Exploration of different adsorption performance and mechanisms of core-shell FeO@Ce-Zr oxide composites for Cr(VI) and Sb(III).

Removal of toxic Cr(VI) and Sb(III) from wastewater is crucial owing to their potential hazard to the environment and human health. In this work, a novel magnetic composite, core-shell FeO@Ce-Zr binary oxide (Mag@Ce-Zr), was synthesized by a simple and eco-friendly co-precipitation method to remove Cr(VI) and Sb(III). The synthetic Mag@Ce-Zr composites exhibited superior magnetic separation (saturation magnetization value was 43.8 emu/g), great maximum adsorption capacities toward Cr(VI) and Sb(III) (66.7 mg/g for Cr(VI) and 365.2 mg/g for Sb(III)) and remarkable regeneration and reusability property. The adsorption mechanisms of negatively charged Cr(VI) oxyanions involved electrostatic attraction and the formation of Ce/Zr-O-Cr complexes. However, Sb(III) was adsorbed mainly through surface complexation with abundant hydroxyl groups to form Ce/Zr-O-Sb complexes. More importantly, based on X-ray photoelectron spectroscopy analysis, partial Cr(VI) and Sb(III) were converted to less toxic Cr(III) and Sb(V) by the core Fe(II) and shell Ce(IV) of Mag@Ce-Zr through electron transfer during adsorption process. Results revealed that the Mag@Ce-Zr composites displayed greater potential in the removal of Sb(III) from wastewater owing to its higher affinity with antimony species.