Submitted | Plasmonic Ag@ZIF-8: Monolith for Enhanced Visible Light Photocatalytic Degradation of Methylene Blue
Updated: Sep 4
Piwai Tshumaa, Mercy Chaparadzaa, Thapelo Seimelab, Mmantsae Dialeb, Nicola Vimbainashe Poshayia, Linia Gedi Marazania and Gift Mehlanaa
Research manuscript submitted to ACS Omega
Abstract: 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 synthesised via a sol-gel approach. Incorporation of Ag species during gel formation ensured homogeneous distribution within the ZIF-8 framework, followed by in situ chemical reduction to produce a reduced material denoted Ag0@ZIF-8. Comprehensive characterisation 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 localised surface plasmon resonance (LSPR). The photocatalytic performance of Ag0@ZIF-8 was evaluated by degrading methylene blue under visible light. The catalyst exhibited significantly enhanced activity compared to pristine ZIF-8 and Ag+@ZIF-8 monolith, achieving a maximum degradation efficiency of 90.4 ± 1.0 % under optimised conditions (pH 8, 60 mg 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 the 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.
Keywords: Metal-organic frameworks, monolith, plasmonic silver, ZIF-8, photocatalysis, methylene blue
