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

Abstract

The sulfonated covalent organic frameworks (COF@SO3H) have been synthesized by a simple one-step solvothermal reaction and used to adsorb Cd2+, Co2+, and Cr3+ 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@SO3H could be observed in the SEM and TEM images. The adsorption behaviors of Cd2+, Co2+, and Cr3+ onto COF@SO3H 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 Cd2+, Co2+ and Cr3+ at 298 K are 81.97, 77.52, and 105.26 mg g−1, respectively. The thermodynamic parameters indicate that the adsorption of Cd2+ onto COF@SO3H is spontaneous, which is more favorable than Co2+ and Cr3+. Moreover, the adsorbed metal ions can be easily eluted by nitric acid or EDTA solution, and the COF@SO3H 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@SO3H could be used to the adsorption and removal of heavy metal ions from wastewater.