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

Abstract

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).