Rationally Designed Core-Shell Structured Fe₃O₄@NiFe-LDH Using MIL-100(Fe) as an Intermediate Linker for Efficient Uranium Adsorption

The extraction and recovery of uranium play a crucial role in ensuring the sustainable supply of nuclear energy and safeguarding environmental security. The ideal uranium adsorbent should have high adsorption capacity, excellent selectivity, and good reusability. In this study, by employing the strategy of using MIL-100(Fe) as an intermediate linker, the core shell, structured of Fe₃O₄@NiFe-LDH, was successfully accomplished via a solvothermal method. The as-prepared Fe₃O₄@NiFe-LDH shows great potential in the field of uranium adsorption.

On one hand, MIL-100(Fe) can act as an iron source for NiFe-LDH, making the core-shell structure more stable. It was observed that after four adsorption-desorption cycles, the adsorption efficiency of Fe₃O₄@NiFe-LDH could still reach 75% in the fifth cycle. By contrast, materials without the MIL-100(Fe) intermediate layer exhibited a relatively lower adsorption cycle efficiency for three cycles. On the other hand, the porous structure of metal organic framework (MOF) doubles the specific surface area of Fe₃O₄@NiFe-LDH compared to Fe₃O₄/NiFe-LDH without a MOF intermediate layer.

The abundant hierarchical pore structure further enhances the performance of Fe₃O₄@NiFe-LDH from 615.6 mg·g⁻¹ of Fe₃O₄/NiFe-LDH(8:1) to 862 mg·g⁻¹. Additionally, in-depth studies on adsorption kinetics and adsorption thermodynamics suggest that the adsorption process is more inclined to monolayer adsorption and is dominated by chemical adsorption, which is a spontaneous endothermic process. When conducting ion competition tests on the adsorbent, it was found that the adsorbent has high adsorption selectivity for U(VI) and good regeneration ability. Therefore, the addition of the intermediate MOF improves the adsorption capacity and stability of the material, indicating that Fe₃O₄@NiFe-LDH has potential advantages in practical applications.