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 resin/magnetite composite microspheres.

Iron-based inorganic-organic hybrid Fenton catalysts, which recently emerged, are recognized as among 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 resin/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 the core-shell sequence on the nano-structure and reactivity of such spherical catalysts is rarely reported. Here, although the apparent degradation efficiencies of the 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 the RF@Fe3O4 catalyst, including a better total content of organic carbon (TOC) removal rate (56% vs. 42.6%), a much larger normalized reaction rate constant k (0.46 vs. 0.27 min-1), an improved degradation rate on anti-interference capacity against foreign ions (Cl-, 98.3% vs. 80%) and its enhanced stability under 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 sheds light on the rational construction of organic-inorganic hybrid catalysts with magnetic recycling features for potential large-scale application in photo-involved AOPs.