Defect-engineered UiO-66/D-AMP composite for highly selective co-removal of cesium and strontium

This study developed a novel defective composite material (UiO-66/D-AMP) based on defect engineering and in situ synthesis of ammonium phosphomolybdate (AMP) for the highly selective capture of Cs + and Sr 2+ . The changes in adsorption capacity and surface functional groups of the composite before and after defect engineering were analyzed by adsorption experiment and FT-IR characterization. It was found that the defect-engineered composite had obvious carboxyl groups, and the adsorption efficiency of Sr 2+ was effectively improved. Several analytical methods were employed to verify the effective incorporation of AMP onto the UiO-66 framework. SEM-EDS was utilized to examine surface morphology and elemental composition. FTIR confirmed the presence of functional groups, while XRD analysis validated the crystalline structure. Additionally, TG assessed thermal stability, and BET measurements determined the material's surface area and porosity, collectively confirming AMP loading. The UiO-66/D-AMP composite exhibited significant adsorption affinity for both Cs + and Sr 2+ ions, demonstrating its potential for radioactive wastewater treatment. Under alkaline conditions (pH 10), the composite demonstrated exceptional removal efficiencies of 98.43% for Cs + and 99.54% for Sr 2+ . The maximum adsorption capacities were determined to be 104.3 mg/g for Cs + and 20.18 mg/g for Sr 2+ . Notably, the adsorption kinetics revealed rapid equilibration times of 5 min for Cs + and 60 min for Sr 2+ . The adsorption kinetics of Cs + and Sr 2+ followed the pseudo-second-order model, while the adsorption isotherms fitted well with the Langmuir model. In mixed solutions containing Cs + , Sr 2+ , and four competing ions, UiO-66/D-AMP exhibited excellent selectivity for both Cs + and Sr 2+ . Remarkably, the adsorption capacities for Cs + and Sr 2+ remained stable following exposure to various adsorbed doses. XPS provided direct evidence for the ion exchange mechanism between Cs + and NH 4 + during adsorption. Sr 2+ first exchanged with H + on UiO-66/D-AMP, then coordinated with the oxygen atom in the carboxyl group to be adsorbed.