, 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 pi-S interactions with N-MoS2/AgNps, were screened with high sensitivity and reproducibility. These findings highlight the excellent functionality of the newly developed NMoS2/AgNps and N-WS2/AgNps hybrid materials as SERS substrates for sensing widespread organic and environmental pollutants as well as carcinogen and mutagen species.