Scalable Construction of Amide-Functionalized Covalent Organic Frameworks for Targeted Trapping of Palladium

Due to the potential toxicity of palladium ions in the environment and the scarcity of resources, the efficient recovery of palladium ions from solutions such as chemical industry solutions is crucial. A novel covalent organic framework adsorbent (COF-BcTd) was developed by a one-step synthesis for the efficient selective adsorption of palladium ions from various industrial solutions containing palladium in this study. The maximum adsorption capacity of COF-BcTd for Pd(II) was found to be 120.3 mg g^-1 at a temperature of 318 K and a pH of 2.5. The favorable fit of the Langmuir model and the Bangham kinetic model indicates that the adsorption of Pd(II) on COF-BcTd is a process involving pore diffusion, ultimately forming a monolayer of chemisorbed species. Analyses of electron paramagnetic resonance revealed the existence of multiple types of vacancies in the COF-BcTd and the same trend of vacancies over time as the kinetic results. Density functional theory calculations confirm that synergistic interactions exist between Pd(II) and the amino, amide, and thiazole ring groups on COF-BcTd, forming stable complexes through electrostatic attraction and multisite coordination. The percentage of Pd(II) selectively adsorbed by COF-BcTd remained above 84.76% in a complex system involving a real industrial waste catalyst leachate of competing ions. It demonstrated excellent anti-interference ability. The results highlight the prospect of scaled-up application of COF-BcTd in precious metal wastewater treatment.