Graphene/Ag–Ag₂S based hybrid nanostructure for methylene blue degradation

Talia Tene¹Lala Gahramanli^2*Mustafa Muradov²Mahammad Baghir Baghirov²Goncha Eyvazova²Stefano Bellucci³Jessica Alexandra Marcatoma Tixi⁴Cristian Vacacela Gomez⁵Rana Khankishiyeva⁶Lorenzo S. Caputi⁷Salvatore Straface⁷

• ¹Universidad Tecnica Particular de Loja, Loja, Ecuador
• ²Baku State University, Baku, Azerbaijan
• ³National Institute of Materials Physics, Atomistilor str. 405 A, Bucharest-Magurele, Romania, Atomistor, Romania
• ⁴Escuela Superior Politecnica de Chimborazo, Riobamba, Ecuador
• ⁵Universidad Tecnológica Ecotec, Guayaquil, Ecuador
• ⁶Institute of Radiation Problems, Ministry of Science and Education of the Republic of Azerbaijan, Baku, Azerbaijan, Baku, Azerbaijan
• ⁷Universita della Calabria, Arcavacata di Rende, Italy

Abstract: In this study, novel 2D/1D graphene/ silver-silver sulphide (Ag–Ag₂S) hybrid nanocomposites were successfully synthesized and characterized by X-ray Diffraction (XRD), Ultraviolet-Visible (UV-Vis), Fourier-transform infrared spectroscopy (FTIR) spectroscopy, and Scanning Electron Microscopy (SEM) analyses. The structural–optical characterization, and dye‐photodegradation performance of Ag nanowires (NWs), Ag–Ag₂S Formatted: Font: Not Italic 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 Eg ≈ 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 hours) 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.