Construction of heterogeneously connected cobalt-based MOF-COF and its application in highly selective separation of trace lead ions.

As a new type of porous crystalline composite material, MOF-COF has shown great advantages in metal separation. Herein, a CoMOF-COF was designed for highly selective separation of trace Pb ions. The designed CoMOF-COF has a high density of nitrogen-oxygen functional groups and can selectively separate metal ions. There is a strong affinity between the designed CoMOF-COF material and metal Pb ions, which can be attributed to the ordered heterogeneous porous structure and large amounts of nitrogen-and oxygen-containing functional groups. The composite showed high adsorption selectivity for Pb ions and had adsorption capacity of 33 mg g, with high chemical stability. Based on this solid phase extraction material, a high sensitivity detection method for Pb ions was established, which has the detection limit of 37.3 ng L, precision of 1.9 %. Linear detection range is 0.2-10 ng mL, and the detection of Pb ions in actual water samples was realized. Through this study, it is proved that the strong affinity between the designed CoMOF-COF materials and metal Pb ions can be attributed to the soft and hard acid-base theory, which reveals the structure-activity relationship between the porous heterostructure of such materials and metal separation, providing a highly selective separation material for the separation of other environmental pollutants.