Palladium recovery from acidic solution with phenanthroline-based covalent organic polymers as adsorbents for efficient heterogeneous catalysis

Abstract

The selective recovery and utilization of Pd(II) from high-level liquid waste (HLLW) is highly desirable for both a flourishing circular economy and the sustainable development of nuclear energy. However, the design of suitable materials is an ongoing challenge due to the complicated composition and extremely radioactive and acidic conditions of HLLW, which requires exceptional selectivity and structural robustness of materials. In this study, two phenanthroline-based covalent organic polymers are constructed through polycondensation of 1,10-phenanthroline-2,9-dicarbaldehyde and 1,3,5-tris-(4-aminophenyl) triazine (COP-1) and subsequent oxidation of imine to amide groups (COP-2). COP-2 demonstrates a high adsorption capacity (318 mg g⁻¹) and outstanding selectivity for Pd(II) over 17 competing cations at 3 M HNO₃ and is stable at high acidity (2–6 M HNO₃) and under a strong radiation field of up to 600 kGy γ irradiation. Additionally, COP-2 is reusable without an obvious decrease in adsorption efficiency after 5 cycles and is feasible for use in the dynamic column separation of Pd(II). More importantly, the Pd(II)-loaded COP-2 obtained from adsorption experiments can be employed as a highly efficient heterogeneous catalyst for Suzuki–Miyaura cross-coupling reactions with excellent reusability for more than 20 successive cycles. This work offers an example of turning wastes into wealth by rationally designing materials for precious metal recovery from HLLW and converting them into valuable catalysts.