Efficient capture performance and mechanism of thiadiazole-functionalized covalent organic framework for Pb(II) ion

Covalent organic frameworks (COFs) are very promising adsorbent developed during recent years. Here, a COFs adsorbent (COF@HPLC) for efficient adsorption of lead is designed by post-modification. The adsorption properties were studied by batch adsorption. It is shown that pH 4 is the optimum value for the adsorption of Pb(II) by COF@HPLC. When the temperature is 25 °C, the maximum adsorption capacity of COF@HPLC reaches 251.37 mg/g. The fitting results of adsorption isotherm indicate that the process is a non-uniform adsorption in a single molecular layer . The activation energy fitted by the Dubinin-Radushkevich model are 16.22 kJ/mol, 21.32 kJ/mol, 18.87 kJ/mol and 16.67 kJ/mol, showing that Pb(II) adsorption by COF@HPLC is a chemical reaction. Kinetic studies show also that Pb(II) adsorption is a chemically controlled process. Thermodynamic shows that the adsorption is a spontaneously exothermic process. Finally, COF@HPLC has good adsorption selectivity and reusability. The adsorption mechanism of Pb(II) by COF@HPLC was the electrostatic and chelating interaction between functional groups containing sulphide and nitrogen and Pb(II) based on the zeta potential , XPS and DFT analyses. This work offers guidance toward the design and preparation of functional adsorbents for the treatment and removal of Pb(II).