Highly Efficient and Facile Removal of Pb2+ from Water by Using a Negatively Charged Azoxy-Functionalized Metal-Organic Framework

Lead (Pb) is one of the most widespread and toxic heavy metals in water, even in an ultralow concentration. Efficient and complete removal of Pb2+ has caught worldwide attention. Herein, a novel metal-organic framework (MOF) decorated with the O- group and N=N unit was elaborately constructed. Without pH adjustment, this porous material shows a significant affinity (K-d = 8.88 x 10(6) mL g(-1)) and high uptake capacity (463.52 mg g(-1)) for Pb2+ removal from aqueous solution. It can efficiently reduce Pb2+ concentration down to the ppb level, which is well below the drinking water standard of the World Health Organization (0.01 ppm). Moreover, highly selective capture can also be achieved against background ions, with a Pb2+ removal efficiency of up to 99.05%. The strong affinity of the MOF adsorbent toward Pb2+ can be accounted for by the excellent removal performance. FT-IR and XPS measurements were performed to investigate the adsorption mechanism, which demonstrated that the strong affinity stems from the interaction between Pb2+ and the highly accessible active sites of O- groups and N=N units.