Constructing adjacent phosphine oxide ligands confined in mesoporous Zr-MOFs for uranium capture from acidic medium

Abstract

Neutral phosphine oxide ligands could coordinate with uranium in acidic radioactive liquid wastes with high affinity and selectivity. Limited success has been achieved in incorporating monodentate phosphine oxide sites into adsorbents to bind actinides due to the improper spatial distribution. Here, we present a deliberate design and construction of phosphine oxide host architectures which are structurally organized in the confined mesopores of MOFs for complexing uranium. By judicious selection of frameworks with an appropriate topology and mesoporous size, stable MOF-808 and NU-1000 were used to postsynthetically install phosphine oxide sites precisely and firmly via the ligand exchange of phosphonic acids. The material shows a high uranium adsorption capacity of 80 mg g⁻¹ in 1 mol L⁻¹ HNO₃, with a high utilization of ligand sites and ultrafast sorption rate. XPS and DFT calculations reveal that the adjacent phosphine oxide sites could coordinate with UO₂²⁺ species simultaneously.