Impact of varying the core–shell structural sequence on the efficiency of cascade reagent-free Fenton-like oxidation: the case of magnetically recycling resorcinol–formaldehyde resins/magnetite composite microspheres

Abstract

Iron-based inorganic–organic hybrid Fenton catalysts, which recently emerged, are recognized as one of the novel materials for the deep mineralization of inert pollutants for environmental remediation in photo-assisted Fenton-like reactions, which are one of the typical advanced oxidation processes (AOPs). In this work, magnetically recycling catalysts of resorcinol–formaldehyde resins/magnetite (RF/Fe₃O₄) core–shell microspheres were rationally designed by tuning the core–shell sequence for visible-light-driven reagent-free Fenton-like oxidation of organic dyes. It is noted that the impact of core–shell sequence on the nano-structure and reactivity of such spherical catalysts is rarely reported. Here, although the apparent degradation efficiencies of organic dye methylene blue (MeB) by these two core–shell catalysts were similar (97.4% by RF@Fe₃O₄ and 98.9% by Fe₃O₄@RF within 20 min), the intrinsic activity of Fe₃O₄@RF was revealed to be superior to RF@Fe₃O₄ catalyst, including better total content of organic carbon (TOC) removal rate (56% vs. 42.6%), much larger normalized reaction rate constant k (0.46 vs. 0.27 min^–1), improved degradation rate on anti-interference capacity against foreign ions (Cl^–, 98.3% vs. 80%) and its enhanced stability in acidic reaction conditions. We confirmed that the core–shell sequence imposed a significant impact on regulating the surface properties and active sites of the composite catalysts. The degradation of organic dyes followed a cascade Fenton-like process. Besides, the participation of Fe₃O₄ endowed the catalysts with a profitable magnetic recovery property. This work shed light on the rational construction of organic–inorganic hybrid catalysts with magnetic recycling features for the potential large-scale application in photo-involved AOPs.