Smart construction of mesoporous carbon templated hierarchical Mg-Al and Ni-Al layered double hydroxides for remarkably enhanced U(VI) management

Designing and fabricating environmental friendly adsorbents with more accessible active sites and higher specific surface area for achieving rapid kinetics and high efficiency have become an impending challenge in radionuclides’ pollution remediation. To overcome these issues, we rationally designed the hierarchical structured layered double hydroxides with mesoporous carbon template (CMK-3@LDHs) by in situ hydrothermal method. The adsorption data could be well simulated with pseudo-second-order and Langmuir model, and the results indicated that the CMK-3@LDHs exhibited higher adsorption capacities (171 mg·g⁻¹ for CMK-3@Mg-Al LDHs and 301 mg·g⁻¹ for CMK-3@Ni-Al LDHs at pH = 5.0) and more rapid kinetics (achieved equilibrium within 30 min) than SBA-15@LDHs towards U(VI). The kinetic model simulation demonstrated that the adsorption rate was dominated by intra-particle and film diffusion models simultaneously. In addition, the interaction between U(VI) and LDHs was pH-dependent and weakly related with ionic strength at pH < 5, suggesting that the process was mainly driven by the combined mechanism of electrostatic interaction and inner-sphere surface complexation. The characterization indicated that U(VI) removal was predominately controlled by isomorphic substitution and complexation with surface hydroxyl groups. In the further simulation experiments, the CMK-3@LDHs exhibited relative high adsorption efficiency in many water systems even in seawater, which confirmed the potential application of CMK-3@LDHs in efficient extraction and remediation of radionuclides from different kinds of wastewater systems.