Effective Removal of U(VI) and Eu(III) by Carboxyl Functionalized MXene Nanosheets

With the development of nuclear power, the negative environmental impact such as radioactive pollution has become an urgent issue to impede the utilization of nuclear energy. The construction of promising organic-inorganic hybrid materials is considered as an effective strategy for environmental remediation of radioactive contamination. In this work, two-dimensional transition metal carbide (MXene), an emerging inorganic layered material, has been successfully modified by carboxyl terminated aryl diazonium salt to both enhance its chelating ability to radionuclides and improve its water stability. The carboxyl functionalized TiCT MXene (TCCH) shows excellent removal ability for U(VI) and Eu(III), evidenced by ultrafast adsorption kinetics (3 min), high maximum adsorption capacities (344.8 mg/g for U and 97.1 mg/g for Eu) and high removal percentage of radionuclides from artificial groundwater (> 90%). The adsorption of U(VI) and Eu(III) on TCCH are in good accord with the Langmuir adsorption isotherm model and the pseudo-second-order kinetic model. Ionic strength experiments, X-ray photoelectron spectroscopy (XPS) and Extended X-ray absorption fine structure (EXAFS) analyses were conducted to assess the detailed adsorption mechanism. The results reveal that the adsorption of U(VI) on TCCH follows an inner-sphere configuration, whereas the adsorption of Eu(III) is determined by both inner-sphere complexation and electrostatic interaction.