Visible-Light-Driven Photocatalytic Degradation of Methylene Blue by a Magnetically Recoverable Fe-Cu@rGO Nano composite: Mechanistic Insights and Thermodynamic Analysis

Abstract

The production of effective, durable as well as regenerative photocatalysts is crucial to achieving sustainable remediation of water. In this work, the authors provide application-based research on a pre-synthesized bimetallic iron-copper decorated reduced graphene oxide nanocomposite (Fe-Cu@rGO) to be used in the visible-light photocatalytic degradation of methylene blue (MB). The catalyst had excellent performance with a degradation rate of more than 90% in a temperature span of 40 to 85 ℃. Kinetic studies showed a pseudo-first-order reaction with an extremely low activation energy at 10.78 kJmol^-1 which is a quantitative measure of a highly facile reaction pathway. Eyring analysis provided thermodynamic parameters (ΔH =8.00 kJmol^-1, ΔS = -120 J mol^-1K^-1) showing that a surface-mediated process with a constrained transition state occurs. The radical scavenger experiments clearly proved the presence of the superoxide radical (O₂●^-) as the primary active species and subsumed a highly detailed charge-transfer thermodynamic reaction in which rGO transfers electrons to O₂ reduction. More importantly, the catalyst itself was found to be very stable in practice showing a 90% recovery of its starting action to perform five consecutive simple magnetic recovery cycles. Besides presenting Fe-Cu@rGO as the best photocatalyst, this study also offers some basic ideas on the synergistic functionality of this photocatalyst, which makes it a powerful photocatalyst in terms of scalable solar-based wastewater treatment.