Abstract In this study, a silica-based thiol unit-functionalized covalent organic framework composite (COF-SH/SiO 2 -P) was synthesized and its adsorption behaviors toward Pd(II) in nitric acid medium were characterized under various parameters, including contact time, acid concentration, and solution temperature etc. Notably, COF-SH/SiO 2 -P exhibited exceptional selectivity for Pd(II) in the presence of 13 competing metal ions, a scenario designed to simulate high-level liquid waste. Moreover, COF-SH/SiO 2 -P exhibited a relatively fast adsorption kinetics which can reach the adsorption equilibrium state within 180 min. Adsorption isotherm fitted well with Langmuir model, indicating the adsorption process occurred as monolayer adsorption. The superior adsorption performance of COF-SH/SiO 2 -P toward Pd(II) was considered to be attributed to the strong binding affinity between thiol units and Pd(II) ions, as confirmed by the comprehensive analysis of X-ray photoelectron spectroscopy (XPS) spectra with the aid of density functional theory (DFT) simulation.
Wu et al. (Fri,) studied this question.