Construction of brick-wall-like topological olefin-linked covalent organic frameworks via a steric-hindrance-mediated strategy for efficient uranium capture.

Abstract

The poor materials stability, sluggish adsorption kinetics, and limited selectivity present major challenges for uranium recovery from tantalum-niobium ore leachate. Herein, by leveraging spatial constraints imposed by cyano groups and the structural robustness of irreversible olefin linkages, a highly crystalline olefin-linked covalent organic framework (COF), TP-BPDAN, featuring a brick-wall-like topology, was successfully constructed through the condensation of top-truncated [1,1':3',1''-terphenyl]-3,3'',5,5''-tetracarbaldehyde (TPTCA) with C2-symmetrical 4,4'-biphenyldiacetonitrile (BPDAN). This alternating mesoporous/microporous architecture was specifically engineered to minimize diffusion barriers and accelerate mass transport compared to conventional homoporous COFs. Subsequently, the adjacent cyano groups were converted into cyclic imidedioxime functionalities, yielding TP-BPDAN-IDO, a material engineered with high-density, optimized coordination sites for uranium binding. As a result, the heteroporous TP-BPDAN-IDO exhibits remarkable improvements in adsorption kinetics, achieving 92% of its maximum adsorption capacity within 10 min, significantly outperforming homoporous COFs. Notably, TP-BPDAN-IDO demonstrates an outstanding uranium uptake capacity from strongly acidic leachate derived from a tantalum-niobium mine, along with exceptional selectivity for U(VI) over V(V), which effectively avoids vanadium interference faced by traditional amidoxime-based materials. This work not only expands the structural diversity of olefin-linked COFs but also provides a promising strategy for designing functional porous materials aimed at advancing energy sustainability.