Efficient capture of palladium from nuclear wastewater by the sulfide and thiol modified covalent organic framework

The effective separation of palladium isotopes from high-level radioactive waste offers significant advantages, not only in ensuring the safe management and disposal of radioactive materials but also in addressing the scarcity of noble metals. In this study, a covalent organic framework (COF-SSH) modified with thiol and thioether groups is synthesized for the purpose of palladium separation. The experimental results demonstrate that the adsorption of Pd(II) occurs rapidly, reaching equilibrium within just 10 min. The adsorption isotherm for Pd(II) aligns well with the Langmuir model, revealing a maximum adsorption capacity of 420.2 mg/g at 3 M HNO3. Through Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Photoelectron Spectroscopy (XPS), and Density Functional Theory (DFT) analyses, the interaction between Pd and S atoms as being crucial for the adsorption process is identified. Moreover, COF-SSH exhibits exceptional selectivity for Pd(II) in simulated nuclear wastewater and maintains its performance throughout six consecutive adsorption and regeneration cycles. These results suggest that COF-SSH is a promising adsorbent for palladium separation, offering both acid resistance and high selectivity, making it a valuable candidate to the field of radioactive waste management and noble metal recovery.