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.