MIL-101(Cr) Coupled with Sulfidated Nano Zerovalent Iron for U(VI) Sequestration under Aerobic Conditions: Synergistic Effects, Mechanisms, and Biotoxicity Assessments

The MIL-101(Cr), a category of MOFs characterized by a notably high specific surface area and well-developed porosity, is extensively employed in removing pollutants from water owing to the material has good stability and adsorption capacity. The sulfidation process markedly improves the performance of nano zerovalent iron, yielding a more effective reducing agent termed S-nZVI. It faces the actual application limitations due to nanoparticle agglomeration. This study prepared composite material (M-S-Fe) by incorporating S-nZVI into the matrix of MIL-101(Cr) via an in situ approach. The results indicated a notable synergy of the two components. This made the composite material highly efficient in eliminating U(VI) at an optimum mass ratio of 1.2:1 and an S/Fe mole ratio of 1:80. Microscopic characterization confirmed an good dispersion of S-nZVI load in MIL-101(Cr) and effectively reducing agglomeration. Batch experiments showed that U(VI) was effectively eliminated using M-S-Fe at pH 6.0 under aerobic conditions, exhibiting a maximum adsorption capacity of 746.3 mg/g. The kinetic data were best fitted by the pseudo-second-order model, while the equilibrium data were well described by the Langmuir isotherm, collectively suggesting a chemisorption mechanism limited to a monolayer coverage. The material maintained over 76% removal efficiency for U(VI) after six reuse cycles, demonstrating excellent reusability. Notably, the material demonstrated significant potential for uranium extraction from seawater, achieving a high removal capacity of 93.4% for U(VI) at an initial concentration of 50 mg/L in simulated seawater. The removal of U(VI) occurred via the synergistic mechanisms of adsorption, reduction, and coprecipitation, as demonstrated by experimental results and XPS analysis. Additionally, M-S-Fe exhibited low toxicity to Hyriopsis cumingii, suggesting its potential as an efficient composite material for uranium elimination in wastewater and seawater.