Insights into the formation of free radicals using metal ferrite nanocatalysts (MFe2O4, M = Fe, Mn, Zn, Co) prepared by a highly reproducible microwave-assisted polyol method

Abstract

Metal ferrite nanocatalysts possess renowned catalytic properties in advanced oxidation processes. This study aims to elucidate the impact of various parameters on their catalytic activity by measuring the formation of reactive oxygen species. Utilizing a microwave-assisted polyol method, we designed specific catalysts, demonstrating high reproducibility (>95%) of their structural, colloidal, and magnetic properties. Electron paramagnetic resonance (EPR) analysis described intricate catalytic dynamics influenced by buffer composition, particle size, and transition metal doping. The presence of buffer in the EPR measurement of the maghemite nanocatalyst with a size of 14 ± 3 nm induced a secondary reaction between ˙OOH and the DMPO spin-trap, shielding the radical signal by primarily generating CH₃ radicals, potentially hindering degradation. Smaller maghemite nanocatalysts (8 ± 2 nm) exhibited enhanced radical production due to increased surface area. Upon metal doping, manganese enhances ˙OOH radical production, while zinc inhibits ROS formation, and cobalt exerts nuanced influence. Additionally, catalytic efficiency in methylene blue degradation varied with the radical species, highlighting ˙OH radicals’ superiority for rapid degradation (1 h) over ·OOH (24 h). Overall, this research provides valuable insights into nanoparticle synthesis, radical formation kinetics, and catalytic performance, contributing to the advancement of sustainable catalysis for environmental remediation.