A novel covalent-organic framework for highly sensitive detection of Cd2+, Pb2+, Cu2+ and Hg2+

A novel covalent-organic framework (COFMELE-BTDD) containing multiple heavy metal ions (HMIs) adsorption sites was synthesized and applied to electrochemical sensing HMIs and Hg2+ adsorption. The COFMELE-BTDD was prepared by amine-aldehyde condensation of 2,5,8-triamino-s-heptazine (MELE) and 4,4'-(benzo[c] [1,2,5]thiadiazole-4,7-diyl)dibenzaldehyde (BTDD). The COFMELE-BTDD is a two-dimensional crystal nanosheet with highly ordered conjugated structure, and the pore size is 3.7 nm. A novel electrochemical sensor for the determination of Cd2+, Pb2+, Cu2+, Hg2+ was constructed with COFMELE-BTDD. Each unit of COFMELE-BTDD has multiple active sites for HMIs (N–S–N, –CN), which can sensitively capture HMIs. The influence of experimental parameters (the amount of COFMELE-BTDD, pH value of electrolyte, deposition time and deposition potential) on electrochemical sensor was studied. The detection limits of Cd2+, Pb2+, Cu2+, Hg2+ are 0.00474 μM, 0.00123 μM, 0.00114 μM, 0.00107 μM, respectively. The sensitivities are 105.0 μA μM−1 cm−2, 405.5 μA μM−1 cm−2, 439.0 μA μM−1 cm−2 and 465.1 μA μM−1 cm−2. The sensor has good stability, reproducibility and anti-interference ability. The COFMELE-BTDD can effectively remove Hg2+ in water samples. The results show that the COFMELE-BTDD has great potential in adsorption and detection of HMIs.