Efficient U(VI) removal by Ti3C2Tx nanosheets modified with sulfidated nano zero-valent iron: Batch experiments, mechanism, and biotoxicity assessment

The MXenes, a new class of two-dimensional layered materials, have found extensive applications in water treatment for its excellent thermal stability, electrical conductivity, and excellent adsorption ability. Sulfidized nano zero-valent iron (S-nZVI) is a good reducing agent, however, the practical application of S-nZVI is currently restricted due to the tendency of nano materials to agglomerate. Herein, MXenes use as a support and in situ loading S-nZVI on it to prepare a new material (S-nZVI/Ti₃C₂T_x), and applied it to U(VI) removal in water treatment. The microscopic characterization proves that S-nZVI on Ti₃C₂T_x has good dispersion and effectively alleviates agglomeration. Batch experiments shown that S-nZVI/Ti₃C₂T_x has a very good effect on U(VI) removal, and the maximum adsorption capacity reaches 674.4 mg/g under the aerobic condition at pH=6.0. The pseudo-second-order kinetic model and the Langmuir isotherm model were found to be more appropriate for describing the adsorption behavior. This indicates that the removal process is a single molecular layer chemisorption. Moreover, the S-nZVI/Ti₃C₂T_x maintained a removal efficiency of over 85 % for U(VI) even after being reused five times, demonstrating its excellent reusability. It is worth noting that the material can remove 79.8% of 50 mg/L of U(VI) in simulated seawater, indicating that S-nZVI/Ti₃C₂T_x possessed an excellent uranium extraction performance from seawater. Experimental results and XPS analysis showed that U(VI) was removed by adsorption, reduction and co-precipitation. Moreover, S-nZVI/Ti₃C₂T_x was a low toxicity material to hyriopsis cumingii. Therefore, S-nZVI/Ti₃C₂T_x was expected to be a candidate as adsorbent with great potential in removal of uranium from wastewater and seawater.