Tripolycyanamide-2,4,6-Triformyl Pyrogallol Covalent Organic Frameworks with Many Coordination Sites for Detection and Removal of Heavy Metal Ions

Abstract Here, tripolycyanamide (TPA) and 2,4,6-triformyl pyrogallol (TDBA) are used to prepare a highly crystalline covalent-organic frameworks based on imine linkages (COFTDBA-TPA) for heavy metal ions (HMIs) detection and removal. Each unit of COFTDBA-TPA had 6 adsorption sites for HMIs (-C=O, -NH2, -C=N), which could selectively capture HMIs. The typical lamellar structure made COFTDBA-TPA have a larger specific surface area, and the mesoporous structure provided numerous channels for the adsorption of HMIs. Therefore, the COFTDBA-TPA-based electrochemical sensor could realize the detection of Cd2+, Cu2+, Pb2+, Hg2+ and Zn2+ in drinking water simultaneously. The limits of detection for five HMIs were as low as 0.922 nM, 0.450 nM, 0.309 nM, 0.208 nM and 0.526 nM, respectively. The adsorption capacity of COFTDBA-TPA for each HMI were as high as 711.6 mg/g, 716.9 mg/g, 603.7 mg/g and 618.3 mg/g, respectively. Compared with other adsorbents, it had higher capacity and faster adsorption kinetics. After being recycled five times, the adsorption performance was maintained. This not only provides a reliable platform for the removal of HMIs in wastewater, but also provides new ideas for the use of COFs in the electrochemical field.