Plasmonic Ag@ZIF‑8 Monolith for Enhanced Visible-Light Photocatalytic Degradation of Methylene Blue

Water contamination by organic dyes remains a major environmental challenge due to their toxicity, persistence, and resistance to conventional treatment methods. In this study, a plasmonic silver-modified metal-organic framework monolith was successfully synthesized via a sol-gel approach. Incorporation of Ag species during gel formation ensured homogeneous distribution within the ZIF-8 framework, which was followed by in situ chemical reduction to produce a reduced material denoted Ag⁰@ZIF-8. Comprehensive characterization confirmed the structural integrity of the ZIF-8 framework, with TEM revealing electron-dense silver domains and UV-vis DRS showing enhanced visible-light absorption associated with localized surface plasmon resonance (LSPR). The photocatalytic performance of Ag⁰@ZIF-8 was evaluated through the degradation of methylene blue under visible light. The catalyst exhibited significantly enhanced activity compared to pristine ZIF-8 and the Ag⁺@ZIF-8 monolith, achieving a maximum degradation efficiency of 90.4 ± 1.0% under optimized conditions (pH 8, 60 mg of catalyst, 60 min irradiation). Kinetic studies confirmed pseudo-first-order behavior with a rate constant of 0.0358 min^-1 (R² = 0.9923). Scavenger experiments revealed that superoxide radicals (•O₂ ^-) played the dominant role in methylene blue degradation, with hydroxyl radicals (•OH) and photogenerated holes (h⁺) making secondary contributions. The Ag⁰@ZIF-8 monolith also demonstrated good reusability, retaining over 75% of its initial activity after five cycles. Overall, this work highlights the synergistic interaction between plasmonic silver species and the ZIF-8 monolith, resulting in enhanced visible-light-driven photocatalytic degradation of organic pollutants, offering a promising strategy for wastewater treatment applications.