Single-step recovery of rare earth cerium on core–shell structured Fe3O4@ZIF-8 under mild conditions: Insights into the formation and evolution of surface ZnO/CeO2 nanocrystals

This study demonstrates a green and sustainable strategy for efficient single-step recovery of cerium through the rational design of core–shell Fe 3 O 4 @ZIF-8 nanocomposites. The material is comprehensively characterized in terms of morphology, magnetic properties, functional groups, and pore structure. Adsorption studies reveal pH-dependent recovery behavior, with optimal performance in the pH range of 3.9–7.2. Analysis of isotherms and thermodynamics confirms the endothermic nature of the recovery process, showing a monotonic increase in the maximum adsorption capacity from 110 mg g −1 to 185 mg g −1 as temperature rises from 283 K to 328 K. Notably, the effect of ionic strength (IS) suggests that NaCl significantly enhances Ce(III) recovery efficiency, while K 2 SO 4 exhibits marked suppression. Competitive adsorption experiments reveal stronger interference from heavy REEs (Ho 3+ /Tm 3+ ) compared to light REEs (La 3+ ). The fundamental mechanisms are elucidated through multiscale interaction analysis, revealing a synergistic process combining dual-phase transition dynamics and photoinduced redox reactions. The surface architecture of magnetic core evolves from initial ZnO-dominant nanocrystals to ZnO/CeO 2 heterostructures, and ultimately stabilizes as a CeO 2 -enriched framework with increasing Ce(III) concentrations. Moreover, across the time scale, the speciation of surface-adsorbed cerium underwent a gradual transition from Ce(III)-dominance to Ce(IV)-dominance, ultimately forming a regime where Ce(IV) (CeO 2 ) served as the primary species. This progressive transformation enables in situ immobilization and single-step recovery of Ce(III) under mild conditions, establishing a novel paradigm for REEs recovery technology.