The Functionalized N‑Rich Covalent Organic\nFramework for Palladium Removal from Nuclear Wastewater

Abstract

Efficiently\nadsorbing Pd­(II) from acidic radioactive waste liquid\nis crucial for ensuring the safety of the radioactive waste vitrification\nprocess and significantly alleviating the scarcity of precious metals.\nHowever, the stability and selectivity of most current adsorbents\nare limited, hindering their practical application under acidic conditions.\nTo address these limitations, a covalent organic framework (DHTP-TPB\nCOF) was prepared with a high nitrogen content, leveraging the high\naffinity of its soft ligand <i>N</i> with palladium to achieve\nhigh selectivity. This work demonstrated that DHTP-TPB COF exhibits\nrapid adsorption kinetics, with equilibrium achieved within 10 min.\nThe framework also boasts a high adsorption capacity of 142.8 mg/g\nand impressive reusability in 1.0 M nitric acid. Moreover, the DHTP-TPB\nCOF displays excellent selectivity for Pd­(II), even in the presence\nof 13 interfering ions. By combining FT-IR, XPS spectroscopy, and\nDFT theoretical calculations, the dense <i>N</i> sites in\nthe framework have a strong affinity for Pd­(II), resulting in exceptional\nadsorption performance that was confirmed. The findings of this study\nhighlight the potential of COFs with robust linkers and customized\nfunctional groups to effectively and selectively capture Pd­(II) under\nharsh environmental conditions of high-level liquid waste.