In situ self-reduction synthesis of silver nanoparticles on MIL-101(Cr)-NH2 for enhanced adsorption of Br- and I-: Synergistic effect a nd mechanism

MOFs materials have attracted much attention in the field of halogen ion adsorption due to their unique structural characteristics and functions. However, for the improvement of ion adsorption capacity and selectivity is still challenging. This study synthesized silver nanoparticles in situ on MIL-101(Cr)-NH2 through chemical reactions, resulting in a silver-loaded MIL-101(Cr)-NH-CH2OH composite adsorbent. The characterization of the adsorbent revealed that the nano silver was uniformly loaded on the adsorbent, and that the adsorbent exhibited good thermal stability. The adsorption experiments show that Br- and I- can be selectively captured by the adsorbent even in the presence of high concentrations of competing ions (Cl-, NO3-, SO42- and CO32-). When the silver loading is 8%, the 8%Ag@MIL-101(Cr)-NH2-CH2OH demonstrates excellent adsorption performance, and the adsorption capacities are 0.947 mmol g-1 for Br- and 1.011 mmol g-1 for I-, with adsorption equilibrium times of approximately 180 min. The adsorption isotherms and kinetics are consistent with the Langmuir isotherm model and the pseudo-second-order kinetic model, respectively. Adsorption thermodynamics suggest that the adsorption process is spontaneous and exothermic. Experiment studies and theoretical calculations have demonstrated that the adsorption of Br- and I- is facilitated through a synergistic process involving precipitation, electrostatic interactions, and ion exchange, while also benefiting from its large specific surface area and abundant pore structure. The matrix material MOF and the loaded silver nanoparticles play a synergistic role in the adsorption process, and the desorption process is realized through desorption solution and light-driven decomposition. The results of this study indicate that the composite material under investigation has the potential to serve as an effective and selective adsorbent for the extraction of Br- and I- from complex ionic solutions.