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.

中文翻译：

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Urchin样的Fe ₃ O ₄微球自模板蚀刻合成，用于增强重金属离子的去除

具有超顺磁性的多层次Fe ₃ O ₄微球以其优异的结构，水分散性和磁分离优点而吸引人。在此，通过使用草酸（H ₂ C ₂ O ₄）作为蚀刻剂，开发了自模板蚀刻路线，以在超顺磁性Fe ₃ O ₄微球中创建最佳的多孔结构。似海胆状的Fe ₃ O _4的合理形成机理在对刻蚀过程进行系统研究的基础上，提出了微球，该过程涉及两个阶段，包括基于尺寸选择刻蚀的孔形成步骤和基于进一步刻蚀的孔扩展步骤。合成后的Fe ₃ O ₄微球表现出具有比表面积和孔径可调，水分散性和超顺磁特性的类顽童结构。最佳的类似顽童的Fe ₃ O ₄微球表现出卓越的性能，包括快速的磁分离和对Pb ²⁺（112.8 mg g ^–1）和Cr（VI）（68.7 mg g ^–1）等重金属离子的高去除能力。）。这项工作将为合成具有优异性能的类海胆微球提供新的思路。