Fabrication of an anionic layered metal-organic framework for the efficient removal of Sr2+

Efficient removal of radioactive 90Sr from solutions is of vital importance due to its radioactive nature and high mobility. Herein, a 2D anionic metal-organic framework (MOF) [Me2NH2][KZn(pydc)2(H2O)2]∙H2O (K-Zn-MOF; pydc = 2,6-pyridinedicarboxylic acid) was synthesized and characterized. The prepared K-Zn-MOF was in turn applied for the removal of Sr2+ ions and various experimental conditions including contact time, initial concentration, and temperatures were optimized. Experimental findings revealed that the adsorption of Sr2+ on K-Zn-MOF reached equilibrium within 60 min at room temperature with Re = 95.39%. K-Zn-MOF exhibited ultra-high adsorption capacity (878.3 mg g−1), remarkable affinity (Kd = 5.8 × 105 mL g−1) in solutions and super-high selectivity in the presence of interfering coexisting ions (Na+, K+, Mg2+, and Ca2+). Mechanistic investigation suggested that free exchangeable [Me2NH2]+ ions and strong interactions between uncoordinated oxygens from COO− groups with target ions significantly contributed to the rapid adsorption of Sr2+ ions.