Efficient and selective removal of Pb²⁺ from aqueous solution by using an O^- functionalized metal-organic framework

Lead (Pb) is one of the most widespread and highly toxic heavy metals in the environment. The design and synthesis of adsorbent materials for the selective and efficient removal of Pb²⁺ from aqueous solution has received much attention. Herein, the ligand 4,4'-azoxydibenzoic acid with the O^- group was elaborately selected to construct a novel Pr-based MOF for Pb²⁺ removal. The as-prepared MOF adsorbents with high stability exhibited ultra-high selectivity for Pb²⁺, even in the presence of various highly concentrated competitive ions (with the ratios from 1 : 5 to 1 : 50). Also, a high uptake capacity (560.26 mg g^-1) can be achieved for the MOF material, due to the availability of sufficient adsorption sites. The strong electrostatic attraction and coordination interaction between the numerous active O^- sites on MOF adsorbents and Pb²⁺ can account for the good adsorption performance for Pb²⁺, which was systematically verified by zeta potential, FT-IR and XPS studies.