In situ decoration of Ag@exfoliated graphite composite catalyst for Fenton-like oxidation of methylene blue dye: kinetic and thermodynamic studies

Amendable nanomaterials are preferred for wastewater remediation. Silver (Ag) and graphene materials have drawn significant consideration for wastewater treatment due to their good dispersibility in aqueous systems, biocompatibility, and catalytic activity. For this purpose, an easy-to-follow procedure has been developed to prepare exfoliated graphite (EG) involving a binary-component system composed of concentrated H₂SO₄ and (NH₄)₂S₂O₈. Afterwards, Ag@EG composite catalysts were prepared by in-situ decoration of silver nanoparticles (AgNPs) over EG by sonication. The prepared catalysts were investigated for methylene blue (MB) dye removal from wastewater using a homogeneous Fenton-like oxidation process (H₂O₂/Ag⁺). Process-controlling factors like H₂O₂ dose, solution pH, and dye concentrations were explored. The results showed that MB dye degradation in the Fenton-like oxidation process can be clarified by a pseudo-first-order kinetic model. The highest dye degradation efficiency (99.8%) was achieved using Ag@EG (1:1). The morphology and structural characteristics of the prepared catalysts were evaluated by SEM, TEM, EDX, XRD, Raman spectroscopy, FTIR, and UV-Vis analyses. The activation energy, enthalpy, and entropy of the catalytic degradation of the MB dye in the presence of prepared catalysts were established. The data elucidated that most MB dye degraded within 120 min when using mesoporous Ag@EG (1:1) catalyst. Ag@EG (1:1), with a high S_BET (87 m²/g), functioned as a Fenton-like oxidation catalyst, exhibiting high degradation efficiency compared to other cited catalysts.