Efficient Separation of Cd from Sn by Phosphazene-Based Covalent Organic Polymers

The accurate and precise determination of cadmium (Cd) isotopic compositions in geological samples is of high significance but still remains challenging due to severe matrix effects. In this work, a phosphazene-based covalent organic polymer, named CPF-T, with abundant P-O functional groups was prepared and explored as potential candidate for the selective separation of stannum (Sn) and Cd. Various factors affecting the separation efficiency, including adsorption dosage, acid concentration, and incubation time were systematically studied. It was found that in 0.1 mol L-1 HCl medium, about 93% Sn(IV) could be captured by CPF-T within 60 min, reducing the initial concentration ratio of Cd/Sn from 1:1 to 1:0.1. In addition, precise determination of Cd was achieved after the purification process, showcasing the promising potential for accurately determining Cd isotopic compositions. Mechanistic insights revealed that both coordination and electrostatic interactions play pivotal roles in the separation of Cd(II) and Sn(IV). This study introduces a potential material for the separation of Cd and Sn in practical sample and offers valuable guidance for the construction of robust materials to achieve the complete separation of Cd and Sn.