Lewis base anchored DhaTph covalent-organic framework for effective capture of thorium(IV) ion

Capture of radioactive thorium (Th) ion from nuclear wastewater is highly necessary. However, current adsorbents show drawback in either adsorption capacity or adsorption rate. In this study, a DhaTph (Dha, 2,5-dihydroxyterephthalaldehyde; Tph, tetra-(p-aminophenyl)porphyrin) covalent-organic framework (COF) with Lewis base sites (C = N and –OH) was applied to capture Th(IV) ions from aqueous solution. DhaTph has a large (d, ∼2 nm) and transparent 1D channel, which makes the active Lewis bases interact with Th(IV) ion easily. Benefited from that, DhaTph exhibits a larger adsorption capacity of 525.0 mg g−1 and rapid adsorption speed (90 min for equilibrium) simultaneously. Besides, this COF owns superior adsorption for Th(IV) ion than various rare earth ions and some other common ions. The systematical characterization and theoretical calculation indicate that the strong chemical chelation interaction from C = N and –OH dominantly contributes to the effective capture of Th(IV) ion. Thus, our work indicates that DhaTph can serve as a potential adsorbent for selective capture of Th(IV) ion, and provides a guideline for designing effective COFs-based adsorbents. We expect this work will promote the application of highly stable COFs in the field of Th(IV) ion capture.