Graphene/Ag-Ag2S based hybrid nanostructure for methylene blue degradation.

In this study, novel 2D/1D graphene/silver-silver sulfide (Ag-Ag2S) hybrid nanocomposites were successfully synthesized and characterized using X-ray Diffraction (XRD), Ultraviolet-Visible (UV-Vis) spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and Scanning Electron Microscopy (SEM). The structural-optical properties and dye-photodegradation performance of Ag nanowires (NWs), Ag-Ag2S core-shell NWs, and a 2D/1D graphene/Ag-Ag2S hybrid nanocatalyst were examined. SEM confirms uniform, non-agglomerated Ag NWs and a layered graphene morphology; after sulfidation, Ag2S (and incidental Ag2O) forms on Ag NW surfaces, while Ag-Ag2S NWs are randomly distributed across graphene sheets. XRD results confirm the presence of crystalline phases corresponding to Ag, Ag2S, and silver oxide (Ag2O), indicating successful hybridization and partial oxidation during synthesis. UV-Vis spectra show the two Ag localized surface plasmon resonances (LSPR) (∼350/380 nm) collapsing into a broadened band upon Ag2S shelling, consistent with higher dielectric loss and interfacial damping; graphene/Ag-Ag2S is dominated by a π-π* transition near 200-250 nm. Tauc analysis yields, E.g., ≈ 2.9 eV (Ag NWs), and after hybridization, approximately 2.5 eV (Ag2S), 3.8 eV (Ag), and 4.6 eV (Ag2O); the composite (graphene/Ag-Ag2S) exhibits two optical gaps (∼3.28 and 4.72 eV), reflecting its multiphase nature and graphene-induced states. Methylene blue (MB) degradation follows pseudo-first-order kinetics with the strongest linearity for graphene/Ag-Ag2S (R2 ≈ 0.89-0.92). At pH 3, the hybrid achieves the highest removal efficiency (89.55% at 5 h) and the largest rate constant (k_obs = 0.5349 h-1). The synergy arises from assisted carrier generation in Ag, heterojunction-driven separation in Ag-Ag2S, and rapid electron transport/π-π adsorption on graphene, which together maximize radical formation and suppress recombination under acidic conditions.