Facile synthesis of sulfonated covalent organic framework for the adsorption of heavy metal ions

The sulfonated covalent organic frameworks (COF@SO 3 H) have been synthesized by a simple one-step solvothermal reaction and used to adsorb Cd 2+ , Co 2+ , and Cr 3+ metal ions from aqueous solution. The structure, composition and stability of as-prepared material were confirmed by FT-IR, PXRD, BET and TGA, and a fiber bundle-like COF@SO 3 H could be observed in the SEM and TEM images. The adsorption behaviors of Cd 2+ , Co 2+ , and Cr 3+ onto COF@SO 3 H were studied through batch adsorption experiments, and the obtained data were analyzed using various models. The adsorption process of the three ions can be better described by the Langmuir isotherm and the pseudo-second-order kinetics than other models tested, and the maximum adsorption capacities for Cd 2+ , Co 2+ and Cr 3+ at 298 K are 81.97, 77.52, and 105.26 mg g −1 , respectively. The thermodynamic parameters indicate that the adsorption of Cd 2+ onto COF@SO 3 H is spontaneous, which is more favorable than Co 2+ and Cr 3+ . Moreover, the adsorbed metal ions can be easily eluted by nitric acid or EDTA solution, and the COF@SO 3 H can be reused for more than 5 adsorption-elution cycles without obvious collapsing in structure and reducing in adsorption capacity. All the results suggested that the COF@SO 3 H could be used to the adsorption and removal of heavy metal ions from wastewater.