Self-Template Etching Synthesis of Urchin-Like Fe₃O₄ Microspheres for Enhanced Heavy Metal Ions Removal

Abstract

Hierachical Fe₃O₄ microspheres with superparamagnetic properties are attractive for their superior structural, water-dispersible, and magnetic separation merits. Here self-template etching route was developed to create optimal porous structure in superparamagnetic Fe₃O₄ microspheres by using the oxalic acid (H₂C₂O₄) as etching agent. A plausible formation mechanism of the urchin-like Fe₃O₄ microspheres was proposed based on systematic investigation of the etching process, which involved two stages including pore-forming step based on size-selective etching and pore-expanding step based on further etching. The as-synthesized Fe₃O₄ microspheres exhibited urchin-like structure with specific surface area and pore-size tunable, water-dispersible, and superparamagnetic properties. The optimal urchin-like Fe₃O₄ microspheres demonstrated superior performance including fast magnetic separation and high removal capabilities for the heavy metals ions like Pb²⁺ (112.8 mg g^-1) and Cr(VI) (68.7 mg g^-1). This work will shed new light on the synthesis of urchin-like microspheres for superior performance.